Special Hose Bib Compression Fitting

I recently had three new hose bib lines installed during a remodel. The plumber elected to use compression fittings to attach the hose bibs to 1/2" rigid copper lines. The male thread on the hose bib is 0.864†o.d. (caliper over the threads) and 20 tpi.

I want to install a tee so that I can attach a drip irrigation valve, vacuum breaker, and filter on one of the hose bib lines. I purchased a compression adapter to allow fitting 1/2" NPT to rigid copper. I find that it measures 0.809†and 18 tpi.

Will someone please explain the reason for this discrepancy? I'd like to avoid having to strip off the existing nut and ferrule if I can.

I've not been able to find a compression to 1/2" NPT that meets the 0.864†o.d. and 20 tpi specs of the hose bib compression nut. Perhaps I don't understand the proper search terms.

Thanks,

baumgrenze

The threads on a compression nut are non-standard, and vary from one manufacturer to the next. In fact, even if the brand is the same, the threads on their compression hose bibb may likely be different than the thread on their angle stop, or any kind of adapter fitting. You will rarely if ever find any fitting other than the nut, which screws onto the male compression threads of a valve. How would it seal???? I really suggest that this all be redone in sweat, or at least sweat a copper X MIP fitting at the wall, and do everything from there in IP threaded fittings and valves.

Hose bibbs have their own size compression nut, because they want a thicker material where it attaches to the copper tubing. It is not "proprietary", but is standard with all compression hose bibbs, just as the standard nut is used for all other compression fittings.

Can you post any pics or sketches? Compression connections' specs are not proprietary - all mfrs' products are compatible with each other. If I understand correctly, you want to remove the hose bibb but leave the nut/ferrule on the copper pipe so that you can use them to retrofit a tee with a compression inlet in between the copper pipe and the hose bibb. Should work just fine so I'm missing something here....

Dahlman said:

- all mfrs' products are compatible with each other...

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I can't agree with that. There are a LOT that are similar. You still come across coarse threads, and they are still made. And I would have to browse some stores and supply houses before I could agree that all compression hose bibbs are the same. MOST yes. I'm just a naysayer and curmudgeon today@!

jimbo said:

I can't agree with that. There are a LOT that are similar. You still come across coarse threads, and they are still made. And I would have to browse some stores and supply houses before I could agree that all compression hose bibbs are the same. MOST yes. I'm just a naysayer and curmudgeon today@!

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Well, I'm a believer in "never say never" so I won't categorically disagree with you. Especially since you are a plumber and you experience reality in the field across a broad array of installations. Machining tolerances will sometimes vary between manufacturers - we've seen that ourselves - even though they are all supposedly producing to the same specification. But when you begin talking about this much of a discrepancy in dimensions and thread count, it piques my curiosity. 55 thou difference in the thread major diameter & 10% difference in thread count says different connections to me. I want to see photos because I've experienced misunderstanding in terminologies more than a few times.

jimbo said:

.... I really suggest that this all be redone in sweat, or at least sweat a copper X MIP fitting at the wall, and do everything from there in IP threaded fittings and valves.

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I thank everyone for their comments thus far.

I did a bit more searching and found a Wikipedia entry on compression fittings:

http://en.wikipedia.org/wiki/Compression_fitting

It ends with this paragraph:

Disadvantages

Compression fittings are not as robust as soldered fittings. They should be used in applications where the fitting will not be disturbed and not subjected to flexing or bending. A soldered joint is highly tolerant of flexing and bending (such as when pipes knock or shake from sudden pressure changes). Compression fittings are much more sensitive to these type of dynamic stresses. They are also bulkier, and may be considered less aesthetically pleasing than a neatly soldered joint.

This reinforces Jimbo's quote above and suggests to me that the choice of a compression hose bib over a sweated on copper X MIP fitting may have been an expedient/aesthetic decision. It seems to me that a hose bib is likely to be subjected to 'flexing and bending' and better served by the sweated fitting. Am I wrong? I'm sure that my supplier will be willing to exchange the compression fitting I bought for a sweated one. I have plenty of ceramic wool to protect the wooden wall behind the hose bib. Should I consider replacing the other two while I am 'in the business?'

Here's a photo for good measure:



My best reading of the initials cast into it is USA (in photo) and A8P (on opposite side.)

Thanks again,

baumgrenze

Get a 1/2" comp. X 1/2" MIP adapter and a hose bibb that has a 1/2" FIP inlet and install it.

Just to be clear, I have such an adapter. I have no problem with replacing the hose bibb with a 1/2" FIP equivalent. The problem is that the thread on the installed compression nut is different from the thread on the 1/2" comp. X 1/2" MIP adapter. That information is in my original post. I appreciate that Dahlman is skeptical about the difference. I reinstalled the hose bibb after I measured it so that I could turn the water back on, so I can't take photos of the two fittings, complete with calipers and thread gauge to show that the differences are 'real' until I have time to shut off the water again.

I appreciate that I may get conflicting advice, but I'm now concerned that I might be better advised to sweat on a 1/2" MIP adapter. I will be installing a tee, away from the wall, with the hose bibb at the end furthest from the wall and the down leg of the tee to a drip irrigation valve system. I will be adding to the lever arm that the joint to the rigid copper will experience when someone inevitably pulls too hard on a hose. Am I correct that a proper sweated joint is stronger than the compression version?

Thanks,

baumgrenze

Get a sleeve puller, pull the compression ring and nut off, and then put on what you want. Note, though, that if the nut was ever overtightened, it may have put a crimp in the pipe, making sealing tough with a new one. If it wasn't overtightened, you might be able to get it off without a puller.

That is Arrowhead Brass and they have their own size compression nut.

The barrel where it slides onto the copper is "larger/thicker", (because it is cast brass), than the standard compression fitting, which is why the nut is larger. You do not have to understand it, you just have to accept it.

You do not have to understand it, you just have to accept it.
hj

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A very classic hj-ism
I like it.

Or to paraphrase a Supreme Court Justice, on a slightly different topic, " I don't know what size it is, but I'll know it when I see it"

Thank you, everybody, for all your input.

Today I picked up the aluminum insert part of a sleeve puller. I plan to use it with my old Sears & Roebuck gear and pulley puller. I trust that it will suffice to pull the nut forwards.

I did not start right in because today I decided that I would 'become informed' on the proper treatment of threaded PVC joints. I will start a new thread, with a proper subject, because what I found on the Lasco website was interesting and perhaps, for many, controversial.

Thanks again,

baumgrenze

asktom said:

That is Arrowhead Brass and they have their own size compression nut.

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How about that? Learn something new every day...can't imagine why they would have done that but I'll take hj's advice and just accept it.