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Pilot valves

Pilot valves control trim operation


High pressure in sensing chamber (4): The pressure in the sensing chamber (4) is overcoming spring (1) resistance, forcing the diaphragm (3) up. (Picture 1)


Low pressure in sensing chamber (4): The spring (1) is compressed by the adjustment bolt (2), forcing diaphragm down. (Picture 2)


The shaft (5) is moving with the diaphragm, actuating the main valve (6) by opening or closing pilot valve’s internal water passages.

Pilot valve set-point

  • The pilot valve’s position is determined by the forces equilibrium of hydraulic pressure and spring resistance.
  • Spring resistance is adjusted by the adjustment bolt (2).
  • Compressing the spring (turning the bolt in clock-wise direction) increases the regulated parameter. For example:  In Pressure Reducing valves- tightening the bolt (turning in clock-wise direction) will increase the maximal downstream pressure. In Pressure Sustaining valves- tightening the bolt will increase the minimal upstream pressure. In Flow Control valves- tightening the bolt will increase the maximal flow rate.
  • A specific spring has specific pressure range in which it can regulate. Springs are marked by different colors representing different pressure ranges. Correct spring selection is critical for the Pilot valve function.
  • Colored rings located on the adjustment bolt specify the internal spring color.
  • The spring selection is usually done by “DOROT” technical department according to the client’s data and demands but spring replacement can be easily done by the client if conditions demand.