Issue with pipe threads: how far do they have to go in?

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Old 10-23-11, 09:17 AM
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Issue with pipe threads: how far do they have to go in?

Hi,

I am about to replace my broken outdoor hose bibb with a new one from Arrowhead. The new spigot has 3/4" male threads at the end. I also have a 3/4" quarter-turn ball valve that I was intending to screw into the spigot end. The ball valve doesn't even go half-way in. It is supposed to be 3/4" FIP, but I am beginning to wonder if there are differences in the thread pitch despite the fact that they are supposedly standardized.

Is it normal/acceptable to have the threads not go in all the way, or should I be looking for a new ball valve?

Thanks,
MM
 
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Old 10-23-11, 09:40 AM
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Hose threads are not the same as pipe threads.

Hose threads are "straight" cut...like a bolt...pipe threads are tapered...kind of like a wood screw.
 
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Old 10-23-11, 09:47 AM
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Originally Posted by Gunguy45 View Post
Hose threads are not the same as pipe threads.

Hose threads are "straight" cut...like a bolt...pipe threads are tapered...kind of like a wood screw.
Sorry, I wasn't clear. The 3/4" MIP is at the end of the hose bibb that attaches to the water supply (CPVC in my case). That's where I'd like to attach the shut-off valve, but the hose-bibb MIP goes only about halfway into the valve FIP . This valve does not accept garden-hose threads, so there is no confusion in that respect.
 
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Old 10-23-11, 10:07 AM
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that is normal, Gunguy eluded to the answer. They are tapered threads and probably wont allow you screw all the way in.
 
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Old 10-23-11, 10:19 AM
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I was kind of wondering why you would want a ball valve on the outside...lol.

Yeah..like hvac said...it won't screw all the way in. The tapered threads are what crate the seal. Even less with a couple of wraps of teflon tape most likely.

Are you using tape or dope or both on the threads?
 
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Old 10-23-11, 10:41 AM
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Originally Posted by Gunguy45 View Post
I was kind of wondering why you would want a ball valve on the outside...lol.

Yeah..like hvac said...it won't screw all the way in. The tapered threads are what crate the seal. Even less with a couple of wraps of teflon tape most likely.

Are you using tape or dope or both on the threads?
I was planning on using tape and dope on metal-to-metal fittings and tape only on the plastic-to-metal fittings.
 
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Old 10-23-11, 10:46 AM
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My suggestion is to toss the Teflon tape and use only a Teflon paste. Be sure the paste is suitable for use on plastic piping. Don't go overboard on the paste, just enough to fill the male threads and try not to get any on the first two threads.
 
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