Greolt was the first, or one of the first, to describe converting a compressor to a vacuum pump.

We have an old two cylinder compressor that had been made redundant so when a need came to make a vacuum hold down for machining some 1/4" polycarbonate I coverted it to run as a pump.

Thre quarter copper now connects the inlets of the cylinders to the port at the top of the tank; the original intake filters are installed on the outlet ports as mufflers, which works very well. The vacuum outlet is on the side with a 3/4" ball valve and a length of swimming pool suction hose.

The vacuum platen is just fabricated out of 1/2" aluminum plate and bolts directly to the machine table. The height is needed because this is a Haas Super MiniMill with the raised Z axis so normal length tools will not reach closer than about 3 inches above the machine table. The aluminum platen is covered with a sacrificial polycarbonate with O-rings seals. At the front is a domestic water filter housing which acts as a primary trap for coolant that gets suckes into the system.

With the main tank ball valve closed the pump can pull 26 inches of negative pressure; with a part in place leakage means it stabilizes at about 22 inches.

The tank is 60 gallons and as is visible in the picture the compressor was rated at 12.5cfm. It can pull the tank down to 20 inches negative in about 45 seconds and it takes almost 2 minutes to get down to 25-26 inches which is more or less consistent with the rating. It had been used as a compressor for over two years. Initial purchase price was almost $800 but that had been effectively amortized over its use as a compressor so the vacumm pump only cost a few hours of work.

I like the idea of the trap for coolant- I wouldn't have thought of that! There's a guy in another thread saying he's getting problems with liquid freezing in his vacuum pipes. That trap would probably solve his problems- apparently his pipes freeze up with liquid and the vacuum fails to hold the part when machining which could be well dodgy!

Nice one Geof.

I'll point him to this thread.

Here's his original thread
http://www.cnczone.com/forums/showthread.php?t=53871

Geof How would this design compare to running a pump off compress air?

Geof How would this design compare to running a pump off compress air?

Much better.

I have used a venturi vacuum generator running of compressed air, the best it could pull was less than 20 inches and it needed something like 10 cfm of air to get maybe 6 cfm of vacuum flow.

If I had used this compressor to run the venturi it would have had to run 100% of the time and piston compressors are not rated for that, also I would have had less vacuum and less flow.

This conversion could run for eight hours without getting the cylinders warmer than could be touched with a bare hand.

What pressure do you achieve with this rig?

Scott

What pressure do you achieve with this rig?

Scott

I mentioned it above; negative 25 to 26 inches of mercury.

Nice, well thought with the coolant trap. Was this a trial and error, or just a brilliant design from the get go?

Nice, well thought with the coolant trap. Was this a trial and error, or just a brilliant design from the get go?

A brilliant design from the get go of course! How dare you suggest otherwise. :D

Actually as I mentioned Greolt had already done a small compressor and I knew that you could easily pull up to 20 inches of vacuum on the intake manifold of a car engine. You are probably too young to remember/know about the vacuum operated windshield wipers on old Fords; I'm not. So I knew it had a good chance for success. The coolant trap was an obvious add-on to avoid filling the main tank with coolant.

Like most of my 'brilliant designs' it was based on trial and error, some mine some taken from others. I practise the C.A.S.E. approach; Copy And Steal Everything.

Well Geof I am using your C.A.S.E approach here I have started this with a smaller compressor. So far my biggest problem is the guy I bought mine off of broke off one muffler and I can't get the old pipe out

You are probably too young to remember/know about the vacuum operated windshield wipers on old Fords; I'm not. So I knew it had a good chance for success.


Oh yeah, I remember those old Fords. We had an old water truck with a 534 (3500 RPM redline) gas engine in it. Had a big old oil bath air filter (nasty) , the water pump was the size of a pumpkin and you could run your arm between the intake runners and the valley cover on the engine. Those old wipers were horrid, kind of slow to take off and then fast, sometimes difficult to get stopped where you wanted too. It had a five speed and a three speed brownie, talk about fun to shift with two different gear shifts. It eventually died, a hole in the piston lead to too much gas in the oil pan. We tried to start it and it blew the valve covers right off of the heads. The valve covers probably weighed about 40 lbs. Everything on that truck was big. Just the front axle could legally handle 10 tons.

CASE & KISS, both great methods/ideas. Overly extra redundant?

Dick Z

CASE & KISS, both great methods/ideas. Overly extra redundant?

Dick Z

I like retarded overkill.