Conceptual: How does vacuum work?
James J. – Production Manager
Essentially, vacuum is the absence of matter in a given volume of space. There is a “normal” amount of air in the atmosphere that we breathe in, and a vacuum would mean that the air is thinner than the normal. A perfect vacuum can be seen in outer space, where there are no gaseous molecules occupying a given space.
Mary C. – Quality Assurance Inspector
- An absence of air can be measured through gauges that can sense negative pressure fluctuations, like vacuum gauges or compound gauges. On paper, we can measure vacuum through units like Torr, millibar, millimeters of mercury, or inches of water. In the Unites States, we most commonly measure by inches of mercury in vacuum (“HgV).
- Some units, like Torr and millibar, are commonly measured as an absolute scale, meaning that 0 is perfect vacuum. Inches of mercury in vacuum (“HgV) is a gauge scale, meaning that 0 represents normal atmospheric conditions. This scale goes up to 29.92”HgV, which represents a complete, perfect vacuum.
- Depending on how deep the vacuum needs to be, using units of smaller scale (millibar goes from 1013 to 0, Torr goes from 760 to 0) is more advantageous so that decimals are as uninvolved in calculations as possible. For example, we can measure 29.33”HgV and run our calculations like so, or we can measure the equivalent 15 Torr and simplify our calculations through the use of a whole number.
Robert M. – Machine Operator
- Gas transfer vacuum pumps come in three general variations: positive displacement pumps, kinetic pumps, and entrapment pumps. The basic principle is Boyle’s law: high-pressure areas will move toward low-pressure areas.
- Positive displacement vacuum pumps move a constant amount of matter, creating a low-pressure region. The continuous movement of these “buckets” of matter creates a process that evacuates air from a particular area, creating vacuum.
- Kinetic pumps accelerate high-speed fluids and create a high-pressure area at the discharge, manipulating gaseous movement at the inlet.
- Entrapment vacuum pumps utilize chemical bonding, adsorption, or temperature to arrest the particles that occupy its inner space, creating a low-pressure environment for incoming particles to tend towards.
Christopher R. – Industrial Engineer
Simply put, the easiest measure of efficiency in vacuum equipment is by a pump’s CFM/HP ratio: how much process material the pump can move in a unit of time, and how much power it requires to move that.
John D. – Maintenance Supervisor
- Wet vacuum pumps are vacuum pumps that are used when there is moisture or small amounts of liquids that need to be evacuated. Wet process material comes in, and wet process material comes out. These kinds of pumps either excel in handling wet process material or use moisture as a function of their vacuum generation. Wet vacuum pumps such as liquid ring vacuum pumps are used, as one might expect, in wet and dirty environments or operating conditions with high relative humidity.
- In contrast, dry vacuum pumps intake dry process material and exhaust dry process material. Moisture in even trace amounts will ruin these pumps. These pumps are best for applications that require high vacuum levels with no contamination or condensable processing.
Ashley F. – Assembly Team Manager
A liquid ring vacuum pump is a rotating positive displacement vacuum pump that utilizes centrifugal force to create vacuum. A motor spins a rotor-shaft assembly that is positioned eccentrically in relation to the casing. The working fluid, or seal fluid, is thrown from the bottom of the casing to form a liquid ring around the walls of the inner chamber by the centrifugal force of the impeller. The space that the liquid has once occupied becomes a low-pressure area for matter to enter. The eccentric placement of the impeller results in volume manipulation as the process material is displaced through the rotary motion, creating a compression and expansion effect that yields pressure differentials magnitudinous enough for sustainable vacuum.
Amanda U. – Safety Coordinator
- Vacuum is directly influenced by the elevation of the site of installation. Imagine a “pillar of air” directly above your shoulders extending all the way to outer space. As you climb higher in elevation, this pillar becomes smaller. As elevation increases, the normal atmospheric pressure decreases.
- When there are fewer air particles, there is less pressure differential that can be feasibly achieved, which means that there is less vacuum performance available. At sea level, a perfect vacuum is reached at 29.92”HgV. At 10,000 feet in elevation, perfect vacuum is reached at 20.92”HgV. Thus, as elevation increases, vacuum level decreases below the expected value.
- Ultimately, when there are fewer air particles, it becomes more difficult to move a large amount of mass in the same amount of time. Thus, as elevation increases, capacity decreases below the expected value.
Brian H. – Plant Layout Designer
A two-stage vacuum pump is a vacuum pump that has two stages within its casing. In the beginning, the process gas enters through the pump inlet and is compressed through the first stage. Subsequently, the process material is discharged and promptly sent to the intake through internal passages onto the second stage, where the pressure differential is made more significant. Two-stage pumps are capable of higher vacuum levels than single-stage pumps at the expense of more moving parts, which means more opportunity for complicated maintenance or replacement.
