DID YOU KNOW?
PVC flowmeters can handle more than you think
What to know before choosing a PVC flow meter
Fittings, pipe schedules, and temperature all play a role in safe PVC meter performance.
Understanding spigot vs. socket ends, Schedule 40 vs. 80 compatibility, and pressure derating can help your PVC flow meter system last longer and perform more reliably.
"Did You Know?"
What You Should Know About PVC Flow Meters
PVC flow meters are a popular, budget-friendly choice for many water applications. But Did You Know that choosing PVC over brass or stainless steel can introduce a few extra considerations? From pipe fittings to pressure ratings, understanding these details can help ensure your system is safe, compatible, and long-lasting.
Here are a few helpful things to know:
PVC Pipe Fittings: Spigot vs. Socket
Have you ever wondered why PVC plumbing is so flexible? You can glue many types of fittings directly onto the pipe: NPT, BSPP, unions, flanges, socket couplers, and more.
But one fitting type often confuses users: Spigot fittings.
- A spigot fitting is the male end of a PVC connection. This is the same end found on standard PVC pipe.
- A socket fitting is the female end, designed to receive a spigot fitting or PVC pipe.
Because spigot fittings match the outside diameter (OD) of PVC pipe, they must connect to a PVC socket fitting, not to smaller-diameter pipe.
The two pictures below show a 1.5” PVC meter with spigot fittings next to a 1.5” PVC pipe. As you can see, a spigot fitting and PVC pipe have the same outside diameter (OD).
Tip: Never glue a pipe one size smaller into a spigot end! It will not seal properly and will break loose under pressure.
So why do some meters use spigot ends instead of socket ends? Flexibility! With spigot ends, you can glue on any PVC fitting you need, without first having to glue on some PVC pipe.
PVC Schedules: Can You Mix Them?
A common customer question is:
“Can I connect a Schedule 80 PVC meter to Schedule 40 pipe?” Yes, you can!
All PVC pipe schedules share the same outside diameter (OD) for a given nominal pipe size. That means a 1-inch Schedule 80 PVC meter with spigot ends will fit into any standard 1-inch PVC socket fitting.
The difference lies in the wall thickness:
- Higher schedules = thicker walls and higher pressure ratings
- Thicker walls = smaller inside diameter (ID)
Remember: Your system’s maximum pressure rating is determined by its lowest-rated component.
Temperature Matters: PVC Pressure Derating
As PVC temperature increases above ambient conditions, its pressure rating decreases, sometimes significantly.
Industry standards such as ASTM D1785 and guidance from the Plastic Pipe Institute provide widely accepted derating factors for PVC at elevated temperatures. These standards have not been verified by FLOMEC.
PVC Pressure Derating Factors
| Operating Temperature | Derating Factor |
|---|---|
| 73°F (23°C) | 1.00 |
| 80°F (27°C) | 0.88 |
| 90°F (32°C) | 0.75 |
| 100°F (38°C) | 0.62 |
| 110°F (43°C) | 0.51 |
| 120°F (49°C) | 0.40 |
| 140°F (60°C) | 0.22 |
Example
If your PVC is rated for 225 psi at 73°F, and your application goes up to 100°F: 225 psi × 0.62 = 139.5 psi Your system should not exceed 139.5 psi at 100°F.
Final Takeaway
PVC flow meters are reliable, economical, and versatile, but like any material, they come with considerations. Knowing how fittings, pipe schedules, and temperature affect performance, you get the most out of your PVC-based system.