HOME      Email

HyVac 28 and 45 Vacuum Pumps 


Problem List

No vacuum
Low vacuum
Pump locked up
Oil problems
Pump leaking oil
Water in pump
Pump corroded
Slow to pull down
How to capture exhaust
Hose nipple too big
Hose nipple too small
Other problems not covered ??
How to change oil.

Other Information

Exploded view

Parts list

Working on this pump.


Return pump for repair. (RGA)

Next pump bigger

Next pump smaller


General practices for long life

Oil change intervals




The HyVac 28 and 45 vacuum pumps are basic oil sealed rotary vane pumps known for years. These pumps are driven by a motor connected to a pulley on the pump using a drive belt. The rotor is offset in and rotates off-center in the stator. The rotor has 2 opposing slots cut in it where the vanes sit and ride in and out maintaining constant contact with the stator using a spring to maintain constant pressure as it rotates eccentrically in the stator. These pumps are relatively simple in operation and are easy to repair. Because of the assembly and manufacturing processes each pump is very consistant and the parts are not unique, are interchangeable and often can even be refurbished. Because they are simple, HyVac Products offers repair kits for all pumps in this generic category.

Even though they are old in design, they are really tough and take a lot more abuse than some of the newer faster pumps in the market place. They are typified by larger oil capacities, slow moving functionality and large lubrication ports. The HyVac 28 and 45, when right, is a tough dependable pump. Due to the use of a heavier viscosity oil they can be expected to produce excellent high vacuum numbers. It is a good pump for applications expecting abuse. It is a reasonable choice for untrapped contaminates.

They vary in size from small to medium (volume wise) and can tolerate small leaks in a system.

These pumps are extensively used in labratories, neon manufacture, degassing, vacuum ovens and a myriad of other applications. They tend to be a little noisier than the newer direct drive pumps and lack some of the newer features found on newer generation vacuum pumps. They still generate vacuum pressures in a very efficient manner and are still a favorite for many applications.

No Vacuum -

The HyVac 28 and 45 pump is tough to have "no" vacuum present on. It is possible, but unusual.

First off inspect the pump for correct oil level.

Second inspect the base of the hose nipple (inlet port) for a good sealant bead. I can't tell you how many pumps we get with the hose nipple replaced with some other fitting that is not properly sealed with a good vacuum sealant. For threaded sealing of HyVac pumps we recommend HyVac PST sealant.

Assuming adequate oil and lubrication has been inspected and is present. Then remove belt guard and turn pump motor on. If the pump pulley is rotating and still no vacuum is present then turn the pump off. Your pump needs to see us or have an overhaul.

Generally assuming no vacuum often means no pump rotation, then your pump may have one of the following problems.

First possibility, the pulley shaft key has come off and the pulley rotates but the shaft doesn't. Need to inspect the shaft for wear and you need a new shaft key or a new drive shaft.

Second the vanes are stuck in the rotor. Your pump rotates but vanes are not working. Your vane springs and vane spring pins could be shot.

Third all valving on the top of the stators is kaput.

Low Vacuum -

First off inspect the pump for correct oil level and oil quality.

Second inspect the base of the hose nipple (inlet port) for a good sealant bead. I can't tell you how many pumps we get with the hose nipple replaced with some other fitting that is not properly sealed with a good vacuum sealant. For threaded sealing of HyVac pumps we recommend HyVac PST sealant.

Assuming adequate oil quality and lubrication has been inspected and is present. Then remove belt guard and turn pump motor on. If the pump pulley is rotating and still low vacuum pressures (500 micron or so) are present then turn the pump off. Best guess is the exhaust valves on the exhaust stator are broken. The pump needs repair or overhaul.

The pump is locked up

Well you gone and done it now. Check the pump for oil. Fill to correct level and manually actuate pump, assuming you can. Sometimes it is possible to manually actuate a pump back into service using the pulley, that has seized due to lack of lubrication. Other potential problem areas include vanes stuck in up or out position. See "No vacuum" section above. Call us if you are unsuccessful. The pump needs repair or overhaul.

Oil Problems

Oil problems come in various shapes and styles and are highly dependant on the vacuum pressure the user is trying to achieve. Because there are many questions related to oil in our type of pumps we have a separate section just for oil questions and tech support. Hot link to Oil Problems.

Why is the pump leaking oil?

Vacuum pumps can leak from 3 basic locations and their causes can be various. The first area and main culprit to examine is the shaft seal of the pump. This is a mechanically rotating shaft in an area that can wear and then leak over time. We improved the HyVac 28 and 45 style vacuum pump in 1997 replacing the mechanical seal with a new generation lip seal. If your pump employes the old style internally mounted mechanical shaft seal then you can not use the new style lip seal with out purchaing a "conversion kit" to accommodate this update. If you look inside the belt guard and down the side of the pump south of where the shaft comes through the pump, you may find evidence of a shaft seal leak. Usually the side of the pump is shiny from the oil. Also running the pump for a period of time on top of a sheet of newspaper can pinpoint a leak.

