I had to revise my air handling piping due to my new compressor. I installed two 3/4" pipe unions, sealed the threads using Rector Seal. Waited a couple of days for the electrician to hook up the compressor, turned it on and both unions leak like sieves. The threaded connections don't leak just the union connection. I have tightened them as tight as they will go. I have the regulator set to 150 PSI. Anyone know of a quality 3/4" pipe union that doesn't leak?
Need Pipe Unions that don't leak
- Thread starter J Persons
- Start date
Flail
Well-known member
Are the copper or steel? The copper being more malleable usually seal better.
claas880
Well-known member
Did you try anti-seize on the threads and mating surfaces? it helps sealing up unions.
sberry
Banned
I buff them a little with the painters secret weapon. Purple Scotchbrite.
matt_i
Well-known member
Ward Manufacturing is where I would go. Typically available at McMaster Carr if local sources don't pan out. All of their fittings I've found accurately machined and easy to use.
The anti seize that Claas mentioned is a good idea to get more torque on the union-nut. Also a set of longer handle pipe wrenches will assist. When I'm sweatin' the black pipe fittings are usually tight enough.
The anti seize that Claas mentioned is a good idea to get more torque on the union-nut. Also a set of longer handle pipe wrenches will assist. When I'm sweatin' the black pipe fittings are usually tight enough.
They are iron pipe fittings, I used Rector seal on the threads, the threaded part doesn't leak. I then tried a smear of Rector seal on the mating surfaces, waited about an hour, turned on the air and they leaked at the center of the coupling I got these at tptools.com I've never had a problem using fittings from TP Tools until now.
Shiftless
Well-known member
That’s my experience as well. The Chinese ones from HD leaked (water) and the USA made ones I bought at my local ACE didn’t.
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theoldwizard1
Well-known member
Buy some valve lapping compound and "lap" the male and female surfaces. Use Rector seal on the back side of the male and female halves and on the joining nut.
bczygan
Well-known member
ard
Well-known member
No?
LifeLongWNYer
Well-known member
I second the motion about using USA manufactured fittings. While the Chinese stuff was junk, today my Home Depot only stocks sh** made in India. That makes the Chinese junk look stellar.
My local "home town" hardware sells American made fittings, I always buy there.
.
My local "home town" hardware sells American made fittings, I always buy there.
.
Busted Knucles
Well-known member
- Joined
- Apr 15, 2016
- Messages
- 437
Flanges may be a good option for you. In any case the 2 pipes must be straight.
We have a winner. Take them apart and buff the faces some. Do not put sealant/lubricant on the faces.
I try and use domestic made, brass seat unions on air service when we're doing new pipe.
But if I have to take something apart on a service call or equipment it supplied with a cheap union and won't seal back up you bet I'll touch up the faces and goop em up if need be. I've even had to put leakloc on less then stellar quality stainless unions before.
But if I have to take something apart on a service call or equipment it supplied with a cheap union and won't seal back up you bet I'll touch up the faces and goop em up if need be. I've even had to put leakloc on less then stellar quality stainless unions before.
^^ This ^^ Out of alignment just a bit and you're screwed.
I would think that lapping them or even the buffing that SBerry mentioned would be a huge help as well.
Personally, I would avoid unions at any cost. Especially for air.
Mr onetwo
Well-known member
You can try regular ward unions https://www.supplyhouse.com/Ward-FBUN3-4-3-4-Black-Union-732000-p or you could try this trick.Use a pair of Taco pump flanges with a good gasket in between.No leaky https://www.supplyhouse.com/Taco-110-251F-3-4-Taco-Iron-Freedom-Flange-Pair-1973000-p https://www.supplyhouse.com/Taco-007-007RP-Taco-Replacement-Gaskets-Pair-4662000-p 
Attachments
bob15
Well-known member
You need either a US made Anvil or Ward:
I like this place and they have free shipping over 99 bucks.
https://www.supplyhouse.com/Ward-FBUN3-4-3-4-Black-Union-732000-p
I like this place and they have free shipping over 99 bucks.
https://www.supplyhouse.com/Ward-FBUN3-4-3-4-Black-Union-732000-p
dr_clyde
Well-known member
Local plumbing supply house always sent me Anvil fittings, never had any leaky unions from them.
