Valves

A valve is a device used to control the direction, pressure and flow of a fluid in a fluid system. A valve is a device that makes or stops the medium (liquid, gas, powder) in piping and equipment and can control its flow. Valves can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media. The valve is a control component in the pipeline fluid conveying system. It is used to change the passage section and the flow direction of the medium. It has the functions of diversion, cut-off, throttling, check, shunt or overflow and pressure relief. Valves used for fluid control, from the simplest shut-off valve to various valves used in extremely complex automatic control systems, have a wide range of varieties and specifications.
 The nominal diameter of the valve ranges from extremely small instrument valves to industrial pipeline valves with a diameter of up to 10m. The valve can be used to control the flow of various types of fluids such as water, steam, oil, gas, mud, various corrosive media, liquid metals and radioactive fluids. From the ultra-low temperature of -269℃ to the high temperature of 1430℃. The control of the valve can adopt a variety of transmission methods, such as manual, electric, hydraulic, pneumatic, turbine, electromagnetic, electromagnetic hydraulic, electro-hydraulic, gas-hydraulic, spur gear, bevel gear drive, etc.; Or under the action of other forms of sensing signals, it acts according to the predetermined requirements, or simply opens or closes without relying on the sensing signals. The valve relies on the drive or automatic mechanism to make the opening and closing parts lift, slide, swing or rotate. Movement, thereby changing the size of its flow channel area to achieve its control function.
(1) Cut-off type: such as gate valve, globe valve, plug valve, ball valve, butterfly valve, needle valve, diaphragm valve, etc. The cut-off valve is also called a closed-circuit valve and a globe valve, and its function is to connect or cut off the medium in the pipeline.
(2) Check type: such as check valve, check valve is also known as one-way valve or check valve, check valve is an automatic valve, its function is to prevent the backflow of the medium in the pipeline, prevent the pump and drive motor Inversion, and leakage of container medium. The bottom valve of the water pump suction valve also belongs to the check valve category.
(3) Safety category: such as safety valve, explosion-proof valve, accident valve, etc. The function of the safety valve is to prevent the medium pressure in the pipeline or device from exceeding the specified value, so as to achieve the purpose of safety protection.
(4) Adjustment type: such as control valve, throttle valve and pressure reducing valve, its function is to adjust the pressure, flow and other parameters of the medium.
(5) Diversion type: such as distribution valve, three-way valve, steam trap. Its function is to distribute, separate or mix the medium in the pipeline.
(6) Special purpose categories: such as pigging valves, venting valves, blowdown valves, exhaust valves, filters, etc. The exhaust valve is an indispensable auxiliary component in the pipeline system, and is widely used in boilers, air conditioners, oil and gas, water supply and drainage pipelines. It is often installed at the commanding heights or elbows, etc., to remove excess gas in the pipeline, improve the efficiency of the pipeline and reduce energy consumption.
According to the driving method, it is divided into automatic valve, power driven valve and manual valve:
(1) Automatic valve refers to a valve that does not require external force to drive, but relies on the energy of the medium itself to make the valve act. Such as safety valve, pressure reducing valve, steam trap, check valve, automatic Regulating Valve, etc.
(2) Power-driven valve: The power-driven valve can be driven by various power sources. Divided into electric valve, pneumatic valve, hydraulic valve and so on. Electric valve: a valve that is driven by electricity. Pneumatic valve: a valve actuated by means of compressed air. Hydraulic valve: A valve that is actuated by hydraulic pressure such as oil.
 (3) Manual valve: Manual valve uses handwheel, handle, lever and sprocket to control the valve action by manpower. When the valve opening and closing torque is large, a gear or worm gear reducer can be set between the handwheel and the valve stem. If necessary, the universal joint and drive shaft can also be used for remote operation.
valve connection
1. Flange connection:
Second, the clip connection:
3. Butt welding connection:
4. Threaded connection:
5. Card sleeve connection:
6. Clamp connection:
7. Internal self-tightening connection:
Daily valve maintenance
1. The valve should be stored in a dry and ventilated room, and both ends of the passage must be blocked.
2. Valves that have been stored for a long time should be checked regularly, the dirt should be removed, and anti-rust oil should be applied to the processing surface.
3. After installation, regular inspections should be carried out. The main inspection items:
(1) The wear of the sealing surface.
(2) The wear of the trapezoidal thread of the stem and stem nut.
(3) Whether the packing is outdated and invalid, if damaged, it should be replaced in time.
(4) After the valve is repaired and assembled, the sealing performance test should be carried out.
The valve in operation, all kinds of valve parts should be complete and intact. The Bolts on the flange and the bracket are indispensable, the threads should be intact, and no loosening is allowed. If the tightening nut on the handwheel is found to be loose, it should be tightened in time to avoid abrasion of the connection or loss of the handwheel and nameplate. If the handwheel is lost, it is not allowed to replace it with an adjustable wrench, and it should be completed in time. Packing glands are not allowed to be skewed or have no preload clearance. For valves in environments that are easily contaminated by rain, snow, dust, sand and other pollutants, a protective cover should be installed on the valve stem. The scale on the valve should remain complete, accurate and clear. The lead seal, cap, and pneumatic accessories of the valve should be complete and intact. The insulation jacket should be free of dents and cracks.
It is not allowed to knock, stand or support heavy objects on the valve in operation; especially non-metallic valves and cast iron valves, it is even more forbidden.