Second, the type, structure and characteristics of the heating air conditioning water system valves commonly used in the heating and air conditioning water system according to the valve body structure and function can be divided into valve, butterfly valve, globe valve, ball valve, plug valve, check valve, Pressure reducing valve, safety valve, steam trap, balance valve, etc. According to the driving method, it can be divided into manual, electric, hydraulic, pneumatic and other four ways. According to the nominal pressure, it is divided into three categories: high pressure, medium pressure and low pressure.
The working principle and characteristics of the commonly used valves for heating and air conditioning water systems are as follows:
1. Explain the valve:
The valve is a valve that moves the closing member (the panel) in the vertical direction of the axis of the media channel. The advantage is that the flow resistance coefficient is small, the torque required for opening and closing is small, and the flow direction of the medium is not limited. The disadvantage is that the structure size is large, the opening and closing time is long, the sealing surface is easy to be damaged, and the structure is complicated.
The description valves are divided into different types. The most common forms are parallel and wedge-type valves. According to the structure of the valve stem, it can also be divided into clear rods.
(1) Parallel valve Description A valve in which two sealing faces are parallel to each other. Suitable for pipes with low pressure, medium and small diameter (DN50-400mm).
(2) Wedge-type valve refers to a valve with two sealing faces that are wedge-shaped. Divided into double interpretation board, single layout board and flexible board.
(3) Ming rod explanation valve Because it can display its degree of opening and closing more intuitively, small and medium diameters have been widely used for many years. Usually, the DN is less than or equal to 80mm.
(4) Dark rod valve The stem nut is in direct contact with the medium in the valve body. Suitable for large diameter valves and pipelines with limited installation space, such as underground pipelines.
2. Butterfly Valve The name is derived from the wing plate of the wing structure. It is mainly used for cutting and throttling on the pipeline. When the butterfly valve is used for cutting, the elastic seal is used. The material is rubber, plastic, etc. When used for throttling, the metal is hard sealed. The butterfly valve has the advantages of small volume, light weight, simple structure, quick opening and closing, good adjustment and sealing performance, and small fluid resistance and operating torque.
The butterfly valve can be divided into a lever type (double rocker), a center symmetrical door type, a bias plate type and a swash plate type according to the structure.
For the butterfly valve with the nominal diameter DN<800mm, the offset plate type should be selected.
3. Shutoff valve Refers to the valve that moves the closing body (valve) along the centerline of the seat. It is generally only used for cutting in the pipeline, and is not used for throttling. Generally, the nominal diameter is limited to DN250mm or less. The disadvantage is that the pressure loss is large.
There are many types of globe valves, which are generally divided into straight-through, positive and direct-type according to the structure. Angle-type globe valves are widely used in refrigeration systems. The inlet passages are at a right angle of 90 degrees, which will produce a pressure drop. The biggest advantage is that they are installed at the corners of the pipeline system, saving 90 degrees of elbows and easy operation.
4. Ball Valves Ball valves are derived from plug valves and are used primarily to cut, distribute and change the direction of flow in the pipeline. It is characterized by minimal fluid resistance, its resistance coefficient is equal to that of the same length of pipe section, fast opening and closing, reliable sealing, compact structure, easy operation and maintenance, so it is widely used in many occasions.
The ball valve can be divided into the following three types according to the structure of the sphere:
(1) The floating ball valve has a simple structure and good sealing performance. Since the working medium load of the ball is transmitted to the outlet end seat sealing ring, the structure is only suitable for medium and low pressure applications, and the disadvantage is that assembly is difficult. The production precision is high, and the operating torque is also large.
(2) Fixed ball valve The ball valve is fixed by a fixed shaft supported by two balls and connected to the ball. Under the action of the medium pressure, the ball will not be displaced. It is suitable for high pressure and large diameter pipes.
(3) Elastic ball ball valve Suitable for high temperature and high pressure media. An elastic groove is formed in the ball body, which can reduce the friction between the two sealing faces when opening and closing, and at the same time reduce the operating torque.
5. Plug Valve An important feature of the plug valve is that it is easy to adapt to a multi-channel structure, so that one valve can obtain two, three or even four different flow paths.
There are many types of cocks, which can be generally divided into:
(1) The setting method is generally used when the PN is less than or equal to 0.6 MPa.
(2) Packing type A large number of applications are used for the nominal pressure PN>1.0MPa.
(3) Self-sealing is mainly realized by the pressure of the medium itself, and is mostly used for air medium. The spring under the self-sealing structure acts as a preload and compression.
