Compressor pump rebuild

[slow-poke]

I have never had the need to do any repairs on an air compressor so I'm posting here to get clued in.

I'm considering placing a compressor pump/motor in my unheated garage separate from the tank. I'm likely going to use either a new or near new tank. For the pump I'm wondering if I'm better off getting an older low RPM pump? They seem to run forever.

A pump in the 10-15 CFM range would be ideal.

I have rebuilt many V8 engines so in comparison I would imagine an air compressor pump rebuild should be pretty simple?

Zero experience with reed valves.

A few questions for those that have done it:

1) From a little bit of internet sleuthing, sounds like the better pumps have actual poppet valves and hence a longer life?

2) What is typically changed when rebuilding an older pump, rings? , bearings, the reed valves if that style?
what else?

3) How easy or difficult is it to get parts, and what is the cost for the parts? Does it make sense to rebuild or just buy a new pump (that may well be inferior in quality to a 30 year old say DeVilbiss)?

4) If you were looking for a good old used pump, any recommendations?

5) Where to find specifications for bolt torque, bearing clearance, ring gap etc?

Any and all advice is welcome, thanks.

 

[Ironman]

It makes sense to rebuild a quality machine. You can often get a worn out one for free, and rebuild it. Cheap junk is always around for sale and you get what you pay for
I've rebuilt my 1932 Quincy Model 325. It's rated rpm is max 900 rpm. If you are buying a compressor, or rebuilding one, make sure that parts are available. This means a good brand like Quincy, Ingersol Rand, Gardner-Denver, Chicago Pneumatic, etc. Good pumps will have disk valves and unloaders.
I honed cylinders, changed rings, con rod bearings and left the crank bearings alone as they are Timkin rollers and were good. I changed all gaskets, and made a couple that were not available. changed valve disks and springs and inspected the seats for wear.
Parts were not expensive, and rebuild manuals are available online if it is a decent quality manufacturer.
I use Rarus 829 oil in my compressor, as it is synthetic and has a -40 pour point. My pump has to start and run in a +80 to -40 range. I use a delay relay to control an electric solenoid valve so that the compressor starts unloaded, and runs for 10 seconds free, before the relay allows the valves to drop and the machine starts pumping. This has many benefits in winter in an unheated building.

 

[slow-poke]

Ironman, thanks that's quite helpful.

Thoughts on Devilbiss pumps?

If aiming for 10CFM @90 , how does one know if a particular pump is capable of that?

 

[Ironman]

Devilbis is a good name, but I'm not sure on their parts availability for older machines.. Maybe it would be good to talk to their parts dept.
Often you will see a compressor and a 5hp motor on a tank and it says "Pumps up to 175 pounds pressure!!!" So you look at the motor amps and find it is really 2hp. Most any pump can pressure up to a silly number like 175 if you wait long enough. But the true answer to pump capability should be in it's continuous duty rating.

For instance, my compressor, (copied from the manual) says, "Our single stage compressors are capable of delivering up to 150 PSIG intermittently (with proper controls and modifications). Two stage compressors can deliver up to 200 PSIG continuously, and up to 250, 350 or 500 PSIG intermittently depending upon the model, controls and configuration."
My particular model is rated for 200psi continuous, and 500 intermittent. So if all you want is 10 cfm at 90, a single stage unit will do it. Do not assume that a bigger tank gives more air(magically), all it does is postpone the refilling event, and make your pump run longer to fill it back up.

I would suggest you consider getting more cfm and pressure than you need. Air consumption needs tend increase with a good air supply, and soon you may have tools that need more cfm than you can supply. My own unit is 18cfm set at 155psi, and it often has to work on/off every 5 minutes, with a die grinder and an impact. A plasma cutter will use 6 cfm, for instance.

 

[StevSmar]

The Quincy website had information on the average lifespan of their compressor motors. Perhaps that can be used as a starting point?