Daniel C. – Production Planner
Fundamentally, vacuum staging is the process of configuring a vacuum system such that a roughing and fining pump operate in tandem to achieve the desired vacuum level or capacity. By using a vacuum booster or vacuum pump in combination with another vacuum pump and starting them up in sequence, vacuum staging accomplishes its intended purpose of vacuum or capacity improvement, along with power requirement reduction.
Michelle G. – Operations Coordinator
- Primarily, a booster’s function is to increase the vacuum level of a vacuum system. It cannot condense moisture and does not do well with moisture inside of it. The discharge pressure is near atmospheric.
- In contrast, a blower’s primary function is to generate vacuum with emphasis on a higher discharge pressure, “blowing” process gas out at higher velocities. It condenses moisture due to the compressive effect of its discharge, but does not do well with moisture retained inside of its chamber. The discharge pressure is almost always above atmospheric pressure; it is designed to function in this way.
Designing: What should I know to start with vacuum?
Jennifer L. – Automation Engineer
A liquid ring vacuum pump is extremely tolerable of liquid carryover, slugs, semisolid sludge, and solid particulates like dirt and dust. Liquid ring units typically last a decade or two with proper maintenance and care, which is sparse. In addition, liquid ring vacuum pumps are good for handling explosive or hazardous material because of the isothermal compression occurring within the pump as the seal fluid absorbs the heat of friction, compression, and condensation. The absorption of the heat of condensation creates more room in the buckets of the pump for intake, resulting in a capacity boost when exposed to humidity or condensable process material. Abrasive material is partially subdued due to the seal fluid acting as a barrier between the process and the pump’s material of construction.
In essence, liquid ring units typically require minimal maintenance, handle tough processes well, and last long.
Elizabeth W. – Product Development Scientist
The most common problems that a liquid ring exhibits are flooding/over amping and cavitation. These translate directly to an excess amount of seal water and an insufficient amount of seal water, so control over the amount of seal fluid flowing through the pump must be carefully monitored and maintained for the maximum performance and life.
The liquid ring vacuum pump exhibits disadvantages such as power inefficiency, constant seal fluid consumption, and ability to produce solely rough vacuum levels.
Kenneth Y. – Manufacturing Engineer
The metallurgy of the pump is determined through the chemical composition of the process material. We provide cast iron, stainless steel 304, 316L, titanium, and Hastelloy as options depending on the abrasiveness and corrosivity of the process gas.
Charles C. – Materials Handler
Port plates, also known as flat plates, are just that: flat plates between the casing and pump head that allow process material to enter and exit the casing and impeller buckets (the spaces in between the vanes). These plates have small holes located at the inlet and outlet sections of the pump and allow the process gas to pass in and out through a small cross-sectional area. This creates a compression effect before the material enters the pump, yielding an increase in vacuum. The amount of matter is limited by the cross-sectional area, however, so port plate units typically exhibit lower capacities. In addition, these units do not excel in the handling of slugs of liquid or carryover that are expected in the wet and dirty environments that liquid ring units are usually exposed to.
Karen M. – Industrial Designer
Gland packing and mechanical seals restrict the amount of fluid that is lost as the pump drips. A certain amount of liquid is required to flow to that area to transfer the heat of friction away, as excess heat will damage the shaft. Gland packing is inexpensive and performs satisfactorily in this regard, dripping approximately 12 times within a given minute (24 times a minute for a double-shaft extended configuration). When there are tighter constraints concerning water consumption or the process gas contains hazardous material that must not be leaked, a mechanical seal is used.
Sarah H. – Shipping and Receiving Clerk
A drop-in replacement is a pump that has the same function, fit, and form as the pump that is to be replaced. NES Company Inc. offers drop-in replacements for Nash liquid ring units such as 904, 905, AT, Siemens L200 2BE, SC, Siemens L200 2BV, AHF, MHF, CL, TC, Flowserve SIHI LPH Two-Stage, and XL Series. NES models feature direct internal and external part interchangeability, so NES spare parts will fit with Nash units as well. In terms of performance, NES guarantees 100% of the performance that would be achieved with a new Nash unit.
Jordan C. – Inventory Control Specialist
The difference is in the impellers. NL Series pumps are designed with a 16-vane rotor, while the N904 pumps are designed with 20-vane rotors. The increase in buckets allows for increased capacity. The trade-off is that the rotors are of the same diameter, so the N904 vanes are thinner and more prone to damage.
