Diaphragm regulating valve (pneumatic)
Product Overview
Pneumatic diaphragm control valves are the execution units of automated control systems in industrial production processes. They change the valve opening degree according to the signals from the regulating instruments, thereby achieving the regulation of parameters such as pressure, temperature, flow rate, and liquid level.
Pneumatic diaphragm control valves have advantages such as small size, simple structure, easy use, fire resistance, explosion protection, and convenient maintenance. Therefore, they are widely used in automatic regulation and remote control systems of industrial production processes in chemical, petroleum, metallurgy, power, and light industries.
Structure and working principle
1. Structure: The pneumatic diaphragm control valve consists of two parts: a pneumatic diaphragm actuator and a control valve. The new series of pneumatic actuators adopts a multi-spring structure. Therefore, the height of the actuator is significantly reduced, and the weight is correspondingly lighter. The valve body is a low-flow-resistance valve body designed according to fluid dynamics principles, increasing the rated flow coefficient by approximately 30%. The pneumatic diaphragm control valve has two operating modes: air-to-open and air-to-close. The selection of air-to-open or air-to-close is mainly based on production safety, considering that when the input signal is interrupted, the valve is in a safe on/off state for the system.
2. Working principle: The pneumatic diaphragm control valve is operated by a signal pressure from the regulator, which is input into the air chamber of the pneumatic diaphragm actuator to generate thrust. This thrust pushes the valve core through the connecting rod, producing a corresponding displacement—the so-called stroke. The change in the position of the valve core causes a change in the flow cross-sectional area of the valve, thereby achieving the purpose of regulating the flow rate of the medium.
External dimensions
Note:
1. The flange connection dimensions of this product PN16 and PN25 conform to JB79.1-94 standard, PN64 conforms to JB79.2-94 standard, and the structural length conforms to GB2221-89 standard.
2. This product has two flange sealing forms: raised face and concave face. It can be customized according to the user's specifications. If the user does not specify, PN16 will be convex face, and PN40 and PN64 will be concave face.
Product Technical Parameters
Key performance indicators
Installation and maintenance
1. The installation position of the pneumatic diaphragm control valve (hereinafter referred to as the valve) should be at an appropriate height from the ground, with sufficient space above and below the valve to facilitate disassembly, transportation, and repair. For valves equipped with pneumatic valve positioners and handwheel mechanisms, it is even more important to ensure safe and convenient observation, adjustment, and operation.
2. To avoid applying additional stress to the valve due to improper installation, such as misalignment between the pipe and the valve or non-parallel flange faces, the combined effects of the valve's own weight, surrounding vibrations, and changes in medium and ambient temperature can cause the flange to crack or deform. To avoid such accidents, the valve should be installed on a bend in the pipe (as shown in Figure 6), and large-diameter valves should be supported.
3. The valve's operating environment temperature should be between -30℃ and +60℃, with a relative humidity not exceeding 95%. This is because rubber-like parts such as corrugated diaphragms and seals harden and become brittle at low temperatures, and age more rapidly at high temperatures. This point should be taken into consideration when the valve is located near a heating furnace or high-temperature pipeline.
4. This valve can be installed vertically, or tilted and inverted. When tilted, the valve core's weight causes it to tilt to one side, accelerating localized wear between the valve core and the bushing, and between the valve core and the valve seat. The disadvantage of inverted installation is that leaked media from the packing may contaminate or corrode the pneumatic diaphragm actuator.
5. Bypass Pipeline. The purpose of setting up a bypass pipeline (Figure 6) is to facilitate valve maintenance without stopping the machine after switching or manual operation.
When valves regulating low-pressure, normal-temperature, non-corrosive media (such as water, air, etc.) will not experience corrosion, wear, or jamming accidents, or when the nominal diameter of the valve is large (DN100 mm or above), the cost of installing bypass pipelines is high and the footprint is large, the bypass pipeline can be omitted. However, a handwheel mechanism should be installed on the valve so that it can be manually operated in case of failure of the automatic control system.
6. Air piping. The air piping is made of copper or plastic with an outer diameter × inner diameter of Ф6 × Ф4 or Ф8 × Ф6. Ensure that the connections are airtight.
7. When installing the valve onto the pipeline, the arrow on the valve body should point in the same direction as the fluid flow in the pipeline. If the nominal diameter of the valve differs from the nominal diameter of the pipeline, a reducer should be inserted between them.
8. Before valve installation, thoroughly clean the pipeline of dirt and welding slag. After installation, conduct a trial run with room temperature water. During the trial run, shut off the valve to bypass the pipeline. If there is no bypass pipeline, keep the valve in the fully open position. Clean the pipeline and test the sealing of the connections during the trial run. After the trial run, put the valve body into operation.
9. The regulating valve should be stored indoors where the ambient temperature is between -5 and +40°C and the relative humidity is not greater than 90%. The air should not contain harmful impurities that can corrode the valve, and dust prevention should be taken into account.