I Broke The Compressor Manifold

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I broke the compressor manifold.

I don’t know how it happened, but all of a sudden I’ve got a continuous air leak from the compressor. It was forever draining air and once the cut in pressure was reached, the compressor would start again. I know I wasn’t using the compressed air, so it had to be a leak.  In tracing the leak down I spotted the problem. The casting on which the pressure switch is mounted had cracked.

To get to the problem I had to remove the pressure switch which, unfortunately, is not mounted on the manifold, but the broken compressor manifold is the actual base of the pressure switch. Now my compressor pressure switch is in pieces. Those inner springs fly a long way.

I also had to remove the compressors pressure relief valve and the tank air gauge, two more things that were installed in this manifold. Also, the air line out to the coupler into which you plug your air line was plumbed from this manifold as well. Here a look at the manifold after I’ve removed all the installed parts, with the crack circled.

I broke the compressor manifold - broken manifold casting

The cracked compressor manifold is cast, meaning it’s made of one piece, and then the various air connection ports – on this manifold there are four – are tapped after the fact, to add the threads. I can only surmise that when they tapped the air port that cracked, is that an already weakened casting developed a hair line crack, and over time, with the compressor use and the vibrations that running air compressors generated, the crack widened.

Here’s a look at this manifold when it’s mounted on the air compressor. The red dot identifies the manifold. You can see the various components that are threaded into it, and the pressure switch sitting on top.

I broke the compressor manifold - compressor manifold installed on air compressor

I broke the compressor manifold – now what?

Did you ever try to find an air manifold like this one for your compressor? Believe me, I searched. No luck. In order to get a new manifold I would have to get a new pressure switch too.

Since I’ve done a lot of plumbing work over the years I know I can build a new manifold using copper fittings and such. Regardless, though, since it was part of the pressure switch that had failed, building a new compressor manifold wouldn’t have accomplished anything, as I would still need to get a new pressure sure. So I ordered one on line.

What kind of pressure switch?

I soon learned that although the tops of air compressor pressure switches often look similar, it’s what’s underneath that counts too. I’ve added an image of the broken compressor manifold below. The red dots show the various ports this manifold has. In this case the four ports are for; threading the manifold onto the nipple from the compressor tank, that’s the top one, the pressure relief valve goes in one of the side ports, the air tank gauge goes in another of the side ports, and the line over to the quick coupling is threaded into the third port on the side.

Four ported air compressor manifold

There are some pressure switches out there that have only a single manifold port in the bottom.

To get the correct pressure switch & manifold you must:

  • identify how many ports your pressure switch and manifold have to get one with the same number
  • make sure that the new pressure switch operates on the same voltage as the present one (most are 120 – 240 vAC – but do check)
  • ensure that the cut in and cut out pressure settings of the new pressure switch are the same as the old one
  • make sure you understand how the unloader valve works on the present switch so you get a new one with the same unloader valve hookup

You may be able to get a good deal on a compressor pressure switch on line, or you may prefer to visit the local air compressor repair or sales outlet and pick up one there.

Reinstalling the air compressor manifold

The big port (it’s a 1/4″ NPT on my tank) in the bottom of the manifold threads onto the nipple from the air compressor, shown below and identified by the red dot.  You will have to thread a number of things into the manifold either before or after you have threaded the manifold onto the tank nipple, so think the process through as to what you install before you add the manifold to the tank nipple or what you will need to install in the manifold base after it’s threaded onto the tank nipple.

air compressor manifold mounting nipple

Either use plumbers thread sealing tape or pipe dope on the threads before you install them. Be careful that the pipe dope or tape doesn’t end up on top of the nipple. If it does, it will blow into the manifold.

Have a look at this next image, and in particular, the size of the hole in the center of the manifold through which the compressed air flows onto the diaphragm to operate the pressure switch. It wouldn’t take much in the way of debris to block this hole, would it? The air flow orifice is just to the right of the red dot.

Picture of the air flow hole in the base of the air compressor manifold

So be careful to ensure no tape or pipe dope can escape into the air flow and perhaps block this, or other important air components.

Carefully reinstall all the components that were threaded into the original base, then wire up the pressure switch, and you are ready to go. How to wire the pressure switch is covered on another page.

Good luck. Questions or comments are welcome below.

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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