The second most common location is from the pumps exhaust port. If the pump is operated at high pressures less than 28" of mercury vacuum, then high gas flows create high levels of lubricant agitation inside the pump which can exit the pump, come down the sides of the pump and create what can be construed as a leak. If this is observed to be your problem we can enclose the top of the pump and trap the exhaust of the pump using an exhaust filter or by enabling the user to port the exhaust to a nearby "hood". Sometimes adding an exhaust port extension using a section of standard plumbing pipe of appropriate size and length 6-10" can help. This will help keep the oil and associated oil mist inside your vacuum pump.

The second solution is to make sure your system is really, vacuum tight because the cause of this problem is basically a leaky system.

The pump will operate over extended periods with this symptom but it is important to monitor the oil level of the pump on a regular basis.

Water in the Pump Water in the Pump -

Hot link for the answers…. This is a big very common problem. One of our most common problems is water in the pump.

Why is it bad? Corrosion. Pump distruction.

How does it happen? Waters vapor pressure less than pumps vacuum pressure.

How do I tell? Oil is milky colored.

What are solutions? Freeze those water molecules.

Pump is corroded. Why?

Water or acids have been present in pump for an extended period of time. See also water in the pump.

I think all high vacuum pumps are made from cast iron predominately, aluminum and steel secondarily. We tried making one from stainless steel and will revisit sometime in future but in a nut shell, it failed. Cast iron and water don't get along. This is the same for acids like hydrochloric or sulphuric. The tend to attack the cast iron of the pump and cause oxidation or rust to form. On the outside this is ok but left standing, formation starts internal to the pump and will cause the pump to seize up after some period of time days to years depending on contaminant source and level.

I have seen ads for corrosion resistant pumps. Right…., great marketing ploy. They fail in 4 months instead of 3. Spend your money elsewhere on solutions that work. There is no cheap solution only correct ones. Teflon coating… phooey. The vacuum pumps lock up because the rust forms on the cast iron rotating parts "period". No teflon coating is going to last long with the metal to metal contact that we have in rotary vane pumps. Coating the oil sump with teflon protects the aluminum housing. I have never seen a pump yet with an uncoated aluminum housing eaten through, although I have seen thousands of pumps with corroded cast iron parts.

The basic fact of the matter is contaminants must be eliminated from the pump. You can either deal with it before the pump or after it gets in the pump. For systems with high contamination potential then probably both types of systems are required. For the front end or suction side of the pump, employ a vacuum inlet trap. For dealing with contamination once it is in the pump consider an oil filtration system that can be hooked up to the pump to recirculate and deacidify the oil.

The poor users solution to oil contamination problems "Change the oil frequently". Create a larger oil sump that lasts longer in getting contaminated.

Why is the pump is slow to pull down?

Assuming the pump is OK (see below). You have air leaks in you system, collapsing vacuum hoses or contaminants which cause "outgassing". Check system for leaks (Link to procedures). Fix leaks and time again. Remove contaminants.

How can I check my pump to see if it is OK?   

Hook you pump up to a good vacuum gauge at the pump intake port with out the system attached in any manner. This is the best and only real way to baseline the pump. In problem areas or troubleshooting vacuum systems this is the first step in the process. Determine the "blank off" pressure of the vacuum pump. For a HyVac 28 and 45 the blank off pressure is .1 micron or .0001mm and for those with inexpensive vacuum gauges roughly 7 micron, .007mm with thermocouple or TC gauge. And for you real mizers out there, 29.99 with Bourdon Tube 0-30" gauges and between 0 and 1mm with manometers (0-760) in both cases depending on atmospheric pressure variables.

How do I capture the exhaust?

The HyVac 28 and 45 vacuum only model pump requires only an exhaust filter of correct pipe size (1.5" MNPT) that allows for capture of the exhaust fumes. This can be ordered from HyVac for this use. As am alternative you then hook up an exhaust line and port the exhaust to a hood or adapt it to an exhaust filter then to the hood. The HyVac 28 and 45 vacuum pumps all have an exhaust port as part of their design.

My hose nipple is too big / too small?

HyVac Products stocks and manufactures a myriad of solutions for conforming to a users system. If we don't have it, we can get it. HyVac manufactures both conventional hose fittings and also the newer generation quick disconnect vacuum fittings often referred to as NW or ISO or KF fittings, flanges, piping, adapters and clamps which allow a wide variety of connection sizes and terminations.

How do I change the oil?

Generally we recommend changing the oil through the exhaust port of any high vacuum pump. This port generally is a straight dump into the oil sump of most vacuum pumps. The intake port should only be used as a last resort, is slow but ultimately acceptable. Manual pump rotation probably will be necessary to accomplish.

Other problem areas not covered.

You get em to me, I'll post em.

11/27/2005 ęCopyright HyVac Products, Inc. All Right Reserved
Toll Free 1-800-628-0850