The proper oil in a vacuum pump acts as a blotter and absorbs all of the moisture and non-condensables. As the oil becomes saturated with these contaminants, the efficiency of the pump is dramatically reduced. Maintaining clean oil in the pump ensures that the pump will operate at peak efficiency and prolong its life.
When the desired vacuum condition isn’t provided at a process plant, production often comes to a halt and all eyes become focused on the vacuum pump as the root cause of the problem. However, the vacuum pump usually isn’t culprit. In almost all cases, either: 1) the pump is being operated in a condition for which it never was intended, 2) one or more of the user’s interface points with the pump (suction/discharge lines, water supply, process contaminant, etc.) are being operated outside of design parameters, or 3) the vacuum chamber or vacuum lines were improperly specified. Each vacuum pumping technology will react differently to various conditions, so it’s not possible to offer a “one size fits all” answer to the problem. The following is a guide to systematically identifying the root cause of the most common problems and correcting them based on general vacuum system recommendations as well as technology-specific issues.
Let’s start by noting that vacuum technologies found at plants generally fall into two categories: wet and dry. The terms “wet” and “dry” refer to whether or not the user’s process gas comes into contact with a liquid as the gas passes through the vacuum pump. Wet technologies utilize a liquid to create a seal between the discharge and the suction of the pump to minimize the “slip” of gas backwards from the discharge to the suction and increase volumetric pumping efficiency. Dry technologies have no liquid contact with the process gas. Table 1 lists common vacuum equipment of both types.
The following points apply to all vacuum systems regardless of pump type:
Vacuum leaks. All vacuum systems have some amount of air-in leakage, which may or may not be known at the time the vacuum pump is sized. Excessive system leaks result in reduced process gas pumping capacity because the pump must move not only the process gas from the vacuum chamber but also the air-in leakage. Leaks occur at the joints of the vacuum lines and at the vacuum chamber. To avoid excessive air-in leakage, bear in mind the general recommendations of operating pressure ranges for various piping materials and joining methods detailed in Table 2. Note that actual limits will depend upon the skill level of assembly personnel.
Vacuum pump or system problem? You must determine if the issue is caused by the pump or by other equipment in the vacuum system. To find out, mount an isolation valve and an accurate vacuum gauge in-line as near to the suction connection of the vacuum pump as possible. Close the isolation valve and then measure the ultimate vacuum (also called blank-off) performance of the pump. Compare the measured vacuum to the manufacturer’s published ultimate vacuum value. A value reasonably close to the published one indicates the issue stems from leaks or outgassing in the vacuum system.
Excessive pump discharge or backpressure. A vacuum pump is designed to discharge to atmospheric pressure or just slightly above unless the manufacturer specifically designates it a compressor. As the discharge pressure of the pump increases above atmospheric pressure, this raises the differential pressure across the pump, resulting in:
• higher pump temperature and possible overheating, leading to pump seizure; and
• increased current draw and subsequent overheating of the electric motor or an overload/fuse/breaker fault.
Improperly sized suction and discharge lines. Sizing of system piping significantly affects pump performance and should be performed by qualified vacuum engineers. However, to avoid problems, apply the following guidelines:
• Suction and discharge lines never should be smaller than the suction or discharge connection size on the vacuum pump.
• For every 50 ft of suction or discharge piping, increase the pipe size by one nominal pipe diameter. Example: A vacuum pump has a 2-in. inlet connection. The suction line between the pump and the vacuum chamber is to be 70 ft long. To avoid restrictions to gas flow and pumping performance issues, increase the vacuum line to 3 in.
Isolation of pumps operated in parallel. Many vacuum pump installations consist of multiple pumps operating in parallel and utilizing a common suction and discharge header. For these type of installations, isolate idle pumps from those in operation at the suction and discharge. Failure to isolate the offline pumps may result in: 1) discharge gas from the operating pumps entering an idle pump and contaminating it, and 2) creation of vacuum in the idle pump and a resulting liquid back-stream into the vacuum lines and chamber.
