Vacuum Furnace  Maintenance Tips

Maintenance Tip: Vacuum Pump Performance Checks

Guest Article from Peter A. Rescsanski, Tuthill Vacuum & Blower Systems

 

The following list is for checking the performance of your vacuum pump or system.  The checklist also has recommended items for improving the overall performance of the vacuum system.  The recommendations are for most types of vacuum pumps & systems.

Steps:

1. Isolate vacuum system from process vessel.  Close the vacuum valve closest to the vacuum system.  Install a gauge connection in the line on the “vacuum side” of the valve.  Check the gauge and measure against the performance of the pumping system.  As a rule of thumb, with a total pressure type gauge (thermo-couple) you should see < .10 torr with a single stage pump, < .03 torr with a two-stage pump and < .015 torr with a booster pumping system.  If the vacuum system has a booster pump readings should be taken with the booster off and the booster on.  A poor reading with the booster off leads to a pump problem.  If you do not see an improvement of at least 10-20 times with the booster on then the booster has a problem.

2. If the vacuum readings are acceptable then the problem is with the chamber, manifold or other items on the “process side” of the vacuum valve.

3. If the vacuum readings are not acceptable, then the following steps should be taken to improve the vacuum performance:

   Check the vacuum gauge.  Check calibration and re-calibrate if necessary.

   If the pump is an oil-sealed pump, open the “gas ballast” valve fully on the pump.  This should be done with the pump running and the booster off.  Run the gas ballast valve open for at least 20-30 minutes.  After that time re-check the vacuum readings. 

   Check the discharge piping to be sure it is clear.  Also, be sure that a “drip-leg” is installed so condensable vapors do not pass through the pump, then re-condense and go back into the pump. 

   Leak check the vacuum system with the appropriate equipment and/or methods.  Fix all leaks.  Re-check vacuum performance.

4. If the items in Step 3 were done and no improvement was made, we can assume that the pumping system itself has a problem.  If the problem is dedicated to the pump itself (not the booster) the first step would be to check the discharge valves.  For most rotary piston pumps this is very easy.  Start with the pumps Maintenance manual.  Drain the pump of oil.  Open the front cover, remove the discharge umbrella and open the valve deck cover.  The pump will have from 1 to 12 valves.  Check the springs on the valves and the valve body condition.  If they are worn or soft then they should be replaced.

5. If the items in step 3 & 4 were done and no improvement has been made most likely there is internal wear and a rebuild may be necessary.  Consult the factory for the nearest repair center.