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What is the principle of operation of a Steam Control Valve?
- Jul 21, 2018 -

The old method of throttling flow or using an orifice plate will result in fluctuations of flow rate. The ideal solution is to adjust the downstream pressure automatically through proportional adjustment of valve opening. This technique will keep the steam pressure unaltered even during the fluctuations of flow rate.

Steam Control Valve-Fig-1-500x211 (1).png

The schematic in Fig-1 illustrates the use of a Steam Control Valve to reduce steam pressure to control heating inside the jacketed vessel. This system will ideally demand for manual interventions. A fully self-contained automatic system will comprise of an actuated Steam Control Valve, a pressure sensor and an actuator. This kind of system senses the fluctuations in the downstream pressure and adjusts it through a quick response actuator.

The typical mechanism to adjust the outlet pressure is through a balance of force adjustment between the steam pressure and the adjustment spring in the valve. The steam control valve is manufactured either by Non-piloted Acting Valve or Pilot-operated Acting Valve.

The non-piloted adjustment spring applies downward force directly on the main valve. The Piloted type adjustment spring executes downward pressure on a smaller pilot valve, which is not the same as the main valve.

The advantages of direct acting type are compact, economic, and straightforward installation. However, the controlling factor have larger variations from the set point, and mostly used for low loads.

Steam Control Valve-Fig-2-570x300 (1).png

The schematic in Fig-2 above is self-explanatory of the Piloted type Steam Control Valve arrangement normally used for a Heat Load along with a Heat Exchanger. The piloted type is used for heavy loads to achieve a fast response in a much broader range of flow range than the non-piloted types. However, these are larger in size and costlier.