Pipe Flow Expert is able to calculate the pressure available at a pump inlet. This pressure will change if the mounting position of the pump along a pipe is changed. The vapor pressure of the fluid being pumped is subtracted from the pump inlet pressure to obtain the Net Positive Suction Head available. The NPSHa must be higher than the pump manufacturer’s NPSHr (Net Positive Suction Head requirement for the flow rate) in order to prevent gas bubbles forming in the fluid.