This is one of the biggest
causes of problems in vacuum systems. Many times we get customer calls for "bad
pumps", not sufficient vacuum or high pressures. Often these problems are caused by
the system being evacuated. Often by some non-vacuum rated component being employed in the
system. High pressure / low vacuum becomes apparent when operating the vacuum pump in a
number of ways. Examples of air leaks and how they appear to the user.
1. Noisy pump. A low rumbling sound coming from the pump.
2. Generation of smoke or oil mist from the exhaust side of the pump.
3. Oil coming from exhaust port and running down the side of
4. Insufficient vacuum pressure to complete task.
Any one or all four symptoms may be present in the operation of
the vacuum pump fighting an air leak.
Typical applications where leaks can be found or are intrinsic to the operation
are as follows. Vacuum ovens ( the door gaskets ), any large gasketed opening subject to
regular open and closing and vacuum filtration to name a few. Other systems may exhibit
leaks and these should be eliminated from the equation if at all possible. Major cause of
these problems, include but are not limited to, improperly sealed threaded fittings, leaks
through ball valves, leaks in hose connections. Use HyVac PST Sealant for threaded
Some solutions that can minimize the impact or the work / time impact of these
difficulties are as follows:
Close the leaks.
Use an exhaust filter to stop oil mist, oil splash from exiting the pump. Increase height of exhaust opening from the top of the pump by using
an extension pipe fitting.
Use band clamps on all hose connectors. Two if using wire reinforced PVC tubing.
Connect system to pump using same sized hose fitting.
Check system for leaks. .
Generally speaking, leak tracing or detection on a vacuum system
can get quite involved depending on the pressure desired and size of system being
1. Start with pump. Blank pump off at inlet.
Cover inlet opening with a rubber stopper, your hand or any suitable non-leaking type of
set up to enable evaluation of the pump. Make sure the pump is not hooked up to any other
part of the vacuum system. Turn pump on and wait about 30-45 seconds. Does pump
still make noise and exhibit symptoms associated with an air leak. If yes, examine
carefully the seal around base of intake hose nipple. Is the base seal present or is it
crack free and appear intact? HyVac recommends a product called "HyVac PST"
sealant which we sell and is well documented for vacuum performance, it is a
per fluorinated sealant. It is available from customer service and does an excellent
job with sealing threaded fittings.
If your pump makes noise for 30 seconds and then is quiet, the
pump could be roughly assumed to be okay. This is how the pump should sound and behave
when it sees a high vacuum pressure on the inlet side of the pump. It should operate
fairly quietly and not gurgle, although a bare wisp of oil mist from the exhaust port is
not totally unusual.
If possible, put a vacuum gauge on the pump attached to the
intake nipple all by itself, no extra fittings except the intake hose fitting. A 1 hole
rubber stoppers work well for this. If the pump pulls down the gauge well, let pump run so
attached for an hour or more (overnight if possible). When you look at your reading on the
gauge you can assume this is your base pressure reading of what the pump is capable of but
remember this value varies greatly depending on the quality and type of gauging employed.
Your system once connected again should also be able to reach this pressure. If with the
same gauge you are seeing a different base pressure on the system you have a leak in the
system. Make sure and allow enough time. Vacuum pressures in the
.01mm - .001mm range take some time to achieve. This time required
deal expands as the size of the system expands.
2. Connect up the next section of your vacuum system to the
pump, not the whole system, the next section. Close off the other end and listen and see
if pump behaves as would be expected when you tested at the inlet. The time to reach a
"no noise", low noise, high vacuum level is proportional to the size of the area
being evacuated but should occur relatively fast. If the noise and gurgling persist after
a reasonable amount of time has elapsed you have found your leak. Continue diagnosing the
system until all leaks have been corrected. Remember, small leaks can cause big problems
with attaining required vacuum pressures.
3. Leak testing can also be accomplished on systems by
pressurizing the system to 5 lbs positive pressure Before attempting
this, read our section on leak
detection. (Check first if your system can
take this option!!! IT CAN BE VERY DANGEROUS) and painting connections and joints
with a soap and water mix. Like finding leaks in your car tire. Look for bubbles. Great
care and safety precautions should be taken if your system employs any glass tubing,
4. Acquiring a true high vacuum gauge will greatly assist in
determining ultimate system performance. This type of gauge will generally start at 5 Torr
(5mm) and read down to .0001 Torr (.0001 mm) of mercury vacuum. 0-30" Vacuum gauges
are not true high vacuum gauges and vary greatly in performance and accuracy but they are
better than nothing.
5. Leak testing with a Helium leak detector. A helium leak
detector is a pretty expensive piece of equipment employing a specially tuned mass
spectrometer to detect Helium. It is used for checking for the presence of helium
molecules in order to determine a leaks location. It is possible to find leaks of very
small size with this equipment because helium is one of the smallest chemical molecules.
This type of testing is generally needed by those involved with vacuum pressures less than
.001 mm Hg vacuum. It can work from outside in or from inside out of your system. HyVac
can arrange to do this testing, but it gets expensive, depending on your physical
location, complexity of the system and the time required to find the leak. Our Leak
Detection Service is based out of the Philadelphia, PA area.
Unit Conversion Chart
Above Sea Level Adjustment (for some gauges)
More Technical Stuff Related to Gas Pressures