Plastic Valve
The plastic valve is the most important part of the fluid conveying system in the plastic piping system. According to its function, it can be divided into shut-off valve, check valve, regulating valve, etc.
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 degree of industrialization is getting higher and higher, and the requirements for valve reliability are getting higher and higher, and even absolute safety is expected. From the perspective of environmental protection, green recyclable plastics are getting more and more attention. The material should not cause low temperature brittle failure, and the corrosive requirements of the medium should also be considered; at the same time, the structure of the material should be stable to avoid volume changes; the selection of materials should avoid the occurrence of card groups under frequent operations.
Different piping systems use valves with different materials, structures, functions, and connection methods. Different valves have their own advantages and disadvantages and application fields. It is necessary to select valves according to the actual needs of the pipeline system to ensure the stable operation of the pipeline system.
Commonly used plastic valves include plastic ball valves, plastic butterfly valves, plastic check valves, and plastic diaphragm valves. Usually plastic valve materials are PVC, CPVC, PPH, PVDF, FRPP and so on.
The opening and closing part of the plastic ball valve is a sphere, and the purpose of opening and closing is achieved by rotating the sphere 90° around the axis of the valve stem. Ball valves are mainly used to cut off, distribute and change the flow direction of the medium on the pipeline.
Advantages :
1. The fluid resistance is small, and the ball valve is the one with the smallest fluid resistance among all valves.
2. The valve body is symmetrical, especially the overall structure, which can well withstand the stress from the pipeline
3. The switch is fast and convenient. As long as the valve stem rotates 90°, the ball valve completes the full opening or full closing action, and it is easy to realize rapid opening and closing.
4. Good sealing performance. The sealing ring of the ball valve seat is generally made of elastic materials such as PTFE, which is easy to ensure the sealing, and the sealing force of the ball valve increases with the increase of the medium pressure.
5. The valve stem seal is reliable. When the ball valve is opened and closed, the valve stem only rotates, so the packing seal of the valve stem is not easy to be damaged, and the sealing force of the reverse seal of the valve stem increases with the increase of the medium pressure.
6. The opening and closing of the ball valve only rotates 90°, so it is easy to realize automatic control and remote control.
Disadvantages :
1. Not suitable for flow regulation.
2. The temperature resistance grade of PTFE is low and can only be used under the condition of less than 180℃.
3. Since the valve seat supporting the ball is usually made of resin, it is not suitable for high-temperature fluids (200°C or higher).
A butterfly valve is a valve that is opened and closed by rotating the disc opening and closing member by 90 degrees.
Advantage:
1. Quick opening and closing, small fluid resistance
2. Simple structure, suitable for large-diameter pipeline system.
It can be used for media with suspended solid particles, and also for powdery and granular media depending on the strength of the sealing surface.
Disadvantage:
1. Restricted by the structure and sealing material of the butterfly valve, it is not suitable for high-temperature and high-pressure piping systems.
2. The sealing performance is worse than that of ball valves and cannot be used in systems with high sealing requirements
The check valve is opened and closed by the power generated by the flow of the medium itself in the pipeline, which belongs to an automatic valve. The check valve is used in the pipeline system, and its main function is to prevent the backflow of the medium, the reverse rotation of the pump and the driving motor, and the discharge of the container medium.
The disadvantage of the check valve is that the fluid resistance is large, which is easy to cause water loss and energy consumption.
A plastic diaphragm valve is a special form of the shut-off valve. Diaphragm valves open and close the flow path by connecting and separating diaphragms made of soft materials such as rubber and fluororesin.
Advantage:
1. The diaphragm valve has a simple structure and low fluid resistance
2. Diaphragm valves can be adapted to a wide range of corrosive media as long as the lining material and diaphragm are properly selected.
3. The valve is closed, with no leakage, and can be used for the adjustment of high viscosity and suspended particle media.
4. The valve is easy to disassemble and repair quickly, and the replacement of the diaphragm can be done on-site and in a short time.
Disadvantage:
1. Limited by the diaphragm material, the diaphragm valve is suitable for applications with low pressure and relatively low temperature.
2. Poor control characteristics and small adjustable range.
