The HWM ControlMate range of PRV controllers can be supplied with a Hydraulic Actuator - a patent pending device used as the interface between the electronic controller and the hydraulic PRV.
The Actuator is fitted in place of the adjusting screw of the standard pilot on the PRV. To adjust the PRV outlet, the ControlMate progressively extends or retracts the moving "rod" of the actuator in small steps under closed loop control. The moving rod exerts a force on the pilot's spring in a similar manner to that of the adjusting screw in a standard PRV installation.
The main PRV outlet follows its pilot valve setting, controlling the Actuator's moving rod. This leads to very accurate and repeatable control of the PRV outlet pressure. In two point pressure control applications, the two required pressure settings are mechanically set and locked on the Actuator. The outlet pressure of the main PRV cannot be outside of these values.
In full modulating applications, the minimum and maximum pressures within which the controller can operate are set and locked on the Actuator. This means that failure of electronics, incorrect operation by the user, burst or frozen pipes cannot cause closure of the main PRV.
The availability of the Hydraulic Actuator eliminates the main technical weaknesses associated with the use of "bias" chambers (or dual-chamber pilots in older controllers. Bias chambers that are sandwiched between the "wet" and "spring" parts of the pilot may adversely affect its operation. The Hydraulic Actuator has,no such effect since no "wet" part of the pilot needs to be accessed and no extra mechanical frictions, O-rings, diaphragm loading, etc. are imposed on the normal operation of the pilot. This allows for much smoother control of the PRV.
Use of the Hydraulic Actuator means that it is no longer necessary to use an MRA (small pressure regulator) to generate an intermediate pressure to carry out a 2-point control function. In addition, the built-in mechanical minimum setting on the Hydraulic Actuator means that there is no longer the possibility of valve closure due to electronics failure, operator error or leakage of the MRA.
For these reasons, HWM recommends the use of the Hydraulic Actuator with its pressure control equipment.