Control knowledge of pneumatic valve
Pneumatic control valve refers to all kinds of pneumatic components that control the pressure, flow and direction of air flow in pneumatic system to ensure the normal work of pneumatic actuator or mechanism.
The components that control and adjust the pressure of compressed air are called pressure control valves. The components that control and adjust the compressed air flow are called flow control valves.
Components that change and control the direction of air flow are called directional control valves. In addition to the above three types of control valves, there are logic elements that can realize certain logic functions, including jet elements without moving parts and pneumatic logic elements with moving parts.
In structural principle, the logic element is basically the same as the directional control valve, but the volume and passage are smaller, and it is generally used to realize the logical operation function of signals. In recent years, with the miniaturization of pneumatic components and the wide application of PLC control in pneumatic systems, the application scope of pneumatic logic components has gradually narrowed.
From the control mode, pneumatic control can be divided into intermittent control and continuous control. In intermittent control system, pressure control valve, flow control valve and direction control valve are usually used to realize program action; In the continuous control system, in addition to pressure and flow control valves, servo and proportional control valves are also used in the continuous control system.
2. How to control the pneumatic valve?
Pneumatic valves have two control requirements. One is two-position control, that is, controlling its on/off, which can be realized by adding an electromagnetic valve. When the solenoid valve is excited, the valve is opened (or closed), and when the solenoid valve is demagnetized, the valve is closed (or opened); The other is adjustable control, that is, the valve can be controlled in any open position except on/off. This control requires adding a pneumatic valve positioner to the valve, and drawing a rod from the valve stem to form a concentric connection with the feedback rod of the valve positioner.
When the valve positioner receives the 4-20mA control electric signal, it will drive the valve to act. When the valve position feedback and the control signal are balanced, the valve opening will be controlled at this position. The electrical signal is variable in the range of 4-20mA, and the valve position of the valve is also variable.
3. The working principle of pneumatic valve
Pneumatic valve is a kind of hardware pneumatic valve which controls the valve by air compression. Its appearance greatly facilitates the engineering operation of related industries and saves a lot of energy costs for enterprises.
Employees who use pneumatic valves must understand their working principle and correct operation methods in order to operate accurately. Working principle: Pneumatic piston actuator takes compressed air as power source, and the crank arm rotates 90 degrees through the movement of the piston, thus automatically opening and closing the valve.
Its components are: adjusting bolt, actuator box, crank arm, cylinder body, cylinder shaft, piston, connecting rod and universal shaft. Working principle of pneumatic control valve: Pneumatic control valve is composed of executive mechanism and regulating mechanism.
The actuator is the thrust component of the regulating valve, which generates corresponding thrust according to the pressure of the control signal to push the regulating mechanism to move. The valve body is the regulating part of the pneumatic regulating valve, which is in direct contact with the regulating medium to regulate the flow of fluid.
4. What is the operation method of pneumatic valve?
Operation method: 1.
The opening and closing direction of pneumatic valve shall be clockwise. 2。
Because the pneumatic valves in the pipe network are often opened and closed manually, the number of opening and closing revolutions should not be too much, even for large-caliber valves, it should be within 200-600 revolutions. 3。
In order to facilitate the opening and closing operation of one person, the maximum opening and closing torque should be 240N-m under the condition of pipeline pressure. 4。
The opening and closing operation end of pneumatic valve should be square tenon, standardized in size and facing the ground, so that people can operate directly from the ground. Valves with pulley (lun) disks are not suitable for underground pipe networks.
5。 Display panel of the opening and closing degree of pneumatic valve ① The graduation line of the opening and closing degree of pneumatic valve should be cast on the gearbox cover or the shell of the reversed display panel, all facing the ground, and the graduation line should be painted with fluorescent powder to show eye-catching; ② Stainless steel plate can be used for indicating dial hands if they are well managed; otherwise, it is painted steel plate, not aluminum skin; (3) The indicating needle is eye-catching and firmly fixed. Once the opening and closing adjustment is accurate, it should be locked with rivets.
6。 If the pneumatic valve is buried deeply, the distance between the operating mechanism and the display panel and the ground should be ≥ 1.
5m, should be equipped with telescopic pole facilities, and fixed firmly, so that people can observe and operate from the ground. In other words, the valves in the pipe network are not suitable for underground operation.
5. How to operate the pneumatic valve
Pneumatic valve is an automatic valve, which is composed of pneumatic devices and various types of valves. Pneumatic control valve, pneumatic ball valve and pneumatic butterfly valve all belong to one kind of pneumatic valve. How should the technicians of Hubei Biaoguang Valve Factory answer your questions about how to use pneumatic valves?
The pneumatic valve has an air pipe above and below the cylinder block. When closing the valve, the upper pipe control valve should be opened to let compressed air enter the upper part of the cylinder, so that the piston moves downward and drives the valve stem to close the valve. On the contrary, close the intake valve on the upper pipeline of the cylinder, open its loop valve to make the medium flow back, and open the control valve on the lower pipeline of the cylinder at the same time, so that compressed air can enter the lower part of the cylinder, make the piston move upward, and drive the valve stem to open the valve.
There are two types of pneumatic valves: normally open and normally closed. Usually, the upper part of the piston has an air tube and the lower part has a spring. When it needs to be closed, open the control valve of the trachea, let compressed air enter the upper part of the cylinder, compress the spring and close the valve. When it is to be opened, the loop valve is opened, the gas is discharged, and the spring is reset to open the valve. Normally closed valve is opposite to normally open valve, with spring at the upper part of piston and gas pipe at the lower part of cylinder. After opening the control valve, compressed air enters the cylinder and opens the valve.
