PRIVATE WATER SYSTEMS - Piping - Proper Size

Proper Size

The amount of water a pipe will deliver at any one pressure is a direct result of the size of the pipe, the smoothness of the inside surface, and the pipe length. The procedures used in selecting pipe size are affected by whether there is only one building or hydrant being serviced by the line, or two or more buildings.


Size

Even a small increase in the diameter of the pipe can greatly increase the amount of water that may flow through it. For example, increasing a 3/4-inch diameter pipe by 3/4 of an inch doubles the water flow (at a flowrate of 5 fps). Increasing the diameter by 1 1/4 inches can increase the flow by over 300%.


Smoothness

Pipes Friction between the inside walls of the pipe and the moving water creates a force that opposes the flow of water through the pipe. The greater the roughness of the inside of the pipe, the greater the force caused by friction, and the higher the pressure required to push the same amount of water through the pipe. Consequently, pipes with smooth inside surfaces can deliver more water than pipe walls with rough surfaces using the same pressure.

Pipe connections - elbows, reducers, tees, unions, etc. - as well as valves, can add greatly to the friction.

Valves

In general, valves with fewer sharp turns and wider openings create the least friction. Four types of valves are discussed here:

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