Air Compressor problems

H

HIG

My air compressor has been acting up. Sometimes when it shuts off I get air continually blowing out of the on/off switch from the small line, this does not happen every time. For some reason I think that small line is a blow off line to remove pressure from the cylinder head - is this correct? Can someone tell me how this works, I'm assuming when it reaches pressure the switch trips off releasing air to blow off from the shrader valve thing on top of the small line. Are there valves in to top head of the compressor that are sometimes sticking? Can I remove the air filter and spray something in the top of the head - carb cleaner/Marvel Mystery oil? Is there any service I can do, it does not happen every time. It has also seems like the belt has been slipping but I saw one of the spot weld that hold the motor to the cradle broke free allowing the motor to move and the belt loosening, I retacked that.





The compressor is just an average single stage 5 hp.

Thanks, Steve
 
The smaller line is an unloader line. As you point out it comes from the head and terminates at the pressure switch.
When the pressure switch reaches max pressure or is manually shut off the shrader valve is held open by the pressure switch linkage. This in turn releases the pressure in the compressor unit.

By doing this the starting load on the motor is greatly reduced.

Why doesn't it let all the air out of the tank? Where the large line enters the tank there is a check valve that holds the compressed air in the tank and does not rely on the reed valves in the cylinder head.

The valves in the cylinder head are stainless steel reeds. they just flex open under pressure or suction depending on their location, inlet or outlet. They do not require lubrication.
They do require periodic replacement as they crack over time and when the crack lets the reed tab break off and it is on the intake reed which is on the inside of the cylinder it causes an expensive mess in most cases.


IF you can determine excess air is being released by the unloader I would first check the nut holding the shrader valve has loosened and let the valve back away from the pressure switch linkage.

If that is good then I would suspect the check valve on the big line isn't holding.
 
Some pumps have a valve that's actuated by centrifugal force to close when the crank starts spinning to close off the bleed line. If you've got air continuously flowing after the head depressurizes then there's a leak somewhere.
 
Pressure switches like that can do that. A slight adjustment to the arm on the left side can stop it(either bend that tab or adjust the valve by the threads if available). That arm presses down on a schrader valve to relieve the head pressure. Sometimes they stick or get out of adjustment. You can't hurt anything by tweaking it. I can't remember for sure but just watch what it does during operation and you'll get it.
 
Brad J.;33482 said:
Pressure switches like that can do that. A slight adjustment to the arm on the left side can stop it(either bend that tab or adjust the valve by the threads if available). That arm presses down on a schrader valve to relieve the head pressure. Sometimes they stick or get out of adjustment. You can't hurt anything by tweaking it. I can't remember for sure but just watch what it does during operation and you'll get it.
Click to expand...

Thanks for the replies.

I pulled the check valve out last night, clean it with carb cleaner and reinstalled it. The valve seemed to be working but when I reinstalled it it still blows off air from the shrader valve after the compressor stops. Sometimes it continues to blow off but sometimes it stops after a while (a longer time than I think it should take to bleed off the head & lines). I've reorder a replacement check valve.

I don't see any issues with the shrader valve or pressure switch.

Thanks, Steve
 
If your still bleeding it tells me your borderline on adjustment. Otherwise it would bleed all the time if the valve was faulty.
 
Brad J.;33504 said:
If your still bleeding it tells me your borderline on adjustment. Otherwise it would bleed all the time if the valve was faulty.
Click to expand...

I sorry but I don't understand, even if the shrader valve is out of adjustment if the check valve is working the head would run out of air and it would stop bleeding off from the shrader valve. I'm just assuming the valve is sticking sometimes and not closing or does not close right away so it bleed off longer.

What am I missing?

Thanks for trying to get it thru my head!!
Steve
 
HIG;33508 said:
I sorry but I don't understand, even if the shrader valve is out of adjustment if the check valve is working the head would run out of air and it would stop bleeding off from the shrader valve. I'm just assuming the valve is sticking sometimes and not closing or does not close right away so it bleed off longer.

What am I missing?

Thanks for trying to get it thru my head!!
Steve
Click to expand...

You got it right, if the check is holding the schrader valve will run out of air. If the check isnt holding then there is a tank full of air for the schrader to bleed off or until the check valve seals.
 
You guys are right. My Eaton has done both of these problems at different times. The check valve would allow it to do this. My Quincy's don't have check vavles since they are built with proper valves in the head. I forgot about that. Those check valves are usually a cheap nylon ball and spring. I've seen the nylon get all dented and scratched from normal use and leak when they land in the wrong spot.
 
Senile Old Fart;33512 said:
You got it right, if the check is holding the schrader valve will run out of air. If the check isnt holding then there is a tank full of air for the schrader to bleed off or until the check valve seals.
Click to expand...

Brad J.;33525 said:
You guys are right. My Eaton has done both of these problems at different times. The check valve would allow it to do this. My Quincy's don't have check vavles since they are built with proper valves in the head. I forgot about that. Those check valves are usually a cheap nylon ball and spring. I've seen the nylon get all dented and scratched from normal use and leak when they land in the wrong spot.
Click to expand...

Thank for the replies. I'll let you know how I make out when the check valve comes in.

Steve
 
Brad J.;33525 said:
You guys are right. My Eaton has done both of these problems at different times. The check valve would allow it to do this. My Quincy's don't have check vavles since they are built with proper valves in the head. I forgot about that. Those check valves are usually a cheap nylon ball and spring. I've seen the nylon get all dented and scratched from normal use and leak when they land in the wrong spot.
Click to expand...

I have not worked on a 340 in 15 years or more so my memory is rusty.
I thought that the 340 like most other centrifugal unloaders, uses a check valve off of one port of the unloader valve. That is how they seal the back pressure from the tank to the compressor so it can start under no load. The unloader releases the air inbetween the check and the cylinder head. Or so that is how I remember them to function.
 
Quincy uses a Hydraulic unloader instead of centrifucal. It's ran off the oil pump pressure and operates a diaphram on the top of the head to bleed the pressure.

They don't use check valves and the head is strong enough it doesn't bleed back through the head valves so their isn't a need for a check valve. Very cool and they are the best Piston compressor period.
 
I replaced the check valve where the air line goes into the tank and it solved my problems.

Thanks for all the help!!
Steve
 
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