Pneumatic Actuators Double Seat Gas Airflow Control Valve

1. General
Pneumatic diaphragm control valve is the terminal industrial process measurement and control system control device, is composed by pneumatic diaphragm actuator, direct through single-seat, double seat and sleeve valve, etc., which can automatically change the valve trim position according to the control signal system, changing the flow area between the valve trim and the valve seat, to change the valve drag coefficient, to realize the regulation for the medium flow, pressure and level and other process parameters adjustment. 
Pneumatic diaphragm valve use dual-oriented structure, equipped with multiple spring actuator, with a compact, light weight, sensitive, valve capacity big, flow characteristics of precision, easy to disassembly. Widely used for precise control of gas, liquid, steam and other media, process parameters such as pressure, flow, temperature, level maintained at a set value. Especially for the smaller amount of pressure and small leakage workplace. 

2. Technical performance and data
Control valve data
Valve body material-cast iron, cast steel and so on
Pressure class: 1.6MPa, 4.0MPa, 6.4MPa
Connected way: Flange connection according to JB79-59
Temperature scope: Normal-20 C~+230 C air cooling fin-60 C~+450 C
Action way: Positive (air to close type)or back action (air to open type)
Flow characteristic: Equal percent/linear
Leakage: Single seat 0.01%× Rated Kv
Ouble seat, sleeve seat: 0.5%× Rated Kv
Actuator data
Referred to the manual

3. Structural principle
Pneumatic diaphragm valve including pneumatic diaphragm actuator and the control valve
BZHP pneumatic control valve is a single-seat control valve with BZH pneumatic diaphragm actuator
BZHN pneumatic double seat valve is a double seat valve with BZH pneumatic diaphragm actuator
BZHM pneumatic sleeve valve is a sleeve valve and BZH pneumatic diaphragm actuator
A. Pneumatic diagram actuator
For the structure and working principal, please take the reference for the manual
B. Control valve
Control valve is contacted directly with the medium in the pipe, the valve trim act in the valve body, to change the flow area between the valve trim and the valve seat, which change the drag coefficient of the valve, thereby adjusting the process parameters. 
Control valve is composed by up cover, valve body, down valve cover, valve trim part, valve seat, stuff and plate. Please take reference of drawing 1, drawing 2
The action way can be divided into positive way (air to close type) and back way(air to open type). The valve will be from fully open to fully close when input signal pressure change from down limit value to upper limit value; The valve will be from fully close to fully open when input signal pressure change from down limit value to upper limit value; 
Pneumatic control single seat valve with good performance of sealing and small leakage, the working pressure difference can not be too high due to the big unbalance force of valve trim
Pneumatic double seat control valve with the performance of big rated flow KV, small valve trim unbalanced force, stable operation and big pressure difference. It is widely used. But compare with single seat control valve, its leakage is bigger. 
The stability and Cavitation resistance of Pneumatic sleeve control valve is better than single seat and double seat valve.

DN	25	32	40	50	65	80	100	125	150	200	250	300
Rated flow Kv	10	16	25	40	63	100	160	250	400	630	1000	1600
PN MPa	1.6         4.0         6.4
BZH pneumatic actuator model	BZHA/B-22		BZHA/B-23		BZHA/B-34			BZHA/B-45			BZHA/B-56
Rated travel (mm)	16		25		40			60			100
Flow characteristic	Equal percent         linear
Action way	Air to open         air to close
temperature	-20C~+230C         -60C~+450C