Pneumatic diaphragm single seat regulating valve_diaphragm single seat pneumatic regulating valve CONTROL VALVE Manufacturer
Model: ZJHP/single seat, ZJHM/sleeve double seat
Overview of pneumatic diaphragm single seat regulating valve:
Pneumatic diaphragm single seat regulating valve is also called diaphragm single seat pneumatic regulating valve, which consists of pneumatic diaphragm actuator and regulating valve. Pneumatic diaphragm control valve is mainly composed of air chamber, diaphragm, thrust disc, spring, push rod, adjusting nut, valve position scale, valve stem, valve core, valve seat, stuffing box, valve body, valve cover and support. The single seat valve body is compact in structure, light in weight, sensitive in movement, S-streamline in fluid passage, small in pressure drop loss, large in valve capacity, accurate in flow characteristics, and convenient in disassembly and assembly. The cage detachable structure design solves the problems of the traditional screw in valve seat, which is difficult to repair on site and high maintenance cost.
Working principle of diaphragm single seat pneumatic control valve:
The action of the pneumatic diaphragm regulating valve is that the signal pressure from the regulator is input into the air chamber of the pneumatic actuator to generate thrust, and the valve core is pushed by connecting the push rod to generate corresponding displacement— That is, the stroke. The change of the valve core position changes the flow cross-sectional area of the valve, so as to achieve the purpose of regulating the medium flow.
Model selection based on safety:
There are two types of pneumatic diaphragm regulating valve: air on valve and air off valve. According to the safety and use requirements of different production processes, when the signal pressure is interrupted, the regulating valve is in the open or closed position, depending on the hazard to process production. If the hazard is small when the valve is in the closed position, the air to open valve shall be selected. When the signal pressure is interrupted, the regulating valve shall be in the closed position. Otherwise, the air to close valve shall be selected.
| Valve action form |
| Air close type (B) - valve position open (FO) in case of air loss; Air to open (K) - valve position closed (FC) in case of loss of air |
| enclosure |
| Positioner, air filter pressure reducer, retaining valve, travel switch, valve position transmitter, handwheel mechanism, etc |
Model selection according to use requirements
Pneumatic diaphragm regulating valve is composed of valve core and valve body (including valve seat), and has different structural forms according to different use requirements. Pneumatic diaphragm regulating valve mainly includes straight through single seat valve, double seat regulating valve and high-pressure angle regulating valve.
1.1 The straight through single seat valve has small leakage, and the imbalance force formed by the thrust of the fluid on the single seat valve core is large. Therefore, the straight through single seat valve is suitable for situations requiring small leakage, small pipe diameter, and low pressure difference before and after the valve.
1.2 There are two valve cores in the body of straight through double seat valve, which are roughly offset due to the opposite thrust direction of the fluid acting on the upper and lower valve cores; Therefore, the unbalanced force of the double seat valve is very small, allowing a large pressure difference between the front and rear of the valve. However, due to the complex flow path in the valve body, the erosion damage to the valve body is serious when it is used for high pressure difference, and it is not suitable for media with high viscosity, suspended particles or fibers. In addition, due to the limitation of processing conditions, the upper and lower valve cores of the double seat valve are not easy to be closed tightly at the same time, so the leakage volume is large when closing. Especially when it is used at high or low temperatures, due to the different thermal expansion coefficients of materials, it is more likely to cause serious leakage.
1.3 The valve body of the angle type high-pressure valve is a right angle type, with simple flow path, small resistance and little erosion by high-speed fluid. It is especially suitable for the fluid with high pressure difference, high viscosity and suspended particulate matter, and can also be used to deal with the situation of vapor liquid mixture and flash cavitation. The valve body can avoid coking, sticking and blocking.
