Gas Ballast and Its Relevance to a Vacuum Pump

Air or gas pumped out of a vacuum system always contains vapor. This vapor will condense in the pump's compression stage. If you don't get rid of it, it will turn into a pollutant that prevents the vacuum pump from functioning at its best. As a pollutant, condensate can also penetrate the pump's mechanism and cause damage, such as the oil in oil-sealed rotary pumps. 

Simply put, the system's gas ballast valve lets air into the last stage of the compression cycle, where the vapor can be released without condensing or otherwise hindering the pump's efficiency.

How Does Gas Ballast Work?

Although the physics behind gas ballasts is straightforward, the reasoning behind their application in vacuum pumps is occasionally clouded by misunderstanding. Therefore, it's easy to dismiss the topic as too complex. Let's discuss the background of gas ballast and how it works so you can learn more about it.

Evolution and Functions

In 1935, Wolfgang Gaede introduced gas ballast as a significant improvement to oil-sealed mechanical vacuum pumps. 

Gas ballasts are employed in mechanical, oil-sealed vacuum pumps to prevent condensation of vapors during pumping, which could otherwise taint the sealing oil. The pump can perform its vapor duty close to full specification by controlling the amount of condensation in the sealing oil. Still, the open ballast air flow affects the pump's maximum pressure.

Water vapor, solvent vapor, and other unwanted substances are common in the gas stream evacuated from the vacuum chamber during vacuum practice. These contaminants arise when: 

  • Pump oil flows back into the pump, where the vacuum pressure transforms the oil back into a liquid form of the contaminant.
  • Ballast is used to exit the pump without contaminating the oil.


To put it, gas ballasting takes place when the condensable components of the air or gas being pumped are forced out of the pump by the entrance of the ballast gas flow before the condensation forms, contaminating the system, and the sealing oil.

By opening the gas ballast exhaust valve before the vapor condenses, the gas ballast mechanism prevents the pump from working a vapor that would otherwise condense in the pump. This condensable vapor is eventually released into the air.

What to Do if Your Pump Has Been Contaminated

If condensed vapor has contaminated your pump, you can "wash it out" with gas ballast. To do this, you must close the pump's inlet port and let the pump run with the gas ballast valve open. Depending on the size of the system and the level of contamination, purging may need to be left running for several hours or even overnight.

Returning to a room full of "oil fog" is possible if the pump is smoking or producing a substantial amount of mist. Venting into an extraction hood or installing exhaust mist filters will solve this problem. A gas-ballast oil return kit is all you need to fix the problem.

Remember that pumped gasses and vapors can reach the surrounding area when they leave the system. That makes them potentially dangerous, depending on their composition and concentration.

Freeze drying, rotary evaporation, distillation, and gel drying all use gas ballasting, typically connected with oil-sealed rotary vane and dry scroll pumps. If you want to know more about Gas Ballast, contact us, and we will happily answer all your questions.

Vacuum Pump Repair USA has specialized in vacuum pump services and repairs in the Southern California area since 1969.  We work with dozens of different vacuum pump brands, and our 54 years of knowledge go into every repair!

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