1. Gate valve
Gate valve refers to the vertical movement of the closing element (gate) along the axis of the medium channel of the valve. Its advantages are small flow resistance coefficient, small torque required for opening and closing, and unrestricted flow direction of the medium. The disadvantages are large structural size, long opening and closing time, easy damage to the sealing surface, and complex structure.
Divide gate valves into different types, the most common being parallel and wedge gate valves, stem structures, and can also be divided into rising stem gate valves.
(1) Parallel gate valve
Refers to a gate valve with two sealing surfaces parallel to each other. Suitable for low pressure, medium and small diameter (DN50-400mm) pipelines.
(2) Wedge gate valve
Refers to a wedge-shaped gate valve with two sealing surfaces. It is divided into double ram, single ram, and elastic ram.
(3) Rising stem gate valve
It can visually display its opening and closing degree, and has been widely used for many years for small and medium-sized diameters. Generally, rising stem gate valves are used for DN less than or equal to 80mm.
(4) Non rising stem gate valve
The valve stem nut body is in direct contact with the medium. Suitable for large-diameter valves and pipelines with limited installation space.
2. Butterfly valve
Its name comes from the wing shaped structure of butterfly plates. On pipelines, it is mainly used for cutting and throttling. When butterfly valves are used for cutting, elastic seals are often used, and materials such as rubber and plastic are chosen. When used for throttling, metal hard seals are often used. The advantages of butterfly valves are small size, light weight, simple structure, fast opening and closing, good regulation and sealing performance, and low fluid resistance and operating torque.
Butterfly valves can be divided into lever type (double rocker), center symmetric gate type, offset plate type, and inclined plate type according to their structure.
For butterfly valves with a nominal diameter DN<800mm, an offset plate type should be selected.
3. Globle valve
Refers to the movement of the closing body (disc) along the centerline of the valve seat. It is generally only used for cutting and not for throttling in pipelines, and the nominal diameter is usually limited to DN250mm or less. The disadvantage is that there is a large pressure loss.
There are many types of globe valves, and their structures are generally divided into straight through, precise, and direct flow. Angle stop valve is widely used in refrigeration systems. Its inlet channel is at a right angle of 90 degrees, which will produce pressure drop. The biggest advantage is that the corner of the Plumbing is installed, which saves 90 degrees of elbow and is easy to operate.
4. Ball valve
Ball valves evolved from plug valves and are mainly used on pipelines to cut off, distribute, and change the flow direction of the medium. It is characterized by the smallest fluid resistance, its Drag coefficient is equal to that of pipe sections of the same length, quick opening and closing, reliable sealing, compact structure, easy operation and maintenance, and is widely used in many occasions.
Ball valves can be divided into the following three types according to their spherical structure:
(1) Floating ball valve
Its structure is simple, with good sealing performance. All the working medium load borne by the ball is transmitted to the outlet valve seat sealing ring. This structure is only suitable for medium and low pressure situations, but its disadvantages are difficult assembly, high manufacturing accuracy requirements, and high operating torque.
(2) Fixed ball valve
The ball valve is fixed by two fixed shafts connected to the ball, and under the pressure of the medium, the ball will not produce displacement. It is suitable for high-pressure and large-diameter pipelines.
(3) Elastic ball valve
Suitable for high-temperature and high-pressure media. There are elastic grooves on the ball, which can reduce friction between the two sealing surfaces when opening and closing, and also reduce the operating torque.
5. Plug valve
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The important characteristic of a plug valve is that it is easy to adapt to a multi-channel structure, so that one valve can have two, three, and four different flow channels.
There are many types of cocks, which can generally be divided into:
(1) Tight set type
Generally used in situations where PN is less than or equal to 0.6MPa
(2) Filler type
Widely used in situations with nominal pressure PN>1. OMPa.
(3) Self sealing type
Mainly achieved by the pressure of the medium itself, mostly used for air medium. The spring under the self sealing structure can play a pre tightening and compression role.
In addition, there are also three-way and four-way plug valves, which are mostly used for distribution, reversing, etc.
6. Check valve
Also known as reverse flow valve, check valve, back pressure valve, and one-way valve. It is a valve used to prevent medium backflow in pipelines and equipment, which automatically opens and closes by generating force from the flow of the medium itself in the pipeline.
The swing check valve disc rotates around the outer pin axis of the valve seat, and is divided into single disc and multi disc. The former is generally used for nominal diameter DN 50-500mm, while the latter is generally used for nominal diameter DN greater than or equal to 600mm.
There is also an air discharge check valve, which is used at the outlet of the boiler feed pump to prevent medium backflow and discharge; The new slow closing check valve has a diaphragm check valve to eliminate Water hammer, which has good performance in preventing water hammer; A spherical check valve is an ideal product to prevent reverse flow of media.
7. Pressure reducing valve
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It is the throttling phase adjustment of the valve opening component, which reduces the medium pressure and directly acts on the medium pressure after the well valve, making the pressure after the valve automatically meet the predetermined requirements. Usually, the pressure behind the pressure reducing valve P2 should be less than the pressure before the valve P10.5 times, that is, P2>0.5P1.
Pressure reducing valves are divided into piston type, diaphragm type, bellows type, spring diaphragm type, lever spring type, etc. according to their structure
8. Safety valve
It serves as a safety protection device on equipment, devices, and pipelines to prevent the medium pressure from exceeding the specified value.
The main structures of safety valves are lever type, spring type, and pilot type (pulse type). Its advantages are small size and lightweight. High sensitivity, unrestricted installation position; The disadvantage is that the force acting on the valve stem changes with the deformation of the spring. Spring type safety valves are divided into micro open and full open types, with and without wrenches, closed and open types, and other different types.
9. Drain valve
Trap valves are suitable for steam heating equipment and pipelines, automatically expelling condensed water, air, and other non condensable gases, and preventing steam leakage, which plays a role in blocking steam and draining water.
When selecting, it is necessary to first select the maximum condensate displacement and inlet/outlet pressure difference, and also make corrections, with a correction coefficient of 1.5-4; Secondly, it is necessary to install it reasonably.
Steam trap valves can be divided into the following categories according to their opening and closing forms:
(1) Mechanical steam trap: It is driven by the condensate level to open and close the valve.
(2) Thermostatic steam trap valve: driven by changes in condensate temperature to open the valve.
(3) Thermodynamic steam trap: It is a valve opening component driven by the dynamic characteristics of condensed water.
10. Balance valve
Balance valve is a valve used in hydraulic pipeline networks to measure and adjust to the design flow rate, and has the necessary measurement accuracy.