Joseph L. – Process Engineer
- Seal water amount and temperature has a direct influence on vacuum performance.
- If you do not have enough seal water, your vacuum will decrease. If you have too much seal water, your costs will increase while your capacity decreases.
- The hotter your seal water is, the lower the capacity will be. This vacuum technology is limited by the vapor pressure of its working fluid. For the vast majority of cases, there is no such thing as water that is too cold; it will only benefit your system.
Luke B. – Technical Support Specialist
- The liquid ring vacuum pump is the only vacuum pump which requires seal water to perform. The hotter the seal water is, the lower the capacity is. This is because the seal water absorbs the heat of compression, condensation, and friction generated by operation. The seal water steadily increases in temperature, which increases its vapor pressure. The vacuum that the pump is generating also influences the vapor pressure and boiling point, so the impeller buckets fill with water vapor, reducing the capacity that the pump has to fill the buckets with process material.
- Other pumps, such as the dry screw vacuum pump, use water as a coolant rather than a seal fluid. The hotter the pump gets, the tighter the tolerances of its constituent parts are until the moving parts make contact and the pump fails due to excessive frictional forces and internal stresses.
Jeffrey S. – Lean Manufacturing Specialist
As relative humidity increases, pump capacity increases. Water vapor condenses once it comes into contact with the cool seal water, which greatly reduces the vapor load of the pump and allows for more process material to enter. Some companies will inflate their performance curves by introducing their pumps to a high-humidity environment for testing. To compare two curves with different relative humidities or different seal water temperatures, calculations need to be made. NES pumps are tested at standard temperature and pressure with no relative humidity. To approximate the values between curves, compare their relative humidities first. Whatever the percentage difference is, multiply that to the capacity with the higher RH. Take the product and subtract it from that capacity value to get a capacity value with closer conditions to that of the other curve.
David R. – Control Systems Engineer
The amount of water that needs to be used as seal fluid depends on which pump you are using, at what vacuum level, and at what capacity. For liquid ring compressors, a rule of thumb is to introduce a quarter-gallon for each unit of horsepower that the process requires of the pump, but it is best to request this information from your pump manufacturer.
Kimberly N. – Production Supervisor
- There are three common configurations of installation.
- Once-through systems are simplest: seal fluid in from source to pump and seal fluid out from discharge separator to waste. The system stays coldest from this configuration, and there are the least moving parts to take into consideration.
- On the other end of the spectrum is full recirculation or full recovery. Seal fluid is introduced, gets processed through the pump into the discharge separator, and is circulated through a heat exchanger to be reintroduced into the pump. This configuration is not as thermally efficient but is extremely useful in cases where seal fluid is scarce.
- The middle ground is a partial recovery system setup, where some seal fluid is reintroduced through a heat exchanger, with the rest discharged to waste while new seal fluid is introduced to the system. For considerations against effluent treatment, seal fluid scarcity, and temperature conditions, this method of installation caters to all major concerns except one: price.
Jessica R. – Facilities Planner
A plant with water consumption concerns will need to speak with an NES representative. In many cases, a liquid ring vacuum pump is still the best option, as liquid ring encompasses a vast capacity range while supplying excellent vacuum levels for years or decades. You may leave it to our team of knowledgeable engineers to select a proper unit or system that is tailor-made for your application.
Matthew M. – Maintenance Mechanic
Having as little pipe as possible arranged with the least bends possible is ideal for piping a vacuum system.
Emily H. – Manufacturing Engineer
- PNEUROP, the organization for vacuum pumps, compressors, and pneumatic equipment, has established various standards by which vacuum equipment can be tested and approved.
- HEI, the Institute of Heat Equipment, also has developed standards by which vacuum systems can be tested and approved.
- NES Company Inc. distributes tested equipment that adheres to both HEI and PNEUROP standards.
Richard E. – Continuous Improvement Manager
It is best to use dry screw vacuum units in a clean, dry process that requires high vacuum. The dry screw vacuum pump is extremely efficient in terms of CFM/HP and reaches up to NES Company Inc. screw units are of variable pitch, which compresses the process material such that the discharge pressure is above that of atmosphere.
Practical: What should I know to maintain vacuum?
Patrick S. – Instrumentation Technician
You can measure vacuum with a vacuum gauge or compound gauge connected as close to the inlet as possible. With a compound gauge, you will be able to see any backpressure that may occur during troubleshooting in unfortunate circumstances.