Now, let’s look at specific issues that might affect particular equipment.
Liquid Ring Pumps
Several possible operating conditions can cause insufficient vacuum in liquid ring (LR) pumps. The most common are:
• too high sealant vapor pressure;
• incorrect sealant flow rate; and
• process contamination of the sealant (in full sealant recovery systems).
Too high sealant vapor pressure. A LR pump utilizes a sealant. Most commonly this is water but other liquids may be used based on the specific application of the pump. Generally, the lower the temperature of the sealant, the lower its vapor pressure, which results in increased pumping capacity and deep vacuum performance. In addition, as the process vacuum level approaches the sealant’s vapor pressure, the sealant will begin to flash from the liquid to the vapor phase (cavitation), subsequently displacing the pump’s capacity. Utilize sealant temperature/capacity correction factors from the specified LR pump manufacturer to properly size the pump.
As a rule of thumb, to avoid pump cavitation select a sealant whose vapor pressure, Pv, at operating temperature is less than half of the required vacuum level, P1, as measured at the pump inlet. For instance, the Pv of water at 60°F (15°C) is 13.3 mm Hg absolute. Therefore, the lowest vacuum operating pressure for the pump would be:
P1 = (۲)(۱۳٫۳) = ۲۶٫۶ mm Hg
Operating the vacuum pump’s suction pressure below this level will result in cavitation of the water within the pump that ultimately can damage the pump’s impeller (Figure 1).
Water at too high a temperature supplied to the pump directly as sealant or indirectly as coolant to the heat exchanger of a full sealant recovery system will increase the sealant’s vapor pressure. As the vapor pressure increases, this value may approach the vacuum level of the pump and cause the sealant to flash and reduce the pumping capacity. In many cases, the use of cooling tower water in high ambient temperature climates (>95°F or 35°C) results in significant capacity reduction. Figure 2 illustrates the capacity reduction when operating a pump at 75 torr should water sealant become much hotter than the desired 60°F.
Incorrect sealant flow rate. Each model of a particular manufacturer’s LR pump has a specific sealant flow rate requirement to achieve the published vacuum performance. Regulate the sealant flow to within approximately ±۵% of the published requirement. Simple and inexpensive flow control devices are available to regulate this flow.
If too much sealant is fed to the vacuum pump, the volume of the liquid ring within the pump will increase. This will reduce the volume of the rotor available for the pump to move process gas and the pump will lose pumping capacity, resulting in a loss of vacuum.
If too little sealant is fed to the vacuum pump, the liquid ring volume will decrease. The liquid ring no longer will be able to create the necessary seal between the rotor and the housing, allowing internal “slip” of the discharge gas back to suction and resulting in reduced pumping capacity and loss of vacuum.
Process contamination of the sealant (in full sealant recovery systems). Such contamination can involve carryover of condensate or particulates.
During the process of moving gases from the vacuum chamber through the LR pump, the process gas will contact the sealant and subsequently may collect in the sealant. If the substance collects in the sealant liquid and has a vapor pressure higher than that of the sealant, it will enter the LR pump and flash from the liquid to the vapor phase, reducing the pump’s capacity. As an example, when using oil as the LR sealant, if water vapor is a carryover product from the process gas, the vapor will condense to liquid in the discharge separator tank and effectively increase the pump sealant vapor pressure and decrease capacity.
Carryover of particulates or other solids may clog sealant piping, strainers, heat exchangers, valves, etc., and restrict sealant flow to the vacuum pump, resulting in reduced pumping capacity and possible overheating of the LR pump.
Oil-Sealed Rotary Pumps
Some of the most common field issues experienced by oil-sealed rotary piston pumps and rotary vane pumps are:
• belt squeal/high amp draw at startup;
• inability of pump to blank-off/milky oil;
• back-streaming of oil into suction lines or vacuum chamber; and
• excessive oil mist discharge.
