Mannesmann Aktiengesellschaft

Alexander Kleist

Wolfgang Backe

Thomas Karte

Heiko Kresse

An apparatus and process for monitoring conditions of a control valve including a valve element operated by a drive controlled by a position controller. A spindle extends into a valve chamber through a dynamic seal and connects the valve element to the drive. The condition of the seal is monitored by measuring start-up time, stopping time and distance travelled. The start-up time relates to the time between application of control current to the position controller and sensing movement of the valve element. The stopping time relates to the interval between application of a second control current to the position controller and sensing the valve element has stopped. The distance travelled relates to distance the valve clement travels during the stopping time. A time difference is determined by subtracting the stopping from the starting time and is calibrated to a seal coefficient of friction. The distance travelled is also calibrated to a seal coefficient of friction. These two coefficients of friction are compared whereby a discrepancy indicates a change in air pressure has occurred during valve operation. These measurements are taken prior to and cyclically during valve operation. The coefficient of friction obtained during valve operation is compared with the coefficient of friction obtained prior to valve operation to indicate a change in the condition of the seal. If a change in air pressure occurred during valve operation, the coefficient of friction obtained by calibrating the travel distance is compared with the coefficient of friction obtained prior to valve operation.

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Aachen, Germany

Alexander Kleist