Jesus S. – Mechanical Engineer
You will need to know what vacuum level and capacity your process requires. Mark your finger on the vacuum level that you need, making sure that you are aware of the units that it is using, and trace your finger up to the capacity value that you require on the Y-axis. Each curve on a performance curve will be labeled with a number, which is the RPM that the pump will need to rotate at to achieve such capacity and vacuum level. On the power curve, look for the same vacuum level at the same RPM, and the Y-axis value will tell you the power that the pump requires to perform satisfactorily. Make sure to adjust this power value depending on the motor-pump connection that you plan to set up.
Lisa K. – Operations Manager
When selecting a pump, proper sizing involves taking into consideration elevation, ambient temperature, seal water temperature, and required piping, as the pump will need to evacuate the volume of the piping as well. It is ideal to select a pump that will achieve the required vacuum and capacity at a lower rotation speed as the pump will last longer with lower speeds. Keeping piping as scarce as possible is beneficial. During operation, maintaining steady seal water flow rates and low temperatures will ensure proper performance. Preventative maintenance and replacing parts instead of the whole proves to be economical in many situations.
Jason M. – Boiler Operator
Pipe leaks are one of the main deterrents of proper vacuum. Leaks in the system have the capability of bringing the vacuum down drastically, even to zero in some cases. This is significant enough that NES Company Inc. calculates leak orifice sizing and its influence on vacuum performance when sizing systems for our clientele.
Donald B. – Field Service Technician
A rotary vane unit consists of a motor, a pump, and an oil reservoir. The oil reservoir has two ports: one for filling and one for draining. There is also an oil level gauge, which is typically marked with fill lines. Adhering strictly to the operation and maintenance manual, as well as any suggestions or guidelines given by the manufacturer, open the oil fill lid and watch the gauge closely as you pour oil in until the oil gauge indicates a sufficient amount has been reached.
Nathan B. – Process Engineer
Following the power curve, multiply the value that you arrive at by a safety factor of 1.1 to properly accommodate for unforeseen power consumption.
George R. – Maintenance Engineer
Seal water should be measured through flow indicators installed in the vacuum system. When troubleshooting, seal water flowrate should be measured at the drain of the discharge separator. This can be accomplished by leaving the drain open and letting it pour into a bucket for a minute. This will provide you the actual GPM flowing through the pump.
Jason M. – Plant Engineer
- The discharge separator should be positioned near the discharge of the pump. The intake of the separator should be above the water line in the separator so as not to back-feed into the pump. If a recirculation pump is in use, then the line connecting the two should be above the recirculation pump to complement the flow. If the recirculation is gravity-fed, then the line to the heat exchanger should certainly tend downwards to encourage proper flow.
- For recirculation, the solenoid should be at the top of the separator. The low-level should be above but close to the recirculation line, and the high-level should be below the intake to prevent back-feeding. Take into consideration the turbulence with which the service fluid enters the separator.
William S. – Plant Operator
This sound is the primary symptom of cavitation. Cavitation occurs when vapor droplets collide with the pump at high velocities, especially damaging the rotor. Reducing the vacuum level and lowering the seal water temperature as much as possible will resolve this issue.
Avery P. – Plant Engineer
We work with Dynamic Descaler to provide you quick and easy descaling solutions for your liquid ring vacuum pumps and compressors; simply ask NES for the help you need and we will respond swiftly.
Our system is supplying too much water to the liquid ring vacuum unit; what is the best thing to do?
Sana M. – Research and Development Engineer
When a vacuum unit receives too much water, its capacity can be drastically reduced. To prevent this, it is necessary to know how much fluid is actually being used in the pump. Fluid can come through the process as well as through the seal fluid connections on the pump, so the first step is to determine how much fluid is actually flowing through the pump. Using a bucket or pail, open the discharge port on the discharge separator and measure how much fluid is passing through the pump during operation within a minute. After this, compare the expected value coming from the seal fluid line with the actual value coming out of the discharge separator and calculate to accommodate the excess fluid coming through the pump inlet from the process. A pre-existing valve or similarly functioning apparatus should be adjusted to reflect such calculations.
Donovan S. – Equipment Maintenance Technician
To change packing, loosen and remove gland nuts, lockwashers, and packing gland assembly. Screw packing pliers into the packing and pull. Remove the lantern gland and the remaining packing layer. Take the opportunity to check the shaft for wear and scoring. Lubricate the inside diameter of the new packing rings and work each layer onto the shaft. Make sure that the slits of the packing are staggered to discourage leaking. Use packing pushers to firmly and evenly place them in the stuffing box, making sure to lubricate and install a new lantern gland.
Dean T. – Field Service Technician
To grease the bearings in a liquid ring unit, open the end cap and fill a third of the cap with fresh EP-40 grease. If there is old grease in the cap that needs to be removed, then remove as much of it as possible. Check your operation and maintenance manual, as well as any grease specification sheets from the manufacturer, to see specific instructions and change intervals.