Beginning to sound like a general consensus to buy quality fittings from somewhere other than a big box store.
Tape and dope on the NPT threads, nothing on the mating seal between the halves.
Beginning to sound like a general consensus to buy quality fittings from somewhere other than a big box store.
Tape and dope on the NPT threads, nothing on the mating seal between the halves.
rayra
Well-known member
No?
you were probably being sarcastic with the suggestion, but with most air tools limited to ~100psi and compressors to ~150, and most smaller sched40 PVC pipe having a burst rating of 400psi AND being available in CPVC or even the simple expedient of UV protection via painting the pipe, I wonder why more folks don't use PVC. Helluva lot easier to work with and seal.
But the lore-howling against it is legend. And I can't seem to find much of a real basis for it.
eta just got a notification today, 220207, 32 months after this post, that rlitman gave me an angry face. Ridiculous.
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speed bump
Well-known member
PVC isn't oil resistant, its working strength varies with temperature, and it doesn't take shock and impact well. Not to mention when metal pipe goes it tends to open on the seam versus PVC that has a higher chance of exploding.
Monza Harry
Well-known member
I have seen the pipe with a Black Blister on it's side hissing away. Oil and plastics (some, many) just aren't friends, bad idea with all of the first hand account here and every other similar (Ok ish +/-) forums telling of the same tales. Have you ever been in an industrial building with PVC Air lines? I have been in 100+ buildings and only one had plastic plumbing and I mentioned that one above, BAD IDEA Period. Just my experience, do what you will with it! Harry
Mr. T
Well-known member
theoldwizard1
Well-known member
My point was to use the lapping compound to "lap" the mating surfaces so they match perfectly. Yes, clean the mating surface after they are lapped.
seems that unions are real bad these days.
when I did plumbing in school they always referred to as ground joint unions, you weren't supposed to mix the halves and we were always taught to put some dope on the mating surface .
if the pipes are out of line,and rigid, the union wont necessarily seal .
too bad so much stuff is on a downward spiral, even with modern machining etc.
when I did plumbing in school they always referred to as ground joint unions, you weren't supposed to mix the halves and we were always taught to put some dope on the mating surface .
if the pipes are out of line,and rigid, the union wont necessarily seal .
too bad so much stuff is on a downward spiral, even with modern machining etc.
Is there such a thing a gas rated unions?
Water unions are made to seal water, a liquid, at less that 100 PSI
You are asking them to work on air, a gas, at 150 PSI
That is way outside the design limits.
I would say you should buy the right product.
Water unions are made to seal water, a liquid, at less that 100 PSI
You are asking them to work on air, a gas, at 150 PSI
That is way outside the design limits.
I would say you should buy the right product.
rburke65
Well-known member
Quality unions ARE worth the money.
Rock knocker
Well-known member
- Joined
- Aug 14, 2014
- Messages
- 704
They are WOG
Hello, If you will look inside a union the collar side has a tapered side that fits into the other side which looks like a funnel, therefore pressure flows thru easier than if the other way around. I have installed thousands of pipe fittings of every size from one quarter inch to forty eight inch pipe in my forty seven years as an industrial pipefitter, trust me it makes a difference.
Mr onetwo
Well-known member
I'd like to see that 48" union
matt_i
Well-known member
How about so the collar doesn't drop down 11 floors when you loosen it, iow keep the collar on the top side if applicable
I'd like to see that 48" union
A 48 inch union is called a flange. I guess there is one in every forum and your it here!!!!
nadogail
Well-known member
Use "Ground Joint" unions.
LS6 Tommy
Well-known member
Folks do use it, but that's only because they don't understand the burst rating is for liquids, not gases. Compressed gases store energy and will have an explosive failure, where liquids don't. That's why using PVC or CPVC for compressed gases is a no go. It's 100% illegal because it's not rated or safe for any compressed gas use, regardless of burst rating.
Tommy
Bluedodge
Well-known member
I worked for one of the five largest Unions in the country.
I hated every minute of it.
Find a better job & employer.
I hated every minute of it.
Find a better job & employer.
theoldwizard1
Well-known member
So how often is the tooling inspected/changed in plumbing fitting factories in India/China/Korea/Philippines ?
Hence my comment. Lapping compound and lap by hand !