Thread: Air compressor woes

They appear to be the "unloader valve" designed to release the pressure in the outlets from the compressors so that they can start when required (the motor will be unable to turn the compressor over with full pressure on the pistons). Being a twin drive unit they are very different to most I have seen.

If I had to guess I would assume that the plastic box you removed is a coil used to activate the valve using a magnetic field, without the coil installed the valve will probably remain open allowing air to purge but this should only be air in the exhaust from the compressor, the air in the tank should not be drained as the device that this valve attaches too that is connected to the tank is a one way valve.

If the valve bleeds air all the time then either the coil is open or not being energized or the valve is stuck / faulty.
If the unloader valve is draining the tank with the compressor turned off then you probably have a stuck / faulty one way valve as well.

Both these parts are pretty unique to that style of compressor and you will probably need to order parts specific to that model.

I was starting to ponder if it was the other side of the valve. I will take so e more pics tomorrow and pull it apart too

The electro magnet makes sense

Dave TTC
Turning Wood Into Art

Hi Dave, Looking at this thing as two separate issues for the moment.

Leak around the head. Can you identify where exactly it is leaking from, is is a very narrow stream or a broad one? Is it near a pipe fitting, or in the gasket face, or even at the junction of the flexihose? Is it the same side as the leaky unload valve?

Leak at the unload valve. Probably was not caused by an unload valve issue, and unload valve should work if you put it back together properly after cleaning and checking.

Let me explain how everything should work for one of the two compressor units installed, both operate the same way. The system is a dual two stage compressor, ie there are two complete compressors feeding a single tank, and each compressor is a two stage unit. The cylinder with the small air filter is the low pressure stage, and the cylinder with the outlet flexihose is the high pressure stage. The output of the low pressure stage feeds the input of the high pressure stage via two transfer pipes that run across the central motor unit.

Each head has two chambers inside, an inlet chamber and an outlet chamber. There is a channel between each chamber and the cylinder, and each channel has a one way valve installed. The valve in the inlet chamber only allows air to flow from the chamber to the cylinder and the valve in the outlet chamber only allows air to flow from the cylinder to the outlet chamber. The technical name for the one way valves is reed valve.

When the motor is running, pistons in the cylinders move up and down. When descending, they create a vacuum in the cylinder. This vacuum draws air through the one way valve (inlet reed valve) mounted in the head. When the piston has reached the bottom of it's travel the motor starts to drive it back up to the top. This immediately compresses air in the cylinder and forces the inlet reed valve to close so the air in the cylinder cannot escape through the inlet system. As the piston continues to rise, the pressure in the cylinder continues to increase, and at some point will exceed the pressure in the output chamber of the head. Then the outlet reed valve will open and allow air to flow from the cylinder to the outlet chamber. Once the air pressure in the cylinder has reduced below that of the outlet chamber this valve will close, stopping the air in the outlet chamber from returning to the cylinder. A the motor makes the piston start to descend again, the inlet valve opens and the cycle repeats itself.

Your particular model compressor is two stage. With the motor mounted in the middle and a cylinder each side, one cylinder is designated as low pressure, and the other as high pressure. The pistons are connected to the motor so that as the low pressure piston is rising, the high pressure piston is descending. The output chamber of the low pressure cylinder is directly connected to the input chamber of the high pressure cylinder by the two transfer pipes running across the motor. So as the low pressure piston rises and the high pressure piston descends, the air in the low pressure cylinder is pumped into the high pressure cylinder under pressure (a bit like supercharging a car engine). This ensures that the high pressure cylinder is more completely filled than it would be if drawing directly from the atmosphere like the low pressure cylinder does.

As the high pressure cylinder rises, it also compresses the air in the cylinder, and forces it through it's outlet reed valve into the outlet chamber of it's head. The air is then carried through the flexihose to the brass fitting at the tank. This is a checkvalve, another form of one way valve that allows air to flow from the flexihose to the tank, but should stop flow from the tank back to the flexihose.

The pressure switch unit attaches at the tank side of the checkvalve and monitors the air pressure in the tank, starting the compressor motor when the tank pressure falls below the preset Start level, and stopping it once the pressure raises to the preset Stop level. The unload valve is mechanically linked to the pressure switch but connects to the flexihose side of the checkvalve. When the compressor is stopped by the pressure switch, a mechanical link opens the unload valve and allows the pressure stored in the high pressure head outlet chamber and the flexihose to escape to the atmosphere with the short sharp blast you get hear when the compressor shuts off. At the end of that blast the flexihose and head outlet chamber should be at atmospheric pressure and no leakage should occur.

In your case, where leakage is definitely occuring, this must be because the checkvalve between the tank and flexihose is leaking, or something in the mounting box between the checkvalve and the pressure switch/unload valve is allowing tank pressure to leak back to the flexihose side. Every compressor I have ever worked with/on has had the pressure switch/unload valve mounted on a tank pressure fitting with a small diameter pipe to the checkvalve to unload the head and pipework. Yours is different in that the mounting is done via the metal box below the pressure switch, and I am not sure what is in that box, but if it contains a diaphragm, it's possible that the the diaphragm has ripped allowing tank pressure back to the flexihose and out the open unload valve. If it is not something in the metal box, then the check valve itself is not sealing properly due to wear, foreign object stopping it sealing etc. Sorry I can't help with the actual contents of the metal box.

