#5 FAQ - Used mechanical pumps - check out - reconditioning

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Richard Hull
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#5 FAQ - Used mechanical pumps - check out - reconditioning

Post by Richard Hull » Mon Dec 20, 2010 4:45 pm

Here is a FAQ devoted to the testing of used pumps of unknown value upon arrival.
It assumes you have just picked up a mechanical pump and want to know just what you have purchased, whether it is shot or if it is redeemable and what you need to do to make it servicable.

Stuff you must have before starting.

1. Vacuum gauge. This should be of the thermocouple or capacitive manometer type.
2. A suitable, short, 6-inch length of vacuum rated tubing to attach the above gauge to the pump. Make sure you have good fittings or clamps needed to secure the hose to both the pump and the gauge, making it vacuum tight.
3. A couple of gallons of good vacuum pump oil, (rated for your type pump). Vacuum pump flushing fluid is optional as is "Marvel's Mystery Oil" (ultra thin oil) Note* Do not use Marvel's unless the pump rotor is seized (see below)

Two hard and fast rules for used pumps, regardless of type........

Rule # 1 Never, ever just turn on a used pump!!!.
Rule # 2 Never, ever just take a pump apart right off the bat!!!
Rule # 3 Never, ever leave a TC vacuum gauge attached to a pump after it is turned off. Remove it just after shutdown as oil might suck back up the short connection into the gauge tube. In short, kill the vacuum in the line immediately after pump shutdown.

There are two types of pump - belt driven and direct driven. In general, belt driven is the more desireable from an amateur stand point of use, repair and maintenance. Make sure that you start by going to the proper pump advice below.

**********Belt driven pumps (motor and pump separated with a belt between two pulleys)**********

Use the following process of discovery......

1. Make sure the inlet and outlet of the pump is open to air and not blocked off.
2. Grab the large pulley of the pump and see if you can turn it freely. If it doesn't turn, try harder. If it finally turns a little then stop and go to the next #

3. Is there oil inside the pump? Check the sight glass. If oil is in the pump and it turns freely go to #6. If you see no oil at all and the pump was locked or if you see no oil and the pump turned but with a lot of effort, then continue to next number.

4. We need to open the oil drain plug and investigate. Sometimes the oil is just low and out of view of the sight glass leaving the pump very tight or locked up. carefully remove the oil drain plug and see if oil runs out. If so, is it black and thick or dirty? If so, let it drain completely.

If no oil comes out, you need to poke a stiff piece of steel wire into the drain hole. If it goes in smoothly to a decent depth then the pump is just dry and needs oil. If you meet resistance, then you have hardened sludge in the bottom. Break through this sludge by judiciously poking the reaming your way into the oil chamber. If there is oil in the pump, it will ultimately show once you break through the sludge. Let this drain.

If you have clogged sludge, locked pump and no draining then you will need to disassemble the pump for sure. You have a nasty pump that might not be worth the effort. Either rebuild it yourself using a rebuild kit or locate another pump altogether.

5. If you had oil in the pump and the pump is locked or was very difficult to turn, after draining the old oil, put in about 16 ounces of a very fine oil like marvel's mystery oil (auto parts stores). Let this set for a few days. Try and turn the pulley after this waiting period. If it is still locked, take a small hammer and tap with increasing energy on the pulley arms using a wooden board until it breaks free or moves. Once this occurs, turn by hand only. It might be tough for a few rotations, but should get a bit easier as the thin oil cleans and distributes. Ultimately, and inorder to move on to the next step, it will now be assumed you have the pump turning freely with the light oil in it.

6. Now that you have oil in the pump and it is turning freely, you can test the motor and pump for some sort of operation. Turn the pump on with the inlet open to air and let it run for about 5 minutes. This frees the pump more, exercises the vanes and scrubs the walls of the pump, distributing the oil inside. After this, drain the pump of all oil. It should be filthy if the pump was stuck, locked of stiff. Examine it carefully. If metal particles are in it you may need to rebuild. It is assumed that at this point you have a smoothly running and free pump that is warm after its 5 minute run and all oil is out of the pump.

