Air Compressor Not Gaining Pressure

[MFGENG]

Ever since we moved a few months ago, my little craftsman air compressor wont go above 45 PSI. I've checked the pressure relief valve, which works and closes; checked the pressure regulator, it releases when cranked to 45psi or below; and checked for obvious leaks or cracks.

What am I missing?

 

[larry_g]

Does it hit 45psi and stop or just runs constantly not going above 45?

lg
no neat sig line

 

[MFGENG]

runs constantly, not rising above 45

 

[siegsuwa]

Is your drain valve on the bottom tight? I have this same compressor and I once forgot to tighten the drain valve before using it and it just ran forever and never built up pressure. Easy to check.

 

[MFGENG]

Was hand tight and I didnt feel anything from there. I'll put a wrench on it.

 

[matt_i]

Somewhere there has to be a check or reed-style valve so the compressor can add a shot of air to the tank for every cylinder stroke.

Think of a bike pump on a tire, if there were no "check" function you'd pump and pump and pump and air would just refill the cylinder as you pulled the T-handle back up, with the resultant of no gain in volume to build up pressure.

In your air compressor that function is likely compromised. Its probably internal somewhere, between the actual cylinder and the tank itself. Possibly in the cylinder head.

 

[MagKarl]

I'd bet on a reed, pull the cylinder head to check.

 

[Citation]

I'd bet on a reed, pull the cylinder head to check.

This is what I would check. Any other leak would be fairly obvious.

 

[nitroracer20]

On my larger Craftsman compressor I had the same symptoms.

Turned out the piston ring deteriorated and wouldn't build pressure. $5 later for a ring and I was back to full pressure.

 

[The Cobbler]

it's a leak somewhere, either in the supply to the check valve, in the unloader circuit, a head gasket , reed valve or rings
often it can be as simple as a leaking connection in the pressure side between pump & check valve .
those compressors are known to blow head gaskets too . I bought several from a clearance place that had blown head gaskets .
do a process of elimination on it .

 

[The Cobbler]

remove the plastic cowling. check all connectios to see if they are tight . soap up all the joints on the pressure side / run the compressor (just be sure to watch for the fan on the back end)
see if you can see any bubbles
spray more soap on while it's running if needed
spray around the head see if there's any leaks . spray the unloader circuit. check it all out.
if no leaks found there, it's likely internal . parts are quite cheap for that model (at least used to be LOL)

 

[LS6 Tommy]

On my larger Craftsman compressor I had the same symptoms.

Turned out the piston ring deteriorated and wouldn't build pressure. $5 later for a ring and I was back to full pressure.

Many of those Craftsman oiless compressors have plastic pistons. There is no ring to replace...

I'd check the reeds first.

Tommy

 

[The Cobbler]

that is an oil piston compressor, good little units actually

 

[LS6 Tommy]

that is an oil piston compressor, good little units actually

I didn't look close enough...

Tommy

 

[MFGENG]

Looks like the head gasket.

Any good places to order a new one? Its a 921.153101.

 

[LS6 Tommy]

Lookieheer, I use these guys for stuff:

https://www.ereplacementparts.com/c...-compressor-parts-c-158286_158287_158570.html

Here's your stuff:

https://www.ereplacementparts.com/gasket-kit-p-962313.html

Tommy

 

[firebirdparts]

You can make one if you have to. All it holds is air

 

[brokeboater]

You can make one if you have to. All it holds is air

Like an idiot I bought a used Makita compressor from a pawn shop. It should be no surprise to anyone it wasn't long before it wouldn't build pressure above about 90#. I disassembled the head, after checking all the other possibilities, and found one of the reed valves and the surface it attaches to, severely corroded. I expected replacement parts to be cheap and easily available but they weren't, in either case. John Deere has nothing on Makita when it comes to overpricing replacement parts. But I ordered gaskets and reeds anyway. I figured it best to throw good money after bad. Toss in a new regulator and a new pressure switch assembly and an imbecile could have done the math to conclude I'd have saved money buying a brand new unit. I couldn't stand it so while waiting for my new parts to arrive I disassemble it and made some replacement reed parts out of an aluminum can. Same with the gaskets just not from an aluminum can. I put it all back together and it runs and hold pressure like new specs say it should. I've got the gaskets and reeds for when/if my jury rig begins to fail but its been running just fine since. On a positive note I got to reinforce something I already knew, don't by used electro mechanical tools, especially from a pawn shop. And I'm knowledgeable enough now about the complete workings of a Makita Mac700 compressor not to get the wool pulled over my eyes again.

 

[The Cobbler]

probably all you need is https://www.ebay.com/itm/sears-craf...197663?hash=item41e8d5c3df:g:JDgAAOSw4QdagkWB

 

[Tracs]

A friend brought over the same compressor that wouldn't go past the same pressure you have. Same as yours the head gasket was blown out between the center. Made a new one with blue gasket paper and its worked good as new for over a year now.

 

[MFGENG]

I swapped out the head gaskets and reeds, and now it runs like a champ. Thanks for the fix GJ!

 

[The Cobbler]

Great, another project resurrected from the trash!