HELP! Compressor Pipe Questions

[Gaffer]

Today didn't go well. My project was to install an aftercooler on my Husky Pro (Campbell Hausfeld) 7.5 HP, 2-Stage, 80 Gal vertical tank compressor. The plan was to remove the copper pipe between the head and the tank and add pipe fittings and pipe to feed the aftercooler, water separator, and tank return. The pipe is an odd size to me. The OD is 3/4", and the inner is slightly shy of 5/8. It doesn't match the copper pipe I'm used to working with. Each end had a ferrule for a compression fit. The fitting at the tank cooperated without persuasion and has a male 3/4" NPT, so it will be easy to attach a standard copper fitting.

The aluminum part that bolts to the head is the problem. The nut was seized, and even with penetrating oil and heat, the aluminum threads sheared off. The parts guy wants $100 plus tax and shipping, a deal breaker, and also because it leaves me with the same problem of having 3/4" NPTF (fine) and is fitted for the less common copper pipe size. The aftercooler is threaded 3/4" NPT.

I attached a few pictures of the part. In the picture of the head, you'll see the part I removed and the matching part next to it if that helps you visualize what I'm working with. I figure I can make the piece to attach to the head, but I am stumped on how to make the fitting for it, preferably 3/4" NPT or something I can solder/braze - IDK. I figure aluminum is fine, and I also have brass stock. Should I consider cast iron? I don't have experience cutting threads, and I wouldn't know where to start for NPT or NPTF. What do you recommend? And @Firstram, I know you did a similar mod to your compressor and hope you can help.

Thanks in advance!

 

[MikeInOr]

Are you SURE that is 3/4" NPT? That looks like a 3/4" straight thread. NPT has tapered threads. They are not the same thing and it is a common mistake to try to interchange them... ask me how I know. Compression fittings usually use a straight thread. NPT and straight threads use the same TPI and will thread together but they won't make a solid connection and they won't seal.

Can you TIG weld aluminum or to you know someone who can? I would consider cutting off the bad thread flush with the big hump and weld a comparable part on.

 

[Firstram]

@Gaffer,
My heads were threaded 3/4 NPT already. If you can braze or weld, build a new manifold out of steel. Duplicate that flange, attach a short 3/4 pipe nipple or fitting and you're off to the races!

 

[Eddyde]

I'd probably remake the entire part out of a chunk of aluminum, but in a straight configuration. You could make any directional changes with a fitting. Taps are readily available for ¾ NPT, dies are available too but you'd need a large diestock to turn it.

 

[tq60]

Compression fitting is straight threads.

The general rule is finger tight until seated, then wrench to seat.

Threads are buggered up at end, get a thread file, this can be used to clean them up.

You may be able to remove some from the end to allow the nut to get more grip, as last resort.

Sent from my SM-G781V using Tapatalk

 

[Nesse1]

The thread does not look like NPT.

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[sdelivery]

Is there enough material in the head to open the outlet port and thread the I.d. for 1/2 or 3/4 npt? and eliminate the outlet casting?
You would need a commonly available npt to tubing fitting and you would be off and running.
Tubing is measured on the outside, pipe is measured on the inside.

 

[Flyinfool]

Why buy a $100 part when you can make it yourself for only @200 in material and new tools??? Maybe even learn some new skills.

I would either make a new manifold or modify that one to something that will work. The outlet end of the new/reworked manifold does not have to match what is there now, You can make it anything that will work for you.

 

[Gaffer]

Are you SURE that is 3/4" NPT? That looks like a 3/4" straight thread. NPT has tapered threads. They are not the same thing and it is a common mistake to try to interchange them... ask me how I know. Compression fittings usually use a straight thread. NPT and straight threads use the same TPI and will thread together but they won't make a solid connection and they won't seal.

Can you TIG weld aluminum or to you know someone who can? I would consider cutting off the bad thread flush with the big hump and weld a comparable part on.

I forgot about the difference between pipe and tube measurements. Yes, the compression fittings on both ends of the pipe are straight. The fitting at the tank is 3/4" NPT male into the tank and female on the other end. This fitting has the 1/4" tube threaded into it for the pressure regulator. The elbow that attached to it was 3/4" NPT on the tank side and straight thread on the other, so I simply removed it and can use standard NPT from there.

I can weld aluminum, but I'm bad at it. I think I'm better off making a new part. Drill America sells a 3/4" NPT tap and drill for $15.25, delivered. I'm leaning toward this. I want the compression business out of there and to stick with NPT, otherwise lots of adapting. I'm going to look it over again today and think about everyone's posts.

I appreciate everyone's input.

 

[Firstram]

While you're at it, move the check valve from the tank to the inlet of the cooler. It will take a long time to unnecessarily bleed the pressure out of everything once the compressor shuts off. If you are blasting or using a large volume of air the compressor will start while still loaded.