The flow rate through a PVC pipe is typically measured in units of gallons per minute (GPM) or gallons per hour (GPH). Flow rates are affected by the pressure of the liquid inside the pipe. Twelve feet per second is an average fluid velocity for a Schedule 40 PVC pipe. At this velocity, the flow rate through a 1- inch PVC pipe is 16 gallons per minute. The flow rate increases by 20 GPM for every half-inch increase in pipe diameter.
• Backpressure occurs when the fluid moving through a pipe encounters a solid surface, such as a bend in the pipe. The result is a fluid hammer, also known as a water hammer, when the shock of the fluid impact on the bend ricochets up the pipe. This puts additional pressure on the pipe at the angle and reduces the flow through the system. Too much pressure in the piping system could damage the pump and the PVC tubing.
• Determining the flow rate of fluid (typically water) through a sprinkler system is different than for standard Schedule 40 PVC pipes. The velocity of water through PVC pipe for a sprinkler system should not exceed 5 feet per second, according to a report from Ohio State University. The pressure put on the top of the pipe will be lost somewhat due to friction, and the amount of friction increases with the length of the pipe and the velocity of the water. The maximum flow through a 1-inch diameter sprinkler system should not exceed 13 gallons per minute (GPM), which is less than the Schedule 40 PVC mentioned above.