I got half of my air pipe system on the wall. 30' of 3/4" with two up and over work drops and a straight drain drop in 1/2" black iron. I've got a union in the middle of the 3/4" and unions for each 1/2" drop. I put 175 psi to it and had leaks at the water filter and the 1/2" union. I expected that would happen because I didn't know how to tape or pipe dope the union. The filter wasn't tight. So how do I seal the unions.
How do you seal pipe unions?
- Thread starter BigOkie
- Start date
pipe threads are tapered, and seal on the threads. To get a good seal, you should use a joint sealing compound that lubes the threads and dries to a semi-hard state that will stop any small leaks. I use either Permatex #2 non hardening sealer or a pipe joint compound I get at my plumbing supply store. I don't recall the name right now, but it's got a "#5" after the name. If I get a leak in an assembled joint, I disassemble the joint and apply sealer to both the male and female sides of the joint and reassemble, usually trying to get it a little tighter than the first time.
Zeke
Well-known member
You can put dope, tape or paste on the threaded surfaces but it won't do any good on the union mating surface. Also, I wouldn't apply much more pressure than you're intending to use. High pressure will blow out a sealed connection. Pump it up to your shut off pressure and spray your soapy water to see how it holds.
Also, if using that type of sealing compound, let it rest for a day before testing.
Do an Advanced Search here on GJ, as bunch of good solutions were listed. There is convenient one in chapstick like container.
Also can use Google to search inside GJ (see below).
Rectorseal #5 is also a great brand that many like. It's in yellow tube in plumbing section of big box stores. Here's what I buy at Lowes:
http://www.lowes.com/pd_44921-72720-25793_?PL=1&productId=1087181
Also can use Google to search inside GJ (see below).
Rectorseal #5 is also a great brand that many like. It's in yellow tube in plumbing section of big box stores. Here's what I buy at Lowes:
http://www.lowes.com/pd_44921-72720-25793_?PL=1&productId=1087181
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BillK
Well-known member
Big,
I have had problems with some of the el-cheapo unions you get from the big box stores. I bet if you take it apart and look at the mating surfaces, you will find some flaws.
I have had problems with some of the el-cheapo unions you get from the big box stores. I bet if you take it apart and look at the mating surfaces, you will find some flaws.
djjsr
Well-known member
What's leaking, the connection where the union flanges meet or the pipe connections screwed into the flanges?
pacmktg
Well-known member
Rector seal #5 was what he was looking for.
MrMark
Well-known member
unions are metal to metal. Some people will put dope on a metal union face but that is putting a band-aid on a bad union.
A coat of dope on the union will usually solve the problem unless it's a really crappy union.
I don't see it as any more of a band-aid than sealing the helical leak path of the truncated NPT thread form with dope and tape.
I don't see it as any more of a band-aid than sealing the helical leak path of the truncated NPT thread form with dope and tape.
Junkman
Well-known member
Pipe unions can have flaws from the manufacturing process. To fix them, I used to use valve lapping compound on the sealing surfaces, and rotate the two parts by hand to clean them up. I used to use Rector-seal 5 on pipe fittings, but I switched to a blue paste after seeing it used by the propane installers. It has some Teflon in it, and it is rated for gas, oil, and just about anything else you can think of. It also doesn't separate if not used for a while. If you have to, you can put a very light smear on the mating surface of the union, and assemble. Also, keep in mind that you need to use pipe wrenches on all fittings, and make sure that they are well tightened.
I bet the lapping compound would work. I might not have got it tight enough standing on a ladder but it felt tight. I'll try some pipe dope on the mating surfaces. I bought Blue Monster non hardening, it's white though.
The soap is bubbling at the threaded side of the union.
The soap is bubbling at the threaded side of the union.
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Lotek
Well-known member
If you used pvc, you wouldn't have this kind of problem.
Lotek runs for cover
Lotek runs for cover
PVC will blow up, so I've been told. I think I can show a pic.
http://i1156.photobucket.com/albums/p561/45Aber/garage017_zps03c15447.jpg
Of black iron pipe not deadly PVC.
http://i1156.photobucket.com/albums/p561/45Aber/garage017_zps03c15447.jpg
Of black iron pipe not deadly PVC.
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Zeke
Well-known member
He was kidding. You have to be around for awhile to get some jokes.
2level
Well-known member
djjsr
Well-known member
If you used pvc, you wouldn't have this kind of problem.
Lotek runs for cover
And repairs can be made with duct tape.
Is the union faced? In other words is the gap the same all the way around it when the nut is removed? Put some grease or never seize on the threads and crank it tight
55bigblockcid
Well-known member
- Joined
- Jun 17, 2011
- Messages
- 250
Ok guys ,sorry for the big picture but it will work.
I learned this from an old plumber who knew his **** and I do it this way as well.
