Compressor Guru Question

[Mark Kauder]

While at the local Flea Market this morning, I picked up a small compressor. From the looks of it, it was cobbled together from parts. A Hausfeld-Campbell tank, A Craftsman 1hp Motor, etc.

The gentleman selling it said that the pully on the pump had been broken, and he stuck another on it, but then the motor would "trip the electrical breaker". All I could do at the time was turn the pump over by hand - and it sounded OK. I turned on the electrical motor w/o belt attached, and it seemed OK.

When I got it home, after cleaning the oil and dirt off of it, I hooked up the belt and fired 'er up. As soon as it built up about 10-15 PSI, the back pressure would cause the motor to drag, and the belt would slip. While running it sounding good.

Questions:
1) What should the ratio on the motor to pump pulleys be?
2) How to I set it up so that the motor shuts off at say 125 PSI?
3) Sources for cutoff relays?
4) Should I abandon.

My needs are few in terms of a compressor - occasional Brad Nailer, and cleanup around the shop.

I Paid $50 for it, and figure that the parts are worth that - I can always use a 1HP motor if nothing else.

I will need a regulator - One guy had a nice new one with a moisture trap for a good price, but I was out of cash. When I when back a couple of hours later, he had packed up. May try next week.

Any advice would be appreciated - even if it is to abandon.

Thanks

Mark


http://www2.freepichosting.com/Images/31246/3.jpg

[Ken Garlock]

Hi Mark. I am not a compressor guru, but I will show my ignorance by making a few suggestions.

1) It looks by your picture that one or both of the pulleys are not the correct size. Along with that, what is the speed of the motor? It seems to me that the compressors like to run around 800 to 1000 RPM, maybe even slower. If you know the motor RPM, you can find the compressor RPM by dividing the motor pulley size by the compressor pulley size and then multiplying that ratio by the motor RPM.

2) How is the tension in the belt? How old is the belt, does it have crack in the rubber? How well does it fit in the groves of the pulley? The belt flat top should be even with the edge of the pulleys. How much can you depress the belt when it is installed on both motor and compressor? The old rule of thumb for cars as I recall was about 1/2 in. You may want less for a short tun like yours.

3) Does it have oil in the crankcase?

4) Does the compressor have any ID so that you might get some information on it?

5) Does the motor kick out of starting winding? You may need to clean the centrifugal switch in the motor.

Just a few things I would check if it were mine.

[Bob Lasley]

Mark,

I don't know exact ratios, but most belt driven air compressors have a rather large pulley on the compressor. My guess would be that the ratios are in the 1:5 area. Compressor pulleys also usually have fan blades built into them to provide cooling to the compressor. Grainger has air compressor flywheel/pulleys listed in their catalog. These are 10" with a 3/4" bore and sell for about $32.00. Grainger also carries pressure switches and regulators though you may find these cheaper elsewhere.

Good luck,
Bob

[Michael Cody]

I posted this here @ on WC also..

I would be careful of you setup. I don't see a safety valve or pressure switch which means you could over pressurize the tank & make you own homemade bomb.

Me I also agree the pulley on the compressor is not big enough, it should 10-12" I suspect..

If'n it was me, I consider not throwing good money after bad and go get a new compressor. They can be had for under 150$ and come with pressure tested tanks, proper safety valves, etc.... by the time you get this on right you are going to have that much into it. No telling how old that tank is either, I would have it pressure checked and make sure it's good before I went another dime into it...

Knowing how my luck goes, the sucker would blow up and kill the neighbor not me and then I would get sued to bankrupcy all the while feeling guilty for causing the poor guy's death.

I guess I am not trying to melodramatic but there are places to cut corners and places where cutting corners can be really dangerous. Compressed air is one of those.

[Steve Clardy]

That copper line that comes from the compressor to the tank SHOULD have a check valve at the tank side. This keeps the pressure in the tank from coming back to the pump. If this valve is not working it can and will overload the motor as there would be the same amount of pressure in both places. The pump has to produce more pressure than what is in the tank to fill the tank. If the check valve is not there or not sealing, the tank pressure will try to lock the pump which overloads the motor and it kicks the reset button. Totally confused now or does this help you out? Steve

[Mark Kauder]

Thanks to everyone that gave me information.

In the end - once I got the pulleys right, and got it working, I found out that it had leaks in the pump itself, that I am not prepared to mess with.

I will be able to take the Pulleys back to Grainger, and my only cost in addition to the purchase price will be a couple of brass fittings.

In the end, I end up with a decent electric motor for $50.

Thanks all.

Mark