Who knows about pipe threads? NPT and NPS?

[stephenspann27]

A while back I bought summit mechanical gauges. I'm just now getting around to installing the "temp probe." I'm putting it in-line in the upper radiator hose. I bought a 1.25'' piece of galvanized pipe to put in the upper radiator hose. I plan to drill a hole in the side of it, and thread in the temp probe. The temp probe threads are 1/2'' straight pipe thread .(NPS). After driving all over town.. the only pipe tap I could find was a NPT 1/2'' tap (tapered).
However, I threaded the temp probe piece into a couple pieces of pipe at the store which probably had tapered threads, and it threaded in fine. I went ahead and bought a NPT1/2' tap ($18..) but I haven't taken it out of the package.. Since the pipe gauge is fairly light, and the threaded area would be fairly short.. could I get away with using the tapered tap, even though the piece I'm threading in is straight?

Here is a pipe thread chart:
http://mpi-online.com/technical/tap-drill.htm

 

[5-90]

NPS and NPT, as I recall, aren't quite compatible. The taper is what seals the joint (theoretically - I'll stick PTFE dope in there anyhow.) I'm surprised that you've got a NPS probe - NPS is fairly rare outside of specific industrial settings.

1) Are you sure that the threads on the probe are NPS? How so?

2) Have you taken the probe to the plumbing department at the hardware store and done a test-fit against 1/2" NPT? Just curious (I don't think they're compatible, but I've been wrong before...)

The taper on NPT isn't great - it's something like 5/8" per foot. If you're not sure of what you're looking for, you'll probably miss it...

 

[stephenspann27]

There reason why I think its NPS and not NPT is because I used dial calipers on the OD threads on at both ends and its the same OD..


I did thread it into what I assume was a NPT fitting.. but I didn't thread it real far.. just a few turns..

 

[stephenspann27]

I used the paste.. and also put silicon over the paste.. just for extra insurance.. and it's seeping.. :-( the silicone takes 24 hrs to fully cure so I'm holding out a little hope that after the silicone cures it will stop leaking. But I bet more than likely I'll have to take it apart and use teflon tape this time.

 

[stephenspann27]

I went ahead and redid it with teflon tape, and new silicone.. I'll give it a couple days to cure and try again.. if that doesn 't work.. I may try JB weld..

 

[hubs97xj]

The local hardware stores have small displays in their plumbing sections- a bunch of fittings carded, and labelled as to the size and connection type. I'd check your sender against one of those, but I'll wager it's NPT, not NPS.

Something else to consider- you can buy adapters for either the rad or heater hoses that accept temp senders, and shouldn't need any cobbling together. Drilled and tapped for NPT threads.

 

[RCP Phx]

Thats the problem with mechanical gauges(they tend to use straight threads),most electric use pipe threads.

 

[westvirginia24976]

I've certainly heard of NPT, but not NPS. What I wonder is if the gage is setup for a compression fitting and is missing the nut and ferrule. I agree a water temp probe should be NPT. Some oil pressure gages are compression. :dunno:

 

[stephenspann27]

I've certainly heard of NPT, but not NPS. What I wonder is if the gage is setup for a compression fitting and is missing the nut and ferrule. I agree a water temp probe should be NPT. Some oil pressure gages are compression. :dunno:

you may be on to somthing... it still leaks after using teflon tape.. going to have to peel the silicon off, and see if I can where its leaking from.. which thread..

 

[stephenspann27]

I figured out that it is for sure leaking where I have it screwed into the piece of pipe that I drilled and taped.. so the gauge set up is fine.... no leaks.. I just need to either buy a kit (I didn't know they existed) or find a T-fitting that is 1.25''

 

[stephenspann27]

I'm a little closer now.. I went to Lowes..and the closest thing I could find was a 1x1x1/2 T fitting.. I screwed 1'' couplers into each end.. and slid the radiator hose over those. The summit gauge probe threads into it perfectly and does not leak a bit.. however.. I'm getting some seapage around the where each radiator hose slides onto the pipe threads. I'm not sure if its coming through the threads between the coupler and T fitting, or if its getting out between the hose and threads.. thinking about heavily wrapping the threads with teflon tape.. then sliding the hoses back on..

 

[hubs97xj]

How about a proper temp sender adapter, either on the rad hose or the heater hose? Maybe putting a second port in the Tstat housing? That's getting a little janky, imho.

btw, that's NPT, which I believe was pointed out initially.

Gah, here we go. Couldn't find the pic and link. Not my junk, but I got this from another forum guy.

http://motors.shop.ebay.com/items/?...w=ac+autotechnic+water+temp+adapter&_osacat=0

 

[souske]

At least go get some proper barbed adapters. that should take care of the leak

 

[stephenspann27]

Thanks guys. Keep in mind... I wasn't trying to be cheap.. I didn't know such a thing existed off the shelf.. This kinda sux because I've already spent well over $16 trying to get this working the ghetto way.. The challenge now is finding an off the shelf in-line adapter that is near the correct size. The NPT fitting needs to be 1/2'' and the barbed hose ends need to be as close to 1.25'' as possible. I haven't been able to find one with those dimensions yet.

 

[hubs97xj]

I didn't either, and wound up with the rad probe. My fan controller will also work with a screw in sender, but I got conflicting info on the sizes at the time.

If you search "water temp adapter" or some such, you can find a lot of different sizes. There are a few that are 1.25" (32mm?), but I think most accept 1/8 senders. Some appear to be large enough to drill out for a larger sender, but I didn't want to order one until I was sure it would work. Not sure how feasible it is to try to step down in size to fit your sender to those adapters- I got my setup working and told myself to leave well enough alone.

 

[stephenspann27]

I wonder what the guy did to get his setup working in the pic above.. maybe he drilled one out? I do have a drill and tap for 1/2'' pipe thread now.. but I hate to risk it. I may try welding my ghetto pipe fitting.. I know weld won't stick well.. but I may try to weld the seam around the couple/fitting, and build up the couplers with weld.. Or.. JB weld maybe?

 

[stephenspann27]

At least go get some proper barbed adapters. that should take care of the leak

I think 1'' barbed fittings will be tough to find.. I"m looking.

 

[kastein]

1" actual or 1" trade size? 1" trade size is pretty close to a garden hose I think, check the plumbing aisle in home depot that has the water heaters and sump pumps in it. They have about a 20 foot stretch of wall with nothing but small brass pipe fittings.

 

[stephenspann27]

The radiator hose ID is really about 1.25'' ... 1'' is bigger than you think.. I'll check it out though.

 

[stephenspann27]

I found barbed fittings at Ace hardware, however the 1'' ones are way too small on the barbed section.. however the 1.25'' ones like good.. the problem is.. 1.25'' T fittings don't have a 1/2'' NPT where the sensor goes it.. I'm, going back to Lowes.. may be able to use a reducer..