Persistent leaks on high pressure fittings (thread sealant)? - Page 2
Close
Login to Your Account
Page 2 of 3 FirstFirst 123 LastLast
Results 21 to 40 of 44
  1. #21
    Join Date
    Nov 2018
    Country
    UNITED STATES
    State/Province
    Michigan
    Posts
    607
    Post Thanks / Like
    Likes (Given)
    317
    Likes (Received)
    362

    Default

    Quote Originally Posted by gustafson View Post
    I am pretty sure you want to spot face the tube to make a space for a washer and that will take care of your problem
    I would also be careful not to thin the tube too much when you do so, per the high pressure vs. wall strength discussion above.

    Seems like a testament to the stuff you're using that it gets you sealed up on straight threads to the pressure it does. As soon as you said straight threads, my immediate impression was that it should include a face seal.

  2. #22
    Join Date
    May 2017
    Country
    FINLAND
    Posts
    2,437
    Post Thanks / Like
    Likes (Given)
    659
    Likes (Received)
    1131

    Default

    Quote Originally Posted by Limy Sami View Post
    With thanks to Mark Rand and others

    Now we have the answer -( I think ) ..........you are using the correct mounting ''female'' fitting

    Because IME pressure gauges with straight threads are sealed on the end face with a washer (copper / fibre / bonded seal etc etc) and not on the threads - which are only there to provide the clamping force for the sealing face.

    If it's leaking past the threads it means the face seal isn't working.
    Pressure gauges are not leaking, leak is between the pressure manifold and pressure gauge adapters. Apparently pushed my luck too far with the straight threads and sealant.
    Has been working fine previously on small fittings but seem like I run out of my luck this time.

    I have used similar gadget with glued BSPP (straight threads) to at least 600 bar pressure without leaks.
    This time had slightly different fittings: Spradow rotating test couplings, still the same 1/8" BSPP. Dunno if the thread is eeny weeny looser fit, is it the zinc plating or did I just run out of dumb luck.

    Spradow test coupling (Yes, only rated for 630 bar(9000 PSI) working pressure but I'm not overly concerned if they fail in a system with one teaspoon of oil inside.)

  3. #23
    Join Date
    Jan 2009
    Location
    Maine, USA
    Posts
    220
    Post Thanks / Like
    Likes (Given)
    124
    Likes (Received)
    104

    Default

    As has been said BSPP to BSPP requires o-ring or copper washer. No sealant needed. Throw a BSPT in the mix and you use sealant, but can’t imagine it’d be good to 14,000 psi.

  4. #24
    Join Date
    Sep 2002
    Location
    People's Republic
    Posts
    5,230
    Post Thanks / Like
    Likes (Given)
    620
    Likes (Received)
    3242

    Default

    Quote Originally Posted by MattiJ View Post
    Pressure gauges are not leaking, leak is between the pressure manifold and pressure gauge adapters. Apparently pushed my luck too far with the straight threads and sealant.
    Has been working fine previously on small fittings but seem like I run out of my luck this time.

    I have used similar gadget with glued BSPP (straight threads) to at least 600 bar pressure without leaks.
    This time had slightly different fittings: Spradow rotating test couplings, still the same 1/8" BSPP. Dunno if the thread is eeny weeny looser fit, is it the zinc plating or did I just run out of dumb luck.

    Spradow test coupling (Yes, only rated for 630 bar(9000 PSI) working pressure but I'm not overly concerned if they fail in a system with one teaspoon of oil inside.)
    I am sure it has worked previously,. but it aint right

    Whitworth is a nice thread profile, side load it with a little goo or tape and yeah, it probably will seal.

    Looking at the pic, sure you aren't winding a BSPT into a BSPP or something? I would think the BSPP would just bottom out

  5. #25
    Join Date
    Jul 2007
    Country
    UNITED KINGDOM
    Posts
    5,211
    Post Thanks / Like
    Likes (Given)
    3120
    Likes (Received)
    2639

    Default

    Quote Originally Posted by Limy Sami View Post
    It's not 200psi Mark it's 1000 bar

    Damn, where did I pick up 2000psi from? We actually worked at 2200psi=150 bar, but not 1000bar...

    Anyway, back to the problem:- The wonderful thing about Dowty seals is that the higher the pressure, the better they seal, because they are a V shaped neoprene seal backed up by a steel washer. The same principle that is used with the gaskets on steam turbine pipe joints (although those are wound 'V' section steel strip). They also don't need annealing like copper washers.

  6. #26
    Join Date
    Sep 2010
    Location
    Oklahoma City, OK
    Posts
    5,288
    Post Thanks / Like
    Likes (Given)
    976
    Likes (Received)
    2278

    Default

    My buddy used to work hi-pressure nitrogen stuff. 50-60ksi in 1" SS tube you could barely slide a pencil through. They'd thread and bevel the tube directly, slip on a tube nute like swagelock, then screw a collar into the threads.

    Nut pulled against the collar and smashed the two tapered faces together. Sealed up tight.

    That has nothing to do with the OP's problem, but it's fun to see how different high pressure issues are solved.

