Pipe joint measurement

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Old 08-27-14, 07:22 AM
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Pipe joint measurement

I'm reconfiguring some piping on my boiler and was curious how much pipe generally goes inside a fitting (for 1.25" black pipe) before it's tight. Just wanted to use a general figure when measuring and lining everything up.
 
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Old 08-27-14, 07:45 AM
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1-1/4" pipe thread is 11-1/2 threads per inch.

Typically you would be looking for 8 threads engaged for proper tightness. Unless you're Hercules you might not be able to get full 8 threads tightness. So, say 7 threads...

7 / 11-1/2 = appx 5/8" if you can get to 8 threads, then a little more.

You would probably be OK if you used 5/8
 
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Old 08-27-14, 07:57 AM
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Excellent... thanks a lot.
 
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Old 08-28-14, 05:41 AM
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Looks like whoever put it together used pipe dope and tape. Is it necessary to use both?
 
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Old 08-28-14, 05:55 AM
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For larger pipe I always use a couple turns of teflon tape and then teflon paste on the threads...

If you don't do that and have a leak, think about what you need to do to take it apart and redo it...
 
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Old 08-28-14, 06:41 AM
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a couple turns of teflon tape
As in a COUPLE... which means TWO! Any more than 2 turns of tape is too much! Using too much tape can actually jam up the threads to the point that you can't get the required tightness and achieve the desired METAL TO METAL seal on the first couple threads.

Too much tape will also FOOL YOU into thinking the connection is tight enough when it is not. This is because the tape compresses in the threads but SQUEEZES OUT VERY SLOWLY and this loosens the joint up again. You can do an experiment if you wish to prove this. Put too much tape on a joint and tighten it to where you think it should be... then come back a day or two later and put the wrenches to it again... it WILL be loose!

Don't apply any tape or dope to those first two threads either, that's where you want to get the tapered threads tight enough to create the seal. If you don't get that metal to metal seal, you end up with a spiral leak path down the threads.
 
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Old 09-22-14, 11:17 AM
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Can black pipe fittings be reused?
 
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Old 09-22-14, 11:29 AM
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yes black pipe fittings can be reused as long as the threads are not damaged .
 
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Old 09-22-14, 12:43 PM
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You might have to crank them down extra tight though...
 
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Old 09-23-14, 08:26 AM
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Yeah I'll remember that.

It seems like since black pipe is put together from one end to another, if you have a leak where you started, you're screwed.
 
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Old 09-23-14, 08:34 AM
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I have always found that since the pipes were together the threads are sort of lapped in and make a better seal.
 
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Old 09-25-14, 07:46 AM
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Can someone take a look at this schematic and tell me if the boiler drains are in the correct spot for purging? I was thinking they should be on the supply side with a valve.

Zone 1 has two returns cause it goes out in a 1" pipe then splits into a loop.

 
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Old 09-25-14, 08:26 AM
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Looks right to me ,close valve below sediment vale and open sediment valve as you add water to system watching gauge to keep pressure below 30 psi.
 
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Old 09-25-14, 08:27 AM
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Looks right to me...

To purge, you close the stop valve below the drain, open the drain and water is forced through the heating loop.
 
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Old 09-25-14, 08:31 AM
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Great, thanks.

Should I purge both zones at the same time or one at a time?

Also, do I need the ball valves below the boiler drains, or is it good enough to just have the isolation valves on the circulator?
 
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Old 09-27-14, 11:12 PM
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I had a Taco Swetcheck on the supply side of each zone, and while redoing some piping I got ride of the zone 1 Swetcheck since my new zone 1 Grundfos circulator has a check valve. Is what I did OK, or do I need to put a Swetcheck back in?
 
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Old 09-28-14, 10:26 AM
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o I need the ball valves below the boiler drains, or is it good enough to just have the isolation valves on the circulator?
On the loop with just the one branch, yes you can use the isolation valve at the pump, there's no need for both.

On the loop with the two branches, you would still need a way to stop the branches individually, so the valves below the drains would be needed. On that loop you would theoretically not need the valve at the pump, but I believe the isolation flanges are sold in pairs.

How about this? Buy one pair of isolation flanges and use them on the bottom of the pumps, and the ball valves as shown below the drains on the loops?

Is what I did OK, or do I need to put a Swetcheck back in?
You MIGHT have to reinstall it. It is still possible for the hot water to float up out of the boiler and into the zones. I would say to try it without and see whether you need it or not.

Is it too late to move your pumps to the supply side?

Google the term " pumping away " and learn why.
 
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Old 09-28-14, 12:27 PM
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I have read about the pumping away stuff, isn't it just about air elimination? Indeed it is too late. Next time I'll do it.
 
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Old 09-28-14, 01:00 PM
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I guess it's about air elimination... but you say that as if it's not that important.
 
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Old 09-28-14, 03:10 PM
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Haha I did't mean it like that, but it wouldn't be important if there was a system without an air problem, would it? I always thought people did that when they had existing air problems. Where does air usually get introduced into the system?
 
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Old 09-28-14, 04:20 PM
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I suppose that's true. I've seen plenty of systems without air problems that aren't pumping away.

It's just that if someone were completely re-doing a system, it doesn't seem to make much sense to not set up for pumping away.

Any installer worth his salt will always pump away on a new install.

The air comes in with fresh water added. After the water is heated numerous times and all the air is out of it, pretty much the only way it can get back in is by fresh water which has the air dissolved in it.

Unless the system has undetected leaks and is constantly taking on small amounts of water...

My own system had that situation. There was a joint that was concealed and leaking for years and years... perhaps decades... there are pictures of it somewhere on the forum... but I always could hear air in the system. And every year had to bleed the system at the start of the heating season.

Found the pics:





Also, if you've got the old style steel compression tank rather than a diaphragm type, the air will slowly migrate out of the tank and deposit itself out in the system. Even the new tanks will migrate some air across the bladder. That's why it's important to check and charge the tank at least every two years. And that air will move into the system as well.

So that's where air can come from...

Since I've got all the leaks fixed and the new system in place, pumping away, I haven't had to add a drop of water for two years, and it's completely air free.

If your system is tight, and has no history of air problems, it's not a big deal.
 
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Old 09-28-14, 05:06 PM
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I agree with Trooper: starting from scratch, I would go with the pumping-away doctrine. There are some theoretical advantages. But, I would not recommend that an existing arrangement be changed.

For many decades, Bell & Gossett, a pioneer of hot-water heating system design, showed in their design manuals the pump on the boiler return and the expansion tank on the system supply. There were (and are) many millions of successful installations just like that. Even today, there may be many more of that type of installation operating than the modern pump-away type, including mine.

A concern is that people may be led to worry that their perfectly functioning system is piped incorrectly and should be changed.
 
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