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Old 30-11-2020, 09:13   #1
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Installing a faucet - NPS thread vs NPT

I am trying to install a new faucet on the boat and am running into a few issues. I searched on the forum, but couldn't find a clear answer to my question.

I have 5/8 hose for my fresh water system. The faucet is a NPS-M 1/2 inch connector (straight threads) All the hose barb fittings I have been able to find online are 1/2 inch Female NPT (tapered). I believe the NPS-M fittings require a rubber gasket on the bottom to seal properly, but I'm not 100% sure here. I don't think I can just run the 1/2 NPT connectors onto the 1/2 NPS connectors. I need something to convert from 5/8 inch hose to plug into the NPS-M 1/2 inch connections on the faucet. Do you have any recommendations here? It seems like others would have run into this issue as well.

I am in Mexico so will need to get parts shipped in to finish this installation so there isn't a home depot close by.
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Old 30-11-2020, 09:43   #2
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Re: Installing a faucet - NPS thread vs NPT

Two options:

1. Order an adapter 1/2" NPS-F to NPT. Here's one that goes to 3/4" MNPT. Then work from there to your hose barb.

2. Go to the hardware store in Mexico and buy a faucet connector hose with the required 1/2" NPS-M connector on one end and whatever on the other end. Cut the other connector off the hose and then use barbed fittings of the right size to connect the hoses. Most faucet hoses are 3/8" or 1/2" so you'll need a reducing barb.
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Old 30-11-2020, 09:50   #3
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Re: Installing a faucet - NPS thread vs NPT

Quote:
Originally Posted by Dsanduril View Post
Two options:

1. Order an adapter 1/2" NPS-F to NPT. Here's one that goes to 3/4" MNPT. Then work from there to your hose barb.

2. Go to the hardware store in Mexico and buy a faucet connector hose with the required 1/2" NPS-M connector on one end and whatever on the other end. Cut the other connector off the hose and then use barbed fittings of the right size to connect the hoses. Most faucet hoses are 3/8" or 1/2" so you'll need a reducing barb.
Does the female NPS connector require a gasket or do I just put them together with teflon tape?
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Old 30-11-2020, 12:11   #4
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Re: Installing a faucet - NPS thread vs NPT

The Home Depot in La Paz has the worst selection of plumbing fittings I have ever seen at a HD. I can’t even find any PEX system components in La Paz, and so am bringing down fittings and tubing to replace my 1980 original flared copper freshwater system. Too much of the Taiwanese copper is turning brittle and beginning to crack.
I might consider goobering up your NPS/NPT mismatch with a good sealant to force it to work.
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Old 01-12-2020, 09:48   #5
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Re: Installing a faucet - NPS thread vs NPT

Are you sure it's NPS and not BPS. BPS utilizes O ring gaskets and washers depending on the fitting orientation (sex). You can order BPS to NPS on line. Hope this helps.
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Old 01-12-2020, 09:51   #6
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Re: Installing a faucet - NPS thread vs NPT

This may not help but with a NPS tap you can convert a female NPT fitting into NPS.

Also, plastic NPT fittings can deform to accommodate NPS threads. Some heat might help get things moving in the right direction.
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Old 01-12-2020, 09:57   #7
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Re: Installing a faucet - NPS thread vs NPT

What you really need is this:

https://www.supplyhouse.com/JMF-H190...NPSM-Lead-Free

but building your freshwater system out of 5/8 instead of standard 1/2" is more of what's causing your issues. All these parts are commonly available for 1/2" PEX which is ideal for boat freshwater systems. Its tough and the parts are inexpensive and easy to find.
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Old 01-12-2020, 09:59   #8
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Re: Installing a faucet - NPS thread vs NPT

If you are utilizing a female synthetic fitting, you can increase it's resistance to cracking as you tighten it by securing a hose clamp over the female. Just a thought.
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Old 01-12-2020, 23:23   #9
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Re: Installing a faucet - NPS thread vs NPT

Quote:
Originally Posted by pcmm View Post
What you really need is this:

https://www.supplyhouse.com/JMF-H190...NPSM-Lead-Free

but building your freshwater system out of 5/8 instead of standard 1/2" is more of what's causing your issues. All these parts are commonly available for 1/2" PEX which is ideal for boat freshwater systems. Its tough and the parts are inexpensive and easy to find.
5/8 is what is in the boat now and it's a pain as there is some half inch hose installed in the boat as well. I have considered ripping it all out and going PEX, but it's hard to justify replacing something that works right now.

I found the following piece and will use the stainless hoses(whips) and then use this adaptor to convert from NPS to NPT then use an NPT hose barb.

https://www.mcmaster.com/pipe-thread...ead-type~npsm/
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Old 14-12-2020, 21:10   #10
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Re: Installing a faucet - NPS thread vs NPT

Finished up the installation today with the new parts from McMaster Carr. I will confirm that the one installation I did leaked when I screwed in a female NPT into a male MPS fitting. The old installation on the boat screwed a male NPT fitting into the 1/2 NPS stainless steel whips. I think these sealed since the male NPT made contact with the washer.

I ripped all of this out and replaced with the new parts that convert from NPT to NPS. No leaks.
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