Belt squeal/high amp draw at startup. Belt squeal of a pump at startup can stem from: 1) improper belt tensioning, 2) cold oil temperature due to low ambient temperature, or 3) improper shutdown procedure.
Typically, a loose belt causes belt squeal. Check for looseness by starting the pump and observing the deflection of the belt during rotation. Do not apply belt dressing to V-belts such as those used on Tuthill vacuum pumps. If the belt appears to have excessive deflection, refer to the manufacturer’s product manual for proper tensioning instructions.
The next likely cause of belt squeal/high amps is attempting to start the pump in low ambient temperature conditions, typically <60°F (15°C). In this case, you must install oil preheaters to increase the oil’s temperature and reduce its viscosity so the internal components don’t create high torque on the shaft. It often makes sense to use a temperature switch to ensure the pump will not start until the heaters have raised the oil temperature enough.
Lastly, oil-sealed rotary piston pumps are particularly prone to improper shutdown. A pump shut down under vacuum will leave an excessive amount of oil in the cylinder. Then, when an operator attempts to start the pump, the cold viscous oil will create high torque on the pump shaft, resulting in high amp draw. Oil-sealed pumps require that the inlet pressure of the pump be increased sufficiently (typically >100 torr for no less than 15 sec.) to allow more gas flow through the cylinder of the pump, resulting in displacement of the oil in the cylinder back into the main oil reservoir.
Inability of pump to blank-off/“milky”oil. Oil-sealed vacuum pumps commonly fail to meet the published blank-off performance due to: 1) substitution of the manufacturer’s vacuum pump oil with an improper oil, or 2) condensable process vapors collecting in the oil.
Vacuum pump operators for various reasons may not use the manufacturer’s recommended oil. This often can result in failure to produce the deep vacuum results as published. Vacuum pump oils are formulated to have a vapor pressure significantly lower than the pump’s ultimate vacuum capability. If a higher vapor pressure oil is substituted, the pump will begin to create vacuum and reach the vapor pressure of the oil in the cylinder. When this occurs, the oil will flash to the vapor phase, displace the pump’s capacity and result in higher blank-off values. The only remedy is to use an oil that has a vapor pressure equal to or less than that of the manufacturer’s vacuum pump oil. Matching the recommended oil’s viscosity also is necessary.
Many processes such as vacuum drying contain moisture that will condense when it reaches the pump’s oil reservoir at atmospheric pressure. The visual result is “milky” oil. Typically, the liquid has a vapor pressure significantly higher than the pump’s ultimate pressure. As the condensed liquid is recirculated with the oil into the cylinder (under vacuum), it begins to flash to a vapor phase. This again results in a higher-than-published blank-off value. The solution is either to: 1) run the pump’s gas ballast valve open (off process) for 15–۳۰ minutes, allowing the incoming air to strip the moisture from the oil, or 2) change the oil more frequently. Note that failure to perform one of these procedures will result in excessive wear of the internals due to increased friction and heat and, thus, reduced pump life.
Back-streaming of oil into suction lines or vacuum chamber. This commonly stems from failure to vent the pump’s inlet prior to shutdown. As already noted, oil-sealed pumps require that the inlet pressure of the pump be increased sufficiently (typically >100 torr for no less than 15 sec.) to allow more gas flow through the cylinder of the pump, resulting in displacement of the oil in the cylinder back into the main oil reservoir.
Excessive oil mist discharge. This phenomenon typically occurs because: 1) the pump has been operated continuously at an inlet pressure greater than the manufacturer’s recommendation, or 2) the pump’s oil mist element has failed.
