What is difference between centrifugal pump and rotary pump?
What is difference between centrifugal pump and rotary pump?
How do Centrifugal and Positive Displacement Pumps Work?
Nearly all pumps fall within these two categories, with centrifugal being the most common. However, positive displacement pumps come in a wider variety such as gear, lobe, peristaltic, screw, and many other types of pumps.
The most common type among centrifugal pump is the radial flow pump. These centrifugal pumps use a rotating impeller to create a vacuum in order to move fluid. The pump’s impeller rotates within the housing and reduces pressure at the inlet. This motion then drives fluid to the outside of the pump’s housing, which increases the pressure enough to send it out the discharge.
There is also the axial flow centrifugal pump which uses a curved propeller-shaped impeller, whereas the impeller on a radial flow centrifugal pump looks more like a fan. Axial flow pumps move fluid by drawing fluid into their axis and using the impeller to send fluid out on the other side of the pump.
Positive displacement pumps draw fluid into a compartment at the inlet and move it to an outlet for discharge, most typically using a rotary, reciprocating, or diaphragm method to move fluid. The main difference between these types of pumps and centrifugal is that positive displacement pumps will move fluid at the same speed regardless of the pressure on the inlet end and centrifugal pumps will not.
Which Pumps Are Used in The Upstream Oil and Gas Industry?
Both of these types of pumps are essential components in the oil and gas industry. They are commonly used as part of tri-phase or multiphase pumping applications in which two or more types of pumps are used to accommodate all fluids, a process that offers reduced equipment costs, simpler installation, improved production, and a smaller footprint.
What is difference between centrifugal pump and rotary pump?
Centrifugal Pumps Used in The Oil and Gas Industry
Electric Submersible Pump (ESP) – These pumps are typically submerged entirely in the fluid to be pumped and are specifically designed to combat pump cavitation. Instead of pulling fluids, the mechanisms in these pumps push fluids, making them far more reliable and efficient than previously utilized jet pumps. Newer ESP models can also include a water and oil separator which permits water to be re-injected into the reservoir without the need to lift it to the surface, saving both time and operating costs.
Helico-Axial Pump – Also called a Poseidon pump, this centrifugal pump uses multiple stages of impellers and vanes to move fluids. Compression is accomplished with the transfer of kinetic energy from the rotating impeller blades through circles of guide vanes in order to move fluid. This pump is often used in offshore and deep water developments.
Deep Well Pump – The industry is beginning to lean more towards these types of pumps especially the deep well seawater lifting and fire pumps. They can have capacities of up to 2,600 cubic meters and offer added safety protection for offshore production. Many of these pumps use radial-designed impellers for smaller capacities and a semi-radial design for larger capacities, which can result in an MTBR of 25,000 hours or more.
Positive Displacement Pumps Used in The Oil and Gas Industry
Progressive Cavity Pump – Also known as eccentric screw or single screw pumps, these types of pumps are utilized for their ability to transfer difficult liquids, such as those that containing solids or highly viscous fluids. They work by using a single screw or rotor inside a double-threaded rubber stator to build pressure and move fluid. They are mostly used in shallow wells or at the surface.
Twin Screw Pump – This pump works by rotating to form chambers with the intermeshing of the two screws inside the pump housing. The chambers fill with fluid and move it from the suction side to the higher pressure discharge side of the pump, a process that can be reversed in some twin screw pumps. They can handle virtually any non-homogeneous fluid with any of abrasiveness, lubricity, and viscosity. Twin pumps are most often used in situations that contain high gas volume fractions and fluctuating inlet conditions.
Other Pumps Used in The Oil and Gas Industry
Deep Well Submersible Pump – Just what it sounds like, this vertical is submerged in deep waters for the purpose of performing a number of upstream processes. The unit is oil-filled, which allows it to be reliable and long lasting while offering reduced cost in total life cycle. It operates with the use of heavy-duty impellers, dual bearings, and multiple seal options. In addition, these pumps can handle flows of up to 6,000 cubed meters, heads to 800 meters, and speeds up to 3,600 rpm.
Chemical Process Pump – These pumps are used in the handling of harmful chemicals in many industries, including upstream oil and gas. They can convey hazardous or corrosive chemicals efficiently in order to avoid any damage occurring at the working place whether to equipment or personnel. The chemical process pump uses a combination of close coupling, heavy duty casing, specialty impellers, a sealed chamber, and other mechanisms to remove the harmful chemicals.
Oil Skimmer Aluminum Lobe – These rotary lobe pumps can be used upstream, midstream, and downstream. The pump is lightweight, compact, has a large flow range, dry run capabilities, and conveys highly viscous fluids.
Multiple Screw Pump Line – One of the newest introductions into the global markets, this Multiple Screw Pump Line includes double, geared-twin, and triple screw pumps. It offers ranges to 2500 gpm / 1160 psi. It can also handle high and low viscosities, as well as lubricating and non-lubricating liquids.
What is a dry vacuum pump?
A dry vacuum pump is a form of pump that does not utilize any fluids in the creation of a vacuum. The dry vacuum pump also avoids contact with processed gas that can dissipate into the atmosphere. As a result, a dry vacuum pump is prone to high temperatures during operation as there are no liquids to absorb the resulting from the pump’s operation.
How Does a Dry Vacuum Pump Beat the Heat?
In order to counteract the heat generated, the dry vacuum pump uses a cooling jacket in its design. The absence of the cooling jacket, or any cooling mechanism, would lead to excessive heat in the unit leading to the failure of the motor.
The only fluids that are present in a dry vacuum pump are the oil reservoirs in the timing gears. To avoid leakage of any fluid of any kind, there are only microscopic clearances between the rotors and the housing.
Vapors are No Match for These Pumps
One of the best attributes of a dry vacuum pump is its ability to handle corrosive vapors as well as substances that run through the pump. The absence of any moisture prevents any corrosion from occurring in the unit.
