What are positive and negative film actuators?

2025-03-17 13:20:23 58

The actuator can be divided into two types according to the action mode: positive action type and negative action type, and can be divided into two types according to the type: air open and air closed. Now it is described as follows:

1. Positive action execution mechanism
When the signal pressure increases, the push rod of the actuator moves downward, which is called a positive action actuator. When the signal pressure increases from 20kPa to 100kPa, the push rod moves from zero to the full stroke position, and its displacement characteristics are shown in Figure 1. The operating principle is shown in Figure 3. When the signal pressure enters the membrane chamber, a thrust is generated on the membrane, causing the push rod component to move. Compress the spring until the reaction force of the spring is balanced with the thrust generated by the signal pressure on the diaphragm. At this point, the displacement L of the push rod is

In the formula, A is the effective area of the membrane; K is the spring stiffness; P is the signal pressure entering the membrane chamber. When the specifications of the actuator are determined, A and K are constants, and the displacement of the push rod is proportional to the signal pressure, that is, the smaller the signal pressure, the smaller the displacement of the push rod; The greater the signal pressure, the greater the displacement of the push rod.


2. Reaction execution mechanism
When the signal pressure increases, the push rod of the actuator moves upward, which is called a reaction type actuator. When the signal pressure increases from 20kPa to 100kPa, the push rod moves from the full stroke to the zero position, and its displacement characteristics are shown in Figure 2. The principle of its action is the same as the positive action, but the difference is that the signal pressure of the reaction actuator enters below the diaphragm. When the signal pressure increases, the diaphragm moves upward.

Explanation: The positive action actuator and valve (with the valve core installed) form an air tight type; The reaction actuator and valve (with valve core installed) form an open type valve