Vacuum pump is a device which gets the drive from engine cam shaft. In some designs, it is driven by the alternator shaft. The main function of vacuum pump is to evacuate the air from the brake booster tank, thus creating vacuum, which can be used for brake application. In addition to this, in new generation engines, to meet the Euro V emission targets, vacuum pump also has to create vacuum in the auxiliary tank which will be used to actuate the turbo charger waste gate actuation mechanism and EGR valve.
Why do diesel engines need a vacuum pump?
The vacuum pump used for brake application when modified to perform the additional function of turbocharger may deteriorate the primary application performance. The tapping position and the size of the vacuum port for the auxiliary tank will influence the primary braking performance of the pump. The work described in this paper involves the systematic analysis of layout study of vacuum pump to meet the performance of the vehicle for brake and turbocharger applications. Steady state bench test conditions were framed to simulate the actual vehicle condition of braking and turbocharger actuation as individual and simultaneous conditions. Design of experiments by Taguchi’s method was adapted to arrive at the number of optimum trials for experimental verification. Proto samples were made and evaluated for the experiments designed. Final design included provision/opening position of additional boss for connection with turbocharger waste gate, optimization of secondary nipple diameter and location, for target performance. Based on the test results the design was finalized to the specific engine requirements.
Finally the pump was fitted in the vehicle and validated for performance for brake application and turbo charger waste gate actuation for the entire engine operating conditions.
Can a vacuum pump run continuously?
Vacuum Pumps—the Work Horses of Many Industrial Processes
Vacuum pumps are an integral part of many industrial facilities and are used in many chemical processing and manufacturing applications. They are the work horses of vacuum processes and can often be in service 24 hours a day/7 days a week. With proper set-up of your system and timely preventative maintenance, your pump can operate effectively for years to come.
You know how important preventative maintenance is, but there are other features like remote monitoring, data logging for tracking and pump down curve creation, and alarm notification that can be easily added to assist you in keeping your processes running without costly interruptions.
5 Key Components of Keeping Your Vacuum Process Going
Can a vacuum pump run continuously?
Frequent oil changes extend the life of your vacuum pump: For example, the Stokes rotary piston pump manual recommends an oil change every 300 running hours, which is less than two weeks if the pump is running 24/7. If you are running a clean process, the oil change could be extended to about 500 hours without harming the pump. But bottom line, if your process is dirty with a high potential for dust or vapors affecting the pump, then the oil can become contaminated quickly and should be changed more frequently. Sometimes in very sensitive operations, the oil must be changed after every run. Proper and timely vacuum pump maintenance can help extend the life of your pump and keep your facility operating smoothly.
Temperature Control: the pump must be well ventilated since too much heat can lead to premature pump failure. For oil-filled pumps, excessive heat makes the oil less viscous making it harder for the pump to pull a good vacuum. In addition, heat makes the rubber parts in your pump more brittle which can lead to failure and leakage.
Beware of Overheated Oil: overheated oil can harden when it cools and lock-up a pump. The most common cause is a gross vacuum leak. Some pumps can fail when run at continuously high pressures (Typically > 10 Torr). A gross vacuum leak can cause pressure fluctuations that overheat the oil. Keeping a vacuum gauge on your system that continuously monitors and can alert you to these fluctuations could be a great asset in maintaining the health of your vacuum pump.
Intake Control: Be careful that only filtered gases enter the pump. Unavoidable vapor contamination requires more frequent oil changes. Vapor, especially water, entering the pump will oxidize the pump’s internal parts leading to premature pump failure.
Monitoring: Monitoring your vacuum process is just one of the many things that take up your day, and as such it’s hard to keep a watch on it all the time. Vacuum Gauge, is the free smart phone app from DigiVac (available for both Andoid and Apple devices), available for use with the Bullseye Precision Gauge® with Bluetooth, and it offers you the ability to monitor your vacuum system process remotely and will alarm you if the vacuum pressure deviates from the set-point.
3 Key Features of Vacuum Gauge App:
Remote monitoring and viewing of current vacuum pressures
Data logging and sharing from anywhere (supports easy creation of pumpdown curves, an important step in vacuum pump monitoring)
Alarm notification when reading fall outside acceptable range
The app combined with the Bluetooth vacuum gauge allows users to Monitor, Save, and Share vacuum pressure reading remotely. Pressure measurement tracking from your smartphone–you can set high and low alarms for pressure readings that fall outside the acceptable parameters for your vacuum process. These features allow you to respond quickly to issues like leaks in your vacuum system. Click here to read more about it.
So you need to vent a vacuum chamber? Whether your reason behind doing so is to replace a sample, take out an instrument, or fix a leak this Instructable will lay out the necessary steps behind this process. Vacuum chambers can be found in most research labs requiring an isolated system. Electron microscopes, material evaporators (as is the case in Figure 1), and plasma research all need vacuum chambers to acquire quality results.
Venting must be a gradual process to avoid complications such as damaging of equipment, especially from high vacuum (10-8 torr). Following these steps in order is imperative in order to not contaminate the quality of the vacuum chamber.
An example vacuum chamber is included to provide guidance, but your specific setup may vary. It may vary in the number of vacuum pumps, accompanying instruments, and other ways, but these instructions serve as a general guidline as to how to properly vent any vacuum chamber.
Atmospheric oxygen is very reactive and if too much of it enters the chamber during periods of being in atmosphere this can lead to poor conditions. Because of this nitrogen, a cheap and nonreactive molecule, will be used through much of this process as the substance to vent the chamber. Gasseous nitrogen may be used to vent vacuum pumps, but it is best to only vent the actual chamber with liquid nitrogen.
The entire process involves much wait time for filaments to cool and internal pressure to reach equilibrium with the atmosphere. As such, set aside about a full day into your plans for the venting process. Again, most of this time you need not actively be performing tasks during this time. In terms of the time it takes for you, the actions needed should only take around 45 minutes to an hour and a half net to complete.
