The Selection of the Valves

The Selection of the Valves


The selection of the valves (How to choose valves?) is critical to the long-term operation of the unit during operation.

Generally, there are two general characteristics of the valves, the useage characteristics and structural characteristics.

Useage characteristics: It determines the main performance and scope of the useage of the valve,such as valve category (closed valve, regulating valve, safety valve, etc.), product type (gate valve, globe valve, butterfly valve, ball valve, etc.), material of the main parts of the valve (valve body, valve bonnet, valve stem, valve disc, sealing surface).

Structural characteristics: It determines the structural characteristics of the valve installation, repair, maintenance. Such as the structural length and overall height of the valve, and the connection with the pipe (flange connection, thread connection, clamp connection, External thread connection, welded end connection, etc.); sealing surface (insert ring, thread ring, surfacing, spray welding, valve body); valve stem structure (rotating rod, lifting rod).

Valve Selection Steps:

1. Identify the use and the operating conditions of the valve: applicable media, working pressure, operating temperature, etc.

2. Determine the nominal diameter and connection: flange, thread, welding, ferrule, quick loading, etc.

3. Determine operate method: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage.

4. Determine the material of the casing and internal parts of the valve: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless steel, copper alloy, etc.

5 Select the type of valve: cut off valve, regulating valve, safety valve, etc.

6. Determine the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap, etc.

7. Determine the parameters of the valve: For automatic valves, determine the allowable flow resistance, discharge capacity, back pressure, etc. according to different needs, and then determine the nominal diameter of the pipe and the diameter of the seat hole.

8. Determine the geometry of the selected valve: structural length, flange connection form and size, dimensions of the valve height direction after opening and closing, bolt hole size and number of connections, and overall valve dimensions.

9. Use the available information: select the appropriate valve product from the valve catalog, valve product samples, etc.

Valve Selection Basis:

1. The purpose, operating conditions and the control method of the valves.

2. The nature of the working medium: working pressure, working temperature, corrosion performance, whether it contains solid particles, whether the medium is toxic, whether it is flammable, explosive medium, viscosity of the medium, etc.

3. Requirements for fluid characteristics: flow resistance, discharge capacity, flow characteristics, seal rating, etc.

4. Installation dimensions: nominal diameter, connection to the pipe and connection size, dimensions or weight restrictions.

5. Additional requirements for the reliability, service life and explosion-proof performance of the valve. (When selecting parameters, note that if the valve is to be used for control purposes, the following additional parameters must be determined: method of operation, maximum and minimum flow requirements, pressure drop for normal flow, pressure drop at shutdown, maximum and minimum inlet for valve pressure).

 According to the above-mentioned basis and steps of selecting the valve, the internal structure of each type of valve must be also well understood in order to properly and correctly select the valve. The final control of the pipe is the valve. The valve opening and closing member controls the flow pattern of the medium in the pipe. The shape of the valve flow path allows the valve to have a certain flow characteristic, which must be taken into account when selecting the most suitable valve for the pipe system.