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  1. #1
    Super Member Henro's Avatar
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    Default A Simple Hyd. Fitting Question...

    Hi,

    This question is so simple I almost hate to ask it! [img]/forums/images/graemlins/blush.gif[/img]

    Is it standard practice to use NPTF male hose ends to screw into NPSM female swivel fittings?

    I know the NPTF is a taper thread and the NPSM is a straight thread. I have found one reference that states that " a properly chamfered NPTF male will also seal with a NPSM female." I wonder how one would be sure the NPTF end is "properly chamfered?"

    I don't see even one NPSM male fitting in my Northern Tool catalog, so I am guessing the reason why is that everyone just uses NPTF males into NPSM swivel females.

    It sort of goes against my grain to put a taper thread male into a straight thread female. But if it is proven to work then I won't argue with success.

    Is this correct? [img]/forums/images/graemlins/confused.gif[/img]

    PS...I am in the learning process which I hope will lead to a T&T on my tractor... [img]/forums/images/graemlins/cool.gif[/img]

  2. #2
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    Default Re: A Simple Hyd. Fitting Question...

    Check here NPTF and NPSM

    and here for the full index full thread index

  3. #3
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    Default Re: A Simple Hyd. Fitting Question...

    Forget Northern Tool for hydraulic stuff. The best places on the internet to get hydraulic fittings and hoses are

    hydraulichosefittings.com

    and

    fittingsandadapters.com

    I think they are both parts of the same company.

  4. #4
    Gold Member uhmgawa's Avatar
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    Default Re: A Simple Hyd. Fitting Question...

    </font><font color="blue" class="small">( Is it standard practice to use NPTF male hose ends to screw into NPSM female swivel fittings?)</font>

    Yes. NPTF hose ends have an internal 30-degree taper which mates
    with a NPSM female. Note NPSM threads are not tapered, do not seal
    via threaded engagement, but seal via the internal 30-degree taper.
    Thus sealing compounds are not required.

    </font><font color="blue" class="small">( I wonder how one would be sure the NPTF end is "properly chamfered?")</font>

    It is the 30-degree taper as above.

    </font><font color="blue" class="small">( I don't see even one NPSM male fitting in my Northern Tool catalog, so I am guessing the reason why is that everyone just uses NPTF males into NPSM swivel females.)</font>

    That catalog belongs in the outhouse IMHO. Try Blum Hydraulics,
    Baileys, Prince Outlet, or Surplus Center for people who know what
    they sell.

    Anyway, any fitting that swivels will mate via the internal taper.
    The swivel nor thread is capable of achieving a seal.

    </font><font color="blue" class="small">( It sort of goes against my grain to put a taper thread male into a straight thread female. But if it is proven to work then I won't argue with success.)</font>

    That is the design of NPSM. The internal taper engages before the male
    taper thread can snug in the straight female thread.

    Other thread standards you are likely to encounter are the JIC 37-degree
    taper (found primarily when joining hydraulic tubing) which has
    straight threads and seals via taper as well as the SAE O-ring standard
    which has straight threads and seal via the o-ring being held captive
    between the female tapered cavity and the external wall of the male
    component.

    Note NPT is not the same as NPTF, the former always requiring a
    sealing compound as the threads are not cut to close mate. The latter
    is cut to close mate and does not require a sealing compound. However
    after initial use the threads will distort due to metal-metal contact
    and normally require use of a sealant for subsequent reuse.

  5. #5
    Super Member Henro's Avatar
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    Default Re: A Simple Hyd. Fitting Question...

    MadReferee,

    I was looking at those sites last night, but I did miss where your first link says "If the male [NPTF as I read it] has a 30- seat it will mate with the 30- cone seat in the NPSM straight thread swivel female, usually found on adapters, and is mechanically held together by the threads. "

    This is the second place I have seen this stated.

    But still, it is a taper thread going into a straight thread...

    Is it safe to assume then that this is what people (including manufacturers) normally do?


  6. #6
    Super Member Henro's Avatar
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    Default Re: A Simple Hyd. Fitting Question...

    Hi Uhmgawa,

    <font color="blue"> That catalog belongs in the outhouse IMHO. Try Blum Hydraulics,
    Baileys, Prince Outlet, or Surplus Center for people who know what they sell.</font>

    I know what you mean, but was using that as a possible indicator...of what people might be doing, since they did not offer a NPTF to NPSM adapter...

    <font color="purple"> ( It sort of goes against my grain to put a taper thread male into a straight thread female. But if it is proven to work then I won't argue with success.) </font>

    <font color="blue"> That is the design of NPSM. The internal taper engages before the male taper thread can snug in the straight female thread. </font>

    I understand that part, but is the internal taper of the NPTF part of the design spec for the NTPF male? If so that would answer part of my question. I questioned that because I had seen it stated that if the NTPF male had an internal chamfer then it would work...

