Can I Use a 1 1/4-Inch Mainline With a 1-Inch Solenoid Valve and an Output to a 2-Inch Lateral Line in a 20.9 GPM Zone?

Question

Can I use a 1 1/4-inch mainline with a 1-Inch solenoid valve and an output to a 2-inch lateral line in a 20.9 GPM zone?

Answer

The difference in sizes will just cause a difference in velocity. In this case, the velocity of the water is 1m/s through the lateral pipes, which is forced by the 2-inch size of the pipes.

Meanwhile, the water rushing through the 1-inch valve will be moving much faster – in fact, about 2.3m/s. That rate is fast enough to generate the 6 psi loss in just going through it, yet is still amply slower than the 3 m/s realistic maximum to which a brass valve should be subjected.

The bigger issue, however, is whether the velocity through the mainline will be acceptable. With 1 1/4-inch pipe, it will run at 1.4 m/s – a perfectly nominal velocity.

For more information on mainlines, see our pages on:

• Initial Mainline and Service Layout
• Sizing the Mainline