General Information:
The safety-type design is available for use when a break in the system, allowing loss of the pressure charge, must result in the valve moving toward the cooler control position.

This action is accomplished by reversing the operation forces. The pressure charge is in the partial vacuum range (below atmospheric) resulting in a pulling force from the bellows against a spring force loading the valve stem into the body. The bellows must now pull the stem out of the body against the spring load. A larger bellows is used due to the very limiting vacuum differential available to the bellows, to develop adequate thrust to the valve stem. The larger bellows requires a larger bulb and less stem movement is obtained. Therefore, less capacity is available by 30% (use 70% of full open C_v factor).

Accuracy:
All previous comments apply, however, the slower vapor pressure changes in the vacuum area required, result in the slower action of the valve. Therefore, stability of the system and valve size are of even greater importance with this model.

Operation:
Adjustment and use of this unit is identical to the standard unit.

Valve Bodies:
Due to the limited stem forces available, pressure limits are reduced as tabulated.

Capacity:
Use 70% of Body C_v tabulated to choose the size for use with the safety actuator.

© Pneumatic Control, Inc. 1999/2000