Quick query on coupling thread types - does this look right?

[gasket999]

Only a quick one folks, just hoping for some advice.

The fixed airlines in my workshop are all 15mm copper pipe with a few manifolds - the manifolds have PCL AC71 XF female couplings. To get the air from the compressor into the airlines as effectively as possible, I have a big PCL 100-series whip hose ending in a male PCL100 connector - these are the giant ones that give the bigger airflow.

I plan to screw a male threaded but female PCL100 receiver connector straight into the end of the compressor tank - this is only a smaller, mobile compressor so it would be nice to be able to disconnect it from the system where needed.

The compressor arrived today, its one of the new NuAir 3hp ones that are apparently quite quiet (ignore the "HP2" sticker on the tank, its an error). The tank bung was not fitted and it came with a generic female euro connector to screw into the tank. All I'll be doing is replacing this normal euro connector with a big PCL100 alternative.

But here's the query:

The connector that came with the compressor has a flat end to the threaded stem. As if it is going to seal against a flat surface. The PCL100 connector I have ends in a chamfer, as if an olive is going to go into it. Am I OK to screw this PCL100 directly into the threaded boss on the end of the tank or will it leak or damage the thread (I do get confused with pipe threads and tapers).

 

[mtt.tr]

If they are the same thread no issue. Might just require extra PTFE

 

[MoreWellie]

The PCL100 connector I have ends in a chamfer

looking at the picture, the chamfer is above the nut used to screw the fitting in and therefore cannot be expected to seal against anything

 

[gasket999]

looking at the picture, the chamfer is above the nut used to screw the fitting in and therefore cannot be expected to seal against anything

Sorry, I should have clarified it is the difference between the ends of the couplings I was concerned about - the internal chamfer on the PCL100 rather than the one in the brass bit above the thread.

 

[Newlands]

If that was me I’d use a soft copper washer for the end of the PCL fitting to squash into. I’m assuming there is a suitable recess in the fitting on the compressor for a washer to seat on.

 

[gasket999]

If that was me I’d use a soft copper washer for the end of the PCL fitting to squash into. I’m assuming there is a suitable recess in the fitting on the compressor for a washer to seat on.

alas, the connectors wouldn't screw that far into the compressor tank boss. Both the oem supplied connector (all brass) and the PCL100 connector appear to have BSPT (Taper) threads - they have 14 tpi and the nominal diameter of the threads starts at around 21mm and drops to 20mm. As such, I don't think they would screw far enough into the tank to engage a copper washer at the root of the thread.

 

[gasket999]

If they are the same thread no issue. Might just require extra PTFE

yes - just measured and they are the same thread. Just PTFE'd the PCL100 and loosely screwed it into place. Not going to break out the spanners to tighten it until after dinner, so a couple of hours to find out if I'm on the way to making a mistake.

 

[Moose McAlpine]

That chamfer in the bore is just for smoother airflow.

It's the tapered threads that seal it. PTFE it up and bang it in tight.

 

[MoreWellie]

two chamfers, that's sneaky, lol

Have seen parallel thread fittings that have a washer at the top of the thread but not seen a washer at the bottom of the hole

I suspect a look in the end of the tank will show the thread just goes right in and there is no bottom to the hole for a washer to fit against

Providing the threads on the two fittings are the same then just wind the thread on your fitting with ptfe tape and put it in. If the brass one is a taper thread and yours is a parallel you may have issues trying to get it to seal

These connectors don't need much force to seal so don't over tighten it, fit then fill the tank and check for leaks with soapy water

 

[gasket999]

All done - and sitting at 10 Bar nicely

Thanks for the reassurance, everyone.

That chamfer in the bore is just for smoother airflow.

It's the tapered threads that seal it. PTFE it up and bang it in tight.

that would make sense. I think my concern was based on past experience with domestic plumbing: yes you can unscrew the collar from a conex fitting and screw on a flexi hose... but the sharp rim of the conex fitting (which looks a lot like this chamfer) will gradually cut into the o ring in the flexi. I remember my dad telling me off for dong that years ago. I had thought the chamfer had something to do with sealing, but airflow would make more sense.

two chamfers, that's sneaky, lol

Have seen parallel thread fittings that have a washer at the top of the thread but not seen a washer at the bottom of the hole

I suspect a look in the end of the tank will show the thread just goes right in and there is no bottom to the hole for a washer to fit against

Providing the threads on the two fittings are the same then just wind the thread on your fitting with ptfe tape and put it in. If the brass one is a taper thread and yours is a parallel you may have issues trying to get it to seal

These connectors don't need much force to seal so don't over tighten it, fit then fill the tank and check for leaks with soapy water

Yes - good shout, looking in the bore was exactly as you say, there was no lip to seal against .

 

[Moose McAlpine]

Come to think of it, i have a short airline for a hose reel and it has a female threaded end, a compression nut that tightens over a fitting with a radiused end. The chamfer may be for sealing that too.



Like that, i'll get a better picture later.

 

[Moose McAlpine]

Rounded fitting end with compression nut, the male threaded fitting also has the chamfer on the bore:

 

[Munkul]

Those ends look like badly finished BSP hydraulic fittings. As long as they seal, happy days. For the female end you might have to bodge it if you don't have a cone-seal to face/thread seal adapter.