HPA Thread Sealing?



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Offline falvesjr

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HPA Thread Sealing?
« on: September 11, 2018, 12:31:59 PM »
Hey Guys,

I'm about to put some HPA fittings together and was wondering what you use to seal the connections, if anything. I know some fittings come with a gray paste pre-installed, but most don't. I've read many previous threads here that point to several options, but I can't really see a consensus on what's best...

Would appreciate if you can take the poll and/or leave a comment below with your thoughts.

Thanks!
« Last Edit: September 11, 2018, 12:55:23 PM by falvesjr »
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Offline Taso1000

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Re: HPA Thread Sealing?
« Reply #1 on: September 11, 2018, 12:47:07 PM »
Fernando,

HPA fittings do not seal via tape, pastes or liquids.  NPT threads are tapered and seal as the threads compress against each other.  BSPP threads are straight and seal against a washer.

The paste's and tapes sole purpose is to provide lubrication to the threads so that they don't bind prematurely.  If you can't get a tapered thread to seal there must be a defect in one of the threads.

I have used Vibra-Tite 444 thread sealer on hpa threads and even after curing for 48 hours before applying pressure I had a leak the first time I pressurized to about 3300 psi.  Once I swapped the fittings, no more leak.  So there was a defect in the threads.

Thanks,

Taso
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Offline falvesjr

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Re: HPA Thread Sealing?
« Reply #2 on: September 11, 2018, 12:54:32 PM »
HPA fittings do not seal via tape, pastes or liquids.  NPT threads are tapered and seal as the threads compress against each other.  BSPP threads are straight and seal against a washer.

Taso,

Thanks for that! It was my feeling too, but there are so many posts about using this or that to seal HPA threads on this forum that I was thoroughly confused.

Cheers,
F
  • USA, IA, Johnston
• Umarex Gauntlet .22 - UTG 4-16x44 30mm AO SW
• Gamo Swarm Maxxim .22 - UTG 3-12x44 30mm AO SW
• Stoeger F40 .22 - UTG 3-12x44 30mm AO SW
• SIG ASP20 .22 - UTG 3-12x44 30mm AO SW
• Diana Chaser Carbine Kit .177 - Red Dot/Laser/Flashlight
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Offline Taso1000

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Re: HPA Thread Sealing?
« Reply #3 on: September 11, 2018, 01:43:31 PM »
I honestly thought the cured Vibra-Tite would act like a sort of o-ring type, squeezed into the void seal in the tapered threads. 

Like I stated earlier it held to about 3300 psi.  There's no guaranty it would have held like that indefinitely after repeated hpa cycles below 3300 psi. 

So your mileage may vary.   ;D

Thanks,

Taso
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Air Arms Pro-Sport .177, T200
BAM B50 .22, 5 X B51 .177
Benjamin 392PA, H9A .177, Marauder .25
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Crosman 1720T, 2100, 2240 W/ 2300S valve and barrel
Daisy CMP 853
Diana 340 N-TEC .177
FWB 124, 300S Mini, 601
2 X FD PCP .177
RWS 48 .177
Weihrauch HW100 T FSB Laminate, HW97 nickel synthetic
Xisico B26 .177, 2 X Sentry 702-3, .177 and .25, XS12 .177, XP-120D, XS-25 .177, XS-28 .22, .25, .177 barrels

Offline T3PRanch

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Re: HPA Thread Sealing?
« Reply #4 on: September 11, 2018, 01:44:07 PM »
On NPT fittings I use a Grey / Black Teflon tape to prevent gauling of the fittings like seen on Ninja fill assembly threads. I used to do ultra pure gas plumbing and although yes the threads are the sealing surface without Teflon tape there is a molecular migration of gas through the threaded area that will not pass helium leak checking (read that as a micro leak). Other fittings according to manufacturer recommendations.
« Last Edit: September 11, 2018, 01:48:35 PM by T3PRanch »
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Offline Fly

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Re: HPA Thread Sealing?
« Reply #5 on: September 11, 2018, 03:18:42 PM »
White Teflon tape works for me in sealing straight & tapered threads. Been using it for 30 years.

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Offline Bigragu

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Re: HPA Thread Sealing?
« Reply #6 on: September 20, 2018, 10:54:02 PM »
Teflon tape with a thin coat of Nylog. Look up the specs on Nylog. Made to seal high pressure refrigerant piping. Can’t remember where I saw it, but a drop of it on your finger will stretch out to like almost 3’.

Also allows easy disassembly of parts later on down the road. Remains flexible. I’ve used that for most fuel and transmission line thread on assemblies, including brake line fittings that were questionable. Never a leak.
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Offline Gippeto

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Re: HPA Thread Sealing?
« Reply #7 on: September 21, 2018, 09:44:27 AM »
I use mostly blue loctite on clean/grease free fittings and let it set overnight before using. For stainless on stainless, I like the higher density teflon tapes, I don't like pipe dopes.

Straight threads get an o-ring or a bonded washer/dowdy seal depending upon design.

Al
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