Another attribute of a dry vacuum pump is its construction. Most often, iron is used as the basic metal for a dry vacuum pump. These pumps are not built from stainless steel or high alloy materials because of the high temperatures generated by the operation of the pump. Alloys are unable to handle the heat during operation, which often leads to breakdown of the overall structure.
As can be seen, there are some basic characteristics that define a dry vacuum pump. These include the absence of any fluids in the pump mechanism except the oil in the timing gears. The dry vacuum pump can ably manage corrosive fluids and substances because of the absence of fluids. The only drawback is the extreme temperatures generated during operation.
How do you replace a vacuum pump?
Vacuum Pump Repair Service
What is the Vacuum Pump all about?
While all gasoline engines create vacuums during operation, sometimes the amount created isn’t enough to power the accessory systems in the car. Diesel engines do not create vacuums at all during operation. In both of these instances, a vacuum pump is used to either augment or provide the vacuum power necessary to operate the various other systems on the car, including the brakes, some HVAC functions and more. The vacuum pump is usually located behind the engine, mounted near the firewall and close to the master cylinder and brake booster. It’s easily recognizable for its two nozzles on top, as well as the design of the canister. It is an electric air pump that maintains a constant amount of vacuum in the vacuum reservoir behind the front bumper. If the vacuum pump stops working or develops a leak, the engine compartment may release a hissing sound, the heater controls may not switch when operated, or the brake pedal may be hard to depress.
Keep in mind:
The vacuum pump is an electronic component that can experience both electrical and mechanical problems.
The vacuum pump is not designed to be serviced, so it will not be inspected during routine maintenance aside from a vacuum line inspection.
Leaks in vacuum lines can mimic symptoms of vacuum pump failure.
How it’s done:
The faulty vacuum pump is located and identified
The valve vacuum pump is then removed
The new vacuum pump is then installed
The brakes are tested for proper vacuum pump operation
The vehicle is road tested and checked for proper vacuum pump and brakes operation
Our recommendation:
The vacuum pump, which is expected to last the life of your vehicle, does not receive any maintenance and is only serviced when it fails. If you are experiencing symptoms related to the vacuum system, have your vehicle diagnosed by one of our expert mechanics.
What common symptoms indicate you may need to replace the Vacuum Pump?
Heater controls don’t operate properly
A hissing air sound is present
Brake pedal is very hard to press
How important is this service?
If the vacuum pump fails, your brakes may not operate properly and vehicle operation becomes unsafe. Have your vacuum pump replaced immediately if it is diagnosed as faulty.
What is the principle of vacuum pump?
Industrial Vacuum Pump Working Principles
In years past, industrial vacuum pumps were known for their loud operation, substantial amount of oil carryover, and large energy costs. No longer! Significant developments in vacuum pump technology have resulted in advances in the energy usage, reliability, noise levels, and overall performance of these machines. Let’s learn more about the current working principles of the four main categories of industrial vacuum pumps.
Rotary Vane Vacuum Pump
This tried and true technology has been the focus of many technology updates over the years. In this vacuum pump, vanes are mounted to a rotor rotating inside of a circular casing and move outwards via centrifugal force. Compared to earlier versions, the current rotary vane vacuum pumps are quieter, more compact, have a lower energy demand, and also operate at lower temperatures. They even incorporate internal injection channels! These are well suited for usage in paper and printing applications, woodworking, and material handling.
Screw Vacuum Pump
In the screw vacuum pump, two screw rotors rotate in opposite directions. Compared to the typical oil-sealed or dry vane vacuum pump, this technology is hallmarked by lower heat and noise levels, but higher performance levels. If you choose to add in electronic process controllers or VSD (variable speed drive), they can be extremely cost-effective choices. Industries that use this pump include glass, canning, plastics, and food packaging.
Liquid Ring Vacuum Pump
As the impeller of a liquid ring vacuum pump rotates, water (which is the typical seal liquid used in this type of vacuum pump, though other liquids can be employed) is thrown about to form a literal “liquid ring.” This, in turn, seals the impeller and creates separate enclosed gas chambers between each blade. Liquid ring pumps are optimal for handling extreme vapor loads, or in applications with high tolerance for liquid carryover. Examples include usage in breweries, food production, and in the dairy industry.
Dry Claw Vacuum Pump
Dry claw vacuum pumps are advantageous in that there is no threat of contamination to the application, as there isn’t any lubrication in the main pumping chamber! The two claw-shaped rotors do not touch during operation, which eliminates wear – and thus decreasing service needs & overall ownership cost. They are also one of the most quiet pumps, and can be combined into one housing with multiple units. Applications such as pneumatic conveying, packaging lines, drying processes, and central vacuum supply systems commonly use the dry claw vacuum pump.
How long do vacuum pumps last?
The hydraulic braking system on your car is very complicated. Without all of the various components of this braking system working together, it will be very hard for you to retain the stopping power of your car. The brake booster vacuum pump is among the most essential and complicated parts of your braking system. When you hit the brake pedal on your car, the metal rod goes through your brake booster and into the master cylinder. In order for the braking system on your car to work in a split second, there needs to be pressure put on the brakes when the brake pedal is pushed. The brake booster vacuum pump is only used when the brakes are activated.
The brake booster vacuum pump helps to create the pressure that is put to the brakes of the car to bring it to a stop. Having optimal stopping power is only possible with a properly working brake booster pump. The brake booster vacuum pump on your car is designed to last for the life of the vehicle. There are so many different things that can lead to this part becoming damage. The continuous use that the brake booster vacuum pump is what will usually lead to it becoming damaged.
Driving your car with a worn out brake booster vacuum pump can lead to diminishing braking power. As soon as you start to notice that there may be issues with this part of your braking system, you will need to get the proper repairs done to avoid the danger that comes with diminished braking power. Here are some of the things that you will notice when it is time to get your brake booster vacuum pump replaced:
Braking response is delayed
More pressure is needed to make the brakes engage
A noticeable hissing sound when the brakes are applied
The brake pedal goes to the floor without pressure being applied
What is the difference between vane pump and gear pump?