  7. #27
    Join Date
    May 2017
    Country
    FINLAND
    Posts
    2,437
    Post Thanks / Like
    Likes (Given)
    659
    Likes (Received)
    1131

    Default

    Quote Originally Posted by Mark Rand View Post

    Anyway, back to the problem:- The wonderful thing about Dowty seals is that the higher the pressure, the better they seal, because they are a V shaped neoprene seal backed up by a steel washer. The same principle that is used with the gaskets on steam turbine pipe joints (although those are wound 'V' section steel strip). They also don't need annealing like copper washers.
    I willing to push my luck with the fitting pressure ratings as they usually have 3x or 4x safety margin. But Dowty seals are getting bit too marginal if 1/8" Dowty has 930 bar min BURST pressure

    In case our American cousins are not familiar with the brand Dowty = bonded seal = Usit. Around here they go usually with the name "Usit"..Swedes probably use "Tredo" from Trelleborg

  8. #28
    Join Date
    Nov 2018
    Country
    UNITED STATES
    State/Province
    Michigan
    Posts
    607
    Post Thanks / Like
    Likes (Given)
    317
    Likes (Received)
    362

    Default

    Quote Originally Posted by MattiJ View Post
    I willing to push my luck with the fitting pressure ratings as they usually have 3x or 4x safety margin. But Dowty seals are getting bit too marginal if 1/8" Dowty has 930 bar min BURST pressure

    In case our American cousins are not familiar with the brand Dowty = bonded seal = Usit. Around here they go usually with the name "Usit"..Swedes probably use "Tredo" from Trelleborg
    And here in the states we call 'em stat-o-seals 'cause that's the Parker brand name.

    I've got 52 ksi of hoop stress on a washer with .380" ID and .500" OD on the back of my napkin, I know we got some beefy ones upstairs, I might see if I can throw the calipers on a few and see what's laying about.

    You can give yourself a safety factor by spot-facing below the surface of the tube, but again, weakening that tube might not be the best idea.

  9. #29
    Join Date
    Jul 2007
    Country
    UNITED KINGDOM
    Posts
    5,211
    Post Thanks / Like
    Likes (Given)
    3120
    Likes (Received)
    2639

    Default

    1/8"BSP seal should have a rminimum burst pressure rating of ating of 1480bar.

    http://www.potterassoc.com/pdf/bonde...zing_chart.pdf

  10. Likes MattiJ liked this post
  11. #30
    Join Date
    Nov 2018
    Country
    UNITED STATES
    State/Province
    Michigan
    Posts
    607
    Post Thanks / Like
    Likes (Given)
    317
    Likes (Received)
    362

    Default

    Quote Originally Posted by Mark Rand View Post
    1/8"BSP seal should have a minimum burst pressure rating of 1480bar.

    http://www.potterassoc.com/pdf/bonde...zing_chart.pdf
    The washer listed in that catalog for 1/8 BSPP are 5/8" OD, which brings our hoop stress down to 37 ksi. That gives us a comfortable safety factor on any halfway decent steel. Don't know why I saw fit to calculate that out, but there we have it.

  12. Likes Mark Rand, gustafson liked this post
  13. #31
    Join Date
    May 2017
    Country
    FINLAND
    Posts
    2,437
    Post Thanks / Like
    Likes (Given)
    659
    Likes (Received)
    1131

    Default

    Machined new distribution block, this time from 20x20mm 1045 square bar so that I can use face seals if needed.
    Being stubborn and wanting to know more I decided to dig further: Had to try with thread sealant first.
    One leaking thread out of 8 and 7 are holding up fine to tad over 1000 bar.
    Leaky one is about 2 drops of oil in half an hour @>900bar.

    Went with smaller tap this time as the 1/8" male thread on the test couplings is probably quite close to lower limit judging by how sloppy it feels in 1/8" BSPP thread die.

    Sooo... if you are going to abuse parallel thread joints with thread sealant past any ratings its better to not use overly sloppy thread.

    Same sealant as before: Loctite 577. Up to 10000 psi
    "LOCTITE® 577 is a medium strength, general-purpose thread sealant for parallel/parallel and taper/parallel threads and fittings. "

  14. #32
    Join Date
    Apr 2015
    Country
    AUSTRALIA
    Posts
    837
    Post Thanks / Like
    Likes (Given)
    39
    Likes (Received)
    190

    Default

    They have your answer...however if the manifold is round you need to spot it so it has a flat face to seal for the dowty, or change it if the wall is reduced to much by spotting.

  15. #33
    Join Date
    Sep 2007
    Location
    Maryland near DC
    Posts
    366
    Post Thanks / Like
    Likes (Given)
    84
    Likes (Received)
    75

    Default

    You can buy a lot of useful bits from High Pressure Equipment Company. Their low pressure line goes to 1000bar. If you need higher they go all the way up to 10,000bar. The nice thing about their stuff was not only was it leak tight under pressure, but if you pulled vacuum on it it was leak tight there was well. Specifically we used the 1/16” 15,000 psi taper seal line. It is also very low dead volume if that matters to you.

