Fire engine pressure: For firefighting an important concept is that of engine pressure, which is the pressure that the pumper requires to overcome friction loss from the hose and to maintain the proper pressure at the nozzle of the hose. One formula14 for engine pressure is
where EP is the engine pressure in pounds per square inch (psi), NP is the nozzle pressure in psi, K is the “K” factor (which depends on which tip is used on the nozzle), and L is the length of the hose in feet divided by 50. This formula expresses EP as a function of NP, K, and L.
a. Find the engine pressure if the nozzle pressure is 80 psi, the “K” factor is 0.51, and the length of the hose is 80 feet.
b. Find the nozzle pressure if the “K” factor is 0.73, the length of the hose is 45 feet, and the engine pressure is 150 psi.
c. Solve the equation for NP—that is, write a formula expressing NP as a function of EP, K, and L. d. Find the “K” factor for a nozzle tip if the length of the hose is 190 feet, the engine pressure is 160 psi, and the nozzle pressure is 90 psi.
e. Solve the equation for K—that is, write a formula expressing K as a function of NP, EP, and L.