What happens when the flow of a liquid is suddenly stopped? A hydraulic transient pressure occurs when the kinetic energy of the moving column of liquid is discharged into the surrounding piping. Transients can be very destructive; there are cases where storm drainage systems, overloaded by a sudden downpour, have been severely damaged. Process piping can also be damaged by hydraulic transients resulting from a suddenly closed valve. The creation and measurement of hydraulic transients in the laboratory is an important field of study. Transients can last just a few milliseconds or continue for several minutes, depending on the size of the hydraulic system under test. Accurate measurement of the pressure increase during a transient event is of critical importance.

Transducers used in hydraulic transient studies must have a fast response to changes in pressure. Validyne variable reluctance sensors have only a single moving part, the sensing diaphragm. The diaphragm is free to move quickly as the pressure changes; there are no linkages or other mechanical connections to slow the sensor down. Additionally, variable reluctance sensors have extremely small displacement volumes. The DP15 for example, needs just 6 x 10-4 cu inches of fluid to go from 0 to full scale reading.

The combination of small displacement volume and only a single moving part makes the variable reluctance sensor ideal for measuring rapidly changing pressures. The DP15, for example, can accurately respond to a pressure wave changing at the rate of 300 times per second.