Types and selection of valves for the hottest heat

Types and selection of valves in heating and air conditioning water system

I. Introduction

in heating and air conditioning water system, valves are widely used to control the pressure, flow and direction of water

II. Types, structures and characteristics of valves in heating and air conditioning water system

according to the structural form and function of the valve body, the valves commonly used in heating and air conditioning water system can be divided into valves, butterfly valves, globe valves, ball valves, plug valves, check valves, pressure reducing valves, safety valves, steam traps, balance valves, etc. According to the driving mode, it can be divided into four modes: manual, electric, hydraulic and pneumatic. According to the nominal pressure, it is divided into high pressure, medium pressure and low pressure

the working principle and characteristics of common valves in heating and air conditioning water system are as follows:

1 Valve:

valve refers to the valve whose closing part (plate) moves along the vertical direction of the axis of the medium channel. Its advantages are small flow resistance coefficient, small torque required for opening and closing, and unlimited flow direction of medium. 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 complex

valves are divided into different types. The most common types are parallel and wedge valves. According to the structure of the valve stem, valves can also be divided into rod valves

(1) parallel valve

refers to the valve whose two sealing surfaces are parallel to each other. It is applicable to low-pressure, medium and small diameter (dnmm) pipes

(2) wedge valve

refers to a wedge-shaped valve with two sealing surfaces. It is divided into double interpretation board, single interpretation board and elastic interpretation board

(3) rising stem valve

because it can visually display its opening and closing degree, small and medium-sized diameters have been widely used for many years. Usually, rising stem valve is selected when DN is less than or equal to 80mm

(4) the stem nut of the Non rising stem valve is in direct contact with the medium in the valve body. It is suitable for large-diameter valves and pipelines with limited installation space, such as underground pipelines

2. The name of butterfly valve

comes from the butterfly plate with wing structure. On the pipeline, it is mainly used for cutting off and throttling. When the butterfly valve is used for cutting off, it is mostly used for elastic sealing. The materials are rubber, plastic, etc. when it is used for throttling, it is mostly used for metal hard sealing. The advantages of butterfly valve are small size, light weight, simple structure, rapid opening and closing, good adjustment and sealing performance, and small 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 structures

for occasions with nominal diameter of dn1.0mpa

(3) self sealing

is mainly realized by the pressure of the medium itself, which is mostly used for air medium. The spring under the self sealing structure can pre tighten and compress

in addition, there are three-way and four-way plug valves, which are mostly used for distribution, reversing, etc

6. Check valve

is also called counter flow valve, check valve, back pressure valve and one-way valve. It is a valve used to prevent the backflow of medium in pipelines and equipment. It automatically opens and closes by the force generated by the flow of medium in the pipeline

the disc of swing check valve rotates around the pin outside the valve seat, and it is divided into single disc and multi disc. The former is generally used for nominal diameter dnmm, and the latter is generally used for nominal diameter DN greater than or equal to 600mm

there is also an empty discharge check valve, which is used at the outlet of the boiler feed pump to prevent medium backflow and play the role of emptying; The new slow closing check valve can eliminate water hammer; Diaphragm check valve has good performance of preventing water hammer; Ball check valve is an ideal product to prevent the reverse flow of medium

7. The pressure reducing valve

reduces the medium pressure by throttling and adjusting the valve opening parts, and makes the pressure behind the valve automatically meet the predetermined requirements through the direct action of the medium pressure behind the valve. Generally, the pressure P2 behind the pressure reducing valve should be less than 0.5 times the pressure P1 in front of the valve, that is, p2>0.5p1

according to the structure, the pressure reducing valve is divided into piston type, membrane type, and the word "unqualified" in red will be displayed if it is unqualified, and the alarm sound will be sent out. Bellows type, spring membrane type, lever spring type, etc

8. Safety valve

it acts as a safety protection device on equipment, devices and pipelines to prevent the pressure of the medium from exceeding the specified value of the PS recycling and regeneration project

the main structures of safety valves are lever type, spring type and pilot type (pulse type). Its advantages are small size and light weight. High sensitivity, unlimited installation position; The disadvantage is that the force acting on the valve stem changes with the deformation of the spring. Spring type safety valve is divided into micro open type and full open type, with wrench and without wrench, closed type and open type

9. Drain valve

drain valve is applicable to steam heating equipment and pipelines to automatically remove condensate, air and other non condensable gases, and prevent the leakage of steam, that is, to block steam and drain water

when selecting, first select the type according to the maximum discharge of condensate and the pressure difference between inlet and outlet, and then correct it, with a correction factor of 1; 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 traps: the opening and closing parts are driven by the change of condensate level

(2) thermal static steam trap: the valve opening part is driven by the change of condensate temperature

(3) thermal power steam trap: the valve opener is driven by changing the dynamic characteristics of condensate

10. Balance valve

balance valve is a valve in hydraulic pipe used to measure and adjust to the design flow, and has the necessary measurement accuracy

III. some reference opinions on the selection of valves in heating and air conditioning water system

1 Characteristics and selection of gate valve, globe valve and butterfly valve

(1) gate valve

the length of valve body is moderate, and the rotary adjusting rod has good adjustment performance, which is widely used in larger diameter pipelines

(2) stop valve

the valve body is long, and the rotary table type 1. The wire rod changes the operating procedures of the experimental machine. The adjusting rod has good adjustment performance, and is suitable for occasions with spacious site and small diameter (generally DN is less than or equal to 150mm)

(3) butterfly valve

the valve body is short, and the handle type adjusting rod has slightly poor adjustment performance and high price, but the adjustment operation is easy. It is suitable for occasions with small site and large pipe diameter (generally dn>150mm)

2. Gate valve, stop valve or butterfly valve can be selected according to the situation for the inlet and outlet of water chillers and heat exchangers and the regulation of main pipelines

3. On the water distributor and collector, as the main function is regulation, the stop valve or gate valve is generally selected

4 A valve is installed at the inlet of the water pump and two valves are installed at the outlet. The outlet end is close to the valve on the side of the water pump until the check valve, and the other two valves can be gate valve, stop valve or butterfly valve

5. Stop valve or ball valve can be used for small-diameter pipes at the inlet and outlet of heating and air conditioning terminal equipment

6. Balance valves can be installed on the horizontal pipes of each floor of multi-storey and high-rise buildings to balance the flow of each floor

7. Blowdown valves are installed at the lowest points of water tanks, pipelines and equipment. Since they are not used for regulation, valves that can be tightly shut off, such as gate valves and stop valves, should be selected

8. In steam condensate piping systems, such as steam heating systems, boiler water systems, steam lithium bromide chillers, and steam water heat exchanger systems, pressure reducing valves are generally installed at the steam inlet; Install safety valves at places where high pressure may occur; Install a drain valve at the place where condensate is discharged

9. The vent valve on the heating and air conditioning water system generally adopts a plug valve