Oil-sealed pumps commonly are used to operate continuously at inlet pressures <10 Torr or for short pump-down cycles that don’t allow oil to saturate the pump’s oil coalescing element. If a pump is operated above the manufacturer’s recommended maximum for prolonged periods, the relatively high gas density will carry the oil into the mist element at rates beyond its maximum filtering capability. The result is oil discharge from the exhaust of the pump. The best way to avoid this situation is appropriate sizing of the pump for the system design to avoid high operating inlet pressures for prolonged periods.
The other possibility is that the pump’s oil mist element fibers have separated due to continuous saturation and high pressure differential, resulting in the escape of oil mist from the pump’s exhaust. Replacing the element commonly will solve the problem.
Dry Screw Pumps
The two most common issues related to the improper application or operation of dry screw vacuum pumps are:
• overheating and pump seizure; and
• high motor amp draw.
Note that while dry screw vacuum pumps all have some common features, the symptoms of each pump will be manufacturer and model specific.
Overheating and pump seizure. Dry screw vacuum pumps are susceptible to several potential causes of overheating. The more common are:
reduced cooling water flow/high cooling water temperature; high inlet gas temperature; and improper staging with a vacuum booster.
The dry screw pump is more sensitive to cooling water flow and temperature than other technologies. A reduction in cooling water flow rate below the manufacturer’s minimum recommendation or supply cooling water temperatures in excess of the manufacturer’s recommendation can result in thermal growth and, ultimately, seizure of the pump.
Because dry screw pumps have no internal liquids to absorb heat, their internal temperatures can range from 250°F to 450°F depending upon the screw design. So, they are sensitive to inlet gas temperatures; each pump has a manufacturer’s maximum inlet gas temperature rating. Unfortunately, this value sometimes isn’t considered during the selection process and, as a result, the pump might encounter entering gas temperatures that exceed this value, resulting in excessively high internal gas temperatures that cause thermal growth and subsequent pump seizure.
The sizing process of a pump with a vacuum booster requires consideration of several parameters. One of the most important when pairing a vacuum booster upstream of a dry screw pump is staging ratio. This is defined as the ratio of the volumetric flow rate of the vacuum booster, V1, to the volumetric flow rate, V2: SR = V1/V2. Applying Boyle’s Law: V1/V2 = P2/P1.
Because V1 always is greater than V2, the pressure between the booster and the dry screw pump, P2, always will be greater than the inlet pressure, P1, to the system. The gas compression across the booster results in a temperature rise of the gas that will enter the dry screw pump. Therefore, carefully consider this ratio to avoid exceeding the inlet gas temperature rating of the dry screw pump.
High motor amp draw. Many types of rotating machinery experience high motor amp draw. Usually the cause isn’t an issue with the motor but rather with the piece of equipment it is driving. In the case of dry screw pumps, high amp draw typically results from: excessive discharge pressure (as noted in the general section); process buildup in the machine; or internal contact due to the cooling water and inlet gas temperature noted above.
Excessive discharge pressure as well as cooling water and inlet gas temperature already have been addressed, so, let’s focus on process buildup in the machine. Many vacuum processes contain chemicals that combine at high temperatures to form sticky or tacky materials that attach and then “bake onto” the screws (Figure 3). Their buildup ultimately creates a “zero clearance” condition inside the pump. This contact within the pump leads to additional torque on the pump shaft, resulting in increased amp draw.
Consult the pump’s manufacturer for a recommended solution. Generally this will involve either: 1) knocking out or filtering the process gases upstream, or 2) supplying a cleaning flush. Option 1 is preferable in extending pump life. However, filtration units can be costly and will require continual maintenance. In addition, as the filter elements clog, a resulting loss of vacuum in the process chamber will occur.
