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The Simple Science Behind Gas Ballast Valves

By Leybold
TRIVAC Gas ballast

Gas ballast valves offer several potential benefits for vacuum pump users but are often overlooked. Learn more about how these simple, effective vacuum pump accessories can add efficiency and reduce contamination risks.

How Does a Gas Ballast Valve Work?

While atmospheric air or a gas may appear pure when used for a vacuum system, the truth is that it will always contain some amount of moisture. Inside the vacuum pump, the vapor will condense because water condenses at pressures below atmosphere, so it will fail to be exhausted from the pump and remain as liquid water. Unless this moisture is vented from the system, it will contaminate the oil. This can harm vacuum pump performance and cause damage by loss of lubrication or corrosion.

The resulting condensate may enter the pump's oil seal, affecting the pump's ability to run. By adding some air to the compression cycle via the gas ballast, the pump generates enough pressure to exhaust to atmosphere, expelling the moisture with the air. Thus, opening the gas ballast valve can eliminate these risks by expelling a small portion of the compressed gas without impacting the pump's overall performance. 

Gas ballasting often accompanies oil-sealed rotary vane and dry scroll pump processes for freeze-drying, rotary evaporation, distillation, and gel drying.

Leybold TRIVAC B using gas ballast

Why Do Vacuum Pump Users Overlook Gas Ballasts?

It's difficult to pinpoint the exact reasons why gas ballast usage is not widespread, but one key factor may be a misunderstanding of how the gas ballast valves work. 

The actual science behind gas ballasting is straightforward. However, since these vacuum pump accessories were developed in 1935, something fundamental seems to have been lost in translation. If more users understood how gas ballasts work and how they can benefit their vacuum pump systems, gas ballast usage would surely increase. 

Examining the Simple Science Behind Gas Ballast Valves

Used with an oil sealed vacuum pump, a gas ballast reduces the amount of vapor condensation — and therefore contamination — of the pump's sealing-oil.

The gas stream evacuated from a vacuum chamber contains water vapor, solvent vapor, and other potential contaminants. This contamination usually occurs because these substances have been converted under vacuum pressure from liquid molecules to gas molecules.

The gas then flows back into the pump, where it is converted back to a liquid contaminant within the pump oil, or exited through the pump itself. 

To understand this gas exchange process, it's important to remember that all gas can produce vapors at temperatures and pressures dependent upon their physical properties. 

Gas ballasting admits air or another gas into a vacuum pump so the vapors can be expelled before they can condense or contaminate the system, or pollute the sealing the gas. Gas ballasting is achieved in the following way:

  1. If the pump is "working" a gas that would naturally condense in the pump, gas ballasting will enable a pre-outlet valve to open before the vapor has had a chance to condense.
  2. The condensable vapor discharges to the atmosphere in its gas phase.

A pump that has been subject to condensed vapor can be cleaned up by using gas ballast technology.

Here’s how this process works:

  1. The pump inlet port is closed to allow the pump to run with the gas ballast valve in the open position, which helps to purge the pump.
  2. This purging is carried out for several hours or overnight, depending on the system's size and the degree of contamination. 

The reduction in condensation risk can allow the pump to achieve its vapor duty at a near-full specification, ensuring its ability to efficiently reach its ultimate pressure level. 

However, if the pump is smoking or emitting a visible mist in large quantities, the room could fill with oil-fog. Venting into an extraction hood, or using capture filters, will help to eliminate the issue. 

Still, even if purging vapor is not visible, precautions must be taken. Workers may be entering a working environment where the content and concentration of contaminants in the atmosphere can pose a health or fire hazard. A gas-ballast oil return kit can mitigate these risks.

Still unsure about the use of a gas ballast in your process? Contact a member of our team to walk through the benefits of implementation.

Tags: R&D, Heat Treatment, Industrial & Process Vacuum

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