Oil sealed vacuum pumps such as vane and piston pumps can tolerate a certain amount of water and other condensable vapors such as alcohols, acetone, and solvents. For the integrity of the sealant oils, and to achieve a good vacuum (lower than the vapor pressure of the liquid), it is best to prevent the condensables from entering the oil sealed vacuum pumps or removing them after they do enter the vacuum pump. The following discusses various methods for this removal and mostly refers to the condensate as water. The discussion of water is also applicable to other vapors and liquids, especially ones having a vapor pressure close to or higher than water.

Trapping and filtering condensable vapors upstream of
the vacuum pump:

1. Sorption: traps water by means of a membrane or media which will, “filter” a vapor to that of a liquid employing either adsorption or absorption. The membrane type typically coalesces the wetted air and the media type (example: activated alumina) absorbs the condensate.
2. Condensing or knock-out pot: vertically-configured tank, pot, or drum that
   has surface area for wetted vapors to condense on. In addition to the
   surfaces, separation is by gravity wherein the liquid falls to and is entrained at the bottom. The vapor travels upward at a designed  velocity and exits at the top of the vessel. These containers will often contain a baffle or designed such that the air has a restricted or obstructed path, thus providing more surface area and for gravity to work for liquid to fall down and the air to travel up towards the exit.
3. Cold Trap: a container in which the traveling air comes in contact with coils or vanes full of a chilled fluid. The vapor will condense on the colder surface, change from a gas to a liquid, and collect onto the cold surface and/or drop to the bottom of the container.
4. Liquid Nitrogen Trap: similar in design to a cold trap except that the
   intention is for the vapors to freeze onto the coils.

Removing condensates from the vacuum pump:

1. Gas Ballast: Gas Ballast means admitting gas (usually air, nitrogen or another non-compressable) during the compression stroke of the pump to change the ratio of non-condensables to condensables and prevent condensing because of the heat of compression (admitted air adds to the gas mass). Using gas ballast reduces the performance of the vacuum pump at low pressures. Gas ballast flows are limited to approximately 5% of the pump displacement. Gas ballast is very effective for condensables with vapor pressure close to or higher than water.
2. Hot Pump: A hot pump handles condensables, such as water, by keeping them in the vapor phase. Elevating the oil temperature above the boiling point of the
   condensable, up to a maximum of 230ºF, can prevent condensing by pumping it
   through the pump and out the exhaust like any other gas. A thermostatically
   controlled device maintains the oil temperature and a high temperature rated oil
   is incorporated to protect the vacuum pump. Hot pump operation can result in a
   higher rate of oil degradation. The use of synthetic oil is recommended or
   aggressive oil changes.
3. Decanting: Immiscible condensables can be handled through phase separation (vapor to a liquid) in the oil reservoir and drained off at the oil sump. Precaution must be taken to prevent the condensed liquid from entering the oil feed line of the vacuum pump. In addition, the inlet pressure of the vacuum pump can be affected adversely.
4. Knox Air Stripping: Knox air stripping involves the admittance of a compressed permanent gas blowing over the discharge valves of the vacuum pump to entrain vapors at the discharge. It is similar to using gas ballast but less efficient. However, it does not affect the inlet pressure of the vacuum pump
5. Vacuum Distillation or Vapor Handling: The vapor handling, or vacuum distillation system, reduces the total pressure at the exhaust of the rotary piston pump by pumping in series with the use of a small liquid ring vacuum pump. The liquid ring vacuum pump reduces the exhaust pressures of the piston pump oil. This together with an elevated oil temperature maintained using a thermostatically controlled valve on the cooling water line keeps the vapor from condensing in the oil. It is important to note that the total pressure must be less than the saturated vapor pressure at the oil temperature within the pump. The vapor handling method handles much more vapor than gas ballast, and it does not increase the inlet pressure of the rotary piston vacuum pump. This secondary pump methodology is most applicable to large oil sealed piston pumps which have a large quantity of oil. A key advantage of the vapor handling system is that the condensable can be recovered in the liquid ring pump and  used as the process sealant if compatible with the process.

Helium leak detectors (HLDers) are single gas mass spectrometer devices. They are tuned to detect the presence of helium and also have the capability of measuring a leak or verifying the absence of a leak to a given value.

Helium is used as a tracer gas because it is a very small atom, is an inert gas, is relatively inexpensive, and is present in ambient atmosphere air in extremely small values (mid range 1^-07). The “leak” is most commonly measured in atmospheric cubic centimeters per second (atm cc/sec). This value will be in Torr or Millibar (mbar). There is 760 Torr or 760 mm of Hg per atmosphere. There is 1013 mbar or 1.0 bar per atmosphere. The described leaks are also commonly referred to as the end pressure that they can detect and are described in either mbar or Torr.

