Power Pump Valve Dynamics

LectureThe dynamics (movement) of the check valves in a reciprocating power pump determine whether the pump will operate quietly and smoothly, or noisily with pulsation and vibration. Although piping pulsation and vibration are, to a degree, function of the system design, improper pump valve dynamics contribute a significant portion of the pulsation problems in many installations. Many reciprocating power pumps, operating in industrial installation, have been found to be fitted with suction and discharge valve springs that are too weak. The weak springs do not close the valves soon enough, as the plunger reverses, causing the valves to be slammed onto their seats, creating a noisy pump, hydraulic shocks, and possible damage to the valves and/or seats. The hydraulic shocks can also cause damage to other pump components, the drive train, and to the system. Suction and discharge pipes may vibrate, piping and instruments may be damaged, and pump net positive suction head (NPSH) requirements may be high. To reduce the pulsations and vibrations, owners frequently resort to the installation of pulsation dampening equipment in the piping, when stronger valve springs may have been adequate to produce a quiet, smooth-running pump. Starting with either the maximum valve lift, or the maximum closing impact velocity, simple equations of motion can approximate the displacement (lift), velocity, and acceleration of the valve, all based on crankshaft rotative speed. The maximum lift can then be used to calculate the NPSH required by the pump