A brief schedule of the steps are as follows:
Turn off all filaments (This takes 5-10 minutes to do, but around twelve hours to let the filaments really cool down).
Acquire liquid nitrogen (This takes 5-10 minutes).
Closing the pump valves (This takes 2 minutes).
Venting the pumps (This takes 15 minutes for each pump).
Venting the chamber with liquid nitrogen (this takes 5-10 minutes to start, but around 3 hours to let the pressure equalize).
Determining if the chamber is full vented (this can be done in seconds)
Resetting the valves (This takes 5-10 minutes).
READ ALL INSTRUCTIONS IN FULL BEFORE ATTEMPTING TO VENT THE CHAMBER
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Step 1: Turning OFF All Filaments
Turning OFF All Filaments
Turning OFF All Filaments
Before you begin, take care that all filaments have been set OFF for a sufficient time (overnight or half of the day). This includes all evaporators, ion gauges, and ion pumps. Without doing so, hot filaments can oxidize (react with oxygen in the air) and be damaged. Figures 2 and 3 show examples of filament controllers that must be turned off for 12 hours before venting.
Step 2: Acquire Liquid Nitrogen
Acquire Liquid Nitrogen
Acquire Liquid Nitrogen
Filled Liquid Nitrogen Dewar: Liquid nitrogen will be the main material used to vent the chamber. It is cleaner than gasseous nitrogen alone, and is used to ensure only pure nitrogen enters the chamber as it approaches atmospheric pressures.
Most universities have a laboratory equipment dispensary where liquid nitrogen can be found. If not, consult commercial sources.
Step 3: Close the Pump Valves
Close the Pump Valves
At this point, any vacuum pumps still on must be closed off from the chamber (these are NOT filament based, and so are able to be turned off in the presence of atmospheric conditions). Many pumps require oil and other dirty contaminants that would be a nightmare if they got inside the vacuum chamber.
To ensure no suction of these contaminants into the chamber, close off the valves the pumps should be connected to. When this is done, the chamber is totally isolated, with no gasses going in or out. The next goal will be to properly power down the pumps themselves.
Step 4: Venting the Pumps
Venting the Pumps
Venting the Pumps
Venting the Pumps
DO NOT JUST TURN OFF THE PUMPS
The vacuum pumps can be contaminated just as the chamber can, and since they are connected to the chamber their contamination could lead to damaging the chamber itself. As such, it is important to take care in this step to vent the pumps with gaseous nitrogen.
How do you vent a vacuum pump?
For this step, gaseous nitrogen will suffice in keeping the pumps themselves clean from atmospheric contaminants. With nitrogen gas flowing, attach the source hose to the outlet on your pump, and then switch off the pump. This step may take around 15 minutes. Once the pump is completely off, repeat the process for any other pumps.
Step 5: Venting the Chamber With Liquid Nitrogen
Venting the Chamber With Liquid Nitrogen
DO NOT PUT ANY BODY PART INTO THE LIQUID NITROGEN DEWAR
LIQUID NITROGEN MAY CAUSE FREEZER BURN ON DIRECT CONTACT WITH SKIN
Now is the time to vent the actual chamber. Depending on the size of the chamber, this may take anywhere from one (small chambers) to three hours (large chambers).
Submerge the liquid nitrogen connection line into the liquid nitrogen.
While in a position where you can hear exchange of liquid nitrogen (this sounds like light ‘gasps’ coming from the dewar), slowly rotate the liquid nitrogen intake valve counterclockwise to allow the uptake of liquid nitrogen to occur. DO NOT TURN ABRUPTLY OR TOO FAR. Go slow here, and stop when you hear the ‘gasps’ about once per second.
Once a steady rate of one ‘gasp’ per second is reached, the venting will proceed for a long time with or without you. If this is your first time, stay and monitor the rate until the chamber is fully vented. If you are comfortable with the procedure, you can go do something else for the next few hours.
Step 6: Determining Whether the Chamber Is Fully Vented
Determining Whether the Chamber Is Fully Vented
If your chamber has an openable window such as the one above, then the chamber will be fully vented once this window is able to be opened with limited force.
If your chamber does not have such a window, the best way to determine the progress of the vent is to listen for the ‘gasps.’ If they are still happening, then the chamber needs more time to vent. If there are no sounds, rotate the liquid nitrogen valve counterclockwise to make sure liquid nitrogen can freely enter the chamber. If after this step there si still no sound, the chamber is vented.
Step 7: Resetting the Valves
At this point, the chamber is vented. However, it is beneficial here to reset the valves to be ready for the next pump down. Doing so now will ensure no mess up occurs later when you attempt to pump down back into vacuum.
To do so, simply rotate the all valves opposite what they are. In the case here, you need to open the two valves to the pumps and close the valve to the liquid nitrogen intake valve.
Once this is done, the chamber is completely vented and you can do your necessary work to the chamber without damaging its integrity.
Step 8: Supplemental Information
The steps above provide a general, quick use guide toward venting a vacuum chamber. However, if more information is needed the following links should serve as excellent sources of information.
The sliding vane design combines low cost with high reliability and easy maintenance. The operating principle is simple. A slotted rotor is eccentrically supported in a cycloidal cam. The rotor is placed close to the wall of the cam so a crescent shaped cavity is formed. Two sideplates seal the rotor to the cam. The clearance between the rotor and sideplates is eight to ten thousandths of an inch depending on the model. Vanes, also known as blades, slide in and out of the rotor slots to seal off a volume between the rotor, cam and sideplate. Liquid enters the crescent shaped pumping chamber through holes in the cam. The blades sweep the fluid to the opposite side of the crescent where it is squeezed through the discharge holes of the cam as the blade approaches the point of the crescent.
What is a sliding vane pump?
For a sliding vane pump to function properly, the blade must always contact the cam wall to form a tight seal. Centrifugal force provides some force to actuate the blade but this force is not adequate by itself. Hydraulic forces exerted by the liquid being pumped tend to push the blades back into the rotor. On Corken’s older standard models, special design features must be incorporated into the pump to counteract these forces. This is generally accomplished by routing discharge pressure under the blade via slots in the sideplates or holes in the blade. Newer models like the Z-Series and PZ-Series have vane/blade drivers that keep the vane/blade against the cam for better seal.
