What is the pump discharge pressure for 300 ft of 2.5 inch hose with a 1-inch smooth bore tip flowing 200 gallons/min with a nozzle pressure of 50 psi using the subtract 10 method?

To determine the correct pump discharge pressure using the subtract 10 method, you need to consider the friction loss in the hose and the nozzle pressure. The process starts with the nozzle pressure, which is the required pressure at the nozzle for efficient operation.

In this situation, the nozzle pressure is given as 50 psi. According to the subtract 10 method, for every 100 feet of 2.5-inch hose, you typically lose around 10 psi due to friction loss. Since the length of the hose is 300 feet, you will calculate the total friction loss based on that distance.

With 300 feet of hose, you would anticipate a friction loss of:

• 10 psi per 100 feet multiplied by 3 (because 300 feet is three times 100 feet) equals 30 psi of total friction loss.

Next, you subtract this friction loss from the nozzle pressure to find the required pump discharge pressure:

• Start with the nozzle pressure of 50 psi,

• Then subtract the friction loss of 30 psi.

This results in a pump discharge pressure of 50 psi - 30 psi = 20 psi. However, the subtract 10 method indicates that as you are calculating, you must always account for an operational margin