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what is the standard for female npt depth?

what is the standard for female npt depth?

what is the standard for female npt depth?

(OP)
say i need a 1/2" npt in a valve body. this will be used to feed hydraulic fluid into the valve.

the material i'm tapping is 1" thk. from machinery's handbook, 1/2" npt has effective ext thread length of .5337, yet an engineer says to drill/tap thru.

isn't that rather illogical? how deep is too deep? hand-tight engagement is only .32. running the nipple in will gouge up and destroy the first threads, won't it?

i appreciate any replies.

peace..out. tk369

RE: what is the standard for female npt depth?

The thread that KENAT sited is good. There you will see that depth of an NPT thread is not specified. A 1/2" internal NPT depth is L1 + L3 or .5343 from the Machinery's Table 3. beyond that you would only need your access bore thru.
 For those familiar with Eugene Megyesy's "Pressure Vessel Handbook", there is a nice table in there on "Length of pipe engagement to make a tight joint". For a 1/2" nipple it gives 1/2" engagement to make a tight joint. Megyesy's table is just a little less than L1+L3 for all pipe sizes, and I have found it to be accurate so I use it to calculate pipe lengths needed.

RE: what is the standard for female npt depth?

From "The Pipe Fitters Blue Book" by W.V. Graves, the length of engagement for a "tight joint" for a 1/2 NPT is 9/16"

RE: what is the standard for female npt depth?

The "General rule" is wrap it with teflon tape, tighten it until it won't go no more and check for leaks.

3 or 4 threads at 1/2" NPT - 14 pitch is only .21-.29" and that is probably not going to seal.
 

RE: what is the standard for female npt depth?

Keep in mind gentlemen these are tapered threads. The thread engagement is not the same as straight threads.

RE: what is the standard for female npt depth?

Exactly.  3 to 4 threads is a seal.  (There is no seal on a straight thread, but 10 threads is considered a flame barrier.)  Anymore than 5 threads on an NPT engagement may cause issues with binding.  Teflon thread would help that, but is not 100% as it will just be cut by the threads at a certain point.  If one tigthens to 3 to 4 threads, one generally won't need teflon tape.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

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