The difference between the positive and negative effects of regulating valves

The positive and negative effects of a regulating valve are relative to the actuator of a pneumatic diaphragm regulating valve, where the upper part of the diaphragm is filled with air and the push rod moves downward, known as the positive effect. The lower intake and upward movement of the push rod are called reactions.

The air opening and closing of the regulating valve is relative to the entire regulating valve. As the signal increases, the valve gradually opens into an air open valve, and as the signal increases, the valve gradually closes into an air closed valve. When there is no signal, the pneumatic valve is in the closed state and the pneumatic valve is in the fully open state.

Flow opening and flow closing are for the medium. When the flow direction of the medium at the throttle port flows towards the direction of valve opening, it is called flow open type; conversely, when it flows towards the direction of valve closing, it is called flow closed type.

　　1、 The functional form of pneumatic actuators

(1) Positive and negative effects of pneumatic actuators. When the input air pressure of the pneumatic actuator increases, the push rod moves downward, which is called positive action; On the contrary, when the input air pressure increases, the push rod moves upward, which is called a reaction (see Figure 9-16),

(2) Adjust the formal and reverse installation of the mechanism. The valve core has two forms: forward and reverse installation. A valve with a downward movement of the valve core and a decrease in the flow cross-sectional area between the valve core and the valve seat is called a positive valve; On the contrary, when the valve core moves downwards, the flow cross-sectional area increases, which is called a reverse valve (see Figure 9-16). For dual directional positive valve, as long as the valve stem is connected to the lower end of the valve core, it is a reverse valve. Valves with a nominal diameter Dg<25mm are generally single directional, so only positive valves are available.

(3) The functional form of pneumatic actuators. Pneumatic actuators come in two forms: pneumatic open and pneumatic closed. When the signal pressure increases, the valve opens, which is called pneumatic opening; On the contrary, when the signal pressure increases, the valve closes, which is called gas closing type. Due to the positive and negative effects of the actuator, as well as the positive and negative effects of the regulating valve (with a dual directional spool), the pneumatic actuator's air opening or closing is thus combined.

For small-diameter regulating valves, it is common to change the positive and negative effects of the actuator to achieve gas opening or closing; For large-diameter regulating valves, it is usually necessary to change the positive and negative effects of the regulating valve to achieve gas opening or closing.

　　2、 Function of regulating valve positioner

The locator is used in conjunction with pneumatic thin film actuators.

(1) The positive function of valve positioner: when the input signal increases, the pressure output to the membrane head increases;

(2) Reaction of valve positioner: When the input signal increases, the pressure output to the membrane head decreases;

① The positive action actuator cooperates with the positive action locator to achieve the function of the positive action actuator;

② The positive action actuator and the reaction locator cooperate to achieve the function of the reaction actuator;

③ Cooperate with the positive action locator to achieve the function of the reaction actuator;

④ Cooperate with the reaction actuator and reaction locator to achieve the function of the positive action actuator;

Pneumatic single seat regulating valve - Shanghai Yonglong Valve Factory

　　3、 Adjust the FC gas on or FO gas off of the regulating valve

(1) The flow area of the pneumatic control valve increases with the increase of signal pressure;

(2) On the other hand, the flow area decreases with the increase of signal pressure in the closed circuit.