Vacuum pump is the power equipment of evaporator, its stable operation is related to the working state of the whole evaporation system, so how to maintain the vacuum pump when the evaporation equipment is running? It is very important to pay attention to the maintenance of vacuum pump, extend the service life of vacuum pump and improve the working efficiency of vacuum pump.
How do you maintain a vacuum pump?
In the daily use of vacuum pump, which maintenance methods should we use? Several maintenance methods of vacuum pump are shared with you. The routine maintenance and service methods of vacuum pump are generally divided into two types: regular routine maintenance and service methods. The following are the specific maintenance methods. You can have a brief understanding.
vacuum pump maintenance steps:
1. Check whether the vacuum pump pipeline and joint are loose. Turn the vacuum pump by hand to see if it is flexible.
2. Add bearing lubricating oil into the bearing body, observe that the oil level should be at the center line of the oil mark, and the lubricating oil should be replaced or supplemented in time.
3. Screw out the water plug of the vacuum pump body, and fill the water or slurry.
4. Close the gate valve, outlet pressure gauge and inlet vacuum gauge of the outlet pipe.
5. Jog the motor, and try to see whether the rotation direction of the motor is correct.
6. Start the motor. When the vacuum pump is in normal operation, open the outlet pressure gauge and the inlet vacuum pump. Gradually open the gate valve and check the motor load after the appropriate pressure is displayed.
7. Try to control the flow and head of the vacuum pump within the range indicated on the label to ensure that the vacuum pump operates at the highest efficiency point, so as to achieve the maximum energy saving effect.
how-to-maintain-the-vacuum-pump
8. During the operation of vacuum pump, the bearing temperature shall not exceed the ambient temperature by 35 ℃, and the maximum temperature shall not exceed 80 ℃.
9. If any abnormal sound is found in the vacuum pump, stop the pump immediately to check the cause.
10. To stop using the vacuum pump, first close the gate valve and pressure gauge, and then stop the motor.
11. The lubricating oil of the vacuum pump shall be changed within 100 hours in the first month of operation, and then every 500 hours.
12. The packing gland shall be adjusted frequently to ensure the normal leakage in the packing chamber, and it is better to leak out in drops.
13. Regularly check the wear condition of the shaft sleeve, and replace it in time when the wear is large.
14. When the vacuum pump is used in the cold winter season, it is necessary to unscrew the drain plug at the lower part of the pump body to drain the medium after the pump is stopped. Prevent frost cracking.
15. When the vacuum pump is out of service for a long time, it is necessary to disassemble the pump completely, dry the water, coat the rotating parts and joints with grease, and properly store them.
What is the most efficient hydraulic pump?
Hydraulic Pumps and Motors: Considering Efficiency
Brendan Casey
In a condition-based maintenance environment, the decision to change out a hydraulic pump or motor is usually based on remaining bearing life or deteriorating efficiency, whichever occurs first.
Despite recent advances in predictive maintenance technologies, the maintenance professional’s ability to determine the remaining bearing life of a pump or motor, with a high degree of accuracy, remains elusive.
Deteriorating efficiency on the other hand is easy to detect, because it typically shows itself through increased cycle times. In other words, the machine slows down. When this occurs, quantification of the efficiency loss isn’t always necessary. If the machine slows to the point where its cycle time is unacceptably slow, the pump or motor is replaced. End of story.
In certain situations, however, it can be helpful, even necessary, to quantify the pump or motor’s actual efficiency and compare it to the component’s native efficiency. For this, an understanding of hydraulic pump and motor efficiency ratings is essential.
There are three categories of efficiency used to describe hydraulic pumps (and motors): volumetric efficiency, mechanical/hydraulic efficiency and overall efficiency.
Volumetric efficiency is determined by dividing the actual flow delivered by a pump at a given pressure by its theoretical flow. Theoretical flow is calculated by multiplying the pump’s displacement per revolution by its driven speed. So if the pump has a displacement of 100 cc/rev and is being driven at 1000 RPM, its theoretical flow is 100 liters/minute.
What is the most efficient hydraulic pump?
Actual flow has to be measured using a flow meter. If when tested, the above pump had an actual flow of 90 liters/minute at 207 bar (3000 PSI), we can say the pump has a volumetric efficiency of 90% at 207 bar (90 / 100 x 100 = 90%).
Its volumetric efficiency used most in the field to determine the condition of a hydraulic pump – based on its increase in internal leakage through wear or damage. But without reference to theoretical flow, the actual flow measured by the flow meter would be meaningless.
A pump’s mechanical/hydraulic efficiency is determined by dividing the theoretical torque required to drive it by the actual torque required to drive it. A mechanical/hydraulic efficiency of 100 percent would mean if the pump was delivering flow at zero pressure, no force or torque would be required to drive it. Intuitively, we know this is not possible, due to mechanical and fluid friction.
Table 1. The typical overall efficiencies of hydraulic pumps, as shown above, are simply the product of volumetric and mechanical/hydraulic efficiency. Source: Bosch Rexroth
Like theoretical flow, theoretical drive torque can be calculated. For the above pump, in SI units: 100 cc/rev x 207 bar / 20 x p = 329 Newton meters. But like actual flow, actual drive torque must be measured and this requires the use of a dynamometer. Not something we can – or need – to do in the field. For the purposes of this example though, assume the actual drive torque was 360 Nm. Mechanical efficiency would be 91% (329 / 360 x 100 = 91%).
Overall efficiency is simply the product of volumetric and mechanical/hydraulic efficiency. Continuing with the above example, the overall efficiency of the pump is 0.9 x 0.91 x 100 = 82%. Typical overall efficiencies for different types of hydraulic pumps are shown in the Table 1.