| performance |
| Project | Without positioner | With locator |
| Basic error% | ± five | ± one |
| Backlash% | ≤ three | ≤ one |
| Deadband% | ≤ three | ≤ zero point four |
| Deviation of constant point% | Air on | Starting point | Soil 2.5 | ± one |
| End | ± five | ± one |
| Gas off | Starting point | ± five | ± one |
| End | Soil 2.5 | ± one |
| Rated travel deviation% | ≤ two point five |
| Leakage 1/h | 0.01% X valve rated capacity |
| Adjustable range R | 30:1 |
Model selection according to flow characteristics
During the design of automatic control system, the flow characteristics shall be taken into account when selecting pneumatic diaphragm control valve. Typical ideal characteristics include straight flow characteristics, equal percentage flow characteristics (logarithmic flow characteristics), quick opening flow characteristics and parabolic flow characteristics. Under the condition of the same change of relative opening, the relative change value of flow is large when the flow rate is small; When the flow is large, the relative change value of flow is small. Therefore, the linear flow regulating valve has poor regulating performance under the condition of small opening (small load), is difficult to control, and often produces oscillation. Therefore, the linear flow characteristic regulating valve is not suitable for the condition of small opening, nor for the regulating system with large load change, but for the regulating system with relatively stable load and small change. Therefore, the linear flow regulating valve has poor regulating performance under the condition of small opening (small load), is difficult to control, and often produces oscillation. Therefore, the linear flow characteristic regulating valve is not suitable for the condition of small opening, nor for the regulating system with large load change, but for the regulating system with relatively stable load and small change. The regulating valve with percentage flow characteristic has weak regulating effect at small load and strong regulating effect at large load. It has weak regulating effect when it is close and works slowly and steadily, while it has strong regulating effect when it is close to full open and works sensitively and effectively. To a certain extent, it can improve regulating quality, so it is suitable for occasions with large load changes, It can play a better regulating role in both full load production and half load production.
4. Selection of regulating valve diameter
The required flow coefficient CV value shall be calculated according to the known fluid, and then the appropriate regulating valve diameter shall be selected according to the product technical parameter table. When calculating CV value, pay attention to the difference between liquid, gas, water vapor and other vapors.
The flow coefficient, namely CV value (called KV value by Chinese industry), is an important process parameter and technical index for industrial valves such as valves and control valves. Correct calculation and selection of CV value is an important step to ensure the normal operation of pipeline flow control system.
Definition of flow coefficient (CV value): refers to the volume flow rate or mass flow rate of pipeline medium flowing through the valve when the pipeline maintains a constant pressure in unit time and under test conditions. That is, the maximum flow capacity of the valve. The CV value of the valve shall be determined by testing and calculation.
| Rated flow coefficient Kv, rated travel, model of matched actuator |
| Nominal diameter DN (mm) | | twenty | twenty-five | thirty-two | forty | fifty | sixty-five | eighty | one hundred | one hundred and twenty-five | one hundred and fifty | two hundred |
| Valve seat diameter DN (mm) | | ten | twelve | fifteen | twenty | twenty-five | thirty-two | forty | fifty | sixty-five | eighty | one hundred | one hundred and twenty-five | one hundred and fifty | two hundred |
| Rated flow coefficient Kv | straight line | one point eight | two point eight | four point four | six point nine | eleven | seventeen point six | twenty-seven point five | forty-four | sixty-nine | one hundred and ten | one hundred and seventy-six | two hundred and seventy-five | four hundred and forty | six hundred and ninety |
| Equal percentage | one point six | two point five | four | six point three | ten | sixteen | twenty-five | forty | sixty-three | one hundred | one hundred and sixty | two hundred and fifty | four hundred | six hundred and thirty |
| Rated stroke L (mm) | | ten | sixteen | twenty-five | forty | sixty |
| Model of matched actuator | | ZJHP/B-22 | ZJHP/B-23 | ZJHP/B-34 | ZJHP/B-45 |
Precautions for Field Installation of Pneumatic Diaphragm Regulating Valve
1. Installation of pneumatic diaphragm regulating valve
The reasonable installation of the regulating valve is not only related to the convenience of installation, disassembly and maintenance of the regulating valve, but also determines whether the regulating valve can play a good regulating role in the automatic regulating system. The following aspects should be paid attention to when installing the regulating valve:
1.1 The regulating valve shall be vertically installed on the horizontal pipeline. If horizontal and inclined installation is required under special circumstances, the support seat shall be added generally. Reduce the jamming or failure of regulating valve switch caused by pipeline vibration.
1.2 In order to prevent the diaphragm of the regulating valve from aging and extend its service life, the installation should be away from the environment with high temperature, vibration and serious corrosion as far as possible.
1.3 In order to facilitate maintenance and overhaul, the regulating valve shall be installed near the ground or floor. In order to facilitate maintenance and disassembly, it should be noted that the regulating valve should be kept at a proper height from the ground (or floor). For positive action air to open regulating valve, the valve core should be taken out from below the valve body when disassembling, and the regulating valve should be kept at a sufficient distance from the ground, which must be considered during pipeline installation.
1.4 In order to prevent production and safety accidents in case of failure of control valve and control system, it is generally necessary to install bypass valve and bypass valve. However, the bypass valve cannot be installed directly above the control valve to avoid the corrosive medium in the bypass valve leaking to the control valve. The automatic control system plays a good role in regulation. Before and after the installation of the control valve, the stop valve should be installed. For high temperature, high pressure, high pressure, easily frozen and viscous media, the drain valve should also be installed.