What is the difference between vane pump and gear pump?
A Positive Outlook
First, a bit of background. Positive displacement (PD) pumps were developed long before centrifugal pumps. Greek mathematician Archimedes is said to have invented the first screw pump around 225 B.C. The operation of PD pumps is signified by the displacement of a known quantity of liquid with each revolution of the pumping elements, which can include vanes, lobes, gears, rotors, screws, etc.
The liquid is displaced through the spaces that are created between the PD pump’s specific pumping elements. After the liquid is collected in this space, the movement of the pumping elements transports it to the discharge port. In general, this method of operation allows PD pumps to handle liquids with viscosities up to 1,320,000 centistokes (cSt)/6,000,000 Saybolt Seconds Universal (SSU); capacities up to 1,150 cubic meters per hour (m3/hr) or 5,000 gallons per minute (gpm); and pressures up to 700 bar or 10,000 pounds per square inch (psi).
a chemical processing facilityImage 1. The operational and energy-efficiency capabilities of positive displacement sliding vane pumps, like those seen above in a chemical processing facility, can help operators successfully overcome processing issues. (Images courtesy of Blackmer)
Today, according to the Hydraulic Institute, pumps account for nearly 27 percent of total electricity use in the industrial sector. While centrifugal-style pumps remain the most-used technology in industrial fluid-handling applications, there is no “one pump fits all” solution. This opens the door for operators to consider the benefits PD pumps can offer from an efficiency and energy-savings perspective, even in applications that have traditionally relied on centrifugal pumps.
When making the final choice in pump type, several crucial factors need to be taken into account, including required flow rate, suction and differential pressure, temperature, viscosity, weight and corrosiveness of the liquid being handled. In addition, facility managers too often choose oversized pumps as a fallback under the erroneous belief that such equipment will address future capacity needs.
These decisions ignore the added energy costs that are inherent in continuously operating oversized pumps.
A mechanical efficiency comparison between sliding vane and gear pumpsImage 2. A mechanical efficiency comparison between sliding vane and gear pumps shows that from the lowest to highest viscosities, sliding vane technology delivers the highest level of mechanical efficiency, which equates to the lowest overall energy consumption.
While the majority of the world’s pumping tasks may be performed with centrifugal-style pumps, PD pumps can become a top-of-mind choice when facility operators are apprised of the functionality PD pumps can offer users, including:
PD pumps are inherently self-priming. Centrifugal pumps must be pre-primed. Industrial facilities can design their process around this by including pre-fill cycles, minimum tank levels or expensive below-grade installations. On the other hand, industrial facilities can reduce or eliminate these considerations by using a PD pump that is inherently self-priming. This capability allows the PD pump to draw a suction vacuum and compress air into the discharge piping, all while dry running. This enables the pump to be used in top-offload suction-lift installations or with long sections of suction pipe.
PD pumps can line strip. Product recovery is critical for both safety and cost savings. PD pumps left on after a batch cycle can evacuate the suction and discharge piping, preventing product spillage when the pumps are maintained or when an operator disconnects a hose. This is a critical safety advantage. Further, PD pumps can extract costly products from the bottom of supply tanks (known as the liquid “heel”). The site may purchase an entire tanker, but a portion of the liquid may be left behind by centrifugal pumps, which creates the risk of product cross-contamination, as well as increased tank-cleaning costs. PD pumps can also recover liquid from within the piping system.
PD pumps are insensitive to the system’s pressure fluctuations. Some operations feature a batch process, have high backpressure or struggle with operating near a centrifugal pump’s best efficiency point (BEP). PD pumps do not have a BEP and are immune to any system pressure fluctuations.
PD pumps are viscosity flexible. There is no reduced performance at increasing viscosity (or decreasing viscosity for ultrathin multiphase liquids). PD pumps can operate continuously at 0.2 centipoise (cP) or 200,000 cP viscosities. In fact, many PD-style pumps can be used on a thin solvent and on thick crude oil, which makes them ideal for liquid-terminal or bulk-transfer applications.
PD pumps operate at reduced speeds. This capability reduces the surface velocity of rotating seal faces and improves seal life. PD pumps often require less than 500 revolutions per minute (rpm), which yields slower sealing velocities, friction-heat buildup and the cooling-lubrication needs of the seal. The result is that seals are more robust, resulting in longer component life and reduced maintenance costs over the life of the pump.
PD pumps are available in two categories—reciprocating and rotary, with rotary pumps consisting of single- or multiple-rotor configurations.
This article will address rotary PD pumps. By their design and operation, rotary pumps displace a fixed quantity of liquid for every rotation of the pump shaft. Again, vanes, lobes, gears and screws are among the pumping elements that can be used to facilitate the transfer of the liquid.
Within the single-rotor rotary-pump family tree resides sliding vane pumps. The design of the sliding vane pump places a series of metal or plastic “vanes” in dedicated slots in an offset rotor in the pump casing. As the rotor spins past the suction port, the vanes are forced out of their slots and ride against the inner bore of the pump casing, forming pumping chambers.
The pumping chambers trap the liquid and transport it around the pump casing to the discharge port, where it flows into the discharge piping. This design virtually eliminates product “slip” (the movement of the fluid being handled against the direction it is being pumped), meaning that the pump’s high volumetric efficiency is maintained.
The method of operation also makes sliding vane pumps ideal for use with thin, low-viscosity liquids, such as propane, ammonia, solvents, alcohol, gasoline, fuel oil, petroleum-based chemicals, refrigerants, and multiphase and high vapor-pressure liquids with zero net positive suction head available (NPSHa).