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System designers use the pump manufacturers’ volumetric efficiency value to calculate the actual flow a pump of a given displacement, operating at a particular pressure, will deliver.
As already mentioned, volumetric efficiency is used in the field to assess the condition of a pump, based on the increase in internal leakage due to wear or damage.
When calculating volumetric efficiency based on actual flow testing, it’s important to be aware that the various leakage paths within the pump are usually constant. This means if pump flow is tested at less than full displacement (or maximum RPM) this will skew the calculated efficiency – unless leakage is treated as a constant and a necessary adjustment made.
For example, consider a variable displacement pump with a maximum flow rate of 100 liters/minute. If it was flow tested at full displacement and the measured flow rate was 90 liters/minute, the calculated volumetric efficiency would be 90 percent (90/100 x 100). But if the same pump was flow tested at the same pressure and oil temperature but at half displacement (50 L/min), the leakage losses would still be 10 liters/minute, and so the calculated volumetric efficiency would be 80 percent (40/50 x 100).
The second calculation is not actually wrong, but it requires qualification: this pump is 80 percent efficient at half displacement. Because the leakage losses of 10 liters/minute are nearly constant, the same pump tested under the same conditions will be 90 percent efficient at 100 percent displacement (100 L/min) – and 0 percent efficient at 10 percent displacement (10 L/min).
To help understand why pump leakage at a given pressure and temperature is virtually constant, think of the various leakage paths as fixed orifices. The rate of flow through an orifice is dependant on the diameter (and shape) of the orifice, the pressure drop across it and fluid viscosity. This means that if these variables remain constant, the rate of internal leakage remains constant, independent of the pump’s displacement or shaft speed.
Overall efficiency is used to calculate the drive power required by a pump at a given flow and pressure. For example, using the overall efficiencies from the table above, let us calculate the required drive power for an external gear pump and a bent axis piston pump at a flow of 90 liters/minute at 207 bar:
External gear pump: 90 x 207 / 600 x 0.85 = 36.5 kW
Bent axis piston pump: 90 x 207 / 600 x 0.92 = 33.75 kW
As you’d expect, the more efficient pump requires less drive power for the same output flow and pressure. With a little more math, we can quickly calculate the heat load of each pump:
Drive power for a (non-existent) 100% efficient pump would be: 90 x 207 / 600 x 1 = 31.05 kW
So at this flow and pressure, the heat load or power lost to heat of each pump is:
External gear pump: 36.5 – 31.05 = 5.5 kW
Bent axis piston pump: 33.75 – 31.05 = 2.7 kW
No surprise that a system with gear pumps and motors requires a bigger heat exchanger than an equivalent (all other things equal) system comprising piston pumps and motors.
What type of oil is recommended for a high vacuum pump?
What type of oil is recommended for a high vacuum pump?
Oil for Vacuum Pumps
In the world of mechanical oil sealed rotary vacuum pumps there is a need for a variety of oils and fluids to suit the specific type of pump, its duty and the process it is used on. This discussion covers high vacuum pumps only, such as are used in the heat treating and vacuum furnace industry. These same vacuum pumps are used in many other industrial and scientific applications and have to work under many different types of conditions including one that many people expose their pumps too – neglect!
Rotary vane vacuum pumps are available as direct drive (usually 1800 rpm) and vee belt drive (between 400 and 500 rpm) versions. Rotary piston vacuum pumps are generally vee belt driven and run at about 500 rpm.
The work duty of a vacuum pump can vary between intermittent use and running continuously. They can also be used for cyclic duty, to evacuate a loadlock for example, where the pump evacuates a chamber from atmosphere to vacuum every few minutes. The vacuum process can also vary, from clean air pumping to hazardous gas, wet vapor pumping and dirty/dusty atmospheres.
All these factors need to be taken into consideration in case the duty or process doesn’t suit the manufacturer’s standard oil or requires accessories to cope with the contaminants being pumped.
fig-1 sm
Fig. 1. Oil is oil, right? NOT
What are the functions and requirements of Vacuum Pump Oil?
We generally think of lubrication as the main use for oil. In vacuum pumps the functions of the oil are:
Oils for rotary vacuum pumps have low vapor pressures, in the range of 10-4 Torr at room temperature. They are mineral oils that are refined until the required vapor pressure is attained. They must also have a sufficiently low vapor pressure at the normal operating temperature of the pump as this determines the lowest pressure that the pump can attain.
When a vacuum pump is first started you may notice that the indicated vacuum is lower than that seen when the pump has warmed up. Cold or cool oil will have a lower vapor pressure and allow the vacuum to create a lower pressure. The vapor pressure will rise as the fluid gets hotter and the pump will not reach quite as low a pressure.
Remember that the “ultimate vacuum” stated by the pump manufacturer in a pump manual is measured with a calibrated vacuum gauge when the pump is new and using perfectly clean and fully degassed vacuum pump oil. It is measured at the inlet to the pump. The vacuum level that you will measure in real work conditions will generally not be as low a pressure due to variables such as the oil condition, the position of the gauge head, the type of vacuum gauge used and the calibration of the gauge. The vacuum pump or pump set should be capable of producing a vacuum at least one decade or more below the required process vacuum.
The requirements for rotary pump oils are:
Sufficiently low vapor pressure
Correct viscosity
Adequate lubrication properties
Chemically suitable for the materials being pumped
Chemically stable at pump working temperature, and
Not hazardous to health
Paraffinic base mineral oils are suitable for the majority of vacuum pump applications in industry and science. Unlike motor oil that contains many additives, vacuum pump oil additives are limited to corrosion resistance, anti-oxidation and perhaps foaming.
For applications that may contain high percentages of oxygen, acids and hazardous gases there are alternative synthetic fluids available. As a development of the semiconductor industry (computer chips) where many hazardous, corrosive and pyrophoric gases are used vacuum pumps have been developed that have no lubricant at all in the pumping chamber areas of the pump. These are called dry pumps and are the subject of another discussion.
