Friday, April 9, 2010

Leaking Air Compressor - Check Valve Repair

This last summer I rebuilt my deck. A friend of mine came over to help install some seismic reinforcements. This included a bracket which tied the deck to the house. The bracket was held in place with many Simpson SDS screws. Since the bracket was located between a set of joists, space was limited when selecting which tool was to be used to drive the screws. Cranking each of the screws by hand with a ratchet was too labor intensive. The solution was a pneumatic ratchet. Pneumatic ratchets however use alot of air. While driving all the screws in, my air compressor must have continuously ran for 30-45 minutes. After this particular job my air compressor developed a slow air leak. Though not terminal, this leak was annoying. Not only was there a constant high pitched hiss, but the compressor would fire up often, even when not in constant use as it would keep the pressure in the holding tank to level.

What I suspect had happened was the prolong running of the compressor overheated a component, most likely one of the valves. So I decided to investigate. At first pass it appears that the unloader valve was leaking. This is a mechanical valve located in the electrical switch area. The valve is a pneumatic/mechanical valve that triggers the electrical switch to turn on, when it senses low pressure. Though leaking, this valve what not the culprit.

Pressurized air is supply to the storage tank through a feed line. This feed line enters a check valve prior to the storage tank. Though it looks like air from the compressor enters the check valve, from the thick brass line, then goes out through the smaller line; the check valve is actually a three way valve with air entering the storage tank at the base of the valve. The thin brass line goes to the unloader valve mentioned earlier.

By removing the cap on the end of the check valve the inside working can be removed. Check valves are relatively simple; consisting of a spring and rubber cap, or seal. The picture of the check valve spring is not the same type as the one I took apart. It is simply there to show the basic make up of such a valve. The overheating of the check valve, over heated the spring. Like taking a torch to your cars suspension coil springs to lower your ride. The heating of the spring weakened it to the point that it no longer sealed the pressurized air from the tank. The air would leak back through the check valve and would enter both the compressor and the unloader valve. That is why at initial inspection it appeared that the unloader valve was leaking.

The proper repair for this job would have been to order a new spring and possible a new sealing cap. However I simply pulled the existing spring apart and stretched it out. This increase in spring tension was enough to return the check valve to full functionality. Though this type of cold working of the spring metal is not recommended, this is a low risk part. If it fails again, I might consider a new spring.

As my friend's grandpa once put it, "Good enough for the girls we go with!"


  1. nice....thanks for sharing....i picked up a free compressor...came without a regulator, but I will be checking these parts to make sure they arent the reason the guy tossed it.

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  3. I am going to new air compressor. This compressor is very noise, my wife angry about this. I want to buy compressor vary less than 60db. Do you have a lot of experience, give me your opinions?

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