Here goes a "for this forum" discussion of the ins and outs of used mechanical pump checkout and restoration short of a rebuild.
The key item is draining and flushing of such pumps.
If you find and want to buy a used pump; do a simple on site, "before purchase check". If it is a belt drive pump, can you turn the large pulley on the pump shaft by hand? If so, buy it. If not, you will need to fully rebuild the pump, most likely. If it is a rare find and a nice pump, you may still choose to buy it. Check the oil level in the sight glass. Can you see oil? If so, and the pump turns, you are really doing well and should consider buying the pump. If no oil is seen, but the pump still turns you are probably looking at an ill maintained pump.
With direct drive pumps, all you can do is to make sure there is enough oil in it to run and, if power is avaialble, see if it runs and pulls a simple vacuum at the inlet. If so, it will probably be OK.
Once you have the treasure home, you must check the oil. Remove the oil drain plug and watch carefully. If the oil flows out smoothly and is messy then it is probably OK. If no oil pours out then you are in trouble. Take a coathanger wire or such and poke up into the hole. This will often poke through sludge and allow the oil to drain. if it now drains OK then you are still probably ok, but have a really crudy pump. Regardless, the next task on a free turning drained pump is to flush it.
Lesker and others make special flushing fluids. I use TKO-FF sold by them. I put this fluid in the pump only after I am satified that the drain hole is clean and clear of bottom sludge.
Fill the pump with this flushing fluid. (note- you can use expensive pump oil if you wish here or old, used, but relatively clean oil drained from good working pumps.)
I next close off the inlet to the pump and open the gas ballast. I run the pump until the pump body is almost too hot to touch and then turn it off.
Now, I drain the system and really eyeball the fluid as it leaves. I also continue to jam the wire up into the oil drain outlet hole to release any more glop in the drain sump area.
If the flushing fluid is filthy or highly discolored, I throw it in a waste bottle and never use it again. If it is just mildly discolored and free flowing, I put this into a container labeled used TKO-FF. If I have a really bad pump in future, I will start with this used stuff instead of new flushing fluid for a first pass.
If the stuff is really nasty and I disgard it and run another batch of flushing fluid through it. This time, the run can just be a few minutes. I then drain again. Hopefully, it is fairly clean now and can go into the used TKO-FF bottle. I run these flushing fluids through until they come out almost as clean as they went in.
Now, I put in my first good oil fill. I place a TC gauge on the inlet, start the pump with the ballast open and keep it open until the TC gauge falls into the 200micron range and then close it. If the pump is in really good shape, the TC gauge should fall into the 100-50 micron range quickly. In a few minutes, you should be well below 50 microns and, hopefully, in the 10 micron range, (though TC gauges are not accurate in this area). If you get anyhthing under 30 microns, you got a great deal and have a pretty good pump.
If the pump refuses to go under 100 microns it may be worn out or just have some retained moisture in it. It may still be able to go lower by pumping on the gauge for an hour or so and quickly dumping the oil, then putting in a new fill. Repump as above and if any improvement is noted you are on your way to having a good pump.
If, after one or two good pump oil changes, the thing is still in the 80-100 micron range, it is just worn out a bit and can still be used with a diff pump to hit decent vacuum levels.
If you are, however, looking at only a single pump solution to hit 10 microns and the above occurs, you are looking at a total rebuild.
Most of my pumps, even the real gross, sludge ridden and nasty used models, pumped to 20 microns or lower after all the above TLC.
Some pumps have real slow leaks around gaskets or seals. If they are indded real slow ( Naturally, I do a complete disassembly of all new, used pumps and clean the bases, pump bodies, sight glasses, etc to make them look nice and to remove all the years of oily grime so often found on the outside as well. I next remount all to the base and most often wind up with a new looking and fine performing old pump.
Good luck!
Richard Hull
Created on Friday, March 30, 2001 11:42 AM EDT by Richard Hull