As a terminal execution unit of the process control system, ZJHP Pneumatic single seat control valve directly contacts with process media including liquid, gas and steam. It undertakes the critical task of converting control system commands into actual process parameter changes. Compared with electric and hydraulic control valves, the pneumatic type features intrinsic explosion-proof performance, low operation cost, strong environmental adaptability and no risk of electrical failure, which makes it more suitable for flammable, explosive, high-temperature and high-pressure harsh industrial environments.

ZJHP Pneumatic single seat control valve Structural Composition 

The complete ZJHP Pneumatic single seat control valve is mainly composed of two core parts: pneumatic actuator andsingle-seat valve body assembly, supplemented by auxiliary accessories such as valve positioner, air filter regulator, solenoid valve, limit switch and packing sealing components. Each module cooperates closely to ensure stable signal response, accurate displacement execution and reliable medium sealing.
 

1 Pneumatic Actuator Assembly

The actuator of ZJHP Pneumatic single seat control valve is the power source of the control valve, responsible for converting pneumatic energy into mechanical linear thrust to drive the valve core movement. The mainstream type is the spring-diaphragm actuator, which features simple structure, stable output force and good linear matching with control signals. A few high-thrust working conditions adopt piston pneumatic actuators.
 

The spring-diaphragm actuator consists of a upper membrane cover, lower membrane cover, rubber diaphragm, actuator spring, spring seat, push rod and air inlet interface. The diaphragm divides the actuator inner cavity into a sealed air pressure chamber and a spring reset chamber. When compressed air enters the air pressure chamber, air pressure acts on the diaphragm to generate downward thrust, overcoming the spring preload and medium unbalanced force to push the push rod down; when the air pressure decreases, the spring rebounds to drive the push rod to reset upward, realizing automatic reset of the valve.
 

According to the action mode, actuators are divided into air-to-open and air-to-close types. The air-to-open valve opens when air pressure increases and closes when air pressure disappears (fail-close), which is suitable for process working conditions requiring safety shutdown during air source failure; the air-to-close valve closes when air pressure increases and opens when air pressure disappears (fail-open), applied to working conditions requiring continuous fluid passage during equipment failure.
 

2 Single-Seat Valve Body Assembly

ZJHP Pneumatic single seat control valve body assembly is the fluid regulation and sealing core, directly bearing medium pressure and flow impact, mainly including valve body, valve seat, valve plug (valve core), valve stem, bonnet and packing box. The overall flow channel adopts an S-shaped streamlined design, which effectively reduces fluid turbulence and pressure drop, optimizing medium flow state.

ZJHP Pneumatic single seat control valve seat is fixed at the bottom of the valve body, forming a precise sealing pair with the upper valve plug. The single-seat structure achieves zero leakage tight shut-off more easily than double-seat valves, meeting the strict shut-off requirements of most precision process working conditions. The valve plug is connected with the actuator push rod through the valve stem, adopting top-guided or upper-and-lower double-guided positioning structure, which ensures high straightness of linear movement, avoids plug deflection and jamming, and improves regulation stability.

The packing box is arranged at the bonnet position, filled with graphite, PTFE and other high-performance sealing packing, which effectively prevents medium leakage from the valve stem gap and ensures the tightness of the valve body under high pressure and high temperature working conditions. The bonnet plays a role of fixing the valve stem guide and protecting the internal sealing structure, with different structural designs such as standard type, high-temperature extension type and low-temperature cold insulation type adapted to different working conditions.
 

3 Core Auxiliary Accessories

Auxiliary accessories are key to improving the control accuracy and operational reliability of the valve. ZJHP Pneumatic single seat control valve positioner is the core accessory, which receives 4–20mA electric signals or pneumatic signals, compares the signal value with the actual valve stem displacement, and dynamically adjusts the actuator air intake pressure to realize precise positioning of the valve plug, eliminating the errors caused by spring hysteresis and medium unbalanced force.