View Full Version : NPT-to-NPS?

09-28-2005, 03:29 PM

Can I put together two fittings if one is NPT and another one is NPS
or this must not be done under any circumstances?

Thank you,

- Vitaliy

09-28-2005, 04:58 PM
What is the application? They will screw together, usually loose; but will not make a seal. A typical situation would be the straight threads on faucet inlet; a female tapered adapter will not seal well, but enough teflon sometimes makes it OK!

09-28-2005, 05:54 PM
Hi Jimbo,

Yes, you made a point!
I bought that Ez-Faucet toy. (BTW so far it works OK)
HJ made a very good point about potential cross connection problem.
I don’t like to introduce problems. The solution is to install check valves.
Unfortunately I did not find any 3/8” check valves but I found this things:
Everything looked OK except for the faucet inlet has straight threads but
the above check valves are tapered. Looks like I should not even try
to install them.

- Vitaliy

By any chance does anybody know where to buy correct check valves?
Please, post a link.

09-28-2005, 08:13 PM
With the right adapters you could connect the check valves in between two flexible faucet connector lines.

I estimate you could pay for about 23000 gallons of water with what you have spent on this, but if it makes the wife happy, it's worth every dime!

09-29-2005, 03:41 AM
Hi Jimbo,

So, could you please advice what adaptors to use or which
check valves to buy and WHERE??? to buy them (for some reason
I cannot find these things at all, i.e. place where to buy)?

Thank you,

- Vitaliy

23000 gallons will cost me about $250
So far I spent only about $70 which is about 6500 gallons.
But you are absolutely right – happy wife is a key point!

09-29-2005, 07:31 AM
Let's assume you have a 3/8 compression outlet from your angle stop. A 12" long faucet connector ( 3/8 compr. X 1/2 IPS ) will connect from the stop valve to the input of the check valve. Now, 1/2 IPS close nipple inserted into the outlet of the check valve, and another faucet flex, 12" long, (1/2 IPS X 1/2 IPS) will connect from the nipple up to the faucet. All of these connections are "normal" and very reliable.

Note that the 1/2 IPS ends of the faucet flex connectors are straight threaded nuts, used only for mechanical strength. The rubber gasket makes the seal.

09-29-2005, 04:44 PM
Hi Jimbo,

Your assumption is correct but now I am confused.
OK, valve outlet is a 1/2 FIP.
If I can screw in 1/2 IPS close nipple then why I cannot screw it right on
faucet inlet which is also 1/2 IPS? Combination of 1/2 IPS x 1/2 IPS flex
with 1/2 IPS close nipple looks like faucet inlet extension. Is not it?
And looks like connecting 1/2 IPS flex to the 1/2 MIP valve inlet is also
not a problem.

HJ and Terry warn me not to go this way.
What I am missing here?

Thank you,

- Vitaliy

09-29-2005, 05:56 PM
Well, if I read the arrows correctly, that would be backwards, but more important the outlet from the valve is that straight thread we have been talking about. It is meant to have a nut-connection with rubber gasket seal. Your taper-thread fitting would screw on bu probably leak.

09-29-2005, 06:40 PM
Hi Jimbo,

OK, forget about that valve.
I really would like to understand threading compatibility issue.
It is clear that NPS-to-NPS is OK with gasket seal and NPT-to-NPT
is OK with Teflon Tape and/or Teflon Dope (or both) seal.
But how about NPS-to-NPT, M-F combinations?
Which combination is OK and which one is not?
A link to the site with good explanation is fine.
Looks like IPS-to-MIP with gasket seal is OK. Yes, no?

Thank you,

- Vitaliy

09-29-2005, 08:10 PM
NPS always has to have a gasket of some kind because there is no way to make the threads seal.