Safety must always be the first consideration. In most cases, the answer to one question will determine the control valve action – What should the valve do if the control signal is lost? The answer to this question should be provided by the user, but for heating applications, the valve should typically fall closed; and for cooling applications, the valve should fall open.

When making this selection, both the action of the valve and the actuator must be considered.

A direct-acting valve is one that closes when the stem is pushed down. A reverse-acting valve is one that opens when the stem is pushed down. Refer to the Selection Guide Matrix for valve action.

The direct-acting actuator is one that pushes down with increasing signal, and is distinguished by the signal connection above the diaphragm. The reverse-acting actuator has the signal connection below the diaphragm, and pushes up on increasing signal.

Figure 2 shows the 4 possible valve/actuator combinations and the resulting actions.

Refer to the Selection Guide Matrix for the standard actuator for your valve type and size. Column 11 shows the maximum allowable inlet pressure for that standard actuator in the closed position. This assumes the worst condition, with downstream pressure at zero. Column 12 shows the standard actuator model numbers. If your application requires higher close off pressures, consult with the factory representative.