Based on their self-compensating design that accounts for pumping element wear through the extension of the vanes during operation, PD sliding vane pumps are energy and mechanically efficient. Other operational advantages of sliding vane pumps include:
dry-priming capability that allows them to run dry for extended periods
superior suction-lift capabilities
ideal operation in low-flow, high-head applications
low-pulsation, low-vibration pumping for shear-sensitive liquids
suitability for use in metered-flow applications
optional sealless construction for elimination of potential leak paths
easy vane replacement
Sliding Vane vs. Gear Pumps
Rotary self-compensating sliding vane pump technology was developed in the early 1900s by an engineer who was looking for a solution to ill-performing gear pumps that were consistently wearing and losing volumetric efficiency, leading to product slip that hampered flow rates.
At the time, gear pumps were far and away the most common type of PD pump used in industrial liquid-handling applications. There are two typical types of gear pumps: internal and external gear, both of which transport liquids through the action of a series of gears coming into and out of mesh. While the pumping action for both is comparable, external gear pumps use two similar rotating gears to mesh, whereas the internal gear pump uses a drive, or rotor, gear operating against a smaller internal, or idler, gear.
Both modes of gear pumps possess some advantages that are similar to sliding vane pumps—nonpulsing, self-priming and dry-run capability; ability to handle thin liquids at varying pressures; and ease of maintenance.
But because of the style of operation, gear pumps wear as the pump’s gears mesh, or come into contact with each other, to move fluid. This increases the internal pumping clearances, reducing flow capacity that results in less fluid pumped per rotation while simultaneously increasing slip within the pump. To compensate for these larger clearances the pump speed or size must be increased, which can result in higher energy consumption and accelerate the pump’s wear.
The alternative in this gear-wear scenario is to tolerate a lower level of pumping capacity until the pump’s performance drops to an unacceptable level.
However, the gear wear can often go undetected by the operator, which can sap the pump of efficiency—both energy- and performance-related—before the necessary maintenance can be performed.
Conversely, because the self-compensating vanes in the sliding vane pump continuously adjust for wear, they can allow the pump to maintain near-original efficiency and capacity throughout their life. The pump speed also does not need to be increased over time, making sliding vane pumps natural energy-savers.
If the sliding vanes wear out or are damaged, replacing them is quick and easy. Vane replacement can be accomplished by simply removing the pump’s outboard head assembly, removing the old vanes, inserting new ones and reinstalling the head, all without the need for special tools. Also, it is not necessary to remove the pump from the system. All replacements can be completed while the pump remains in line.
Future Energy Consumption Predictions
To the surprise of probably no one, in its International Energy Outlook 2017 report, the U.S. Energy Information Administration (EIA) predicted world energy consumption would rise 28 percent between 2015 and 2040, from 573 quadrillion British thermal units (Btu) in 2015 to 736 Btus by 2040. This extrapolation is supported by the EIA’s “Reference case,” which “assumes continual improvement in known technologies based on current trends and relies on the views of leading economic forecasters and demographers related to economic and demographic trends for 16 world regions based on Organization for Economic Co-operation and Development (OECD) status.”
world energy consumptionImage 3. According to the Energy Information Administration’s (EIA) International Energy Outlook 2017, world energy consumption will increase from 575 quadrillion British thermal units (Btu) in 2015 to 736 quadrillion Btu by 2040. This will put pressure on operators in the industrial sector to optimize energy consumption while still satisfying demanding production rates.
What is the OECD? Founded in 1961, the OECD is an intergovernmental organization that is committed to stimulating economic progress and world trade. There are 36 OECD countries, including the United Kingdom and the United States.
Related to the rate of growth in world energy consumption, the EIA predicted that the global industrial sector—for this article’s purposes, the manufacturing, mining, agriculture, and construction industries—will continue to account for the largest share of energy consumption through 2040. At an annual growth rate of 0.7 percent, global industrial energy use will increase a total of 17.5 percent from the 240 quadrillion Btus in 2015 to 280 quadrillion Btus by 2040.
the industrial sector will continue to account for the largest share of energy consumption through 2040Image 4. The EIA’s International Energy Outlook 2017 predicts that the industrial sector will continue to account for the largest share of energy consumption through 2040.
The main reason behind this steady increase in energy consumption should be equally obvious—the world’s population continues to increase, with the United Nations’ Department of Economic and Social Affairs saying that the current population of 7.6 billion people will expand to 8.6 billion in 2030 and 9.8 billion by 2050. This consistent population growth is most significant in developing, non-OECD countries, and is being driven by improvements in infrastructure, food production and health care that have created a better standard of living for many of those countries’ residents.
Meeting Demands
Today, the task of outfitting an industrial facility with pumps is so much more complex than picking a technology, turning it on and watching it go.
With demanding production schedules, tight operating budgets and environmental-safety concerns to consider, facility operators must identify and implement pumping technology that can reliably satisfy these demands, which can appear to be at odds with each other.
The operational characteristics of sliding vane pumps have held many advantages over centrifugal pumps and other PD-pump technologies in the areas of maintaining flow rates and optimizing energy efficiency—especially if the application requires the handling of nonabrasive liquids at temperatures less than 500 F (260 C) and with viscosities less than 22,500 cP.
In the end, the main goal of today’s industrial manufacturer is to improve pump performance in an era where consistent global energy consumption and population growth continue to put pressure on them to control energy usage while maintaining strict production rates. Sliding vane pumps can play a role in meeting those demands.
Mechanical vacuum pumps used in laboratories pose many hazards. There are mechanical hazards associated with the moving parts. There are chemical hazards of contaminating the pump oil with volatile substances and subsequently releasing them into the lab. There are also fire hazards when pumps malfunction or overheat and ignite nearby flammable or combustible materials.
Follow these Guidelines for Safe Pump Operation:
Physical (injuries/fires)
Ensure that pumps have belt guards in place during operation to prevent hands or loose clothing from getting caught in the belt pulley.
Ensure that electrical cords and switches are free from defects.
Do not place pumps in an enclosed, unventilated cabinet allowing heat and exhaust to build up.
