OC, do you us the gas ballast on your pump (if it has one)? These are generally good at purging crap while you are pumping down a vacuum system. I've never bothered with a cold trap. I open the ballast a bit when pumping down and then turn it off. If things get bad, I'll just change the oil.
The Gas Ballasthttp://www.hyvac.com/tech_support/Gas%20Ballast%20Valve%20Explanation.htm
Gas Ballast Valve, What it do?
Most HyVac Products, Inc. vacuum pumps are shipped and contain a feature known as the gas ballast valve. This is viewed as a black adjustable knob on top of the pump.
Often in vacuum work, the user will get water vapor, solvent vapor or other bad contaminants as part of the gas stream being evacuated from the vacuum chamber. These contaminants come over because they have turned into a gas molecule from a liquid molecule under "X" vacuum pressure and the pump pumped them out of the system. They then travel to the pump and turn back from a gas to a liquid in the pump oil.
All liquid chemicals have a value known as vapor pressure. This vapor pressure is a function of physical chemistry law. The basic formulae is PV=nRT. I could get into an explanation more detailed here, but suffice to say that as a result of this formula, water will boil at room temperature when a vacuum pressure of roughly 29.5" mercury vacuum is achieved. When water boils it is turning from a liquid into a gas. All chemicals have this feature, just at varying temperatures and pressures based on their molecular construction.
It is possible to throughput some of these contaminants from your system and through the pump and that are where the gas ballast valve comes into play. If you do not require high vacuum less than say 300 micron for instance, then you can open up the gas ballast valve during the evacuation procedure and get some of these bad molecules out of the pump through the exhaust port of the pump. Remember also if they are coming out the exhaust they potentially are entering your workplace. This may pose a hazard either health based or fire based. If you are looking for better vacuum pressures, the valve is adjustable. This feature is not the total answer; it helps, but should not be considered the solution in problem applications with lots of contaminates.
If and once the pump is contaminated you can again use the gas ballast valve to assist in purging some of these contaminants from the vacuum pump oil in which it now resides. Close the pump inlet port off to full vacuum and allow pump to run/actuate with gas ballast valve in open position. This again will help purge the pump. Take a long lunch or let the pump actuate overnight with the valve open. Care again should be considered to the exhaust stream. If the pump is "smoking" or exiting oil mist in good quantity, you may come in the next morning to a room full of oil mist. Piping to a hood or using a coalescing filter like the HyVac Capture filters can help eliminate this problem area.
If you have big problems in this area, or if you are always finding contaminants in your oil, you probably need a different solution and should call us.
It is common during operation of the pump with the gas ballast open for there to be seen oil mist or "smoke" coming from the exhaust of the pump. Continuous duty at these pressures generally causes the user to desire a HyVac Oil Mist Eliminator or HyVac Capture filter available from us for most vacuum pumps.
If you have no problem with contaminants you should use pump with the gas ballast valve closed. We consider this normal operation.