I plumb gas,air,water,oil and anything needing a pipe also repairs on piping.
To get a leak free seal on a union,apply teflon pipe dope where the nut meets the back side of the union[ left arrow] and on the threads of the union,normally no pipe sealant is needed on the sealing faces of the union.
This gives the metal on metal contact of the nut and union some lubrication when it is tightened,you will be able to get the union tighter thereby allowing the sealing faces of the union halves to make contact with each other.
Also Use two wrenches when tightening.
Hope I helped some.
Tape and dope the threads and you should be good to go.
China pipe wont hold that kind of PSI and will probably rust threw within two years. The China pipe on my compressor has developed a pin hole in the middle of the fitting in probably two years of service.
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BINGO we have a winner. Works 99.99% of the time.
Ok guys ,sorry for the big picture but it will work.
I learned this from an old plumber who knew his **** and I do it this way as well.
I plumb gas,air,water,oil and anything needing a pipe also repairs on piping.
To get a leak free seal on a union,apply teflon pipe dope where the nut meets the back side of the union[ left arrow] and on the threads of the union,normally no pipe sealant is needed on the sealing faces of the union.
This gives the metal on metal contact of the nut and union some lubrication when it is tightened,you will be able to get the union tighter thereby allowing the sealing faces of the union halves to make contact with each other.
Also Use two wrenches when tightening.
Hope I helped some.
BD1
Well-known member
175 pounds ?? What is the pressure rating on the union ? If it was bought from big box store does it have the pressure rating on it ? 
I would use a 250 pound REAL union that have a brass seat and more body to it. A 150 pound will work since it is rated at 300 pound for WOG.
As for a lubricant, use never seize on the union faces , union collar so it spins easier on the union half, and on the union thread that the collars attaches to.
I would use a 250 pound REAL union that have a brass seat and more body to it. A 150 pound will work since it is rated at 300 pound for WOG.As for a lubricant, use never seize on the union faces , union collar so it spins easier on the union half, and on the union thread that the collars attaches to.
55bigblockcid
Well-known member
- Joined
- Jun 17, 2011
- Messages
- 250
^^^^^^^^^ This.
stonesfan68
Well-known member
175 pounds ?? What is the pressure rating on the union ? If it was bought from big box store does it have the pressure rating on it ?
The pipe and fittings found in big box stores are rated for Schedule 40. Assuming a 1/2" pipe, then the pipe is rated for 2300 PSIG and a burst pressure of nearly 16,000 PSIG.
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BD1
Well-known member
The never seize will allow the mating surfaces in a misalignment to slid rather then have the faces dig into one another . By using it on the collar it makes disassembly easier. If it is a cheap *** union nothing will help. Some job specifications state that never seize must be used on all unions and must be installed according to flow direction. This really makes a difference on steam. Air really don't care.
RAYJAY
Well-known member
BD1
Well-known member
I was discussing the pipe fitting pressure rating and NOT the pipe.150 pound FITTINGS are not in the thousands . A 150 pound fitting is rated at 150 pounds steam and 300 WOG, water, oil, gas. You can get forged steel fittings 2,000 to 6,000 pounds. Home depo and Menards don't carry them.
Here's something that explains 125, 250, and 300 pound fittings.http://firesafelife.com/class-pounds-rating-fittings.html
stonesfan68
Well-known member
I was discussing the pipe fitting pressure rating and NOT the pipe.150 pound FITTINGS are not in the thousands . A 150 pound fitting is rated at 150 pounds steam and 300 WOG, water, oil, gas. You can get forged steel fittings 2,000 to 6,000 pounds. Home depo and Menards don't carry them.
http://firesafelife.com/class-pounds-rating-fittings.html
I did write that the pipe is rated for 2300 PSIG. You are correct, the fittings sold in retail stores are rated for a whole let less pressure.
Another poster was trying to state that the fittings weren't rated for a home air compressor. Clearly, a SCH40 150# fitting rated at 300 PSIG is more than sufficient for a 175 PSIG compressor.
Mr onetwo
Well-known member
Back in the day, we always used 300 lb. brass to iron unions because they don't distort and leak.If you use proper sized wrenches and don't over tighten you should be OK.Tighten your unions hand tight and then 1/2 turn with no pressure on them.Pressurize the system to working pressure and then tighten them until the hissing just stops.I am not against using a little Rectorseal #5 on the faces to seal a stubborn leaker...good luck!
sberry
Banned
Trying to do too good of a job strikes again.
greenghost
Member
Blue Monster is what we use for stainless steel pipe fittings, costs to much. Gasoila I do not know about. Brass and steel fittings we use a paste with Kevlar in it. Rectorseal is a leading manufacturer of chemical specialty sealants and get my vote. A good union will have a brass too steel seal and need no dope or tape.