The cleaning flush option avoids the cost of the filtration system but may pose its own operational issues that could result in damage to the pump. Moreover, there’s no guarantee of success with the flushing process. Proper choice of flushing medium is most important and requires determining whether a solvent is needed to dissolve material or if a mechanical cleaning fluid such as water will suffice; the pump manufacturer should approve the selection. When injecting a direct liquid flush into a dry screw pump, take care not to flood the pump’s screw chamber as this can result in the pump attempting to compress liquid and subsequent mechanical failure requiring a major rebuild of the machine. Lastly, when injecting a flushing liquid into the pump’s process chamber, elevate the pump’s inlet pressure sufficiently above the vapor pressure of the liquid to avoid flashing. Such flashing to vapor will compromise cleaning as well as potentially create freezing problems within the machine due to the Joule-Thompson effect.
Achieve Long-Term Success
The process of creating a successful vacuum installation consists of several steps:
• Determine the parameters of the entire cycle of the vacuum operation from startup to shutdown.
• Select the appropriate vacuum technology and material of construction to match the process vacuum and flow requirement and gases to be handled.
• Properly size the vacuum pumping equipment, vacuum chamber and suction and discharge lines.
• Commission and leak check the vacuum system and validate on the process.
The vacuum pumping technologies addressed in this article are time-proven and will give years of reliable service when appropriately applied and operated. However, when troubleshooting is required, the pointers provided here should help you properly diagnose and address issues.
Proper Maintenance of OilSeal High Vacuum Pumps
Practical, step-by-step instructions for oil changes and
John L. Brock, Sales Engineer
Welch Vacuum Pumps, a Gardner Denver Product
Properly maintained vacuum pumps will provide many
years of reliable, maximized performance. This article
addresses simple ways to maintain such vacuum
pumps and options for what to do when pump
performance is compromised due to oil contamination
Principles of Operation
Oil-Seal, Rotary Vane vacuum pumps pull millitorr-level
vacuum (‘high vacuum”) by sweeping intake air and
vapors from the intake port around to the exhaust port.
Note in the diagram above how the rotor is offset in the
chamber, or “stator”. The rotor is set with only 1/1000”
clearance from the top of the stator. Vacuum pump oil
seals this tiny gap and prevents regurgitation of the
airflow. For this reason this technology is referred to as
“oil seal, rotary vane” vacuum pumps. Vacuum pump
oil also lubricates the vanes, which are spring loaded
so they always push to the inside wall of the stator,
allowing for very efficient sweeping action. In a “two
stage” pump, the exhaust from the first stage chamber
is fed into the intake of the second stage and lowers
the vacuum level achieved down to, or below, 1 millitorr
(۱ X 10-3 mm Hg) residual pressure.
When a vacuum pump is first evacuating, the oil vapor
pressure is high enough that a visible amount of oil
continued on page 2
continued on page 3
Vacair Superstore offer the latest technology within the new Vacuum Pumps and Blowers sector, with vacuum and pressure being given as efficiently and economically as possible. We have over 20 years of dedicated proven supply to a vast array of vacuum pump applications within many industries. By choosing Vacair Superstore you will gain access to the widest choice of Vacuum Pumps from stock, for immediate delivery in the UK.
Vacair Superstore provide you with the latest in vacuum pump technology including but not limited to:
Claw pumps are one of the latest technologies within vacuum pump and pressure pump technology. The working principle of this pump allows 2 claw shaped rotors to rotate in a synchronised way within a moulded cylinder body. They work with fine tolerances and because the unit claw used to generate the vacuum or pressure are contactless there is no need for lubrication within the cylinder body. Because of the lack of contact within the cylinder body they have a much longer life than traditional pumps and have very little need for maintenance over this extended life.
Applications include: Wood working, Printing, Cardboard Box Manufacture, Sewage Treatment, Pneumatic Conveying plus many others.
These pump units have a rotor position eccentrically in a cylindrical body. The rotor is made with slots in it to house graphite pump vanes, more commonly knows as carbon pump vanes. The rotor is turned usually by a motor creating a centrifugal force which pushes the carbon pump vanes outwards from the slot to run against the cylinder body, which then creates separate chambers between each carbon pump vane.