The typical oil used in a large rotary piston vacuum pump is a mineral oil that has been through a distillation process to reduce its vapor pressure. These vacuum pumps have an ultimate vacuum, sometimes called “blank off” vacuum, of 0.010 Torr (10 microns, 1 x 10-2 Torr or 0.0133 mbar). The oil has a viscosity similar to SAE 30 oil.
The SAE 30 viscosity vacuum pump oil is also used in smaller rotary vane design pumps driven by a vee belt drive from the motor. In the newer design direct drive vacuum pumps that run at around 1750 rpm, thinner SEA 20 vacuum pump oil is used. In some applications, where the vacuum pump may be colder than room temperature, there are SAE 10 oils available.
How often should I change the Vacuum Pump Oil?
fig-3 sm
Fig. 2. Vacuum pump oil
What type of oil is recommended for a high vacuum pump?
Vacuum pump manufacturers will recommend when to change the oil in a pump, but it is usually meant only as a guide and for pumps running on a clean process. For example, the Edwards Stokes Microvac rotary piston pump manual recommends an oil change every 300 running hours. This is less than two weeks if the pump is running 24/7. For a clean process that time may be extended to about 500 hours with no harm to the pump. However, if the process is dirty and sends dust or vapors to the pump, the oil can become contaminated quickly and should be changed more frequently.
This means that it is up to you, the pump user, to establish guidelines for oil changes based on your process. If the pump oil becomes contaminated with condensed vapor the vacuum generated will soon deteriorate due to that liquid mixed with the oil. Often this is water, which has a vapor pressure of about 18 Torr at ambient temperature. That means this liquid will re-evaporate on the inlet (low pressure) side on the pump cycle and fill the pumping volume with vapor. Then the pump has little of no volume left to pump gas from the process and the process chamber pressure will rise.
If the contaminant is dust or powder from the process chamber it will mix with the oil and then cause mechanical wear in the bearings and and on any close fitting metal surfaces that have an oil film between them. You may have seen the effect of contamination by solids on the lower hinge bar of rotary piston pumps. What you may not see, because the oil circulates through the bearings and then to the interior of the pump, is wear and tear on the pump bearings.
Preventing contamination of vacuum pump oil.
There are several ways to prevent the oil from being contaminated, depending on the type of contamination, by using gas ballast, traps or filters.
If the amount of condensed vapor contamination is relatively low, opening the gas ballast valve will allow water vapor to be passed through the pump without condensing. The manufacturers specification usually shows the water handling capacity of a specific pump in grams/hour or ounces/ hour. If the amount of condensed vapor is above this limit some type of condenser or cold trap should be installed on the inlet side of the pump.
If the process is dusty, i.e. a solid contaminant, an inlet filter can be installed, designed to suit the type and amount of dust. Some filters have a cyclone design that causes the gas flow to circulate around the filter interior so that heavy solids drop to the bottom. The exit from that type of filter is from the top of the body where the gas flow should be cleanest. There are also filter elements available that will catch the solids, either a pleated style element for fine solids, or a wetted metal mesh element for high flow applications. Remember that filters will reduce the effective pumping speed and they also do need to be maintained regularly.
Another option if solid contaminants are getting into the oil is to install an external oil filter on the pump. This device takes the contaminated oil from the reservoir, passes it through the filter unit and then returns it to the oil piping before the oil reaches the bearings. That gives the bearings clean oil and will extend their life.
Remember to use the necessary PPE (personal protective equipment) when changing oil, and to dispose of any contaminated fluids in a safe manner.
Mineral oils and other vacuum pump fluids
Oil seems such a simple product until you do some research and find out how many different types of oil there are. Most lubricating oils are paraffinic based oils that are processed to create the best product for the application. The product is refined using solvent separation methods from paraffinic crude oil. (Other base oils are Naphthenic and Aromatic)
Singly distilled oil
Processing the base oil through a single distillation reduces the vapor pressure of the oil so that it is suitable for single stage oil sealed vacuum pumps. It also reduces the sulphur content of the oil, which is one of the first constituents to break down in high temperature conditions. This oil has a straw color.
Double distilled oil
Going through a second distillation reduces the vapor pressure and the sulphur content even more. This oil can be used on slightly more aggressive processes and is used in two stage vacuum pumps that create a lower pressure. This oil has a paler straw color due to the lower sulphur content.
Ultra Grade Oil
This oil is a fairly recent addition to the vacuum pump industry, and used mainly on small laboratory sized two stage pumps. When Edwards introduced the RV model vacuum pumps in the early 1980s the running temperature of the pump was higher than other pumps to help increase the water vapor handling capacity. The double distilled oils available at the time had a shorter life when operating at a higher temperature. I was slightly involved in the project to develop hydro-treated oils for vacuum pump use that had a higher temperature rating and improved chemical resistance. Hydro treating is an alternative process to solvent refining.
White or Technical White oil
This oil has even more processing than single and double distilled oils to reduce the sulphur content, to the point that it has very little color at all. It can be used on processes that have chemical contamination, such as LCMS instruments (liquid chromatography mass spectrometer), and has a longer life than less processed oils. It appears that oil called “45” oil may be similar, but is a semi-synthetic oil. This “45” oil has fixed peaks on a mass spectrometer analysis that allows the mass spec user to eliminate these peaks when analyzing samples. Regular oil from oil wells around the world has similar peaks but they are not as stable as for the semi-synthetic product.
Flushing oils
Flushing oils are sold by a number of companies to help clean pumps that become contaminated. They are typically used only during a vacuum pump service to soften and remove baked on contaminants. The oil contains a higher amount of solvent product and may have a higher vapor pressure than regular vacuum pump oil.
Inert fluids
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Fig. 3. External oil filtration unit.
When vacuum processes include high concentrations of oxygen or other hazardous gases or gas mixtures a hydrocarbon based pump fluid becomes a problem. It can either be a fire hazard in the case of high oxygen flows or be chemically attacked in the case of many semiconductor type processes.
