Oil backstreaming can occur in the event of a power outage when oil from the rotary vane pump backs up through the forelines into the vacuum chamber of the turbo pump. In some applications, minor backstreaming has no impact; in others, where the purity of materials is critical, backstreaming cannot be tolerated. It is advantageous in high vacuum systems to include automatic interlocks to avoid the effects of backstreaming and contamination of the turbopump.
This can happen during a power outage or other system failure. Many high vacuum systems do not have built in automatic protection mechanisms. If everything works fine, then there are no worries. It’s when unexpected events happen that a “do nothing” approach could cost time and money.
Some options to prevent backstreaming are:
- Purchase a turnkey system from a manufacturer. This is probably the best solution, but costs the most.
- If you do nothing else, install a vacuum break valve; this is the least expensive solution. Tee the line and install a vacuum break valve near the pump, and wire this normally open solenoid in parallel with pump wiring. That way if power gets lost, the backing pump is vented to Atmosphere.
- Implement Interlock Foreline Solution: serves both the function of preserving your turbopump from backstreaming and the added benefit of being able to test the base pressure of the roughing pump in-situ.