Because the rotor is in an eccentric position within the cylinder body, as the rotor turns this then compresses or expands the volume of air in each chamber, meaning the pump unit draws air in from the inlet port and exhausts compressed air through the outlet port, thus creating vacuum and pressure.
The Carbon Pump Vanes that are used are self lubricating meaning there is no need for the unit to have a lubrication agent like oil so hence the unit is called a dry running vacuum pump.
Applications include: Woodworking, Pick and Place, Water Aeration, Sewage Treatment, Printing, Print Finishing plus many others.
Oil lubricated rotary vane vacuum pumps units work on very much the same principle as dry running rotary vane pumps. Except that the presence of oil as a lubricant enables finer tolerances in the vacuum pump, thus meaning higher levels of vacuum can be achieved, so these units are used when applications demand a higher level of vacuum.
Applications include: De-Gassing, Vacuum Bagging, Food packaging, Vacuum Forming, Hospital Vacuum, Laboratory, Autoclave plus many others.
The operating principle behind Side channel blowers is simple. Internally the side channel blower has an impellor (fan) with small fins on it, the rotation of this impellor within the impellor housing (stator) creates a centrifugal force and this in turn creates small vortexes of air that are drawn by these fins from the intake to the exhaust. The unit is mechanically contactless meaning there are no parts that come into contact leading to the units themselves not requiring any routine maintenance. One of the major advantages to Side Channel Blowers are the units can run continuously when fitted with pressure or vacuum relief valves to protect the pump making them a robust unit that can deliver large volumes of air.
Applications include: Pneumatic Conveying, Vacuum Holding, Water Aeration, Sewage Treatment, Vacuum Lifting, Paper Handling plus many others.
Invertors can be fitted to several pumps to help with efficiency, as the pumps speed can be variably driven and worked in tandem with the machine it is serving. In today’s world where costs have to be examined, these variable speed units can play an important part in reducing energy consumption as the invertor driven units are super-efficient due to the ability to fine tune the speeds they work at.
Invertor driven vacuum pumps are used on dry running unit applications.
Liquid Ring pumps have an impeller with fins attached to a central shaft, that is mounted eccentrically inside a cylinder body. The working principle is very much the same as rotary vane pumps for this reason. When working the impeller pushes the liquid sealant (water) to the outside of the cylinder body using centrifugal force, hence forming a liquid ring at the outer edge of the cylinder body.
Applications include: De-Gassing, Vacuum Forming, Extruding machines, Vacuum Holding, Pottery, Chemical/Pharmaceutical plus many others.
We offer vacuum pumps from some of the world’s leading manufacturers such as Becker, Busch, DVP, Elmo Rietschle, Gardner Denver, Oerlikon Leybold, Orion plus many others but we also offer our own branded European made vacuum pumps too! This gives you the ultimate choice for your vacuum pump requirement.
By choosing Vacair Superstore you will also gain access to experienced and expert advice from our factory trained technical staff. They know everything about Vacuum and have experience of vacuum pumps working within many different industries requiring vacuum, from new projects to established common applications. So please call us on +44 (0) 113 2088 501 if you are unsure of your vacuum requirement or indeed which vacuum pump technology would best serve your application.
Medicinal Chemists, Organic Chemists, Biochemists,
Biologists, Molecular Biologists and other scientists rely
upon vacuum-driven devices to concentrate, dry, or
filter their materials.
If a Vacuum System is not performing optimally, it can
slow preparation of research-critical samples by as
much as 50%-100%! This can have significant impact
on time-to-market, or on research paper productivity.
Doesn’t it make sense to be certain that your Vacuum
Systems are operating at peak efficiency?
Vacuum System Audits
Welch Vacuum Pumps (a Gardner Denver Product)
provides a free service to its customers: the Vacuum
System Audit Program. This service is designed to
raise awareness on the importance of the subject, and
teach researchers the steps in the process. These
steps are also outlined below.