Do not operate pumps near containers of flammable chemicals, flammable chemical wastes, or combustible materials such as paper or cardboard.
Use correct vacuum tubing (thick walls) not thin Tygon-type hoses.
Replace old tubing; crumbly tubing can degrade performance.
Use the shortest length of tubing that reaches where needed.
Chemical
Do not use solvents which might damage the pump.
Always close the valve between the vacuum vessel and the pump before shutting off the pump to avoid sucking vacuum oil into the system.
Place a pan under pumps to catch oil drips.
Check oil levels and change oil when necessary. Replace and properly dispose of vacuum pump oil that is contaminated with condensate. Used pump oil must be disposed as hazardous waste.
With oil rotary pumps many vapors condense in the pump oil. Solvents in the oil degrade its performance (and eventually ruin the pump), create a chemical hazard when the oil is changed, and are emitted in an oil mist vented from the system. Other vapors pass directly into the exhaust stream. To avoid these problems:
Trap evaporated materials with a cold trap before they reach the pump. Depending on the material that is to be trapped, this can be a filtration flask either at room temperature or placed in an ice bath. For more volatile solvents more sophisticated options exist (e.g. dry ice trap).
Vent the pump exhaust properly.
Personnel
Conduct all vacuum operations behind a table shield or in a fume hood and always wear safety glasses, lab coat, and gloves.
Keep a record for each pump to record oil change dates and to keep track of the maintenance schedule.
Vacuum Pump Oil: The “Circulatory System” of the Vacuum Furnace
One of the most critical parts of a vacuum system is the pump oil. Just as vacuum pumps can be considered the heart of the vacuum furnace, so too can the oil be thought of as its circulatory system. The selection and properties of the oil are critical to proper furnace operation. Pump oil serves different purposes in different types of pumps and even has different functions within the same pump. In addition to lubrication, it helps to provide the seal on the rotary vane and other wet pumps and serves as the media to propel the pumped gas via kinetic action in diffusion pumps.
“Oil” is a bit of a misnomer because modern pump oil technology has evolved well beyond the original distilled petroleum products. There are now double- and triple-distilled oils available, as well as hydro-treated oils, low sulfur oils, silicone-based synthetic oils, and flushing oils used to clean the pump. Due to the wide variety of formulations available, these are often now referred to as pump “fluids” rather than pump “oils”.
The oil in a vacuum pump serves several purposes. In addition to providing lubrication for mechanical components such as found in rotary vane pumps, the oil also provides the following:
A seal across the vanes and duo seal between the high pressure and low-pressure side of the pump.
Cooling of the pump by conducting heat from the stator to the outer casing where it can be dissipated.
Protection of the metal parts from corrosion caused by the pumped gas.
In diffusion pumps, the oil is used to trap and remove gas molecules from the vacuum chamber through kinetic motion.
Due to these multiple roles, the properties of the oil selected by the manufacturer must be carefully evaluated. If the oil is not properly selected, pump performance will be negatively affected and the pump possibly even damaged.
Different pump oil formulations are specifically designed for different pumps and different vacuum applications. Therefore the user of the vacuum system must have a basic understanding of pump oils in order to make the correct selection. SAE 30 motor oil, for example, is not properly refined for use in a vacuum pump, has inadequate chemical resistance, and contains additives such as rust inhibitors that would separate out from the base fluid and deposit on interior surfaces as a gummy residue. Vacuum pump oil additives are limited to corrosion resistance, anti-oxidation, and anti-foaming. Although vacuum pump oil costs much more, it cannot be substituted by motor oil. In order to choose the correct pump oil, it is useful to understand vapor pressure, viscosity, and distillation methods.
Oil Formulations
Different pump oil formulations are specifically designed for different pump applications and careful consideration must be given to the oil selection. Typical motor oil, for example, is not sufficiently refined for use in a vacuum pump,
has insufficient resistance to chemical attack, and contains additives that may be detrimental to the process being performed in the vacuum furnace. In addition, the viscosity must be considered. Lower viscosity oils are used for lower operating temperatures, and for smaller pumps, and medium viscosity oils are used for medium to large pumps. Temperature resistance is also critical, as many pumps operate at high temperatures, and the oil must be rated for these temperatures. Many of the oils used in vacuum pumps are not traditional oils at all, but made of silicone or other non-hydrocarbon fluids.
What is Vapor Pressure
In all vacuum pumps, the oil vapor pressure is important because the oil is exposed to the gas being pumped from the chamber. If the oil vapor pressure is too high, it will vaporize when exposed to vacuum, and the vapor can contaminate the vacuum chamber (referred to as backstreaming). For this reason, the vapor pressure is one of the factors dictating the ultimate vacuum the pump can achieve.
Vapor pressure (evaporation pressure) is best understood as the tendency of pump oil (and all other liquids) to evaporate and can be thought of as the pressure with which the oil molecules try to escape the oil as a vapor. A higher vapor pressure refers to a higher tendency to evaporate, and a lower vapor pressure indicates a lower tendency to evaporate. More specifically, a lower vapor pressure means the oil will not evaporate as easily when exposed to a given pressure and temperature in the surrounding environment (the pump chamber). Since it is desired that the oil not evaporate when exposed to the low pressures in a vacuum pump, low vapor pressure is a desirable property of pump oils. For example, if an oil has a vapor pressure of 10-3 mbar at a certain temperature, it will start to evaporate if the pressure inside the pump drops below this value at that temperature. For this reason, the oil vapor pressure is one of the factors limiting the ultimate vacuum the pump can achieve.
The viscosity of Pump Oil
The viscosity of a fluid is a measure of its resistance to flow and can be thought of as the thickness or stickiness of the fluid (Fig. 1). Viscosity is expressed in units of centipoise (cP), and the higher the viscosity, the greater the “stickiness” of the liquid. An oil’s viscosity is determined mainly by the size of the molecules. Larger molecules result in higher viscosity, and smaller molecules provide lower viscosity. The size and structure of mineral oil molecules, for example, vary, so the average molecule size dictates the viscosity (Fig. 2), whereas synthetic oil features consistently sized molecules of an identical structure.
