No. 22 – Rotary vane pumps and use of gas ballast
Question: A colleague told me to use gas ballast on my rotary vane pump if the oil changes colour. What will this do for me?
Answer: Use of gas ballast increases temperature in your rotary vane pump. The gas ballast valve allows additional gas into the pump and creates a positive flow through the pump, this increases the temperature, therefore vapours can be pumped better and they do not condense in the pump oil or pumping stages.
Isolate the inlet flange of your RVP and leave the pump running for approximately 30 to 60 minutes with gas ballast valve open.
You should do this if your oil appears slightly discoloured or cloudy. After longer intervals when the pump was out of use or if moisture might have condensed in your pump. If the oil already has the look of a white emulsified deposit you should change the oil.
Additional information:
Condensation of vapour in a rotary pump may occur if you:
- Pump a vessel with residual humidity – this applies also for accumulation of many components containing just ambient humidity.
- Pump water vapour or solvents
- Observe condensation after storage of the pump filled with oil
The higher the pump temperature, the lower the danger of condensation, so your pump needs to be hot before you are pumping a “wet” vessel. For that reason you should leave the pump running prior to process start. If you do not want to disconnect your pump use an isolation valve in the pumping line and keep this closed during the warm up of your pump. Gas ballast accelerates the temperature increase in the pump due to additional compression, generating heat.
If the use of gas ballast is not sufficient to keep the oil clear you should use a cold trap in the pumping line.
In addition to pump design and temperature the exhaust line has a strong effect on condensation in the pump.
Avoid high exhaust pressure at the pump exhaust due to long exhaust lines with vertical orientation or thin pipes.
Use a condensation trap at the exhaust, this collects reflux of condensable media from the exhaust line and protects the pump.
Avoid using an oil mist eliminator or use it on top of a condensate trap.
Remove the exhaust flap valve – any additional pressure is detrimental!
If possible feed your exhaust line into a ventilation system or an additional pump which creates lower pressure than ambient.
Please note the use of gas ballast will increase the ultimate pressure of the vacuum pump in the case of an RVP it restricts the ultimate pressure to the 10-2mbar range rather than the 10-3 range without gas ballast.
If you are using gas ballast regularly check the oil level. If the level drops oil is being lost. If the level rises, condensate is added. You should refill lost oil.
Do not permanently use gas ballast, you should only use it when required.
Your colleagues will be grateful due to the increased noise level during pump operation with gas ballast. In addition gas ballast will shorten the service interval of your pump due to increased temperature and going along with that additional wear.
By the way, there are a lot of excellent hints for pump operation in the pump’s user manual – did you ever read it ? If you are not sure – please ask us !