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Roger
06-10-2003 19:18:14
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Re: Re: Re: Re: Re: Re: Re: Gilbert Barker Compre in reply to Richard Fazio, 06-10-2003 18:21:05
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This valve is the hydraulic unloader valve. If you look in the bore on the side of the case, you will see a small oil hole leading from the oil pump. When the compressor starts, oil pressure builds and forces the spring loaded pistons apart. This closes off the needle valve inside the assembly and cuts off air to the head unloaders. They retract, and the compressor starts to pump. Conversely, when the compressor stops, and oil pressure drops, the pistons in this bore retract, opening the needle valve and letting air to the head unloaders to hold the intake valve plates open. You should get a small shot of air from the high pressure unloader when this happens. This will let you know the compressor has unloaded. Sometimes, this air is vented back into the head just before the low pressure intake valve, so it might not be too easy to hear. This hydraulic unloader not only serves to unload the compressor, it also prevents the pump from compressing if there is no oil pressure. Sometimes this will give the operator enough warning (no air production) to prevent the compressor from seizing up, but it is just better to do a little preventive maintenance (i.e. check the oil level once in awhile). If you cannot blow through it when you remove it from the compressor, it is full of crap, usually rust, or seized shut. There should be a small screen filter in the inlet port, and I believe there is a small felt filter inside the valve itself. You should be able to buy an overhaul kit for the hydraulic unloader valve from the same place you get the head overhaul kit. This valve must be working properly for the pump to unload. It might be worth buying an entire new one. BTW, you plumb this hydraulic valve directly from the tank valve.
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