Overview of pneumatic diaphragm control valves, the composition of pneumatic diaphragm double seat c

Control valves are the most widely used type of final control element. Other final control elements include metering pumps, adjusting baffles and louvered baffles (a variant of the butterfly valve), variable inclination fan blades, current regulation, and motor positioning devices that differ from valves. Despite the widespread use of control valves, none of the other units in the control system require as much maintenance.

In many systems, control valves are subjected to more severe operating conditions such as temperature, pressure, corrosion and contamination than other components, however, when it controls the flow of process fluids, it must operate satisfactorily with minimal maintenance.

The control valve is composed of two parts: electric actuator or pneumatic actuator and control valve. The latter has the characteristics of large flow capacity, small unbalance and stable operation, so it is usually especially suitable for occasions with large flow rate, high pressure drop and less leakage.

Here are some of the well-known brands recognized in the valve industry, which are widely recognized and have a high reputation. While rankings may vary depending on time and market conditions, the following brands are generally considered to be among the top brands in the valve industry:

The following influential first-line brands of water system valves and industrial valves can be used as a reference, but for reference only: Suzhou Neway Valve, Shanghai Guanlong Valve, Shanghai Qizhong Valve, Sanhua, Chaoda, Shentong, Su Valve, Nanfang, Jiang.

First, the word Yao. The above manufacturers are only estimates and references, and the specific situation may vary or fluctuate at any time due to changes in a series of factors such as changes in the market, the size of the competition pattern, and the stability of product quality. As an indispensable key device in industrial production and civil facilities, the quality and reputation of the valve brand directly affect the satisfaction and trust of users.

These brands are known in the valve industry for their innovative technology, high-quality products and reliability. It is important to note that the market and industry are evolving rapidly, and different rankings may vary depending on time and region. For the most up-to-date ranking information, it is recommended to refer to industry reports, professional organizations or market research data for more detailed and accurate information.

Answers]: a, d

The pneumatic diaphragm double-seat control valve includes: pneumatic diaphragm actuator, straight-through double-seat valve.

The adjustment principle is: with compressed air as the power, the size of the air source pressure is controlled by the electrical valve positioner, so that the air acts on the rubber diaphragm of the regulating valve, and the contraction and expansion of the diaphragm then drives the valve stem to move up and down, so as to achieve the purpose of controlling the medium.

The regulator (DCS signal) converts the electrical signal into a gas signal through an electrical valve positioner, which acts on the diaphragm of the regulating valve. The diaphragm compression spring drives the spool action of the regulating valve to control the opening of the valve, so as to realize the adjustment of the medium to be adjusted. According to the needs of the process, the control valve is divided into air opening valve (fault opening) and gas closing valve (fault opening).

The electrical conversion component converts the electrical signal into a pneumatic signal, and the electrical signal input controls the pneumatic output. The most commonly used electric-pneumatic conversion components are solenoid actuated valves. The solenoid valve is not only the interface between the electrical control part and the pneumatic actuation part, but also the interface with the air supply system.

The solenoid valve accepts the command to release, stop or change the flow direction of the compressed air, in the electro-pneumatic control, the solenoid valve can achieve the following functions: the direction control of the action of the pneumatic actuator, the ON OFF switch control, or not and logic control. The most important of the solenoid valve family is the solenoid actuated directional control valves.

The working principle of solenoid control reversing valves.

In pneumatic circuits, the role of the solenoid control reversing valve is to control the on/off of the airflow channel or to change the flow direction of the compressed air. The main working principle is to use the electromagnetic force generated by the electromagnetic coil to promote the switch of the valve core and realize the commutation of the air flow. According to the different ways of pushing the reversing valve in the electromagnetic control part, it can be divided into direct-acting solenoid valve and pilot-operated solenoid valve.

The direct-acting solenoid valve directly uses electromagnetic force to push the valve core to reverse, while the pilot-operated directional valve uses the pilot air pressure output by the solenoid pilot valve to push the valve core to reverse.

The figure shows a simple cross-sectional diagram and working principle of the structure of 3 2 (three-way, two-position) direct-acting solenoid valve (normally interrupted type). When the coil is energized, the static iron core generates electromagnetic force, the valve core moves upward under the action of electromagnetic force, the sealing gasket is lifted, so that the connection is disconnected, and the valve is in the air intake state, which can control the cylinder action. When the power is off, the valve.

The core is restored to its original state by the action of the spring force, that is, it is turned on, and the valve is in an exhaust state.

The figure shows a simple cross-sectional diagram and working principle of the structure of 5 2 (five channels and two positions) direct-acting solenoid valve (normally interrupted type). Starting state, 1,2 intake 4,5 exhaust When the coil is energized, the static iron core generates electromagnetic force to make the pilot valve act, and the compressed air enters the valve through the air path The pilot piston starts the piston, in the middle of the piston, the sealing circle opens the channel, 1,4 intake, 2,3 exhaust When the power is off, the pilot valve is reset under the action of the spring and returns to its original state.

Valve function: (function).

The solenoid valve's menu shows the complexity of its electrical-pneumatic conversion. The function of the valve is represented by two numbers: m and n, which are called m-way n-position solenoid valves, and the "n-position" indicates the switching position of the reversing valve, which also indicates the state of the valve.

