Compressor tank check valve failing

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It’s been some time since a visitor wrote in and asked about why their compressor tank check valve was failing. The answer provided then was brief. This page adds data to the response in order to help others  if this is an issue you are experiencing with your compressor.

A common symptom of a failing tank check valve is that tank air leaks out of the unloader valve when the air compressor stops.

The air compressor tank check valve is the device that is in place to keep compressed air in the tank when the compressor unloader opens to atmosphere between compressor run cycles.

The check valve is commonly located where the line from the pump head, the one that feeds compressed air to the tank, is actually connected to the tank.

Compressor Leaking Air Under The Hood - check the tank check valve
Small air compressor tank check valve

What fails on a compressor tank check valve?

Not much normally can fail. The original poster was asking about why the threaded cap on the tank check valve on his compressor was fractured. This isn’t a common issue, and may have been caused by over-tightening in the factory. Also, in the drive to offer lower and lower prices for the DIY type air compressor, compressor assemblers tend to acquire parts from the cheapest source. A cheap source may not have all the checks and balances in their quality control and manufacturing processes to weed out the the poorly built parts, and it sounds like you that compressor user may have got a piece of crap part on the air compressor. We wont know for sure as the individual did not post a reply.

What normally fails on a tank check valve?

Inside the typical tank check valve, in the barrel that goes into the tank, is most often a simple flapper valve. Picture a blind on a window, with the blind secured at the top, and you are watching as the wind blows into the house, and the blind flaps open. The same blind flaps closed when house pressure exceeds the outside pressure as the wind shifts, and the blind is blown right up tight to the window.

A similar scenario unfolds inside the tank check valve.

When the air compressor is running, and as air from the pump flows down the hose to the tank fitting, it flows into the tank through the check valve fitting, blowing the flapper valve in the check valve open.

When the pump stops, air pressure in the tank is higher than that of the air line going into the fitting, and the air flows back up the check valve, blows the flapper valve shut, and is trapped in the tank.

Can you fix a tank check valve?

Really no. If the flapper is broken, the time cost and parts cost – assuming any can be found – would far outstrip the cost of a new tank check valve, hovering in the area of $12 – $15.

What can happen, particularly if there is a lot of air use or the tank hasn’t been drained often enough, is debris from the air flow may build up on the flapper or sealing surface and prevent a tight enough seal to stop air flow.

Try rinsing the tank check valve in solvent, or even boiling water, let it dry and reinstall. If air stops leaking out you’re good, if not, pop in a new one and that will resolve the issue right quick.

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