تابلو وکیوم چیست ؟ مزایا و قیمت تابلو وکیوم چگونه است ؟
محفظه خلأ محیط بسته صلبی است که توسط پمپهایی مخصوص، هرگونه گاز و هوای موجود در آن تخلیه شده تا شرایط خلأ جهت انجام آزمایشهای فیزیکی را فراهم آورد. این شرایط جهت آزمایش عملکرد تجهیزات مختلف از جمله سنجندههای فضایی کاربرد دارد.
Air-cooled, compact and oil free, dry claw vacuum pumps are increasingly becoming the pump of choice for medium vacuum applications. Designed for long life and ease of maintenance these pumps exhibit modern design features such as corrosion resistance and modular configuration for easy disassembly and repair.
Typically applications include CNC routing, pneumatic conveying, milking parlors ans central hospital vacuum. VFD compatible
Made for laboratory or office use, these pumps are small & compact. Operating on 115v power, these pumps can operate anywhere a power outlet is available.
Applications include medical, dental, biological filtration, chip mounting/holding, air sampling, packaging and others. Flow 4.5-11.6 cfm
These pumps are made for process vacuum applications where heavy contaminated gas streams are present. The ability to pump heavy vapor loads and off pH gases at low pressures (<0.5mm Hg), these units are ideally suited for chemical and pharmaceutical processing, solvent reclamation, dehydration and crystallization.
Flow capacities up to 470 cfm
How Liquid Ring Vacuum Pumps Work
Liquid ring vacuum pumps are rotating positive displacement machines providing process vacuum in industrial applications such as chemical, electrical power, environmental, food & beverage processing and packaging, marine, mining, oil & gas, pharmaceutical, pulp & paper, and textiles. Liquid ring vacuum pumps utilize water or other processes compatible liquid as the sealant. The simple operation, with no contacting parts, make liquid ring vacuum pumps a safe and reliable choice for handling dirty and potentially dangerous gas streams. Liquid ring pumps are available in single and dual stage designs and also configured as compressors for even more versatility.
Principle Of Operation
The seal liquid forms the ring inside a pump body as the impeller spins creating small chambers for gas to be trapped. The axis of the rotor is eccentric from the body allowing the liquid to almost fill, and then almost empty each rotor chamber during a single revolution, forming the compression of the gas for the pumping action. Vacuum inlet and atmospheric discharge ports provide flow paths for the gas mixture being handled. The heat of compression of the gas is dissipated into the seal liquid, and some of the liquid flows out to discharge. The exhaust gas and residual water discharge is separated from the gas stream and directed to the house exhaust and returned to the pump respectively. Seal fluid is replaced by a constant flow of cooler seal fluid.
Watch This Video To Learn “How It Works”
Characteristics Of Liquid Ring Vacuum Pumps
Accepts Carryover – Soft solids, moisture, slugs, chemicals and more will not harm the pump. These impurities will simply be washed out through the pump discharge.
Cool & Quiet Operation – The pump runs cool owing to the circulation of the sealing water inside the pump. The operation is relatively quiet – not exceeding 85 dBA.
Constant Operation For Any Vacuum Level – Pump can operate constantly and continuously at any vacuum level – from 29 in. Hg to atmospheric pressure.
Liquid Ring Technology How it Works
Easy Maintenance & Longer Pump Life – Liquid ring vacuum pumps are robust in construction and have only one moving part, the rotor, which is mounted on a shaft supported by a set of bearings designed for a long service life of continuous operation. This benefits the user with less wear and simpler, affordable maintenance.
Environmental – Pumps do not require an oil change, filter, oil-pans, condenser or etc. For that reason, plant rooms run clean, free of oil contamination and oil discharges to sewers.
