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Female NPT

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Threadquestion

11-27-2007 06:59:10

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Hi All, this isnt much to do with tractors but here goes,this is part of an industrial machine which I am working on
I have a 3 way ball valve , which is threaded 1/2" NPT female at its three outlets. This valve has to have a male NPT connector fitted to each connection however the connections listed on the assembly drawing are NPT but appear to be tapered and do not screw into the valve body only a few turns. However we can get another type of connector with a straight thread 9/16-18 is this compatible with the NPT in the valve body?

Sorry if this sounds a bit silly but i'm not familiar with NPT its usually metric fittings I work on

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Walt Davies

11-27-2007 10:49:17

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Re: Female NPT in reply to Threadquestion, 11-27-2007 06:59:10

If it is straight (not tapered) thread for use with an "O" ring then it will have a machines 45% taper at the mouth of the hole. If not there then its not for use with an "O" ring. These type will have the same threads per in. as the same size pipe and take a special adapter. Walt

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Tom N OK

11-27-2007 08:52:12

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Re: Female NPT in reply to Threadquestion, 11-27-2007 06:59:10

If the valve body is 1/2" NPT use 1/2" NPT connectors and everything will be fine. They only hand thread in part way because of the taper...so have to wrench them up the rest of the way like someone else said.
9/16"-18 straight will not work.

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dobber

11-27-2007 08:39:40

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Re: Female NPT in reply to Threadquestion, 11-27-2007 06:59:10

Check you valve threads like someone else mentioned with thread guage or tap and see what you really have or if someone else already crossed the threads messing them up. I'd bet someone put wrong ends on it sometime and it needs the straight thread industrial fittings with O ring seal. There is also a NSPT or NPST or NPTS ? national straight pipe thread but was usually only made in larger sizes used on older early fire hose fittings.

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johnand cindy

11-27-2007 08:38:31

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Re: Female NPT in reply to Threadquestion, 11-27-2007 06:59:10

Where was the product made? as others have said I would check the threads with a tap for the valve body and a die for the pipe or hose. The drill tap size is 23/32 for 1/2 in.npt and 37/64 for 3/8 npt projection min. .517 min. and .641 max. ream dia large end .7213 hope this helps. John

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nballen

11-27-2007 08:34:03

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Re: Female NPT in reply to Threadquestion, 11-27-2007 06:59:10

Threadquestion,

Not silly at all. NPT is not as well known / understood as the standard bolt threads (UNC / UNF).

As others noted, NPT is a tapered thread, ~1.8 deg from the pipe centerline.

If you have 1/2" NPT, the standards required 14 threads per inch. Therefore the 9/16-18 thread will not fit. You should be able to hand thread the 1/2" NPT nipple into the ball valve ~5/16".

Anymore questions, keep asking!

Nathaniel

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Vern-MI

11-27-2007 08:29:39

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Re: Female NPT in reply to Threadquestion, 11-27-2007 06:59:10

Are you sure it is NPT with a taper? Could it be a JIC/SAE Hydraulic Straight thread requiring an O-ring seal. Usually those industrial machine hydraulic systems require the straight thread fittings to prevent any leakage. A 1/2" taper fitting will start in a straight thread hole but will only go in a thread or two.

I wrote industrial machine specs and one thing we would not allow were the tapered pipe fittings on an oil circuit in an industrial machine because of the leakage.

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Bob From Paradise

11-27-2007 08:03:26

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Re: Female NPT in reply to Threadquestion, 11-27-2007 06:59:10

The thread could also be british pipe thread.

Take a picture of the valve and post it.

What markings are on the valve as to who made it ?

Also try running a tap for the thread that you think it may be.

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Walt Davies

11-27-2007 07:59:48

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Re: Female NPT in reply to Threadquestion, 11-27-2007 06:59:10

NPT threads are all tapered. This so that when put together they tighten up as you screw them in. Your Female threads just may need to be re-tapped to allow the male fitting to go in farther. make sure that they are actually NPT first if a 9/16 bolt will screw in all the way then they may bot be NPT. I would use a thread gage to check them and see if they are what the directions says they are.
Walt

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Emanon

11-27-2007 07:59:35

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Re: Female NPT in reply to Threadquestion, 11-27-2007 06:59:10

Hello, Sometimes the thtrads are cut,but not always a perfect fit , try another nipple or male pipe and see if it goes in any farther. HTH E.

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Will- Tx.-Mn.

11-27-2007 07:09:47

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Re: Female NPT in reply to Threadquestion, 11-27-2007 06:59:10

The NPT is National Pipe Thread,but I'm sure you know that, and it is indeed "tapered threads)

So therefore when you say it only goes in a few turns,you must be speaking of turning it in by hand.. go ahead and tighten it up with a wrench

if it is made of iron or black pipe, perhaps some
pipe goop should be used on the threads.

I know there are others here more knowledgable in this field than me,so I am sure you will receive
some expert advice

~Will

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