Whether the pneumatic device works normally can be reflected by the signal fed back to the control panel by the up and down position of the valve stem. If it is not tight, you can adjust the adjusting nut at the bottom of the cylinder, and it can be eliminated by slightly adjusting the adjusting nut.
If the pneumatic device fails and needs to be turned on or off in time, manual operation should be adopted. There is a pneumatic device connected to the valve stem at the upper part of the cylinder. When the valve cannot be operated pneumatically, it is necessary to put the lever in the ring, lift the ring to open it, and press the ring to close it. This manual mechanism is very laborious and can only solve temporary difficulties. At present, there are pneumatic gate valves with manual valves. Under normal circumstances, the handle on the manual mechanism is in the pneumatic position. When the air supply fails or the air flow is interrupted, first cut off the air supply channel, open the loop valve on the cylinder loop, and turn the handle on the manual mechanism from the pneumatic position to the manual position. At this time, the opening and closing nut is engaged with the drive screw, and the valve can be opened or closed by rotating the handwheel.
6. Pneumatic valve principle
Working principle of pneumatic valve: Pneumatic valve is a kind of pneumatic control valve which uses compressed air to enter the pneumatic actuator to drive the piston to move and rotate or lift the torsion shaft to drive the valve stem to move.
Pneumatic valves are divided into single-acting, double-acting and intelligent adjustment. The piston structure in a single-acting pneumatic actuators is driven by a spring. There are two principles of opening and closing, and the valve is closed by spring when no gas enters. This principle is normally closed. When the gas enters the cylinder, the valve is closed. When the gas is cut off, the valve with piston is opened by the spring, and the eating structure is opened.
Care should be taken to prevent the spring from losing its function after long-term compression. Double action is the principle of opening and closing gas. Double-acting pneumatic valves need to be equipped with two-position five-way solenoid valves. When the gas enters the cylinder from the hole A, it drives the piston to rotate and the torque valve closes. When the valve is opened, the gas enters from the hole B, the port A is disconnected, and the piston drives the torque valve to open.
7. How to control the flow of pneumatic ball valve?
Pneumatic ball valves are divided into O-type ball valves and V-type ball valves.
O-type ball valve adopts floating structure, the ball core is precision cast, the surface is plated with hard chromium, the valve seat is made of reinforced PTFE material, the orifice is the same as the pipe diameter, the flow capacity is large, the flow resistance is small, and there is no leakage when it is closed. It is generally used as an on-off valve, especially suitable for high-viscosity V-type ball valves with fixed structure. The ball core is provided with a V-shaped notch, which can realize the shearing of fibrous and granular media. According to different process equipment, pneumatic or electric actuators can be selected. Pneumatic ball valve and electric ball valve are composed respectively, in which pneumatic ball valve must be equipped with valve positioner to realize proportional adjustment, and electric ball valve must be equipped with electronic electric actuator or servo amplifier to realize proportional adjustment.
8. What are the precautions for the use and maintenance of pneumatic valves?
1. The purpose of operation and maintenance is to prolong the service life of the valve and ensure the reliability of opening and closing.
2. The thread of the valve stem often rubs against the nut of the valve stem, so it should be lubricated with a little Huang Gan oil, molybdenum disulfide or graphite powder. 3. For valves that don't open and close frequently, turn the handwheel regularly, and add lubricating oil to the thread of the valve stem to prevent it from seizing.
4. For outdoor valves, the valve stem should be sheathed to prevent rain, snow, dust and rust. 5. If the valve machinery waits, lubricate the gearbox on time.
6. Always keep the valve clean. 7. Always check and maintain the integrity of other parts of the valve.
If the handwheel fixing nut falls off, it should be completely matched and cannot be used, otherwise it will wear out the square on the upper part of the valve stem, gradually lose the reliability of matching and even fail to start. 8, don't rely on the valve to support other heavy objects, don't stand on the valve.
9. The valve stem, especially the threaded part, should be wiped frequently, and the lubricant that has been polluted by dust should be replaced with a new one, because the dust contains hard impurities, which is easy to wear the thread and the surface of the valve stem, affecting the service life of the pneumatic single-seat regulating valve.
9. What are the control transmission modes of valves?
Valve is the control part in the pipeline fluid transportation system, which is used to change the cross section of the channel and the flow direction of the medium, and has the functions of shunting, cutoff, throttling, check, shunting or overflow pressure relief.
Valves used for fluid control range from the simplest shut-off valve to various valves used in extremely complicated automatic control systems, with nominal diameters ranging from extremely tiny instrument valves to industrial pipeline valves with diameters of 10m. It can be used to control the flow of water, steam, oil, gas, mud, corrosive medium, liquid metal and radioactive fluid, and the working pressure of the valve can be from 0.
The ultra-high pressure ranges from 00 13MPa to 1000MPa, and the working temperature can range from the ultra-low temperature of c-270℃ to the high temperature of 1430℃. The valve can be controlled by various transmission modes, such as manual, electric, hydraulic, pneumatic, turbine, electromagnetic, electromagnetic hydraulic, electrohydraulic, pneumatic hydraulic, spur gear and bevel gear drive. Under the action of pressure, temperature or other forms of sensing signals, it can act according to predetermined requirements, or it can be simply turned on or off without relying on sensing signals. The valve moves, slides, swings or rotates the opening and closing parts up and down by driving or automatic mechanism, thus changing the size of its flow area to realize its control function.