ZHAN Pneumatic Diaphragm Double-seat Control Valve

I. Introduction:

       The ZHAN pneumatic diaphragm double-seat control valve consists of two parts: the ZHA-type pneumatic diaphragm multi-spring actuator and the VN-type straight-through double-seat valve. Principle: The working principle of the pneumatic double-seat valve is as follows: The signal pressure from the regulator is input into the air chamber of the pneumatic diaphragm multi-spring actuator, acting on the diaphragm to generate thrust. This force compresses the spring set, causing the push rod to displace. It drives the valve core through the connecting rod to produce a corresponding stroke, changing the throttling area between the valve core and the valve seat, thereby achieving the purpose of regulating the medium flow. Features: It has advantages such as large flow capacity, small unbalanced force, and convenient switching of action modes; it also has advantages like compact structure, large output force, low height, light weight, and convenient installation and adjustment. The pneumatic double-seat valve has two action modes: air-to-close and air-to-open. The valve core adopts a double-guided structure. Simply by installing the valve stem into the other guide end of the valve core, inverting the valve body, and swapping the positions of the upper valve cover, it can be switched from air-to-close to air-to-open.

II. Principle:
       When pneumatic diaphragm double-seat control valves are used in series, the pressure difference before and after the valve changes as the opening degree changes, causing the valve's working characteristic curve to deviate from the ideal characteristic. If the pipeline resistance is large, the linear characteristic will turn into a quick-opening characteristic, losing its regulating ability. The equal percentage characteristic will turn into a linear characteristic. In the case of small flow, since there is little pipeline resistance, the above characteristic distortion is not significant, and for the equal percentage characteristic, it is actually unnecessary. From a manufacturing perspective, when Cv is below 0.05, it is impossible to produce the side shape of an equal percentage. Therefore, the main problem for small flow valves is how to control the flow within the required range.

III. Performance Indicators:
1. Spring range: 20-100, 40-200 KPa
2. Supply air pressure: 140-300 KPa
3. Air source interface: Rc1/4
4. Ambient temperature: -30 to +70℃
5. Accessories: Positioner, air filter regulator, holding valve, limit switch, handwheel mechanism, etc.

IV. Main Parameters:
1. Model: ZHAN
2. Type: Double-seat
3. Valve body material: WCB, 304, 304L, 316, 316
4. Valve core material: WCB+PTFE, 304+PTFE
5. Process medium: Crude brine (2% solids), sodium chloride solution (with solids), sodium chloride solution
6. Medium state: Liquid (with solids)
7. Operating pressure: (0.6MPa ≤ 32MPa), (PN10 ~ PN320), (150LB ~ 2500LB)
8. Pressure before valve: ≤0.5MPa
9. Pressure after valve: ≤0.2MPa
10. Leakage class: Class V, Class IV

V. Working Principle:
       When used in pipe networks, flow control valves can directly set the flow according to the design. Under the action of water, the valve can automatically eliminate the remaining pressure head of the pipeline and the flow deviation caused by pressure fluctuations, maintaining the set flow constant regardless of changes in system pressure. These functions of the valve enable one-time completion of pipe network flow regulation, simplifying the pipe network adjustment work to simple flow distribution and effectively solving the hydraulic imbalance of the pipe network. Flow control valves are mainly applied in water systems such as central heating (cooling), enabling on-demand distribution of pipe network flow, eliminating hydraulic imbalance in water systems, solving the problem of uneven heating and cooling, and achieving energy and electricity savings of 15%-20%.