Figure 1 | Viscosities of various liquids 3
Figure 1 | Viscosities of various liquids3
Figure 2 | Duo seal in a rotary pump4
Figure 2 | Duo seal in a rotary pump4
One can easily understand how oil viscosity would help coat the pump interior and moving parts, allowing them to operate smoothly, but viscosity also helps seal the pump by preventing the pumped gases from crossing the duo seal (Fig. 3) and the gap between the vanes and the stator. The viscosity must be high enough (the oil must be “sticky” enough) to fill these gaps even while operating at elevated temperature. For these reasons, viscosity is considered one of the oil’s primary properties. Lower viscosity oils are used for lower operating temperatures and on smaller pumps, while medium viscosity oils are used for medium to large pumps. Typical pump oil viscosities range from roughly 25 to 100 centipoise at room temperature. The oil viscosity goes down considerably at a higher temperature (meaning it becomes thinner and less sticky) and it drops by 75% to 90% at 93°C (200°F).
Figure 3 | Molecule size of synthetic oil vs. mineral oil5
Figure 3 | Molecule size of synthetic oil vs. mineral oil5
Oil Distillation
The most basic pump oil is derived from petroleum-based mineral oil, which contains nitrogen, sulfur, oxygen and aromatic hydrocarbons. Of these, sulfur is particularly troublesome as it is one of the first constituents to break down as the pump temperature increases. To prevent sulfur contamination, sulfur and other impurities are removed using distillation.
Single distilled oil is produced using a single stage distillation process. It is used in certain single stage, rotary and other oil-sealed pumps with an ultimate vacuum of 1 x 10-2 Torr. The distillation process reduces the sulfur content and the vapor pressure resulting in a light brown color.
Double distilled oil goes through a two-stage molecular distillation process, which further reduces the sulfur content. It is more expensive than single-distilled oil but less so than triple-distilled oils. Double distilled oil has a moderate vapor pressure and sulfur content. Typical vapor pressure is 8 x 10-4 torr and ultimate vacuum is 1 x 10-3 torr. This oil can be used in moderately corrosive applications and has a lighter brown color than single-distilled oils.
Triple distilled oil is distilled a third time and contains practically no sulfur or other volatile impurities. It is chemically inert and provides excellent resistance to both oxidation and reaction with process gases. It is clear in color and allows an ultimate vacuum of 6×10-4 Torr.
Solvent Refining
Solvent refining involves a process referred to as liquid extraction or solvent extraction. It is used to remove most of the aromatics and undesirable constituents of oil distillates. In the solvent refining process the oil is first dried of moisture, then washed with an extractant called furfural, a liquid that readily combines with the soluble oil contaminants and allows them to be removed. After solvent refining, the oil is ready to be blended with the appropriate additives even though some contaminants, called aromatics, remain. Aromatics, which serve as “natural” seal swell agents, can be a source of sludge formation in the pump under conditions of high temperature and low pressure.
Hydrotreating
Many high-end pump oils are hydrotreated, which provides an even higher purity than distillation. It involves combining a hydrocarbon-based oil with hydrogen and then sending it through a selective catalyst under high pressure and temperature to remove the sulfur, nitrogen and trace metals. The sulfur and nitrogen in the oil combine with the hydrogen and leave as hydrogen sulfide (H2S) and ammonia (NH3).
Hydrotreated oils are virtually contaminant-free and clear in color. Although there is no doubt about the higher purity of hydrotreated oils, they do have a disadvantage in that they don’t retain their solubility for some additives. Therefore, they cannot be blended with certain beneficial additives. In addition, because hydrotreated base oil contains almost no aromatics, these oils must be fortified with seal swell agents in the additive package.
Synthetic Oil (Perfluoropolyether)
PFPE is a synthetic, highly inert, non-hydrocarbon fluid commonly used in corrosive pump applications. PFPE fluids are designed for high oxygen applications or where the process gas contains aggressive chemicals such as hydrazine, nitrogen tetroxide, hydrogen peroxide, chlorine, nitric acid, or hydrogen fluoride. If a typical mineral oil is used in a chemically aggressive environment, it will break down and leave a tar-like residue, which will block the internal passageways and cause pump overheating and damage resulting from insufficient lubrication. PFPE’s are generally considered non-toxic under normal operating conditions and are nonflammable.
These oils are available under the trades names Fomblin® (Solvay Solexis) and Krytox® (Dupont). Although they can typically withstand temperatures up to 400°C (750° F), they may suffer degradation at temperatures above 205°C (400° F) when in contact with non-passivated aluminum or titanium alloys, at which point toxic and corrosive gases may be released. Untreated PFPE’s are permeable to water, and additives must be used to provide moisture resistance when the process gas contains water vapor.
Flushing Oil for Vacuum Pumps
Flushing oil is a high solvent oil used to clean baked-on contaminants from mechanical pumps. It also removes condensables, such as water and undesirable solvents. In addition, flushing oil can be used before filling the pump with new oil to minimize contamination of new oil by residue from old oil.
Rotary Pump Oil
The rotary vane pump utilizes an eccentrically mounted rotor that contains two or more vanes which propel the pumped gas through the pump as the rotor turns (Fig. 4). The vanes seal against the pump housing (stator) while rotating, relying on a thin film of pump oil to help provide the seal.
