Cal-Val 49-01 and 649-01 Rate of Flow and Pressure Reducing Valves automatically reduce higher inlet pressure to a steady lower downstream pressure regardless of changing flow rate and/or varying inlet pressure, as long as the flow rate is below a preset maximum. They also prevent excessive flow by limiting flow to a preselected maximum rate using a direct-acting pressure reducing pilot and a rate of flow differential control. The pressure reducing pilot is responsive to slight variations in downstream pressure and immediately controls the main valve to maintain the desired line pressure.

The rate of flow control responds to the differential pressure produced across an orifice plate in the mainline. Accurate control is assured as very small changes in the controlling differential pressure produce immediate corrective action by the main valve.