Morgan F. – Safety Engineer
Bearings should usually be allowed to reach no more than 140°F. Refer the operation and maintenance manual for your unit to find the exact temperature that is recommended by the manufacturer. If it gets hotter, open the end cap, clean out all the grease, and replace with fresh grease.
Ashley K. – Maintenance Planner
NES Company Inc. often comes across scoring on the shaft and bearing journal in a liquid ring unit, and we confidently repair such issues promptly and effectively.
Edward C. – Purchasing Agent
The difference is in the conical lobes of the pump. A 2001 model will have large inlet and outlet ports, increasing capacity at a rougher vacuum, around 5-12”HgV. 2003 models have much smaller ports, exhibiting a decrease in capacity but reaching its maximum at 18-22” HgV. 2002 models are the middle ground, with medium capacity at 12-18”HgV.
Anthony G. – Mechanic
When calibrating a dual conical lobe vacuum pump for assembly, end-to-end and hard-to-hard tolerancing are the methods by which a rotor-shaft assembly is properly positioned in the pump a set distance away from the tapered surfaces of the conical lobe. The hard-to-hard travel is the distance the rotor travels from being locked tight against the drive-end cone to being locked tight against the free-end cone. The touch-to-touch travel is the distance the rotor travels from first touching the drive-end cone to first touching the free-end cone. Always use the free end to measure the distance using a dial indicator. Make sure the outer free and bearing cap is installed without the shim gaskets.
For single cone units, there is a hard-to-hard tolerance between the cone and rotor. There is no touch-to-touch because there is no cone to touch off of on the other side; it is only an idle end.
Taylor B. – Laboratory Technician
Wear on the rotor or cone, or both, after time is the most common reason that we encounter. Another cause could be a change of seal water temperature.
Timothy R. – Electrical Technician
Motor overamping is likely occurring due to flooding in the pump. There is too much fluid in the pump, which requires much more power than is typically expected. 80% of issues are flooding related. To resolve this issue, provide the minimum amount of seal fluid as recommended by the manufacturer. In this scenario, less is more (to an extent).
Quinn J. – Manufacturing Technician
It is best to have an individual line for each pump. When multiple pumps are connected like this and one performs more than the others, it will pull vacuum on the other pumps. These will “compete” against each other, and you will not get vacuum.
Anna A – Procurement Specialist
Depending on the unit, it can be more profitable to repair or replace parts rather than to replace the entire unit. This depends on sourcing, quality, and metallurgy. With NES, any cast iron liquid ring unit that is capable of less than 2000 CFM is not worthy to repair, as it will cost more to repair than to simply install a new unit. An NES stainless steel liquid ring unit of 1000 CFM or less is not worthy of repair.
How can NES Company Inc help me to start and maintain vacuum?
Ryan C. – Maintenance Supervisor
NES Company Inc. carries repair kits for all units. Simply ask, and we will fulfill your needs.
Logan L. – Quality Manager
Yes, NES Company Inc. does initial inspections followed by complete teardowns as necessary. Once disassembled, we measure critical tolerances and give our opinion on repair vs. replacement, prioritizing what is most cost-effective for you to have better performance for longer.
Sarah B. – Environmental Compliance Specialist
Yes. We do on-site inspections, fiberscope inspections, system evaluations, performance testing, troubleshooting, and preventative maintenance.
Emily S. – Process Chemist
NES Company Inc. distributes new standalone bare pump units as well as custom-engineered systems.
Michael D. – Research Engineer
NES Company has been designing vacuum and compressor packages for decades, and we have been reliably distributing bare pumps for even longer.
Paul K. – Warehouse Manager
- NES Company Inc. provides drop-in replacements for certain Nash liquid ring units, but not the entirety of the Nash portfolio. If unsure, please ask your NES representative about the specifics of the function, fit, and form of the NES product that you are interested in.
- You can rest assured that NES Company Inc. will provide the competitive pricing and quick communication that we pride ourselves in.
Cynthia Z. – Systems Engineer
Nash/GARO compressors are designed in a cantilever configuration. This configuration is structurally unstable and prone to vibration. NES liquid ring compressors are designed to be more stable and robust for long-lasting service, with a port near the shaft to open and clear debris and impurities without having to disassemble the compressor.
Steven F. – Logistics Coordinator
NES Company Inc. offers fiberscope inspections and reports to determine the current performance of the unit as compared to a new Nash unit. Repair can be done with the aid of NES repair kits or through our repair shop. Through Dynamic Descaler, descaling operations are made streamlined.