Figure 4 | Internal view of a rotary vane pump (Figure courtesy of Nigel S. Harris M. Sc, C. Phys., author “Modern Vacuum Practice“, 3rd Revised Edition, Kurt J. Lesker Company, 2007)
Figure 4 | Internal view of a rotary vane pump (Figure courtesy of Nigel S. Harris M. Sc, C. Phys., author “Modern Vacuum Practice“, 3rd Revised Edition, Kurt J. Lesker Company, 2007)
The oil used in a rotary vane pump not only provides lubrication of the pump rotor bearings. It must also (a) provide a seal between the vanes and the rotor (the “Duo seal”), (b) generate the seal between the tips of the vanes and the stator, (c) provide cooling of the stator by transferring heat to the outer casing, and (d) offer corrosion protection of the metal parts from the gas being pumped.
Oils designed specifically for rotary pumps are distilled mineral oils to which hydrogen atoms have been attached to any loose molecules in the chain. This process, referred to as hydro-treating, provides a strong, stable formulation
with a low vapor pressure. For applications where the vacuum pump may be exposed to reactive or corrosive gases carried in the pumped gas, specially engineered oil is used which has been further processed to remove impurities. Where a high concentration of oxygen or other chemically reactive gases are present, highly inert, man-made lubricants are recommended. These perflouropolyether (PFPE) fluids have good temperature resistance but must not be exposed to temperatures above 280° C, at which point they release toxic vapors. PFPE fluids are available under the trades names Fomblin (Solvay Solexis) and Krytox (Dupont). If the incorrect oil is used in a chemically aggressive environment, it will break down and leave a tar-like residue which will block the internal passageways and cause pump overheating and failure resulting from insufficient lubrication.
Diffusion Pump Oil
Diffusion pumps operate by boiling the pump oil into a dense vapor and forcing it through multiple angled jet nozzles that capture the pumped gas and carry it to the pump outlet through kinetic action. To serve this purpose, the fluid (Fig. 5) used by this type of pump must have very specific properties.
Figure 5 | Diffusion pump fluid6
Figure 5 | Diffusion pump fluid6
When diffusion pumps (Fig. 6) were first introduced, they used mercury as the pump fluid. Due to mercury’s toxicity, hydrocarbon diffusion pump oil was introduced and was the most prevalent type of diffusion pump oil for many decades. More recently, silicones, hydrocarbons, esters, perfluorals, or polyphenyl ethers are used. The primary properties of these oils are high molecular weight, low vapor pressure, and low chemical reactivity. Since the temperature of the boiler that generates the oil vapor ranges from approximately 190 – 280°C (374 – 536°F), the oil must have a boiling temperature lower than this.
Figure 6 | Internals of a rotary vane pump with the end cover removed (courtesy of Edwards Ltd)
Figure 6 | Internals of a rotary vane pump with the end cover removed (courtesy of Edwards Ltd)
Diffusion pump oils are silicones, hydrocarbons, esters, perfluorals, or polyphenyl ethers (Table 1). The primary properties of these oils are high molecular weight, low vapor pressure and low chemical reactivity. Since the temperature of the boiler that generates the oil vapor ranges from approximately 190° C to 280 °C (374° F to 536° F), the oil must have a boiling temperature lower than this. Oils having lower molecular weights tend to boil at the lower end of this range.
Table 1 | Typical properties of certain fluids used in diffusion pumps for ultra-high vacuum applications (below 10-8 Torr)8
Table 1 | Typical properties of certain fluids used in diffusion pumps for ultra-high vacuum applications (below 10-8 Torr)8
The oil must be changed at proper intervals, otherwise, it can breakdown over time and contaminate the pump. Contamination can also occur if the oil is not rated for the operating temperature, in which case oxidation or thermal breakdown can occur. Other selection criteria are for the pump fluid include low vapor pressure at room temperature, low toxicity, and reasonable cost. To prevent overheating and thermal breakdown of the oil and resulting pump contamination, an interlock may be incorporated into the vacuum chamber to automatically shut the pump down if the temperature exceeds a certain value. Oils with low boiling points also tend to have lower thermal breakdown temperatures. It is important to properly select the oil considering expected temperature and other operating parameters.
Traps to Reduce Backstreaming
In order to reduce backstreaming, one or more oil traps, baffles, or cold traps are typically located between the pump and the furnace. A baffle is made of high conductivity metal and is in tight contact with the pump walls, to promote good heat transfer away from the pumped gas. In higher capacity pumps the baffle is water cooled. Baffles reduce the pumping speed somewhat but can reduce backstreaming by about 90 to 95%. In diffusion pump applications where oil contamination of the chamber must be minimized, liquid nitrogen cooled cold traps are used.
Rely on the Experts
Due to the many formulations available for each type of pump and different operating conditions, the selection of pump oil can seem daunting (Fig. 7). The key to success is to partner with a reputable supplier. They will be able to help you find the best oil for your specific application at the most cost-effective price.
What is the use of a vacuum pump?
What Are The Different Uses Of Vacuum Pumps? What You Need To Know
A vacuum pump is really nothing more than a device that pumps air or water out of a sealed container to make a vacuum. It is nothing new and the very first vacuum pump made its way into the world in 1650. However, it has only been within the last few decades that we’ve witnessed how this device can be used. So, what are the different uses of vacuum pumps?
There are many industrial uses. The most common perhaps is the electric lamp. Yes, electric lamps use a vacuum pump to take gas out from the bulb enabling it to light. Aside from this, vacuum pumps are also used in the processing of semiconductors. But this is not the end of the story. In aircrafts, the gyroscopes of some flight instruments are powered by a vacuum source of power in case there is an electrical failure.
There are many types of vacuum pumps just as there are many uses for them. While classification is a complicated process, it is possible to narrow them to two broad categories. The first type is the transfer pump and the second is the entrapment pump. Entrapment pumps trap molecules within a confined space. Some examples are cryopump and the ion pump. The former traps liquified gas molecules while the latter traps ionized gas.
On the other hand, a transfer pump is also known as a kinetic pump. It uses momentum to, for example, transfer gas from the vacuum to the exhaust, as in the case of a turbomolecular pump.
