Choosing the right valve body is pivotal in the selection process of a diaphragm valve. A variety of valve body types are available, such as straight single seat, straight double seat, angle shape, diaphragm, small flow, tee, eccentric rotation, butterfly, sleeve type, and spherical, among others. Before making a selection, it is essential to conduct a thorough analysis of the medium, process conditions, and control parameters. Adequate data must be gathered to comprehend the system's requirements for diaphragm valves, which will guide the determination of the appropriate valve type.

Here are key considerations for the selection process:

(1) Valve Core Design: The shape and structure of the valve core should be chosen based on the flow characteristics and the forces that are unbalanced.

(2) Durability Against Wear: For media that contain a high concentration of abrasive particles, the valve core and seat are subjected to significant wear during each closure. Thus, the valve's flow path should be streamlined, and the internal materials should be selected for their hardness to resist wear.

(3) Corrosion Resistance: When the medium is corrosive, opt for a valve with a simple structure that can meet the regulatory function, as simplicity can often enhance resistance to corrosion.

(4) Temperature and Pressure Stability: For applications where the medium's temperature and pressure are high and subject to significant changes, select a valve core and seat that exhibit minimal sensitivity to these variations.

(5) Avoidance of Flash and Cavitation: These phenomena should be prevented in liquid media, as they can impact the calculation of the flow coefficient and lead to issues such as vibration, noise, and a reduction in the valve's service life.

In summary, the selection of a diaphragm valve requires a meticulous approach that takes into account the valve's structural integrity, material properties, and operational environment to ensure optimal performance and longevity.

The selection of an appropriate actuator is critical for the proper functioning of a diaphragm valve, as the actuator's output force is essential to counteract the effective load, which includes unbalanced forces, moments, friction, sealing forces, gravity, and other related forces. To ensure the diaphragm valve operates effectively, the chosen actuator must generate sufficient force to overcome these resistances and maintain optimal sealing and valve operation.

For double-acting pneumatic, hydraulic, and electric actuators, the force exerted is independent of the direction of operation, as these types typically lack a return spring. The primary selection criterion for these actuators is to ascertain their maximum output force and the motor's rotational torque. In contrast, for single-acting pneumatic actuators, the output force is valve-opening dependent, and it can influence the valve's movement characteristics, necessitating a balanced force approach throughout the valve's opening range.

Once the required output force is established, the selection of the actuator should align with the specific environmental demands of the process. In environments with explosion-proof requirements, pneumatic actuators with explosion-proof junction boxes are the preferred choice, precluding the selection of electric actuators. In the absence of such requirements, both pneumatic and electric actuators are viable options, with a preference for electric actuators due to their energy efficiency. Hydraulic actuators, while less common, offer precision, rapid response, and stable operation, making them ideal for applications demanding high regulatory performance, such as speed control in power plant machinery or temperature regulation in refinery catalytic reactors.

Regarding the operation mode of the diaphragm valve, the choice is influenced by several factors, including process safety, medium characteristics, and the imperative to ensure product quality while minimizing economic losses. The valve's action mode is determined by the combination of the actuator's positive and negative actions, with four possible combinations leading to two operational modes: air-to-open and air-to-close. The selection of the valve's action mode should be guided by considerations of safety, medium behavior, and economic efficiency.