A HLDer is comprised of a high vacuum pumping station, an analyzer compartment (cell), and a read-out device to indicate the pressure and/or leak rate. The high vacuum station is comprised of a high vacuum pump, which will be a diffusion or turbo molecular vacuum pump, and a secondary pump or pumps to do the initial pulling of vacuum and to back (work in union with) the turbo or diffusion pump. This secondary pump is often referred to as the rough, hold, or backing pump. Traditionally this rough pump is/was an oil sealed mechanical vane pump. The trend of late is to substitute this vane pump for that of a non-oil sealed pump. These “dry” pumps as they are called, will either be a diaphragm/membrane, screw, or the most popular today, a dry scroll pump. An oil sealed vane pump is
the superior pump for that of helium, but the recent trend is to be, “all
dry”.

Here in the US, Varian (now Agilent) has the largest market share of existing working HLDers. The other big names in the industry are Alcatel (now Adixen), Leybold/Inficon (now Oerlikon) and Veeco/VIC. Lesser players would be Edwards and Pfeiffer. A couple of Asian companies make HLDers (Ulvac is the biggest name here in the US) and some manufactures, like anything else these days, buy from another company and put their name on it. A new helium leak detector is going to vary in price from ~$20,000 – $50,000. A refurbished unit is going to cost ~ $8,000 to $25,000.

The Alcatel models have for many years been known for their ability to detect very small leaks. The Varian was known for a large range of pressures that they can detect helium. If one looks at various HLDer literature over the years, one will note that everybody makes claims on what small leaks their detectors can detect, anywhere from 1 x 10^-8 to 5x 10^-12 Torr (or atm cc/sec). This “claim” could be described with an analogy to automobiles, especially 30 plus years ago. Most all cars claimed or had on their speedometers an upper speed of 120 to ~ 150 MPH. For certain cars, there is no way you’d speed up to 120 MPH whereas with some high-end cars, it would be no problem for the car. And keeping with this analogy, if the desired task was to transport a load of gravel 100 miles, you would want to use a truck, not a fast sports car.

For cars, the need to achieve 120 MPH speeds is insignificant for most people. Likewise, most applications for HLDers really do not need to test at the 10^-10, 10^-11 or 10^-12 range. That said, often engineering specifications will be made by engineers who will specify a leak tightness requirement based on what is available to test or verify. Another driving force with HLDer specs or leak specs is the military. They are always pushing the envelope on specifications for acceptable product. Anything of military grade these days that has a leak spec will be in the 10^-9 range. This is also the upper specification for most semiconductor manufacturers, the pharmaceutical industries, and anything related to handling reactive or dangerous gases. Again, with 10^-9 being the upper value.

The exception to the above leak value description would be with the nuclear industry. They wrote the book on methodologies and the basic technology utilized in today’s HLDers was invented during the advent of the first nuclear bomb during the Manhattan Project. This industry likes to determine leaks to the 10^-11 range.

There are many comparative aspects to the various HLDers on the market. The typical ones are:

Sensitivity rating: its smallest leak it can detect and the largest leak it can handle.

Response time: time from the HLDer’s first ingestion of helium to a leak rate being displayed on a read-out)

Roughing time: how long it takes to evacuate a given volume to a pressure in which the HLDer can start detecting range of sensitivity: This can be anywhere from atmosphere on down to ~ 5 x 10^-12.

Measurement range of the detectable leaks: gross leaks (atm to 10^-4), medium leaks (10^-5to 10^-7), or fine leaks (10^-8 to 10^-11). Ideally, the unit is to be able to find gross leaks and fine leaks.

Automation: does one want a one button operation for a person leak checking small devices all day or is this a large singular system
in which a skilled operator wants to see how gauges behave?

Ease of use: this will include calibration and ruggedness (or ability to withstand abuse).

Others: cost, maintenance, type of backing/roughing pump, clean-up time (ability to digest and exhaust a flood of helium) customer service/warranty issues, size, types of displays etc.

For high sensitivity (better than 10^-9 value) there are three key aspects: the ability to detect the presence of small amounts of helium, the leak or pressure measurement capabilities, and the ability to calibrate the instrumentation. Calibration will drift or change due to many variables. How much they will drift will vary from manufacture to manufacture. The ease or ability to calibrate will also vary. A key to calibration is the exactness of the calibration. The ideal is both the least amount of drift as well as ease of calibration and exactness of correct calibration.

The issue of calibration is very important to HLDers. Calibration is achieved with use of a small capillary vessel, about ~ 200 ml that has helium in it. This vessel, known as a calibrated leak will have a small orifice leak, allowing for an extremely small “leak”. The calibrate leak will have a known leak rate at a constant temperature. Depending on make and exact style of manufacture, this rate of leak will only degrade 3% per year. It will also vary an average of 2% per degree Celsius.

Typically one would take a calibrated leak, install it to the inlet of an HLDer, put the HLDer in a test mode, and then adjust the instrumentation potentiometers to read the known leak rate value. Many HLDers today will have an auto-calibration feature. An HLDer with an auto-cal feature will have an internal calibrated leak which at the push of a single button will valve the system to that of the calibrated leak and automatically adjust the instrumentation to that of the known leak value. The auto-cal process requires some sort of microprocessor or computer. In the evolution of HLDers, circuitry went to microcircuitry and IC chips.