Vacuum pumps can also be classified as either mechanical or compressed-air. Working off the Bernoulli principle, a compressed-air pump relies on the differences in pressure to create a vacuum. Meanwhile, the mechanical vacuum pump has an electrical motor as a power source, although it can also use an internal combustion engine, drawing air from a closed volume and releasing it to the atmosphere.
Probably the most popular mechanical vacuum pump is the rotating-vane, which has individual rotors around a shaft that spin at high velocities. With this, the air is trapped and taken through the intake port, leaving a vacuum behind it.
As you can see from above, the simple vacuum pump has many different uses across different industries. It is basically a general type of device that only has one function, however, it can be customized and added to in order to fulfill the needs of a particular industry.
Vacuum pumps are widely available and can be found for sale online. You can even find one on eBay or search online to find vacuum pumps for sale. A simple vacuum five-gallon degassing chamber is being sold for $175. Still, an air compressor is being sold for $30. And there is a two-stage pump that is being sold for $500. Again, the different pumps have their different uses, hence their differences in price.
If there is a particular pump you need, make sure to check out the different online retailers. There are many items for sale.
Two Cars, Two Tests
To test this procedure we changed the oil on a 2005 Lotus Elise and a 2007 Honda Fit Sport. We had great results in both cases and believe that this is an attractive option for car owners who like to do oil changes themselves. As one user commented, “If you can cook yourself dinner, you can change your own oil. The most difficult part is getting underneath the car to drain the old oil. Now that is no longer an issue!”
Changing your own oil, whether “top-down” or the old-fashioned oil change from under the engine, is a great way to save money. Recently, we went to a fast oil change chain outlet and it cost $40, and they tried hard to upsell us an additional $60 in services. The oil filter and 4 quarts of oil costs as little as $23.
Performing a Top-Down Change
The Lotus Elise belongs to Edmunds Associate Editor Mark Takahashi, who had recently driven it hard at a track day. Therefore, he wanted an oil change only and would continue to use the same filter until his next oil change.
Takahashi said that he has been charged as much as $170 for an oil change. “In order to do a conventional oil change, the car must be elevated,” Takahashi said. “Not just because of its low ride height but because the entire underside of the car is flat to maximize aerodynamic performance. Accessing the drain plug and filter requires you to unbolt the undertray. In the absence of a lift, ramps are the only alternative. Even then, the ramps must be of the low-profile variety in order to avoid destroying the fiberglass bodywork of the chin spoiler.”
We found a nice shade tree on a Santa Monica side street, parked the Lotus and went to work. We opened the cover of the midengine car and inserted the thin flexible tube down through the dipstick opening. We connected the other end to the extractor, pumped the handle about 15 times and the hot oil began flowing. It took about 8 minutes to drain the engine, which holds 5 quarts.
The oil extractor we used, a $63, 5-quart Moeller Fluid Extractor, has an automatic shut-off. Since Takahashi had topped off the engine, he had more than 5 quarts, causing the extractor to stop draining. We had to pour some oil out into another container and continue the procedure, a minor delay. After refilling the engine with new oil and double-checking all our work, we finished the whole job in about 20 minutes.
It was then easy to put the rubber stopper into the oil extractor, take the container to a local auto parts store and have them empty the old oil into their recycle bin.
Can You Get All the Oil Out?
While researching this story, we found that some people have posted Internet messages saying they are doubtful of this method. Wouldn’t there be some oil left in the lowest part of the oil pan? And wouldn’t this oil contain harmful sludge? Sludge is actually an extremely harmful gelling that occurs when water is combined with oil. This has little to do with a successful oil change.
Skeptics were probably intending to say they wanted all particulate matter removed along with the old oil. If the car has been warmed up before the oil change, as recommended, any particulate matter would flow out with the oil.
We decided to do an oil change on a Honda Fit belonging to Consumer Advice Editor Philip Reed to investigate this further. We sucked out the 3.8 quarts of oil and then removed the oil drain plug to see how much more flowed out. We were pleased to see that it was less than 3 tablespoons. This oil didn’t appear to be any more contaminated than what had been sucked out by the extractor. We also unscrewed the filter and found it still contained about a quarter cup of oil.
Are There Drawbacks?
An oil extractor is perfect for anyone with a car that has the oil filter located on the top of the engine, such as certain BMW and Mercedes models. In these cases, there is no need to get under the car at all.
For all other cars, it is still necessary to remove the oil filter, in which case you will probably have to slide underneath the vehicle. Often this means jacking up the car and leaving it supported on a jack stand for safety reasons. Still, the extractor eliminates the difficulty of wrestling with a stubborn drain plug bolt while in an awkward position under the car. Also, anyone who has drained oil knows that removing the drain plug often means having hot oil gush onto your hand.
What To Look for in an Oil Extractor
Buy an oil extractor with a large enough reservoir to hold the entire contents of your engine’s crankcase (our model held only 5 quarts, not large enough for many vehicles).
Some models not only suck the oil out, but they can then pump it out of the reservoir into recycling containers, a handy feature.
Hand pump models seem to create plenty of suction for passenger vehicles, so electric pumps or vacuum-powered extractors may not be necessary.
Look for a model that makes it easy to pour the used oil into recycling containers.
A Few Oil Extractor Tips
While doing a top-down oil change greatly reduces the handling and possible spilling of old hot oil, some oil will drip out of the tubing after it is removed from the dipstick opening. Be ready with a rag or old newspapers to catch these drips. Also, never let oil drip on your car’s finish.
We found that with the Lotus, the dipstick was slanted so that when the tube hit the bottom of the oil pan it didn’t stop but continued feeding in through the opening. We solved this by holding the dipstick next to the tube to estimate the correct insertion depth. With the Honda, it was clear when we had the tube inserted the right amount since it hit the bottom and stopped.
Remember to keep records of when you change the oil. If you have a maintenance minder, such as that used in the Honda Fit, remember to reset it so it will remind you the next time an oil change is needed.
Consider taking a sample and having your engine oil analyzed to fine-tune your oil change intervals.
