By Jim Grann, Ipsen Technical Director
Nobody wants to open their vacuum furnace door and see oil everywhere. Diffusion pump backstreaming can be frustrating for operators and sometimes tricky for maintenance staff to diagnose. It may also impact processes and vacuum gauge sensors.
Whenever there are signs of backstreaming, it’s a good idea to check on the usual suspects. Here is a checklist of likely culprits to review when you find yourself dealing with diffusion pump backstreaming:
☑︎ Is the cooling water supplying the diffusion pump at or below 90° F? (Ideal temperatures should be between 60° F and 80° F.)
☑︎ Is the cooling water exiting the diffusion pump at or above 125° F?
☑︎ Are all three power phases that supply the diffusion pump drawing the same amperage? (If not, there may be heater issues, broken jumper wires, blown fuses, or something else electrical service related)
☑︎ What are the oil levels for the diffusion pump?
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- Too high may make the system run cold
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- Too low and the system will run hot
- Either to an extreme will create circumstances leading to backstreaming
☑︎ Is your crossover set to 90 microns or above?
☑︎ In a cold furnace, does your pumping time to go from about 80 microns down to 1 micron last more than 3 minutes?
☑︎ Have you left your furnace in high vacuum pumping while cold for more than a day?
☑︎ Has there been a recent oil change that involved using a different fluid, reclaimed fluid, or a different family of fluid?
☑︎ Is the roughing valve seat leaking when closed?
☑︎ Have you leak-tested the furnace while in a cold condition as well as when at peak temperature levels? (Often, leaks will show up when a furnace is hot that will not be present when cold as a result of expansion.)
☑︎ Are you using copper or stainless steel wires and lugs instead of the recommended nickel wires and lugs?
If you’ve run through the checklist and still haven’t discovered the problem, it’s a good time to call an Ipsen Service Technician and schedule a service call. Reach out to your local Regional Service Manager, or call us at 1-844-GO-IPSEN (1-844-464-7736).