Initially, in my career, the first application that I saw requiring pump fluid other than oil was in the gas cylinder filling industry. Gas cylinders are evacuated one or more times during the process to dilute and eliminate any remaining gas from them before they are refilled. Cylinders containing different gases may be processed on the same filling system so there is a chance that oxygen gas may enter the vacuum pump on the system. Consequently, the standard vacuum pump fluid used by most gas cylinder companies was a fire “retardant” phosphate ester fluid. This fluid was not completely inflammable.
Later, when the semiconductor industry was in its infancy (1980s) most gas cylinder filling companies changed to using completely inert (inflammable) vacuum pump fluids called perfluoropolyethers (PFPE).
The brand names for these inert fluids are Krytox and Fomblin. They were developed for the space industry (NASA et al.) but were found to have lubrication properties in addition to being completely inert to any chemical attack.
By the end of the 1980s these inert fluids were being used in all “wet pumps” (fluid lubricated) in the semiconductor industry. Since then “dry pumps” (no fluid in the pumping volume) have been designed and perfected, but inert fluids are still used to lubricate gears and bearings that are outside the vacuum envelope of the pump.
Where to buy Vacuum Pump oils and fluids
This is not a forum to advertise or promote specific suppliers, but let me say this. No vacuum pump manufacturer or vacuum pump industry distributor processes oils or fluids for its own use. There are three companies that I know of in the USA who probably or possibly process base oils for vacuum pump use, I have not seen their plants to show otherwise. All vacuum pump manufacturers have their own “name and/or grade” for oils that they warranty as a suitable product for their pumps. Most vacuum pump oils, with low vapor pressure, are refined by specialized oil companies that can process relatively low volumes of product. These companies can “private label” the vacuum pump fluids they process in any container size and with any name on it.
You may pay a premium to buy your vacuum pump oils from a vacuum pump manufacturer, but you are assured of the correct fluid. Other suppliers may offer a cross reference to their product, but be careful that it is an equivalent. Lastly, I suggest that you never buy “vacuum pump oil” without knowing that it is the correct oil for your pump and application.
There are many different types of vacuum pumps, but what works best for vacuum forming and specifically our table top vacuum press? Each work differently and produce different levels of vacuum. Here is a quick run down of the common types and why we do or don’t recommend it.
Diaphragm Pumps are very quiet and durable and don’t use oil or have any oil mist. This type of pump can only produce medium vacuum levels (about 83.5%) and low CFM. These are not recommended for our thermoforming vacuum press.
Vacuum Generators require an air compressor and venturi pump to create a vacuum. They are very noisy and can create inconsistently high levels of vacuum. This type of pump transfers all the wear and tear to your air compressor and other expensive equipment. We do not recommend this for our presses.
Oil Filled Rotary Vane Pumps (RECOMMENDED) create the best vacuum for the cost. They are designed to run continuously for extended periods of time. There are lots of options for every budget. They are durable, inexpensive, easy to work with, require no additional equipment, and are easily adaptable to vacuum pressing.
What does 2 stage vacuum pump mean?
We believe Oil Filled Rotary Vane Pumps are the best choice and have designed our vacuum formers specifically to work with them. Each press includes fittings to convert this kind of pump to our easy connect system which is plug and play, or you can purchase one of our pre-converted vacuum pumps here
Single stage vs two stage
Two stage pumps cost up to twice as much as single stage…Say what? What is the difference other than price? A two stage design has two rotors and vanes. This means that the first stage generates vacuum and the second stage cleans the system, leading to a deeper ultimate vacuum level. As a result, two stage pumps can produce a deeper vacuum than single stage pumps.
Both single and two stage pumps can reach 29.92 inches of mercury at sea level (inHg possible based on altitude, see conversion chart here). When making your choice you should consider what you want to achieve. If your goal is faster evacuation, cleaner process, and quieter operation, then the answer is a two stage pump.
Centrifugal Pumps are the most popular and commonly used type of pump for the transfer of fluids. In simple words, it is a pump that uses a rotating impeller to move water or other fluids by using centrifugal force. These are the undisputed pump choice especially for delivering liquid from one location to another in numerous industries including agriculture, municipal (water and wastewater plants), industrial, power generation plants, petroleum, mining, chemical, pharmaceutical, and many others.
Centrifugal Pumps are useful since they can generally handle large quantities of fluids, provide very high flow rates (which may vary with the changes in the Total Dynamic Head (TDH) of the particular piping system) and have the ability to adjust their flow rates over a wide range.
Centrifugal pumps are generally designed and suitable for liquids with a relatively low viscosity that pours like water or light oil. More viscous liquids such as 10 or 20 wt. oils at 68-70 deg F will require additional horsepower for centrifugal pumps to work. For viscous liquids of more than 30 wt. oils, positive displacement pumps are preferred over centrifugal pumps to help lower energy costs.
The following information shall help you to understand more about these pumps and enable you to select the best kind of pump for your operations.
Power Zone Centrifugal Pump
Working of a Centrifugal Pump
Let us understand in detail, how a Centrifugal pump works. Centrifugal pumps are used to induce flow or raise a liquid from a low level to a high level. These pumps work on a very simple mechanism. A centrifugal pump converts rotational energy, often from a motor, to energy in a moving fluid.
The two main parts that are responsible for the conversion of energy are the impeller and the casing. The impeller is the rotating part of the pump and the casing is the airtight passage which surrounds the impeller. In a centrifugal pump, fluid enters into the casing, falls on the impeller blades at the eye of the impeller, and is whirled tangentially and radially outward until it leaves the impeller into the diffuser part of the casing. While passing through the impeller, the fluid is gaining both velocity and pressure.
The following chief factors affect the performance of a centrifugal pump and need to be considered while choosing a centrifugal pump:
What are the types of centrifugal pumps?
Working Fluid Viscosity – can be defined as resistance to shear when energy is applied. In general, a centrifugal pump is suitable for low viscosity fluids since the pumping action generates high liquid shear.
