More compressor problems

[robinj66]

I have a direct drive compressor which I have owned for a fair few moons and it has always worked perfectly. However the other day the note of the compressor changed slightly and after that it wouldn't build up full pressure.

The unit is made by Valley (USA) and is a 3 HP direct drive unit sitting on a 100 litre tank. It used to build up to approx 8 bar and cut off. Now it can only make 6 bar and keeps on running.

I couldn't find any leakage of air except from the air filter and the small hole in the (plastic) oil filler plug. My best guess was either piston rings or valves. The piston moved freely in the cylinder (just by turning the fan on the electric motor with one finger)

I have taken it apart and some photos are attached - to my eyes the cylinder wall looks perfectly serviceable and the piston rings are fine (sorry the photos weren't clear but the were all intact and the gaps were well staggered). There doesn't appear to be any obvious damage to the intake or exhaust valves but that remains my best guess for the fault.

Unfortunately the UK Valley agent is no longer trading and the original vendor is also no longer trading. Before i try to contact our American cousins i thought I would try here.

Could I try the reed valve upside down? Are they standard and if so where can I get such things?

Any further advice or info

 

[normspanners]

Have you checked the copper pipe to the check valve ? a slight leak there will not allow it to go over certain pressure also check the gaskets above and below the valve plate

 

[Paul99]

It sounds exactly the same as the old compressor I tried to revive not long ago. In my case and yours (going by the statement that it's leaking air from the oil filler cap) it's knackered piston rings (or bore). It's worth checking and cleaning the compressor plates and reed valves and replacing all the gaskets too as that did improve things slightly with mine to the point where the piston ring / crankcase being pressurised problem revealed itself.

 

[robinj66]

Have you checked the copper pipe to the check valve ? a slight leak there will not allow it to go over certain pressure also check the gaskets above and below the valve plate

I did check extensively for leaks before I took it apart. There was no discernible leak from the gaskets or copper pipe.

 

[robinj66]

It sounds exactly the same as the old compressor I tried to revive not long ago. In my case and yours (going by the statement that it's leaking air from the oil filler cap) it's knackered piston rings (or bore). It's worth checking and cleaning the compressor plates and reed valves and replacing all the gaskets too as that did improve things slightly with mine to the point where the piston ring / crankcase being pressurised problem revealed itself.

My first thought was the piston rings but on strip down the rings are all intact, no discernible damage and the gaps are staggered. The bores are smooth and well lubricated. No scratches evident.

The gaskets didn't appear to have any damage until I took the machine apart. I will have to make new ones.

Any thoughts on whether it will make any difference if the reed valve is turned over on replacement? If it's already weakened will it make any difference?

 

[Paul99]

It's got to be worth trying it with the reeds flipped over and I did try that with mine as its only 7 bolts involved - in my case it made no difference. If the crankcase is being pressurised I just can't see that the piston rings are sealing right?

 

[robinj66]

Thanks - I'll give it a go

 

[lexi]

It is also the same problem as mine. I made a new reed valve.......no difference.
Like yours my rings are intact and all nice and smooth. I think the rings wear as mine has no lip at the top. It also has no hone marks in bores, should there be?

If you search some of those Chinese sell everything sites, there are pistons and rings of a few different sizes that are cheap enough.