How much base pressure in compressor pump is normal?

[mineallmine]

I am trying to button up my compressor install and have run into a couple snags. Most I have already solved but one remains.

When I turn the pump by hand I hear (and can feel) air coming out of the crankcase breather. It doesn't feel like a lot but again I am only turning it by hand. At first I figured for sure it was the rings being bad but now I'm not 100% sure.

The reason I am unsure is that at first I was trying to pressurize the tank by the reverse method (using another smaller compressor hooked into one of the line drops to back feed the tank (confirming leaks before firing up the main pump) and at that time discovered my check valve was stuck. This allowed air to back pressure the pump and "hold" it in one position as the air would try to prevent me from turning the pump by hand (was at 30psi). At this point I was not getting any air through the crankcase.

I have since fixed the check valve and am getting ready to finish wiring up the motor and before I add oil to the pump and actually run it and find it is an issue and have to do a full teardown I would like opinions if there is already an issue or is this just a normal byproduct of the pump cycling?

I got a great deal on the compressor and even if I have to rebuild the pump I still did really good so I am not concerned there. Just don't want to rebuild it if this is normal.

It is a Techquip 80 gallon upright compressor with a k30 Chinook pump (same as the rolair k30). It had an intake gasket blown when I got it but I am figuring that was a result of it running with a stuck check valve and resulting backpressure.

I got the compressor for $300cdn and sold the original 3phase motor for $100 so pump and tank I'm only in $200. The tank is spotless inside and the pump appears in good shape. I have since added a 5hp Baldor farm duty motor I already had and built a vibration damper platform and will be adding a magnetic motor starter when I wire it all up. I also added a kaeser auto drain I picked up cheap and rebuilt this week due to rotten seals and leaking. Should be a nice setup when completed.

Any input would be appreciated.

 

[mineallmine]

Here's my setup. Not shown is the belt guard, the magnetic starter or the auto drain.

 

[sberry]

Probably going to pulsate as the piston goes up and down.

 

[mineallmine]

Probably going to pulsate as the piston goes up and down.

I figured there'd be some. This is a 2 stage pump so I would guess the pressure in the base wouldn't be as much as in a single stage as some of the volume of one stage would go into the other as one piston goes down and one up but as they are different size pistons there would have to be some excess volume of air in the base to be pushed out. I just wasn't sure how much to expect.

I guess I will have to add oil to it and fire it up to see if there's any other issues to look at. I do have a backup pump if ever needed. It's much heavier though. It's an old Webster pump that's in great shape. I would only use this if there's a major problem with the original Italian pump that can't be rebuilt.

 

[sberry]

Ya, see if it works. A lot of things ain't worth the worry of being perfect, a lot of air comp rings,are replaced that are not worn out.

 

[mineallmine]

Success!!

Finished wiring it up today and filled it with oil. Turned out on and voila....we have air. The pressure coming out the breather was minimal....actually less than when turned it by hand.....and quiet too....can easily have conversation with it running. It runs up to 130psi in just few minutes...really good for an 80 gallon tank.

Thanks for the advice.

 

[American Locomotive]

It's normal for single cylinder, and two stage compressors to have pulsing breathers.

A two-cylinder single stage generally won't do that, though.