Specific density and gravity of working fluid – The density of a fluid is its mass per unit of volume. A fluid’s mass per unit volume and gravity of a fluid is the ratio of a fluid’s density to the density of water. It directly affects the input power required to pump a particular liquid. If you are working with a fluid other than water, it is important to consider the specific density and gravity since the weight will have a direct effect on the amount of work performed by the pump.
Operating temperature and pressure – Pumping conditions like temperature and pressures are an important consideration for any operation. For example – High-temperature pumping may require special gaskets, seals and mounting designs. Similarly, an adequately designed pressure retaining casing may be required for high-pressure conditions.
Net Positive Suction Head (NPSH) and Cavitation – NPSH is a term that refers to the pressure of a fluid on the suction side of a pump to help determine if the pressure is high enough to avoid cavitation. Cavitation refers to the formation of bubbles or cavities in liquid, developed in areas of relatively low pressure around an impeller and can cause serious damage to the impeller and lead to decreased flow/pressure rates among other things. One must ensure that the system’s net positive suction head available (NPSHA) is greater than the pump’s net positive suction head required (NPSHR), with an appropriate safety margin.
Vapour pressure of the working fluid – The vapor pressure of a fluid is the pressure, at a given temperature, at which a fluid will change to a vapor. It must be determined in order to avoid cavitation as well as bearing damage caused by dry running when the fluid has evaporated.
Owing to the use in the diverse range of applications, pumps come with different capacities and in various sizes. You should also consider the pressure and volume requirements of the specific operations for which you need the pump. The horsepower required is another important consideration when it comes to volume and discharge pressure.
Applications of Centrifugal Pumps:
The fact that centrifugal pumps are the most popular choice for fluid movement makes them a strong contender for many applications and as mentioned previously, they are used across numerous industries. Supplying water, boosting pressure, pumping water for domestic requirements, assisting fire protection systems, hot water circulation, sewage drainage and regulating boiler water are among the most common applications. Outlined below are some of the major sectors that make use of these pumps:
Oil & Energy – pumping crude oil, slurry, mud; used by refineries, power generation plants
Industrial & Fire Protection Industry – Heating and ventilation, boiler feed applications, air conditioning, pressure boosting, fire protection sprinkler systems.
Waste Management, Agriculture & Manufacturing – Wastewater processing plants, municipal industry, drainage, gas processing, irrigation, and flood protection
Pharmaceutical, Chemical & Food Industries – paints, hydrocarbons, petrochemical, cellulose, sugar refining, food and beverage production
Various industries (Manufacturing, Industrial, Chemicals, Pharmaceutical, Food Production, Aerospace etc.) – for the purposes of cryogenics and refrigerants.
Types of centrifugal pumps
Centrifugal pumps can be classified into several types depending on factors such as design, construction, application, service, compliance with a national or industry standard, etc. Therefore, one specific pump can belong to different groups and at times pump is known by its description itself. Some of these groups have been highlighted below:
Depending on the number of impellers in the pump, pumps can be classified as per the following:
Single stage – A one impeller pump, single stage pump has a simple design and easy maintenance. Ideal for large flow rates and low-pressure installations. They are commonly used in pumping services of high flow and low to moderate TDH (Total Dynamic Head).
Two-stage – This type of pump has two impellers operating side by side which are used for medium head applications.
Multi-stage – pump has three or more impellers in series; for high head service.
What is Pump Head? In simple words, the pump head is pressure defined as the height to which the pump can raise the fluid to. It is important as it evaluates a pump’s capacity to do its job. The most important specifications of a pump are its capabilities regarding flow and pressure.
Type of case-split
The Orientation of case-split is another factor used to categorize Centrifugal pumps:
Axial split – In these kinds of pumps, the volute casing is split axially and the split line at which the pump casing separates is at the shaft’s center-line. Axial Split Pumps are typically mounted horizontally due to ease in installation and maintenance.
Radial split – Here, the pump case is split radially; the volute casing split is perpendicular to the shaft center-line.
Categorized by type of impeller design
Single suction – This kind of pump has a single suction impeller that allows fluid to enter the blades only through one side; It has a simple design but impeller has a higher axial thrust imbalance due to flow coming in on one side of impeller only.
Double suction – This particular type of pump comes with a double suction impeller that allows fluid to enter from both sides of the blades and has lower NPSHR than a single suction impeller. Split-case pumps are the most common type of pump with a double suction impeller.
If a pump has more than one impeller, the design of the first stage impeller will determine if the pump is of a single or double suction type.
On the basis compliance with industry standards
While choosing a centrifugal pump, the buyers should be selective based on the quality standards they have to achieve. They need to check for the following:
ANSI pump – (American National Standards Institute) – ANSI standards refer to dimensional standards. The pumps are also required to meet ANSI B73.1 standards, also known as ASME B73.1 – (American Society of Mechanical Engineers). The objective of this standard is to ensure interchangeability of ANSI process pumps of similar sizes. These centrifugal pumps are horizontal, end suction, single stage pumps and are comparable regardless of manufacturer.
API pump – (American Petroleum Institute) API’s standard refers to the parameters of pump’s construction, design, and ability to handle high temperatures and pressures. API 610 specifications and a variety of API types include API VS4, API VS7, API OH3, API OH2, API OH1, API BB1, API BB2, API BB3 etc. Centrifugal pumps must meet the requirements of the American Petroleum Institute Standard 610 for General Refinery Service.
DIN pump – DIN 24256 specifications. Centrifugal pumps satisfying these standards are used in installations requiring large flow rates, abnormally high working pressures or very high temperatures. Rarely used in mechanical building services.
ISO pump – ISO 2858, 5199 specifications, the international standard ISO 5199 specifies the requirements for class II end suction centrifugal pumps of single-stage, multistage, horizontal or vertical construction, with any drive and any installation for general application.
Nuclear pump – ASME (American Society of Mechanical Engineers) specifications
By type of volute
Centrifugal pumps can also be categorized based on volute namely Single volute and Double volute:
Single volute – This kind of pump Is usually used in small low capacity pumps where a double volute design is impractical due to a relatively small size of the volute passageway which makes obtaining good quality commercial casting difficult. Pumps with single volute design have higher radial loads.
