I am having an issue with what I think may be an unloader valve?

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I am having an issue with what I think may be an unloader valve. I’ve attempted to add an air dryer between the cylinder outlet and the tank.

I’ve checked and all my connections and no leaks. the elbow valve (unloader?) coming directly out of the cylinder head does not close when the dryer is in place. Take the dryer out of the loop and all is fine. When the tank is empty with no dryer in the loop the valve stays open until the tank reaches about 10 psi and then closes.

Any help appreciated.

Well, it may be the unloader valve, but we doubt it. And, it’s particularly difficult when we don’t know the make or model of air compressor we are talking about.

When you say that you have added an air dryer between the cylinder outlet and the tank, what kind of air dryer. One like the following?

In line air dryer
A low cost in-line compressed air dryer.
Photo: www.princessauto.com

If what you have installed is really and air dryer, and not just an air filter / water separator, we can say we wouldn’t put the compressed air dryer where you say you’ve installed it. Reason? The air coming from the pump is typically hot, has an even higher level of moisture than cooled compressed air, and quite possibly has free water in it. By putting the dryer between the pump (what you call the cylinder?) and the tank, you are ensuring that the dryer is seeing the most inhospitable level of moisture possible making it having to work harder to reduce the moisture level to the desired point, or forcing an over-sizing of the dryer to account for the extremely hot, moisture full, air.

We aren’t clear on what type of dryer you speak of? Since your email address suggests that you are in the cabinet making business, it were me, I would have a desiccant dryer installed in line just before each application where I was using air and particularly in those where the air was used for spraying paint or lacquer.

Compressor tank is 1st step in dewatering compressed air

Let the air compressor tank be the first step in dewatering the compressed air.

If the air gets a chance to cool in the compressor tank, it will drop out a great deal of the water entrained in the air stream from the pump. The longer it sits in the tank the cooler the air gets, and the more water that will condense out in the tank, and not in your air lines.

Use an auto tank drain to ensure that the tank is drained regularly and frequently to prevent a water buildup in the tank. Not draining the tank often enough will, eventually, allows the liquid water in the tank to re-entrain back into the air stream as the air leaves the tank..

It is clear from what you have written that whatever dryer you installed is causing the problem.

If you could provide more info about the compressor, the dryer you are using along with a couple of photos of the installation, we’d be pleased to help if we could.

Short term, rather than reinvent the wheel, take the dryer out of that location. We think that would be best for now.

By Ashley Pearce

As a passionate manufacturing and mechanical engineer, I've had my fair share of run ins with air compressors and compressed air systems. With over a decade of experience in the industry, I have both a fresh perspective and time-served hands and mind to help you with your compressor problems (along with our able community!)

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