Choosing PVC Pipe for a Sprinkler or Irrigation System
Choosing PVC Pipe for a Sprinkler or Irrigation System
Underground irrigation is mostly pipe. Choosing the wrong type either wastes money or fails early. This guide explains the labels you will see (Schedule 40, Class 200 and so on) so you can ask for the right thing. Most of the specifics below come from one irrigation tutorial site written by an experienced installer, so treat them as practical guidance, not code. Always check local rules.
Two ways pipe is labeled
- Schedule (SCH) 40: a thick-wall pipe whose dimensions follow steel pipe sizes. The source notes that as the pipe size increases, strength and pressure rating decrease.
- Class (CL) 160, 200, 315: the class number equals the pressure rating in PSI. Class 200 is rated for 200 PSI.
What the source recommends
- Mainlines (always pressurized): SCH 40 is often used up to 1 1/2". Class 315 is described as the choice for mainlines of 2" and larger.
- Laterals (the pipes after the zone valves): Class 200 is called the standard. Class 160 is sometimes used where budget matters.
- Class 125: a thin-walled, low-cost pipe the author advises avoiding.
- 1/2" pipe: generally sold only as SCH 40, and the author does not recommend using it at all.
Pressure ratings by size (SCH 40)
The same source lists these ratings. Treat them as reference values and confirm against the printed markings on the pipe you buy.
| Size | Rating (PSI) |
|---|---|
| 1/2" | 600 |
| 3/4" | 480 |
| 1" | 450 |
| 1 1/4" | 370 |
| 1 1/2" | 330 |
| 2" | 280 |
| 2 1/2" | 300 |
| 3" | 260 |
| 4" | 220 |
Do not run at the rated pressure
The source gives a rule of thumb: normal operating pressure should not exceed half of the rated pressure, because a valve closing quickly can cause a surge that may double the pressure. Its example is that 1 1/2" pipe should stay at or below 165 PSI. The author says this applies to all PVC pipe, including class-rated pipe. Surge is also known as water hammer, and a licensed irrigation or plumbing professional can advise on how to limit it.
Fittings and joints
- Most fittings are SCH 40. The source says codes typically require SCH 80 fittings for 2" and larger, but SCH 40 fittings are often used up to 3". We could not verify which code applies to your location. Not verified: for your area.
- Gluing joints on 3" and larger pipe is described as very difficult.
- For 4" and larger, the source recommends non-glued rubber ring-joint fittings and says they are usually required by code. Again, check your local code.
- Follow the pipe and cement manufacturer's instructions for primer, cement, and cure time. We did not verify cure times, so we give none here.
Burial depth
The source says codes generally require pressurized mainlines to be buried at least 18 inches deep regardless of pipe type or size. Laterals can be buried at any depth, but the author generally recommends at least 10 inches to reduce breakage. Requirements vary by state and city, and frost depth matters in cold climates. Confirm with your local building or water authority before you dig. Call your local utility locating service before any digging.
Planning checklist
- Measure your flow (gallons per minute) and static pressure with a gauge. A flow figure helps you choose pipe size; undersized pipe increases friction loss.
- Draw the zones and decide where mainline and laterals will go.
- Choose mainline and lateral pipe types as above.
- Decide whether you need a backflow preventer. Requirements are set locally; ask your water utility.
- Plan drainage or winterization if your area freezes.
Common mistakes
- Using thin Class 125 pipe to save a few dollars.
- Operating at the pipe's full rated pressure.
- Burying the mainline too shallow.
- Mixing pipe types and then discovering the fittings do not match.
- Skipping the permit or the inspection where one is needed.
Comparing quotes
Ask each supplier or installer for the pipe type (SCH or class), size, fitting grade, and the working pressure the system is designed for. Compare total installed cost and warranty, not only the price per foot.
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General information only. Not engineering, legal, or financial advice. Confirm design, code and permit requirements with a licensed professional and your local authority.