Double volute – This kind of pump volute has two partial volutes which are located 180 degrees apart resulting in balanced radial loads; most centrifugal pumps are of double volute design.
Depending on where the bearing support is
Bearing support is also often used to categorize Centrifugal Pump:
Overhung – where the impeller is mounted on the end of a shaft, supported by bearings on only one side. Further, the overhung pump type has a horizontal orientation of shaft or can be vertical in-line with bearing bracket.
Between-bearing – where the impeller is mounted on a shaft that has bearing support on both ends, thus impeller is located in between-bearings. Examples are Axial Split Vertical Split Case
Depending on shaft orientation
Shaft orientation is another characteristic which distinguishes the type of Centrifugal pump:
Horizontal – These are pumps with the shaft the in horizontal plane; popular due to ease of servicing and maintenance. It is sometimes overhung or placed between bearing design.
Vertical – Vertical centrifugal pumps have their shaft in the vertical plane. They utilize a unique shaft and bearing support configuration that allows the volute to hang in the sump while the bearings are outside the sump. it is generally an overhung and of radial-split case type design.
The following highlights the difference between the above two:
Horizontal Centrifugal Pump
Vertical Centrifugal Pump
Easy availability of its rotor and internals makes it easier to install, inspect, maintain, and service.
It can be coupled directly to a variety of drivers includian ng electric motor, engine, and turbine (steam, gas or power recovery hydraulic turbine
It is available in either overhang design for low suction pressure service, or in between-bearing design for high suction pressure service.
It is available in various nozzle configuration to simplify, or match the external site piping. The nozzle configuration can be of end suction top discharge, top suction top discharge, or side suction side discharge.
Its low headroom requirement makes it suitable for most indoor installations.
It has limited applications where the NPSHR exceeds the site NPSHA; Large pumps usually require an auxiliary booster pump. (With a vertical lineshaft pump, the NPSHA can be increased by lowering the setting of its impeller.
Bigger footprint is required for horizontal designs.
Most of them require large headroom for installation, servicing, and maintenance. Being of an overhang design, its hydraulic axial thrust is difficult to balance in high pressure service.
Usually suitable for direct coupling to an electric motor. Using an engine or turbine, will require a right-angle gear drive and a universal shaft joint and a clutch.
It can more easily withstand higher pressure service because of its simplified bolting and confined-gasket design
It requires a smaller footprint and is suitable for installation where the ground surface area is limited, or is at a premium.
With a vertical lineshaft pump, the impeller setting below the ground can be lowered to increase the site NPSHA.
Vertical lineshaft turbine pumps, require large headroom for installation, servicing, and maintenance.
Expensive sump pit and barrel in a multistage pump is usually required.
There can be mechanical seal problems when pumping liquids with high dissolved or entrained gas which accumulates at the top of the stuffing box or seal chamber where venting can be difficult or less effective.
A positive displacement pump. For each revolution of the pump, a fixed volume of fluid is moved regardless of the resistance against which the pump is pushing. It is self-priming, and gives practically constant delivered capacity regardless of the pressure. The rotary pump consists of a fixed casing containing gears, cams, screws, plungers or similar elements actuated by rotation of the drive shaft. A number of pump types are included in this classification, among which are the gear pump, the screw pump, and the rotary vane pump.
Rotary pumps are useful for pumping oil and other liquids of high viscosity. In the engine room, rotary pumps are used for handling lube oil and fuel oil and are suitable for handling liquids over a wide range of viscosities. Rotary pumps are designed with very small clearances between rotating parts and stationary parts to minimize leakage (slippage) from the discharge side back to the suction side. Rotary pumps are designed to operate at relatively low speeds to maintain these clearances. The operation at higher speeds causes erosion and excessive wear which result in increased clearances with a subsequent decrease in pumping capacity. Classification of the rotary pumps is generally based on the types of rotating element.
– Gear pump – The simple gear pump has two spur gears that mesh together and revolve in opposite directions. One is the driving gear, and the other is the driven gear. Clearances between the gear teeth (outside diameter of the gear) and the casing and between the end face and the casing are only a few thousandths of an inch. As the gears turn, they unmesh and liquid flows into the pockets that are vacated by the meshing gear teeth. This creates the suction that draws the liquid into the pump. The liquid is then carried along in the pockets formed by the gear teeth and the casing. On the discharge side, the liquid is displaced by the meshing of the gears and forced out through the discharge side of the pump.
How does a rotary pump work?
– Rotary vane pumps – The rotary vane pump has a cylindrically-bored housing with a suction inlet on one side and a discharge outlet on the other side. A rotor (smaller in diameter than the cylinder) is driven about an axis that is placed above the center line of the cylinder to provide minimum clearance between the rotor and cylinder at the top and maximum clearance at the bottom. The rotor carries vanes (which move in and out as the rotor rotates) to maintain sealed spaces between the rotor and the cylinder wall. The vanes trap liquid on the suction side and carry it to the discharge side, where contraction of the space expels liquid through the discharge line. The vanes slide on slots in the rotor. Vane pumps are used for lube oil service and transfer, tank stripping, bilge, and in general, for handling lighter viscous liquids.
– Screw pump – There are several different types of screw pumps. The differences between the various types are the number of intermeshing screws and the screw pitch. Screw pumps are used aboard ship to pump fuel and lube oil and to supply pressure to the hydraulic system. In the double-screw pump, one rotor is driven by the drive shaft and the other by a set of timing gears. In the triple-screw pump, a central rotor meshes with two idler rotors. In the screw pump, liquid is trapped and forced through the pump by the action of rotating screws. As the rotor turns, the liquid flows in between the threads at the outer end of each pair of screws. The threads carry the liquid along within the housing to the center of the pump where it is discharged. Most screw pumps are now equipped with mechanical seals. If the mechanical seal fails, the stuffing box has the capability of accepting two rings of conventional packing for emergency use.