Originally Posted by malb

Hi Dave, Looking at this thing as two separate issues for the moment.

Leak around the head. Can you identify where exactly it is leaking from, is is a very narrow stream or a broad one? .

The leak around the head is coming from what i think is the upper sirface of the gasket. Area highlighted in yellow



From that the pipe highlighted in pink leads to the tube that is the major leak. Im not with the init right now but presume the hasket only leaks when running and perhaps bak pressure from the tank.

Ill get back to the rest of your comment



Dave TTC
Turning Wood Into Art

Originally Posted by DaveTTC

yeah .... google translate, though Ido know a few words in polish as I do Dutch and a few other languages (very little)

Dave TTC
Turning Wood Into Art

Working knowledge of any language: "Good evening Miss" and " not guilty Your Honor."

Originally Posted by DaveTTC

The leak around the head is coming from what i think is the upper sirface of the gasket. Area highlighted in yellow
From that the pipe highlighted in pink leads to the tube that is the major leak. Im not with the init right now but presume the hasket only leaks when running and perhaps bak pressure from the tank.

Leaks from compressor head gaskets are relatively common.
Several things can cause the leak, one being the vibe loosening the head itself - have seen this on several cheap compressors and all they needed was tightening.
The other is the head gasket itself.
On one compressor I had, the head gasket, made of a thickish Al foil, was cracked.
I cut a new one out of a piece of similar thickness and that fixed that - my son has that compressor and its still running strong.

One thing that amuses me about your compressor is that it says it has an Al tank but it looks like it has rust on the tank - or is that dust?

Thats dust. I should clean it lol

Dave TTC
Turning Wood Into Art

Hi again Dave, If the head leak goes away when the motor for that set is idle, the there is no leak back via the check valve at the tank into the pink tube you so nicely coloured. If there is a permanent leak there when the tank is pressurised, there definitely is a fault in the checkvalve or the metal box between the check valve and pressure switch/unload valve.

As Bob has suggested, tightening the head bolts might solve the leak there, and I would attempt that as a first priority for the head leak, if that fails, then the heads probably have to come off both cylinders on that unit, and both head gaskets would need to be replaced with new units or home made ones. Hence suggestion to tighten head bolts first.

The leak between tank/check valve/pressure switch and unload valve is of more importance.

Hope to pull the check valve apart again in the arvo and post some pics


Dave

The Turning Cowboy

You're certainly getting stuck in clearing and sorting the shed Dave..... interesting thread! Cheers, Peter

D

Originally Posted by A Duke

Working knowledge of any language: "Good evening Miss" and " not guilty Your Honor."

Don't forget "Two beers please, my friend will pay". Which by amazing coincidence, I can actually say in Polish.

Still cleaning the shed. Man my feet are sore form all the walking back and forth. Ill get to the compressor but may not be till friday now.

About to post in hand tools, found some old saws plus a few given me on a job

Dave TTC
Turning Wood Into Art

Ok finally

Went to Sydney tools last year to check out if they stilk sell them.

Yes still available but design aeems to have changed as there is only one check valve for the two motors.

This mine



Eventually ended up in the maintenance work shop. The guy there was the most helpful guy ever. The sales rep took me there with a view to me getting my compressor serviced. The service guy did some teouble shooting via my relating the issues.

Not only did he tell me how to fix it he took one apart and showed me. He have me a spare check valve and some head gaskets. Now that is service.

Good one Sydney Tools

Wind forward 3 months and finally got around too it. Pulled the plug out the problem check valve



With the hose off too you can see right through



All looks good internally but what about the plug



No idea what that is but it was enough to cause a leak



What ever it was it was hard. Its gone and after starting up .....

Holding pressure

Head only leaks while motor running now so will save gaskets for future use.

This one will be able to go in my tool trailer and stay there. I now have another one I can keep in the cave thx to gordo. It needs a new regulatir whih i think I may stilk have on an old compressor that never found its way to the tip.

Dave TTC
Turning Wood Into Art

The piece of crud stuck to the plastic valve is probably some excess gasket goo or jointing solution that has dried in the head or plumbing then worked itself loose some time later and ended up on the first thing it could stick to while being blown through the plumbing, the plastic valve. I think that I said in an earlier post that it didn't take much to stop the valve closing. The spring ensures that the valve seats properly in the metal valve housing, but it is the pressure difference between the tank side and pump side that actually makes or breaks the seal, a very thin film like that will stop the valve seating fully, then there is no pressure difference as tank pressure appears both sides of the valve, so the valve leaks back to the head. Provided that the head itself seals properly, a leak in the check valve should only make starting harder, but a leaky head provides an exit path so the tank can bleed out via a faulty check valve and head seal. Ideally, you should correct the head seal as well ASAP, as it is affecting the efficiency of that motor/comp unit.