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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 ©Copyright HyVac Products, Inc.
All Right Reserved
Toll Free 1-800-628-0850 |