    While the taper NPTF thread will screw into the strait NPSM female, it seems to me that it would not have the same mechanical holding power that a NPSM male would (which would be a straight thread). This has nothing to do with the seal, which occurs between the two 30 degree surfaces, I know...

    I guess the difference is not that much in practical terms though, if it is common to use the tapered thread in straight thread swivels.

    Thanks for the help!

  7. #7
    Gold Member uhmgawa's Avatar
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    Default Re: A Simple Hyd. Fitting Question...

    </font><font color="blue" class="small">( But still, it is a taper thread going into a straight thread...

    Is it safe to assume then that this is what people (including manufacturers) normally do? )</font>

    Yes. It was a compromise between creating a taper seal standard given
    the existing NPT standard.

  8. #8
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    Default Re: A Simple Hyd. Fitting Question...

    I would be more concerned the the "seal" than the mechanical holding of the threads. I have mixed and matched on tractor applications with no problems.

    Here is one for you, according to Jim McC at Integration Engineering, the fittings on their cylinder check valves are 3/8 BSPP. My tilt cylinder should be here today or tomorrow then I will have to order the BSPP to NPxx adapter.

    BTW, for those who are confused by NPxx terminology, here is the breakdown:

    NPT- National Pipe Taper. Pipe thread per ANSI B1.20.1
    NPTF- National Pipe Tapered for Fuels. Same as above except dry-seal per ANSI B1.20.3
    NPSH- National Pipe Straight Hose per ANSI B1.20.7
    NPSM- National Pipe Straight Mechanical. Straight thread per ANSI B1.20.1
    NPSL- National Pipe Straight Loosefit per ANSI B1.20.1
    BSPP, BSPT- British Standard Pipe Parallel, British Standard Pipe Taper. BS21.

  9. #9
    Gold Member uhmgawa's Avatar
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    Default Re: A Simple Hyd. Fitting Question...

    </font><font color="blue" class="small">( I understand that part, but is the internal taper of the NPTF part of the design spec for the NTPF male? If so that would answer part of my question. I questioned that because I had seen it stated that if the NTPF male had an internal chamfer then it would work...)</font>

    NPT/NPTF does not specify the 30-degree internal taper.
    However hose connections do have this taper. In the rare
    case you need to connect a NPT/NPTF male to a NPSM female
    it would be a simple matter to turn the taper with a small lathe.

    Most NPT/NPTF often have a chamfer relief cut in the internal
    tip which may be confused with a 30-degree taper. This is just
    to dress the edge and is not reliable to mate with the taper in the
    NPSM connector.

    </font><font color="blue" class="small">( While the taper NPTF thread will screw into the strait NPSM female, it seems to me that it would not have the same mechanical holding power that a NPSM male would (which would be a straight thread). This has nothing to do with the seal, which occurs between the two 30 degree surfaces, I know...)</font>

    True technically but the strength difference is not an issue in practical
    usage.

    NPT/NPTF is about the worst way to make a sealed connection and is
    only still haunting us for historical reasons. It can be problematic to
    seal when you require a fitting to be in a particular orientation which is
    fairly common. You will find most of the hydraulic plumbing on your
    machine to be JIC-37 and SAE O-ring. The only place you are likely to
    encounter NPT/NPTF is in the front hydraulic block and on any
    quick-connects present.

    That said as long as ASAE cylinders show up with NPT ports we'll
    never be rid of this archaic standard.

    Incidentally to circumvent the entire issue of dope vs. teflon tape I'd
    recommend an anaerobic sealant such as Loctite 545 which is specifically
    designed to seal NPT/NPTF hydraulic threads. As you don't need to
    mechanically torque the threads to full closure this help alleviate the
    fitting orientation problem as well.

  10. #10
    Gold Member uhmgawa's Avatar
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    Default Re: A Simple Hyd. Fitting Question...

    </font><font color="blue" class="small">( NPT- National Pipe Taper. Pipe thread per ANSI B1.20.1
    NPTF- National Pipe Tapered for Fuels. Same as above except dry-seal per ANSI B1.20.3
    NPSH- National Pipe Straight Hose per ANSI B1.20.7
    NPSM- National Pipe Straight Mechanical. Straight thread per ANSI B1.20.1
    NPSL- National Pipe Straight Loosefit per ANSI B1.20.1
    BSPP, BSPT- British Standard Pipe Parallel, British Standard Pipe Taper. BS21.)</font>

    Enough to have you screaming into your pillow. I suspect a conspiracy
    brought on by adapter manufacturers. SAE ORB and JIC-37 are far
    superior but haven't yet displaced NPT on Ag equiment though
    they have been around for 50-80 years respectively. Ironically they are
    running out of design margin w/r/t maximum pressure and other
    standards have sprung up to address this limitation.

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