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VACUUM PUMP PROBLEMS LEAKS


Disclaimer : All efforts have been made to offer good hearted information on how, over the years, we at HyVac have solved some problems. We are not suggesting in any manner that you or your subordinates should follow ANY of the information outlined below. If you insist on ignoring this advice proceed at your own risk. The information provided should NEVER be attempted without complete consultation with your companies engineers and plant safety officers. Some of the procedures outlined could be hazardous to your or others health. We feel it is ridiculous to have to include this disclaimer but feel we also have an obligation to help others with their problems.

Failure To Attain Vacuum
Leakage, contamination and unusual out-gassing are the general causes of problems associated with poor vacuum. To operate at maximum efficiency a system must be leak tight and completely clean. Often, poor system performance is related to system leaks, (not necessarily pump malfunction) that can not be overcome by the capacity of the vacuum pump in service.

If the system is completely clean and free from leaks, and unwarranted vacuum problems still exist, the pump should be checked. A simple test for the condition of a mechanical pump is a determination of its ultimate pressure capability. This can be accomplished by attaching a vacuum gauge directly to the pump at the pumps intake connection. This is often referred to as the "blank off pressure" by us vacuum pump people. The gauge may be any suitable type, provided consideration is given to the limitations of the gauge being used. If the pressure is unusually high, between atmosphere and 1 torr, the pump may be badly contaminated, low on oil or malfunctioning. On the other hand, if the pressure is only slightly higher than the guaranteed pressure of the pump, an oil change may be all that is required. Sometimes use of the pumps "gas ballast" valve can lower the pressure by purging the pump of condensable vapors (water, solvent contamination).

Leak Detection
System leaks often are a root cause of high system pressures. It is important to understand the concepts available for determining leaks and finding them. For large leaks, pressurize the system with a small amount of air pressure 5 psi.
(Use extreme caution since positive pressure can cause glass to shatter and system components to explode.) Paint suspected area with a thick soap solution. Escaping air will produce soap bubbles just like the tire on your car. For metal piping and seal leaks, place a thermocouple gauge between the vacuum pump and the suspected leak area. Spray suspected area with acetone and observe sudden increase in pressure on the thermocouple gauge if a leak is present. (Use extreme caution since organic solvents such as acetone are highly flammable and combustible).)

For very small or molecular sized leaks it is advisable to employ a specialized piece of equipment known as a helium leak detector which is basically a mass spectrometer tuned to detect helium gas. Because helium is such a small molecule, it has an affinity to find it's way through any small opening present on a system. The system can be checked from outside in or from inside out. An individual specifically trained in this procedure is advised. The equipment required tends to get expensive.

Contamination
Another common cause of loss in efficiency in a mechanical pump is contamination of the oil. It is often caused by the condensation of vapors and by foreign particles. The undesirable condensate emulsifies with the oil which is re-circulated and subjected to re-evaporation during the normal cycle of pump activity thus reducing the ultimate vacuum attainable. Some foreign particles and vapors may form sludge in the oil, impair sealing and lubrication and cause eventual seizure.

Therefore, periodic oil changes and use of HyVac Flushing Oil are necessary to maintain efficient operation of the system. The required frequency of changes will vary with each particular system. Experience with the individual process will help determine the normal period of operation before an oil change is required.

Damage to Vacuum Pumps
There are three common causes of damage to vacuum pumps. All involve ingestion of foreign materials into the pump. They are gross contamination of the oil with condensable vapors such as water vapor, contamination of the oil with acids and other reactive chemicals, and ingestion of dusts or other solids into the pump mechanism. Most of these materials are generated within the vacuum system itself. Therefore, when setting up a new vacuum system or troubleshooting an existing system, it is critical to identify the presence of such materials and take steps to eliminate them from the gas stream being ingested into the pump. This is generally accomplished by using vacuum traps.

There are several methods for eliminating damaging materials from a vacuum system. A combination of these methods is often recommended for best results. They are use of an appropriate vacuum trap or combination of traps, frequent oil changes or an oil filtering system, and use of the vacuum pump's gas ballast valve which acts as a vented exhaust valve. It can help to throughput vapors out of your system through the pump during the pump down cycle and out via the exhaust port of the pump.


11/26/2005 ęCopyright HyVac Products, Inc. All Rights Reserved
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