Read-outs went from analog to digital, calibration of potentiometers by hand transitioned to computers running everything and so forth. The trend has been to dummy down the units such that a briefly trained technician can hit one or two buttons and assume all is well while testing.

In conclusion,  for choosing a helium leak detector, having a good understanding of the type of leak to be determined (or lack of), methodology of how it is to be used, who is going to use it (degree of knowledge) initial cost, and cost of ownership (maintenance repairs) are all factors to be thought out. For any follow-up questions/issues/quotations, Provac Sales, Inc. can help you. Give us a call or email us.

Yes, the vacuum pump world has been confusing recently.
The short story is there has been much consolidation, name changing, and
company purchases within the last 10 years. Many of the purchased companies are companies with 60 to a 100 year history.

Brooks Automation bought CTI (and MKS).

Edwards Vacuum bought the Seiko Seiki Vacuum Company a few years back. At first, the Seiko Seiki Pumps (STP) still were referenced as Seiko Seiki, but since the last few years, they now all state Edwards. They are still manufactured in Japan.

Edwards bought Stokes Vacuum (and subsequently cancelled  much of the Stokes line). BOC Edwards is now known as Edwards Vacuum as BOC sold
the vacuum pump line.

Gardner Denver, a Thomas Company has purchased Nash, Welch, Rietschle, Hoffman/Lamson and Champion.

Leybold changed their name to Oerlikon Leybold Vacuum.

Pfeiffer Vacuum recently bought Alcatel which had just changed its name to Adixen.

Tuthill bought Kinney Vacuum, MD Pneumatics, and Atlantic Fluidics and consolidated all three in Springfield, MO.  All three companies are slowly getting rid of the original names and are going with Tuthill Vacuum & Blower Systems.

Varian Vacuum is now owned by Agilent Technologies. Varian sold their cryo business to Ebara who then sold the line to Genesis.

Have any questions about the new manufacturer’s names? Contact us, and we would be happy to help you sort it all out.

Years ago, when web pages were a new concept, Provac Sales was one of the first companies to post a listing of products and services. Years later, after thousands of visits, this web page was looking outdated.  Working with a local web page developer, Sleepless Media, we kept the original format of listing vacuum pumps and prices, but made our site easier to navigate, and with more information.  

David Hoyle started Provac in June of 1990. Prior to that, he was a regional manager for Stokes Vacuum for 3 1/2 years and a direct sales person for Alcatel Vacuum for 3 years. While at Alcatel, he landed and managed the largest single contract Alcatel ever had in the US: Applied Materials.

“Working in Silicon Valley was a lot of fun in the 80′s” he states. “The semiconductor industry was booming. Most of the big domestic equipment manufacturers were actually manufacturing in Silicon Valley. The cold war was peaking with defense contractors working on huge orders. The local universities had research contracts and new types of technology were constantly being introduced. It was a great time to learn the many facets of the vacuum pump business”.           

Paul Flood, General Manager of Provac for the last 11 years, came to Provac with an extensive background in the manufacturing industry. Being from a family of noted physicists, he is a quick learner and is now an expert on most vacuum pumps and applications.

In the late 1990’s to early 2000’s, when manufacturers and their service groups were leaving Silicon Valley and laying people off, Provac started hiring their top-of-the-line technicians, some with 20+ years in their areas of expertise. It was a good opportunity: with a roster of highly experienced people, Provac filled the void created when the vacuum pump manufacturers cut back on people and service.

Since the 1990 inception, Provac Sales, Inc. has been the factory authorized sales representative for Tuthill/Kinney and Inland Vacuum (vacuum pump fluids and greases) for all activity in Northern and Central California.

The collective mantra of Provac is to maintain an extensive inventory of ready-to-ship rebuilt vacuum pumps and provide immediate technical support to people when they need it. In the current business environment, it can be difficult to get a fast response from companies. Try finding somebody who can take your call at 3:00 PM, help you figure out the best solution to a problem, take an order and ship out the needed product the same day. This is what we do, every day.   

We offer expertise for Alcatel, Busch, CTI, Ebara, Edwards, Leybold, Kinney, Pfeiffer, Stokes, Varian, Veeco and Welch for blower booster, cryo, diffusion, dry, helium leak detectors, liquid ring, piston, scroll, turbo, vane pumps and all vacuum pump fluids and greases. 

Call us. E-mail us. We want to hear from you. 831-462-8900. provac@provac.com.

Provac Sales, Inc buys, sells and services vacuum pumps. We are also a manufacture’s representative and authorized distributor for Tuthill Vacuum & Blower Systems and Inland Vacuum, having maintained these relationships since our inception. We maintain a large inventory of rebuilt and ready- to-ship UHV pumps including turbo, cryo, diffusion, mechanical, blower and various dry pumps.