In addition, there are three-way, four-way plug valves, which are mostly used for distribution and commutation.
6. Check valves Also known as counterflow valves, check valves, back pressure valves and check valves. It is a valve used to prevent backflow of media in pipes and equipment. It is automatically opened and closed by the force generated by the flow of the medium itself in the pipeline.
The valve flap of the swing-type return valve rotates around the pin shaft outside the valve seat, and is divided into a single flap and a multi-lobed. The former is generally used for the nominal diameter DN50-500mm, and the latter is generally used for the nominal diameter DN greater than or equal to 600mm.
There is also an empty row check valve, which is used for preventing the backflow of the medium and the emptying of the boiler feed water pump outlet; the new slow-closing check valve has the function of eliminating water hammer; the diaphragm type check valve prevents the water hammer performance from being good; The ball check valve is ideal for preventing media from flowing backwards.
7. The pressure reducing valve is to reduce the pressure of the medium by the throttling and adjustment of the valve opening, and the pressure behind the valve automatically meets the predetermined requirements through the direct action of the medium pressure after the valve. Generally, the pressure P2 after the pressure reducing valve should be less than 0.5 times the pre-valve pressure P1, that is, P2>0.5P1.
The pressure reducing valve is divided into a piston type, a film type, a bellows type, a spring film type, a lever spring type and the like according to the structure.
8. Safety valve It acts as a safety device on equipment, equipment and piping to prevent the pressure of the medium from exceeding the specified value.
The main structure of the safety valve is three types: lever type, spring workmanship and pilot type (pulse type). Its advantages are small size and light weight. The sensitivity is high and the mounting position is not limited; the disadvantage is that the force acting on the valve stem changes with the deformation of the spring. The spring-loaded safety valve is divided into a micro-open type and a full-open type, with and without a wrench, closed and open type.
9. Traps The traps are suitable for steam heating equipment and pipelines to automatically remove condensate, air and other non-condensable gases, and prevent the loss of steam, that is, the role of steam trapping.
When selecting, first select according to the maximum displacement of condensate and the pressure difference between the inlet and outlet, and also modify it, the correction coefficient is 1.5-4; secondly, it should be installed reasonably.
Steam traps can be divided into the following categories according to the opening and closing form:
(1) Mechanical steam trap: The opening and closing member is driven by the condensate level.
(2) Thermostatic steam trap: The valve is driven by the temperature change of the condensate.
(3) Thermodynamic steam trap: The valve is driven by the dynamic characteristics of the condensate.
10. Balance valve The balance valve is a valve used in the hydraulic network to measure and adjust to the design flow and has the necessary measurement accuracy.
Third, the heating air conditioning water system valve selection of several points of reference 1. Gate valve, globe valve and butterfly valve characteristics and selection (1) gate valve body length is moderate, turntable adjustment rod, good adjustment performance, in larger diameter pipe It is widely used.
(2) Globe valve The valve body is long and the rotary disc type adjustment rod has good adjustment performance. It is suitable for occasions with large space and small diameter (generally DN is less than or equal to 150mm).
(3) Butterfly valve The valve body is short, the handle type adjustment rod has poor adjustment performance and high price, but the adjustment operation is easy. It is suitable for occasions with small space and large diameter (generally DN>150mm).
2. The chiller, heat exchanger inlet and outlet, main pipeline adjustment, can choose gate valve, globe valve or butterfly valve according to the situation.
3. On the sub-catch, because the main function is to adjust, generally choose the stop valve or gate valve.
4. One pump is installed at the inlet of the pump, and two valves are installed at the outlet. The outlet end is close to the valve on the side of the pump, and the other two valves can be selected as gate valves, globe valves or butterfly valves.
5. Heating and air conditioning end equipment inlet and outlet small diameter pipe can be used as a shut-off valve or ball valve.
6. Multi-layer, high-rise buildings can be half-piped on each horizontal pipe to balance the flow of each layer.
7. The drain valve is installed at the lowest point of the water tank, pipeline and equipment. Since it is not used for regulation, it is recommended to use valves that can be shut off strictly, such as gate valves and globe valves.
8. Steam--condensate piping systems, such as steam heating systems, boiler water systems, steam lithium bromide chillers, steam-water heat exchanger systems, generally equipped with pressure reducing valves at the steam inlet; Set a safety valve; install a trap at the condensate.
9. The exhaust valve on the heating and air conditioning water system generally adopts a plug valve.
I. INTRODUCTION In heating air conditioning water systems, valves are widely used to control the pressure, flow and flow direction of water.