Plumbing Picks is reader-supported. As an Amazon Associate, we earn from qualifying purchases at no extra cost to you.
Quick answer: To install a PVC union, Charlotte Pipe says to slide the union nut (shoulder piece) onto the pipe before you cement, keep cement off the union threads and face, let the joints cure, line the two halves up flush, then tighten the nut by hand or with a strap wrench only. Two things people miss:
- No lube or thread sealant on the union nut, and no metal-pipe wrenches.
- The union is the weak link on pressure. A 1/2″ Schedule 40 PVC union is rated 150 psi at 73°F, while the pipe is rated 600 psi. At 140°F the union drops to 33 psi.
All rules and ratings here come from Charlotte Pipe’s Plastics Technical and Installation Manual (pages 30, 31 and 67), read October 9, 2026 from the rendered pages. Ratings are for Charlotte’s PVC unions; other makers set their own. This page has no buy buttons.
Step by step
- Put the nut on first. A union has three parts: two ends and the ring/nut that pulls them together. Charlotte reminds installers to place the union shoulder piece on the pipe before solvent cementing. Forget it and you have to cut the joint out.
- Cement or thread each end. Join the union threaded piece and the socket end the same way as any other joint: solvent cement or thread, following the manual’s cementing steps.
- Keep cement off the sealing parts. Charlotte says take care that cement does not touch the union threads or the union face.
- Don’t disturb the joint until it has initially set, and let the joints cure fully before tightening the union.
- Line up the halves. The two mating pieces should sit flush before you tighten. The nut should not be used to pull piping together or to correct bad alignment.
- Tighten by hand or with a strap wrench. Charlotte says never use common wrenches or tools designed for metal pipe, and no lubricants or thread sealants on the ring/nut.
#ad Buying for a shop? Amazon Business (opens in a new tab) accounts are free to create, with business-only prices and bulk quantity discounts.
If you work in the trade and want a note when a new guide goes up, leave your email below. No spam, no course funnel — written by a licensed Georgia plumber.
Union pressure ratings (Charlotte PVC)
Charlotte explains that flanges, unions and valves carry their own maker pressure rating, usually lower than pipe of the same size. The whole system must be de-rated to its lowest-rated part at the highest expected temperature.
| Union | Sizes | At 73°F | At 140°F |
|---|---|---|---|
| Schedule 40, socket or threaded | 1/2″ to 2″ | 150 | 33 |
| Schedule 80, socket | 1/2″ to 2″, and 3″ | 235 | 52 |
| Schedule 80, threaded | 1/2″ to 1-1/2″ | 235 | 52 |
| Schedule 80, threaded | 2″ | 200 | 44 |
| Schedule 80, threaded | 3″ | 185 | 41 |
For comparison, Charlotte rates 1/2″ Schedule 40 PVC pipe at 600 psi and 2″ at 280 psi (73°F). Charlotte’s table lists no Schedule 40 unions above 2″, and no Schedule 80 unions at 2-1/2″ or above 3″.
What this means: on a hot line or a high-pressure line, size the system to the union, not the pipe. If the line runs warm, a Schedule 80 union keeps more of its rating than a Schedule 40 one in Charlotte’s table.
Union or flange?
Both let you take a line apart. Charlotte’s table covers unions only up to 3″, while its flange table runs up to 12″. For larger pipe or a plastic-to-metal joint, see our PVC flange bolt torque guide.
Don’t air test it
Charlotte’s warning on the same page: never test ABS, CPVC or PVC pipe or fittings with compressed air or gas, or with air-over-water boosters. Test with water.
FAQ
Do you put Teflon tape or pipe dope on a PVC union nut?
No. Charlotte says not to use lubricants or thread sealants on the union ring/nut.
Can I use a pipe wrench on a PVC union?
No. Charlotte says to hand tighten the nut or use a strap wrench only, and never common wrenches or tools made for metal pipe.
What pressure is a PVC union rated for?
In Charlotte’s table, Schedule 40 PVC unions (1/2″ to 2″) are rated 150 psi at 73°F and 33 psi at 140°F. Schedule 80 unions run 185 to 235 psi at 73°F, depending on size and type.
Can a union pull a misaligned pipe together?
No. Charlotte says the two halves should be flush before you tighten, and the nut should not draw piping together or correct poor alignment.
Related guides
Sources
- TM-PL (PDF) (charlottepipe.com), read 2026-10-09