Compressor mishap

[DLF]

Well, long story short, I bought a brand new Fini compressor and found out it was assembled by half brain monkeys.

The compressor arrived from dealer and I was super excited about the new toy.

Because of the location in the shop I decided to use the rear airtank port for the high pressure output, port which was plugged from factory.

No problem, took a spanner and tried to undo the plug. It was stuck. Figured they used the liquid sealant, so I heated it with the blowtorch. Again, no deal.

So... decided to stick to my motto: if it’s stuck force it, if it breaks it needed replacement anyhow

Therefore I took out the welder and welded the spanner to the plug. Not the best weld since I did not want to put a lot of heat into the airtank and damage the nice paintjob.

The weld held but the spanner broke next the weld Perhaps the spanner was heat treated, don’t know.

Buy I was becoming super frustrated, went to the hardware store and bought a crowbar. Welded it in the middle to the plug. Success, I managed to undo the plug


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[DLF]

The proof is in the pudding, so...

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[DLF]

Conclusions:

1. Managed to do the job without damaging the paintjob. Only minor coloring of the paint around the port rim

2. Postmortem shows damaged threads on the plug. Turns out the airtank thread is 1/2 BSPT thread, which is tapered and the idiots at Fini used a BSPP thread plug (G thread). The 2 thread types are identical except that G thread is parallel while the BSPT is tapered. So the factory monkey just used an impact wrench to jam the plug and destroy the threads.

3. There was very minor damage to the airtank threads, so I will have to run a tap to chase the threads.

4. At this point I am inclined to run a G thread tap so I can use parallel thread fittings which are more common in my country. To be decided


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[Flyinfool]

Parallel threads are a lot harder to seal, they are intended to be used with a gasket or some other sealing device. That is why things you don't want to leak use tapered threads.

 

[Ulma Doctor]

i would concur with a tapered fitting for a pressure vessel

 

[Buffalo21]

nothing holds like a good cross-thread.........

 

[Jim F]

nothing holds like a good cross-thread.........

Cross threads is better than no threads.......

 

[DLF]

nothing holds like a good cross-thread.........

It looks worse in the picture than it actually is. There are no cross threads. But the bottom threads on the plug are squashed because the airtank female thread is tapered and they used a parallel thread plug.

But the plug metal is soft as cheese and so the air port threads did not sustain damage.

I have to buy a BSPT tap and chase the threads to clean them a bit.

IMO parallel threads also work for an airtank otherwise there would not be pneumatic fittings with parallel threads, but I agree that tapered threads provide a better seal. So I will keep them


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[NC Rick]

Parallel threads are a lot harder to seal, they are intended to be used with a gasket or some other sealing device. That is why things you don't want to leak use tapered threads.

Man, sorry but I disagree with your statement. I'll take a straight thread and a sealing element all day long over a taper thread if I want something sealed. The threaded joint must be designed for it however.

 

[Suzuki4evr]

i would concur with a tapered fitting for a pressure vessel

Listen up...........the doctor has spoken