A Look Inside A Liquid Ring Vacuum Pump
Flat Sided Liquid Ring Vacuum Pump
Conical Liquid Ring Vacuum Pump
The Technology Behind Liquid Ring Vacuum Pumps
The design technology behind liquid ring vacuum pumps is advanced to achieve optimum, reliable performance for the rigorous demands of harsh industrial environments. Liquid ring vacuum pumps are an economical and robust solution engineered to meet specific customer requirements.
Condensation Of Vapors Can Yield A Capacity Bonus
Dry air or a dry gas mixture is compressed from vacuum to atmospheric pressure in a liquid ring pump much the same way as it would be in any other displacement type pump, except that there is less of a temperature rise of the gas stream through the pump.
Humid air or gas mixtures containing condensable vapor behave quite differently. Some of the vapor that enters a liquid ring pump condenses when it is cooled by the lower temperature seal liquid. The condensate mixes with the seal liquid. Now, it occupies a much-reduced space as contrasted with its former volumetric dimension when it was a component of the inlet gas stream. This volumetric reduction becomes a capacity bonus.
The only vapor that can be condensed early enough to escape compression contributes to the inlet capacity bonus. In each rotor chamber, the condensation must occur before that chamber passes its inlet port. Any condensation that occurs after the cutoff will not have an effect on pump inlet capacity.
Liquid ring vacuum pumps can handle large amounts of liquid through its inlet port with a negligible reduction of gas capacity. To maximize the condensation bonus some of the liquid is often sprayed into the inlet piping, upstream of the vacuum pump itself.
Backed by over 110 years of experience, NASH CERTIFIED experts provide aftermarket support with maintenance, service, parts, and repair. Service centers are globally located to protect your vacuum system investment and provide quality, reliable, and efficient solutions.
Picture1Usually, a liquid ring vacuum pump is used as a rotating positive displacement vacuum pump but it can also be used as a gas compressor compressing gases to pressures above the atmospheric. As far as function, liquid ring pumps have similarities with a rotary vane pump but differences are crucial for achieving highest reliabilities and trouble-free operation. For instance, a liquid ring vacuum pump is designed with the rotor as being the only moving component. There are no metal-to-metal contact within the pump, no valves, no sliding vanes, no need for lubrication (other than outboard mounted bearings). The water provides the sealing while acting as the compressing media within the pumping chamber. Compression is isothermal with very little temperature rise during compression, low noise without silencers, low vibration, cool and safe operation.
How a Liquid Ring Vacuum Pump Works
Using some form of liquid (usual water), which is also referred to as sealant, compression is achieved as soon as pump is started and vacuum is created. Before the pump is started, there needs to be some liquid sealant inside, some of the sealant is discharged with the gas being pumped, the same amount of liquid must be replenished or sent back to the pump after it has Picture3been cooled. Based on the exact application, sealant can be water, solvent, oil or other liquids. Once the pump has been started, the sealant is slung by the impeller using centrifugal force to the outer walls of the body. With this, a ring of liquid is formed.
As mentioned, the impeller is eccentrically mounted within the pumping cylindrical casing, because of this some blades are almost out of the liquid ring while others are completely submerged. The volume without any liquid sealed between the liquid, Picture2impeller hub and impeller blades is occupied by the gas to be pumped away. As the impeller rotates the liquid begins to recede from the center hub serving as a piston drawing gas in, continuing with the rotation the impeller blades go deeper into the liquid ring thus impeller cells (pistons) compress the gas until discharged through the strategically placed discharge port. This action creates the liquid ring vacuum pump’s suction that draws in gasses and vapors through the inlet port. The outcome is compression. Gasses and a certain amount of liquid are exhausted through the discharge port to atmospheric or even higher pressure. Because some liquid sealant is discharged along with gases the same amount of liquid must be replenished or sent back to the pump after it has been cooled.
Getting Professional Assistance
As with all equipment, there are times when a vacuum pump needs to be serviced.
The professional team at Premier Fluid Systems is highly qualified for handling repairs and it is important to remember the Picture5team can
provide assistance with installation as well as start-ups