    HiP | We are High Pressure | A Leader in High Pressure Products

  16. #34
    Join Date
    Jul 2011
    Country
    UNITED STATES
    State/Province
    Pennsylvania
    Posts
    244
    Post Thanks / Like
    Likes (Given)
    41
    Likes (Received)
    36

    Default

    I used triple wrapped and doped fittings and handle up to 15000 psi hydrogen. And of course having fittings that arent undersized helps. Ive noticed lots of the new swagelock stuff is undersized.

  17. #35
    Join Date
    Oct 2017
    Country
    UNITED STATES
    State/Province
    California
    Posts
    748
    Post Thanks / Like
    Likes (Given)
    199
    Likes (Received)
    226

    Default

    I used loctite 545 for all of my hydraulic and pneumatic stuff no problem. Used it again to plumb in a bunch of fancy air filters for a laser and general plumbing to a few machines and of course the compressor/tank. I get to redo most of it because the loctite is bubbling like soapy water at every joint.

    I had used the last of one bottle for some of it, which worked fine, then used my other bottle on the rest and those are the parts giving me issue. Turns out that first bottle was a year old, but the second bottle was two years old. Apparently the lifetime for that stuff is something like 6 months after opening it.

    Can't say I've ever used it on anything above 3000 psi, but I've sure used it on some sloppy fittings and those terrible chinese fittings with a huge sharp cut in a line down all of the female threads where teflon just couldn't do it.


    I will say that I hate pipe dope with a passion. At my last job I had to replace a lot of leaky connections, and the ones done with pipe dope always failed well before any of the teflon ones did. It could very well be that they were installed wrong, but for anything prone to twisting loads I use teflon where possible.

  18. #36
    Join Date
    May 2017
    Country
    FINLAND
    Posts
    2,437
    Post Thanks / Like
    Likes (Given)
    659
    Likes (Received)
    1131

    Default

    Quote Originally Posted by nissan300ztt View Post
    I used triple wrapped and doped fittings and handle up to 15000 psi hydrogen. And of course having fittings that arent undersized helps. Ive noticed lots of the new swagelock stuff is undersized.
    That sucks.
    Stainless fittings are usually closer tolerance. Test couplings(galvanized or something similar) that I used were so much smaller than some other fittings that I actually used the intermediate tap in the three tap set. (mainland Europe style serial taps with smaller pitch diameter on intermediate tap, not same as plug&taper system usually used in US)

  19. #37
    Join Date
    Mar 2007
    Location
    On Elk Mountain, West Virginia, USA
    Posts
    2,155
    Post Thanks / Like
    Likes (Given)
    990
    Likes (Received)
    756

    Default

    I have worked with and designed seals for pressures up to 200KPSI. The key is to realize that everything will distort, and to design so that your seal improves/clearance decreases/mating force increases as the parts distort.

    O-rings do that at low and medium pressures, moving to occlude leak paths, and getting pressed against the surfaces by the pressure. Problem with O-rings is that rubber is soft and if there is a gap, either on assembly or after the parts stretch under load, the O-ring will extrude through it.

    The stat-o-seal works like an O-ring, and as long as the straight thread is torqued so that the elastic axial pre-load exceeds the pressure load, no clearance will develop and the joint will hold until the washer (or something else) bursts. One poster mentioned that you can sink the washer into a shallow counterbore/spotface to support it.

    Sealing a straight thread with goop relies on the long-term viscosity or creep resistance of the goop along the thread clearance.

    Here is a chart that shows BSPP threads used to capture an O-ring against a spot-face, within a washer...says use for low pressures BSPT & BSPP Threads – RYCO Hydraulics

  20. Likes BoxcarPete liked this post
  21. #38
    Join Date
    Feb 2010
    Location
    ch
    Posts
    2,806
    Post Thanks / Like
    Likes (Given)
    234
    Likes (Received)
    378

    Default

    just a thought: anaerobic locktite has very low shear strenghts on zink. no idea about sealing compound.

  22. #39
    Join Date
    May 2017
    Country
    FINLAND
    Posts
    2,437
    Post Thanks / Like
    Likes (Given)
    659
    Likes (Received)
    1131

    Default

    Quote Originally Posted by dian View Post
    just a thought: anaerobic locktite has very low shear strenghts on zink. no idea about sealing compound.
    That what I had also in my mind.
    I re-applied glue to that last leaking thread and now they all hold 1000 bar test without any leak. Including two M5 machine screws used to plug the bore holes.

    So:
    -tighter tolerance threads
    -cleaning the fittings with die to get most of the plating off
    -apply sealing compound to both female and male part

    Still parallel thread and no face seals.
    (I wanted to avoid the empty convoluted space created by standard BSPP fitting sealed with face seal. Difficult to de-gas and any gas is pain in the butt on pressure calibration system)

  23. #40
    Join Date
    Jul 2007
    Country
    UNITED KINGDOM
    Posts
    5,211
    Post Thanks / Like
    Likes (Given)
    3120
    Likes (Received)
    2639

    Default

    Are you using a dead weight tester or some other method to calibrate the gauges?


Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •