This is from a 2-stage, 5HP air compressor, made in USA. I'm replacing the tank, so I have to remove all of the working components from the old one. The new tank will have a 1" NPT inlet.

This came from the old tank's inlet. I'm fairly certain the tapered side is 3/4" NPT. Its outer diameter tapers from 1.06" to 1.03", approximately.

The straight threading is connected to the metal tube/compression fitting. A rough TPI is 18-20. It's OD is nearly 1" even. The tube is 3/4" OD. Chat GPT's best guess was 3/4-20 UNF.

Just get a 1”npt to 3/4”npt bushing to adapt to the new tank rather then trying to replace the fitting.

https://a.co/d/7sJoQre

https://a.co/d/3O8WsdD

Pretty sure that is just a compression fitting that uses a "olive" to perform sealing function. The small taper is probably inconsequential.

Make sure your old tank doesn't have a check valve below that fitting. If it does, it will need to be swapped over to.

quote:

Originally posted by Mustang-PaPa:
Just get a 1”npt to 3/4”npt bushing to adapt to the new tank rather then trying to replace the fitting.

Sure...if you want to do things the EASY way. Then, we wouldn't get to test our Scooby Crew skills. I wanted to ID it in case I'm not able to fit another piece with the new tank. The dimensions and spacing of the top plate welded to the tank will not be the same. It also may not be necessary, since I need to replace the check valve (see below). I could use one with the applicable threads like this .

quote:

Originally posted by shiftyvtec:

Make sure your old tank doesn't have a check valve below that fitting. If it does, it will need to be swapped over to.

It did and was pretty gummed up. I will be replacing it. Also, it didn't have a factory unloading valve, which I thought was odd. Unless we can come up with a reason it didn't have one, I'll likely install one of those with the new check valve.

Is the unloader not built into the pressure switch? Mine has a small bleeder valve that is a activated by the switch opening once the tank is charged. Plumbed right above the check valve body.

Could be integral to the pumps as well.

quote:

Originally posted by shiftyvtec:
Is the unloader not built into the pressure switch? Mine has a small bleeder valve that is a activated by the switch opening once the tank is charged. Plumbed right above the check valve body.

Could be integral to the pumps as well.

I removed the pressure switch from the side of the tank. The only line to it was electrical; there was no air tubing connecting it to the fill line or compressor pump where an unloader valve would normally be plumbed in.

I do wonder if this has some kind of built-in design...It never seemed to have an issue starting up under pressure, but I wasn't able to use it a ton before needing to replace the tank.

Here's a photo of the compressor unit. The intake manifold has been removed from the top. Perhaps the brass valve on the upper left is an unloader? I originally thought it was a pressure relief valve, but it's in an odd spot for that, plus the tank had one mounted directly to it.

There is also the odd triangular device on the front. It has open vent holes. Perhaps a crankcase relief vent?

After some more research, the brass valve in the picture appears to be a 150psi interstage safety relief valve (Bendix 205105). If the 2nd stage fails for some reason, it prevents the first stage from blowing it out. It does not appear to be an unloader.

If you haven't id the thread size on your compression fitting, here's a link to a chart.

https://www.jiayuanfitting.com...g-size-44478460.html