Used pumps are often a good buy, but can become a nightmare as well. New pumps are expensive with small, new, direct drive pumps being the cheapest in the $500.00 range.
I personally like belt driven pumps, like the old Welch or Precision types. They run slower, are less noisey, and seem to outlast direct drive pumps. Their main drawback is size and mass. If you need portability of sorts, you must opt for a direct drive pump.
The cheapest and best working old used pump I have ever picked up was my first old welch 1400 1cfm belt driven unit. It wouldn't pull real deep, and took forever to pump down a small bell jar to 20 microns, but it only cost me $25.00 at a hamfest and another $20.00 for new oil. I have never really been burned on an old used pump, but have had to spend an afternoon or two tearing them down or draining them of the gloppy sludge in the bottom of the oil reservoir. After this odious task, they pulled down much lower and all worked well enough for the price I paid.
In fact, I have never purchased a new pump. One of our local physics group guys did go to an air conditioning maintanence supply place and got a nice brand new 5 cfm Robinair direct drive unit for about $450.00 on sale and it runs like a top and serves his purposes very well.
When you select a pump, at least try to see it run. If that is not possible, check the oil level. If the oil is there; is it murky or discolored? Finally, unscrew the oil drain plug and see what comes out. If the thing is full of oil and nothing comes out, then you are in deep trouble. sludge and dried silt are blocking the drain system! The pump may be, internally, nothing but pure rust or deposited crud.
With belt drive systems you can at least turn the pump pulley by hand to determine is the unit is siezed or locked up. If so, you are looking at a major rebuild.
Used, working, direct drive pumps are usually $100.00 - $300.00 up to 6cfm. Above that, the price rises quickly.
Belt driven pumps can be anywhere from $50.00 to $1000.00 used depending on size and condition, but usually, because they are so big and heavy, the price can be negotiated downward.
I would like to hear some tales of pump buys by other folks. Some can be quite interesting, terrifying and humorous.
Richard Hull
Created on Thursday, January 04, 2001 5:51 PM EDT by Richard Hull