# Compressor mishap



## DLF (Dec 11, 2020)

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 (Dec 11, 2020)

The proof is in the pudding, so...


















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## DLF (Dec 11, 2020)

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 (Dec 11, 2020)

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.


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## Ulma Doctor (Dec 11, 2020)

i would concur with a tapered fitting for a pressure vessel


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## Buffalo21 (Dec 11, 2020)

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


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## Jim F (Dec 11, 2020)

Buffalo21 said:


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


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


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## DLF (Dec 12, 2020)

Buffalo21 said:


> 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 (Dec 12, 2020)

Flyinfool said:


> 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.


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## Suzuki4evr (Dec 12, 2020)

Ulma Doctor said:


> i would concur with a tapered fitting for a pressure vessel


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


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## addertooth (Dec 12, 2020)

Just machine a new cap-plug, with a J-groove on the wrench-cap face for a O-Ring.  Then apply silicon oil to the O-Ring, and tap and screw down with whatever thread pleases you.  I do it, and it is good to 4500 pounds/310 Bar.

It is always important to throw in a superfluous option, when several good options have already been proffered. 

Be sure to have a Gelatin ballistic block aligned with the path of travel with the plug, there are too few good ballistics studies on high-velocity plug penetration


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## markba633csi (Dec 12, 2020)

Yikes what a mess.  Poor quality control.
-M


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## Flyinfool (Dec 12, 2020)

Flyinfool said:


> *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.





NC Rick said:


> 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.



It sure looks to me like you just agreed with me, You prefer straight threads with a sealing element and I said straight threads must be used with a gasket or other sealing device. Different words saying the same thing.

In the case of this air tank I doubt if the surface of the bung is machined to accept a sealing element. Or in your words "designed for it". Thus the consensus to use a tapered thread in this case.


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## DLF (Dec 12, 2020)

markba633csi said:


> Yikes what a mess. Poor quality control.
> -M



Poor supplier management. I bet you this is not just a one time error and they used a whole batch of wrong plugs. 

I am quite disappointed especially when this is advertised as “Made in Italy”. So it should have way better quality compared to the china built tools.


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## addertooth (Dec 12, 2020)

DLF,
You do realize that China has bought out a lot of companies in Italy, and flew in their own workers to operate the plants.  This has happened to the shops which did the "fine Italian leatherwork".  This is why they had one of the worst Covid spikes in Europe.


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## DLF (Dec 12, 2020)

Let’s agree to disagree (about the Chinese)

I live in Europe and I like to think I am a well traveled guy. But never seen the case you described (factories full with Chinese workers). And I do work in engineering and have constant contact with many OEMs.

I mean it is cheaper to produce in China and ship it via container freight instead of bringing many many workers from China and paying then European wages and housing. If you want cheap you produce in mainland China, cheapish but better built is Taiwan and usually good quality means Europe or USA. But this is the subject of a different forum topic.

And Fini is one of the better brands, with tradition in making compressors.


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## addertooth (Dec 12, 2020)

DLF, 
I agree why argue.  People are free to google "Chinese workers in Italy" and form their own opinions.  
This way, they aren't unreasonably influenced by our subjective experiences.


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## NC Rick (Dec 12, 2020)

I don't think they brought those workers for low cost, I think they brought those workers because they can sew and work with leather.  I know of one case of that precedent in California with a german immigrant I know who made motorcycle racing leathers.
@Flyinfool sorry I misinterpreted but yes, we agree.  I have a rather rabid dislike for tapered pipe threads.


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## sdelivery (Dec 18, 2020)

Buffalo21 said:


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


Years ago I started in a machine tool rebuild company, we specialized in Devliegs.
During the first week of my employment I was working with the shop Forman on a nearly finished machine...well within ear shot of nearly all the other employees. 
The shop Forman told me they use loctite on a particular fitting that typically loosens during operations. 
I responded with " cross threading is the same as locktite" with a straight face and no pause in what I was working on. 
That was the day they realized I had a sense of humor


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## DLF (Jan 6, 2021)

The 1/2x14 BSPT tap arrived today and I was able to chase the threads. Tapered threads are not common around here so before Christmas I ordered it online from UK.

Verdict: Definitely no cross-threading and the new plug screws in really nice 


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## NC Rick (Jan 6, 2021)

Flyinfool said:


> 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.


Parallel  threads are fantastic assuming there is enough flange on the spigot to properly support the sealing element (oring or crush washer).  To me it looks like you may be stuck with a tapered fitting and goop which will also work.


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## Lo-Fi (Jan 6, 2021)

For a point of reference regarding parallel Vs taper threads in a pressure vessel: I have yet to see parallel threads on any of the heritage steam boilers I work on, all of which have at least a dozen or so tapered "washout" plugs. Larger fittings are always flanges with bolts.
Washout plugs are sealed using nothing more than heavy graphite grease, are removed regularly and _very_ rarely give trouble despite suffering ~200psi pressure and a couple of hundred degrees thermal cycling.

The only caveat I'd add is that tapered threads do require more care when tapping and seating, but you simply won't beat the sealing ability a taper gives, all else being equal.


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## NC Rick (Jan 7, 2021)

I don't know about steam.  How about high pressure gas or hydraulic systems?  Taper threads are rough, have price advantages and simple alignment control.  Reliance of thread wedging as opposed to engineered sealing joins.


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