The number of positions of the valve is the value of n, for example, the two-position valve has two position options, that is, there are two states, and the three-position valve has three position options, that is, there are three different states. "M-way" means the passage of the external interface of the valve, including the air inlet, outlet and exhaust port, and the number of channels is the value of M, such as two-way valve, three-way valve, etc. The valve in the example is a 3 2 direct-acting solenoid valve, pronounced as "three-way two-position valve", which means that the valve has two positions, namely "on" and "off", and has three ports, which are 1:

Air intake, 2: outlet, 3: exhaust.

Quite simply, it is driven by compressed air, and the valve opening change is changed through the 4-20mA signal, so as to achieve the purpose of flow rate change.

The control valve is called the control valve in foreign countries, and it is commonly called the control valve in China, which is used to regulate the process parameters such as medium flow, pressure, temperature, and liquid level in the field of industrial automation process control. According to the control signal in the automation system, the opening of the valve is automatically adjusted, so as to realize the adjustment of medium flow, pressure, temperature and liquid level.

The pneumatic diaphragm regulating valve is made by the change of the working air source pressure to change the position of the diaphragm, and the position of the membrane that changes drives the valve stem to move to drive the change of the position of the valve core, or open or close, under the action of the valve positioner, the valve core can stay in any desired position.

There are two types of membrane control valves, i.e., air-open and air-closed. Because the actuator of the membrane control valve, that is, the membrane actuator only has a single acting form, due to the different positions of its return spring installation, it can be air open or air closed.

The selection of the membrane control valve is determined according to the process requirements of the process equipment, and the safety of the equipment will be destroyed if it is used incorrectly. For example, there is a gas tank, the pressure of the stored gas is controlled between 490kpa-510kpa, and it is equipped with an inlet valve, an outlet valve, and a safety release valve.

The gas tank has a pressure test, and the outlet gas has a flow test. The process requirement is that the pressure of the gas tank must be within the working pressure range, when the pressure of the gas tank reaches 520kpa, there is a fault alarm, when it reaches 550kpa, it is a heavy fault alarm, and the inlet and outlet valves must be closed by the interlock, and the pressure relief valve is opened, so the configuration requirements of these three valves are not the same. The requirements for the inlet valve are:

When the pressure of the gas tank is low, it is opened large, when the pressure is high, it is closed, and it is closed when the interlocking action is used, so the gas opening type is selected, and the regulator is selected as reaction; The requirements for the outlet valve are: open large when the outlet flow rate is low, close small when the outlet flow rate is high, and close when the chain action is closed, so the air open type is selected, and the regulator is selected as reaction; The requirements for the release valve are: the pressure of the gas tank is lower than 510kpa, the opening is higher than 510kpa, and the interlocking action is open, so the air-closed type is selected, and the regulator is positive.

The pneumatic diaphragm control valve is composed of two parts: pneumatic diaphragm actuator and regulating valve, which is used in conjunction with pneumatic regulators, pressure reducing valves, positioners or other instruments to control the temperature, pressure, liquid level, flow rate and other process parameters in the pipeline. The single-seat control valve has the advantages of easy sealing and small leakage, but the balance force is large, so the working pressure difference should not be too high. The double-seat control valve has the characteristics of large flow coefficient and small unbalance force, so it is widely used.

The pneumatic membrane control valve is composed of two parts: pneumatic membrane actuator and valve body, and the valve body structure is generally linear stroke, and there are common structures such as single seat, double seat, sleeve, angle type, tee, slide plate, diaphragm and so on. It is mainly composed of bonnet, spool, seat, stem, stuffing box, etc. The upper end of the valve stem is connected with the lower end of the push rod of the membrane mechanism, and the push rod drives the valve stem to move, so that the valve core moves, and the flow area of the fluid between the valve core and the valve seat is changed, so that the flow rate of the fluid is changed to achieve the purpose of adjustment.

The upper bonnet is available in normal (-17 230 operating temperature), heat dissipation (-45 450) and long neck (-196 -100 or 230 566). The lower the temperature of the fluid, the longer the upper bonnet and stem should be. The valve body part is divided into two types: single-seat valve and double-seat valve.

Single-seat valves are suitable for low differential pressure; The double-seat valve is suitable for applications with large differential pressures.

Pneumatic film actuators are divided into old-fashioned pneumatic film actuators and small pneumatic film actuators. It is mainly composed of upper and lower membrane heads, corrugated diaphragms, compression springs, push rods, etc. When the signal pressure of the regulator or manual operator enters the membrane chamber composed of the diaphragm of the membrane head, a thrust is generated on the diaphragm, which causes the actuator to move and the spring to compress.

When the reaction force generated by the spring is balanced with the thrust of the film, the push rod stops moving. Generally, the signal pressure of the film adjustment mechanism is or. That is, when the signal pressure is or, the putter starts to act; When the signal is or, the putter travels full stroke.

The membrane adjustment mechanism is divided into two types: positive and reaction. The signal pressure of the positive-acting type is introduced by the upper part of the diaphragm, and when the signal pressure increases, the diaphragm drives the push rod to move downward. In the reaction mode, the signal pressure is introduced from the lower part of the diaphragm, and when the signal pressure increases, the push rod moves upward.

Pneumatic diaphragm control valves are generally equipped with a handwheel mechanism, which can be manually adjusted at any time when the air supply is interrupted. Some are also equipped with valve positioners, which can improve the adjustment performance of the control valve.