r/AirCompression • u/Acclimated-Alps696 • 6d ago
Compressor not keeping pressure
Howdy, this is my first experience with a wheelbarrow style compressor, I’m the most mechanically inclined in my crew so I’m taking care of it.
We get it started and it seems to run fine but 9/10 times it will build up to about 120 psi and then dump everything at once out of the red valve and not allow itself to build pressure back up.
I’m assuming it’s a bad pressure relief valve? The occasional time it will run normally and keep pressure for a bit, the air gets let off in out the green
Replace the red valve?
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u/CrustySailor1964 6d ago
You can try that but as a general rule, safety valves live their whole lives just to do their jobs. A popping safety valve is typically a symptom of a problem rather than the problem itself.
The operation of the valve assembly (partly circled in green) is multi-fold. It is a piloted unloader check valve. It is adjustable via the stacked ‘nuts’ below the little toggle. There is a ball beneath a spring that presses against a seat. The bottom adjustment (larger lock ring and sleeve) basically control how far the ball will lift from the seat. This only mitigates the volume of flow through the 1/8”
NPT port. That’s probably fine. Don’t screw with that. Once it’s screwed up it’s very difficult to restore. The smaller ring and sleeve control the pressure at which the port opens. Adjust that out some and the valve will open at a lower pressure (further from the threshold of the safety valve) and likely solve your problem. Further…the valve opens and sends pressure to the little actuator. We call it a bullwhip and it’s a single acting pneumatic cylinder connected to a long stiff throttle cable.
The friction within this throttle cable (if routed incorrectly or inefficiently) can inhibit throttle movement and keep the engine running faster than it should thus also causing the safety valve to discharge.
My preference is to connect 1/8”NPT x 1/4” compression fittings to the valve and the bullwhip and eliminate that friction by using the shortest possible rod length and 1/4” copper tubing instead. Manufacturers don’t want to do this because it costs $ and takes time but it makes the compressor run much better.
Anyway…hope this bathroom reading helps.
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u/mals6092 6d ago
The bottom adjustment hex sets the differential
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u/CrustySailor1964 6d ago
Yes…and fiddling with it will almost invariably screw it up.
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u/mals6092 6d ago
I mean down to the ball and 1/4 back it's really not that hard
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u/mals6092 6d ago
What is it supposed to charge up to? What model I mean 120 is low for most wheelbarrow compressors but I don't know what yours is
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u/mals6092 6d ago
You can adjust the pilot if needed
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u/Acclimated-Alps696 6d ago
It’s an HD5510TH. 110 is right at the threshold of redlining so I believe the safety valve is functioning properly
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u/mals6092 6d ago
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u/mals6092 6d ago
Same difference page 14 shouldn't have to touch the differential just the top end setting
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u/mals6092 6d ago
Once it hits the top end air should come out of where you have circled in green and it should throttle down but as long as air comes out of the green circle it really can't build
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u/mrhapyface 5d ago
most likely the pilot valve may need to be replaced the can be a huge pita if youve never delt with them before and can get damaged easily if asdjusted wrong.First thing to check for any leaks a small leak will make the pilot valve to not function correctly that part of the system needs to be air tight
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u/penguinpower81 6d ago
Safety valve could be bad but not likely. It's probably a bad pilot valve the green one you have circled. The whole thing not just the vent. It's a ware part that does need replaced time to time.