7. Replace the drain plug and fill the pump to the sight glass with good, but not expensive pump oil. This is a flushing run and special flushing oils can be purchased as this oil fill will be discarded in an hour or so. Now, seal off the inlet with a short length of hose attached to a good thermocouple vacuum gauge. (NOTE: It is critical to have a good seal on the tubing at the pump and the gauge at this point, as a leak could make a great pump look bad.) Turn the pump on and run it for 30 minutes to one hour. Check the gauge reading. If at anytime the gauge goes below 100 microns you are probably ok and have a good pump. Record your lowest reading during this run. If it hangs up around 300 microns to 100 microns, then you may just have a really filthy pump and need another purging of fresh oil. At the end of the pumping, drain the oil and look closely at what comes out. diagnose as follows..........

a. Pump oil fairly clean. Gauge read below 50 microns. You have a winner!!! go to #8.
b. Pump oil dirty and gauge was below 100 microns but above 50 microns. You could still have a winner and it is trying to right itself. Go to #8
c. Pump oil is filthy and gauge never got to 100 microns but is below 300 microns. You still have possibilities
d. Pump oil is clean and never got to 100 microns. Pump is worn a lot.
e. Pump oil is clean and never got to 200 microns. Pump is heavily worn and may need rebuilding.

8. You need to take another pass with fresh oil and the gauge. This oil should be vacuum pump rated oil and not flushing fluids unless your last run still showed filthy oil. Refill and re-run for 1 hour. This is an acid test! If the gauge drops lower than the #7 run then you are going in the right direction and cleaning up what might be a usable pump.

Drain the oil after this run and if clean and you are under 50 microns. You have a fully usable pump. If under 20 microns it is in really good shape. If the oil is still dirty and you did get a lower reading, keep up the drain-and-run process until you can't go lower in pressure and the oil is clean after running.

A really good pump should have no problem hitting 20 microns or lower, dead heading to a vacuum gauge at the end of a short 6-inch length of tubing. Let this be your guide.


********Direct Drive pumps (motor and pump in a single unit) **********

You can't easily test as above for locked rotor conditions and it is up to you on how to proceed in step #2 here.

1. Make sure there is a full load of oil in the pump.

2. Test for locked pump.
a. Remove the motor from the pump, (often just four screws). take a towel or cloth and rap around the pump shaft while placing place a pair of vise grips on the shaft so that you can turn it without scaring the shaft. If the shaft turns easily, then reassemble pump to motor. If shaft is locked, try to free the shaft by tapping with hammer on the vice grips to force it to turn. If unsuccessful, you need to rebuild.
b. Test for operation by just turning on the pump motor. This is risky and you should be ready to turn off the motor quickly if it will not turn. If the pump runs then this is great. If not, follow step 2. (a) above to attempt to free the pump rotor.
Before going on to step three, you must have a turning pump with oil in it.

3. Run the pump open to air at the inlet for 15 minutes.

4. Checking for oil cleanliness..... Remove the drain plug and check the oil. If discolored go to step #7 and all succeeding steps above as given for the belt driven style pump.


If your pump remains locked or has a high final pressure above 100 microns, then you might consider either rebuilding the pump or buying another pump.

Bottom line and parting shot............ Even if your used pump turns freely, has decent oil in it right off the bat from purchase and pulls to 50 microns, You should still change the original unknown oil and consider yourself among the most blessed of used pump buyers.

Once a pump is working and has good oil in it, never allow it to suck in outside air while running again. It should always be connected to a sealed system when pumping. This avoids atmospheric moisture from condensing inside. What little that does get in during system pump downs from atmospheric pressure is "ballasted" out.


Once a pump is started in pumping down a system, the gas ballast needs to be used. This is usually a thumb screwed cap or knob that is left tightly closed on the body of the pump when in normal use.

1. Turn on the pump and open this knob or capped screw plug. The sound will change, especially on belt drive systems to a gurling sound that is slightly louder than the normal run sound.

2. Let the pump run this way for a few minutes. This helps rid the oil of superficial water vapor trapped in the oil.

3. After a few minutes, end the ballasting process by turning or tightening the screw or valve down securely. The pump will quiet down a good deal and the pressure will drop a bit more as the second stage of the pump is now allowed to operate to its full potential.

This FAQ is not the final word in used pump check out, but does lay a ground work for those not familiar with vacuum pumps or their checkout procedures.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Chris Bradley
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Re: FAQ - Used mechanical pumps - check out - reconditioning

Post by Chris Bradley » Mon Dec 20, 2010 5:19 pm

My Edwards E2M2 can be rotated by simply inserting a screwdriver through the cooling openings at the motor end and pushing the cooling blades around. This is what I did when I first got mine, and it rotated even with the oil drained. Don't push too hard, mind, the cooling blades are plastic - I presume a pump left for a long time might still be OK but be stiff enough that you could break the blades if you push too hard. Just a quick trick to try before you need take the motor off.

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Adam Ingle
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Re: FAQ - Used mechanical pumps - check out - reconditioning

Post by Adam Ingle » Wed Dec 22, 2010 10:26 pm

Thank you very much Richard!

That's prefect timing. I should have my used pump here tomorrow. Scrounged up a Welch 7 - 8920 DirecTorr.

Wish me luck!

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