Air Compressor fail to build pressure


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Old 07-14-10, 08:51 PM
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Air Compressor fail to build pressure

Have a Craftsman 7 Gallon, 1 Hp, oil lubricated air compressor model 921.166390 that I use to run nail guns. Unit is 2.5 years old. Has worked fine to this point. That is until this weekend I was using it and was close enough to it to hear a slight change in its running sound. After which the unit failed to build pressure. Gauge did not come off the peg. I pulled the head to inspect the reed valves (1 for intake and 1 for exhaust). Seemed ok. Piston did not seem to be a problem and the cyclinder wall did not show any signs of damage, say from a broken or the like. Did wipe the valves down to make sure no dirt was present and holding one open. After reassembly the unit would build pressure to about 20 PSI but nothing more. Wondering where my problem might be. Any help, comments, suggestions and advice is appreciated.
 
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Old 07-14-10, 09:58 PM
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The valves are almost certainly the problem with the gaskets the number two suspect. If you can get a valve rebuild kit that is what I would try. It takes just a teeny tiny leak across an air compressor valve to cause it to not build pressure.
 
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Old 07-15-10, 12:43 PM
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Air Compressor fails to build pressure

Thanks for the comments. I checked on parts availability. I can come up with some gaskets and I can make the other gaskets. Unfortunately, the reed valves are not available. Valves are (WAG, unit is currently still reassembled) about 1/2" wide, 2" long, and maybe 0.0625 thick. Valve seats are simple concave cuts in valve plates. There are no springs behind the valves (which is common for a reed valve setup). Wonder if lapping would do anything or if I could eliminate/reduce what is called "Gasket, Valve Plate" and gain anything. the gasket valve plate is a shim like plate of about 0.015"or less. Design/Engineering wise I would not want to do so but I am grabbing at a few straws right now. Another question that comes to mind is did the valves loose any inherent spring action or strength over the 2.5 years of intermitant use? An exploded view can be seen in you look up model No. 921.166390 at the Sears Parts site.
 
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Old 07-15-10, 09:20 PM
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I'm too lazy to look that part number up on the Sears site. It is possible that the valves themselves have lost some kind of spring temper. It is also possible that there has been some corrosion or erosion on either the valve or the seat. As I stated earlier it only takes a tiny amount. Can you reverse the reeds to see if that makes a difference?

Since Sears doesn't "make" anything it is possible that replacement parts are available for your pump IF you can determine just what company did make it. Maybe if you posted some pictures someone would recognize the original manufacturer and be able to direct you to a site that may have the necessary parts.

Worst case is that you would simply toss the pump and replace it with a similarly sized unit.
 
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Old 07-20-10, 12:37 PM
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Reference to the P/N and exploded view was for the benefit of anyone who viewed the write up and desired a pictorial to go with the written explanation.
 
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Old 08-14-10, 07:25 AM
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Up-Date on compressor failing to come up to Pressure

This is just an up-date to perhaps help all those out there with a "one lunger" (read that to mean single cylinder) compressor. Although this would apply to a dual cylinder unit with a single head, like the Craftsman 3.0 Hp family of the late 1980s. Anyway, finally took a serious look at this unit. Problem ended up being a failed head gasket which allowed a breach between the inlet side and the exhaust side of the head, above the valve plate. The breach at a certain point allowed the discharge side to overcome the intake valve thus putting air back into the cyclinder rather than into the storage tank. The head gasket is a simple consocko (fiber gasket material) which might have broken down over time due to lubrication oil vapor in the system. In the end the problem was rather simple and the fix painless and inexpensive.
 
 

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