How to use Meritor Wabco air dryer for shop air compressor?

I am trying to use a Meritor Wabco System Saver™ 1200 Plus Air Dryer to produce dry air with my shop air compressor. I am having trouble with leaking air out of the bottom discharge during compressor building up pressure. I tried to get tech support from the manufacturer but was not helpful at all.

Before I take the unit apart to look for mechanical problem I figured I could ask here. I think the issue is with the 1/4" line I ran from the electric pressure switch on the compressor to the air dryer in order to control the discharge of water each time the compressor cycles. Right now the air dryer is letting air out of the discharge port when the compressor is running. If I remove the 1/4" tube from the air dryer while the compressor is running there is no discharge from the port.

There is air pressure in the 1/4" tube while the compressor is running. There is no pressure in the tube once the compressor stops pumping.

The question is: Does the air dryer normally discharge when there is pressure in the 1/4" control tube or when there is no pressure in the tube?

Wix makes a filter for that, much easier to use. It is a simple spin on filter comes in 2 or 3 sizes.

goldneagle said:

The question is: Does the air dryer normally discharge when there is pressure in the 1/4" control tube or when there is no pressure in the tube?

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The control line usually only gets air pressure when the air governor sends the pulse of air (same thing with the compressor unloader) when the set air pressure has been arrived at. How to hook it up on a standard shop compressor would be a puzzle in that you need "a pulse of control air" at the point that the compressor shuts off. You might accomplish this will a secondary circuit with relays and electric valves.

MtnSnow said:

The control line usually only gets air pressure when the air governor sends the pulse of air (same thing with the compressor unloader) when the set air pressure has been arrived at. How to hook it up on a standard shop compressor would be a puzzle in that you need "a pulse of control air" at the point that the compressor shuts off. You might accomplish this will a secondary circuit with relays and electric valves.

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That gives me an idea. Run a electric auto drain valve to the 1/4" port. It cycles every x minutes and stays on y seconds in order to drain water from the bottom of the air tank. I would tie that into a airline and it would force the air dryer to discharge through the drain port for y seconds.

goldneagle said:

That gives me an idea. Run a electric auto drain valve to the 1/4" port. It cycles every x minutes and stays on y seconds in order to drain water from the bottom of the air tank. I would tie that into a airline and it would force the air dryer to discharge through the drain port for y seconds.

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That sounds plausible

Well I ordered the auto tank drain valve the other day. I installed it Friday. I ended up tapping into the DRY discharge air line to feed the auto drain valve by using a T fitting. I rand the output in 1/4" black tubing to the 1/4" port on the air dryer. The port controls the dumping of moisture from the bottom of the air dryer. Now I am able to time the discharge intervals as well as the duration of the moisture discharge.

I will make the intervals more frequent when sand blasting and other high volume air usage. (since that would produce more moisture.

Nicely done GE.

A thought for your consideration, if applicable: Hook your shop air compressor reservoir drain plug/line to your new auto drain tank valve system. By doing so both the dryer and the reservoir can be drained by the same set up.

joshuak said:

Nicely done GE.

A thought for your consideration, if applicable: Hook your shop air compressor reservoir drain plug/line to your new auto drain tank valve system. By doing so both the dryer and the reservoir can be drained by the same set up.

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Not a good idea since the tank drain valve has a lot of moisture coming from the bottom of the tank. You need to keep the air dryer as dry as possible. I am using the dry air to blow out the air dryer. A dry air dryer is a happy air dryer.


If the air dryer spits too much moisture inside my compressor shed I will have to pipe the moisture out of the shed with 1-1/2" to 2" pvc pipe.

I'm sorry I didn't explain myself very well. I completely agree it would be a bad idea to feed your air dryer from the bottom of the reservoir tank. All air dryers should be happy ones.

This picture may explain better what I was trying to, it has worked for me.

goldneagle said:

...If the air dryer spits too much moisture inside my compressor shed I will have to pipe the moisture out of the shed with 1-1/2" to 2" pvc pipe.

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Yes, either a drain pipe or a dedicated purge tank.



Either way, great work as usual thanks for posting up.

joshuak said:

I'm sorry I didn't explain myself very well. I completely agree it would be a bad idea to feed your air dryer from the bottom of the reservoir tank. All air dryers should be happy ones.

This picture may explain better what I was trying to, it has worked for me.

View attachment 614967




Yes, either a drain pipe or a dedicated purge tank.



Either way, great work as usual thanks for posting up.

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Have you ever seen the purge valve on a MV air dryer? The valve is about the diameter of a quarter. There is not threaded or hose connection available. It just spits out. I was thinking of putting a 2-1/2" or 3" pvc pipe to encircle it and capture the spit when it discharges. I will use a reducing coupling further down to reduce it to 1-1/2" pvc pipe. I will post pictures once I assemble the drain.

goldneagle said:

Have you ever seen the purge valve on a MV air dryer? The valve is about the diameter of a quarter. There is not threaded or hose connection available. It just spits out. I was thinking of putting a 2-1/2" or 3" pvc pipe to encircle it and capture the spit when it discharges. I will use a reducing coupling further down to reduce it to 1-1/2" pvc pipe. I will post pictures once I assemble the drain.

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On a civilian truck yes, not on a MV nor associated to a shop air compressor. My bad.

joshuak said:

On a civilian truck yes, not on a MV nor associated to a shop air compressor. My bad.

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I guess you thought it was like a tank drain.