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MegaVac 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.

Accessories

Return pump for repair. (RGA)

Next pump bigger

Next pump smaller

Specifications

General practices for long life

Oil change intervals

Applications

 


Introduction

The MegaVac vacuum pump is an old style vacuum pump we often refer to as a trap plate pump. Some people call these piston pumps, but to us they still are in the rotary vane family. The rotor is offset in and rotates off-center in the stator (or ring). The stator (or ring) has slots cut in it where the vanes sit and ride up and down maintaining constant contact with the rotor using a spring and lever arm to maintain tension as it rotates eccentrically in the ring. These are one of our most difficult pumps to assemble for all the parts have to be just right. Because of the assembly process each pump is almost unique in nature although we are working to make them more consistent allowing the parts to be more interchangeable. The uniqueness of each pump also makes them very, very difficult to field repair and bring back to original specification. We The MegaVac vacuum pump is an old style vacuum pump we often refer to as a trap plate pump. Some people call these piston pumps, but to us they still are in the rotary vane family. The rotor is offset in and rotates off-center in the stator (or ring). The stator (or ring) has slots cut in it where the vanes sit and ride up and down maintaining constant contact with the rotor using a spring and lever arm to maintain tension as it rotates eccentrically in the ring. These are one of our most difficult pumps to assemble for all the parts have to be just right. Because of the assembly process each pump is almost unique in nature although we are working to make them more consistent allowing the parts to be more interchangeable. The uniqueness of each pump also makes them very, very difficult to field repair and bring back to original specification. We do not recommend field level repair on this pump unless, it is very minor in nature.

On the positive side, the MegaVac, when right, is a tough dependable pump. If the shaft rotates and the vanes go up and down, one can usually expect a pretty good number for the vacuum specification. It is a good pump for applications expecting abuse. It is a reasonable choice for untrapped contaminates.

It is relatively small pump (volume wise) and can not tolerate too leaky a system. It is important to have little or no air leaks on the system being evacuated.

It has been in use extensively in the neon light business and is a good medium to small system pump. It tends to be a little noisy due to it’s design, which can be a drawback or benefit depending on system setup and monitoring. The pump sound will change when high vacuum is reached and users don’t have to watch a gauge, just keep an ear cocked as to when the system is at high vacuum (full vacuum) pressure.

No Vacuum No Vacuum -

The MegaVac 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 and get some screw drivers and some old rags, we are going to operate. Remove the top off the pump and the oil baffle plate which is present inside the pump and visible after removal of the top plate. Remove the oil baffle plate also. You should now be able to see into the top of the pump. You should see "two springs" attached to two "lever arms". (sometimes there are more than two springs). The lever arms press and force the vanes down onto the oscillating, rotating surface of the rotor. When no vacuum is present you might see the vanes stuck in the up position. At this time manually actuate the pulley and review vane and lever arm actuation. The vanes should move up and down with the lever arms actuating in tandem.

If vanes are stuck in up position find a set of blunt nose pliers. Remove springs from back of lever arm and put aside pump. Move lever arms out of the way and firmly try and accurate vanes up and down in the pumps vane slots. No gorillas please, this is a firm but gentle operation. Tolerances of slots are +.001" and can get rusted up or have contaminants "plate out" on surface causing vanes to stick in the up position. We are trying in this operation to get plating or scale scrapped off so the vanes can ride freely in the slots.

If the vanes are not stuck in the up position, I am stumped for the simple things, so it is best to send the pump in. It maybe that the shaft is broken or the shaft keys are gone. In any case it is a job for HyVac unless you are very mechanically inclined. Call us for an RGA / repair order at 1-800-628-0850.

Low Vacuum Low Vacuum Low Vacuum

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 low vacuum pressures are present then turn the pump off and get some screw drivers and some old rags, we are going to operate. Remove the top off the pump and the oil baffle plate which is present inside the pump and visible after removal of the top plate. Remove the oil baffle plate also. You should now be able to see into the top of the pump. You should see "two springs" attached to two "lever arms". (sometimes there are more than two springs). The lever arms press and force the vanes down onto the oscillating rotating surface of the rotor. When low vacuum is present you might see one of the vanes stuck in the up position (usually the exhaust vane). At this time manually actuate the pulley and review vane and lever arm actuation. The vanes should both move up and down with the lever arms actuating in tandem.

If a vane is stuck in up position, find a set of blunt nose pliers. Remove the springs from back of lever arm and put aside pump. Move the lever arm out of the way and firmly try and actuate the stuck vane up and down in the pumps vane slots. No gorillas please, this is a firm but gentle operation. Tolerances of slots are +.001" and can get rusted up or have contaminants "plate out" on surface causing vanes to stick in the up position. We are trying in this operation to get plating or scale scrapped off so the vanes can ride freely in the slots.

If vanes are not stuck in the up position. ???? I am stumped for the simple things, so it is best to send the pump in. It maybe that the shaft is broken or the shaft keys are gone. In any case it is a job for HyVac unless you are very mechanically inclined. Call us for an RGA / repair order at 1-800-628-0850.

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 that has seized due to lack of lubrication. Other potential problem areas include vanes stuck in down position. See "No vacuum" section above. Call us if you are unsuccessful.

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 felt that specifically the MegaVac style vacuum pump had a weak area here and we moved to improve it in 1996. The new shaft seal is a lip seal. If your pump employed the old style packing material then you can not use the new style lip seal with out purchasing a new style trap plate 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 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". This will 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 ia 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

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 destruction.

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 or collapsing vacuum hoses. Check system for leaks (Link to procedures). Fix leaks and time again.

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 MegaVac the blank off pressure is .3 micron or .0003mm 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 MegaVac pump has the ability to capture the exhaust of the pump through the standard national pipe threaded (NPT) exhaust port. You can hook up an exhaust line and port the exhaust to a hood or simply thread in an upgraded exhaust filter. 

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