Types of Valves and How to Choose One

While the flow of electricity can be easily controlled with a single small switch, this is not the case with gas and water. To control the movement of water and gas, which are substances, we need valves. In this article, we will explain how to choose the right valve and the types of valves.

   

What is a valve?

Just as electricity is transmitted through wires, gases and liquids flow through pipes. Valves control the flow of these pipes, acting like switches in the piping system. There are various types of valves for different purposes and applications, and they must be used according to the need.

 

Types of Valves and How to Select One

There are many types of valves depending on the control method.

 

Selecting a Valve by Type

In general, valves are classified according to how they control substances (fluids) in piping.

 

Ball Valves

A ball with a hole is directly connected to the handle of the valve, and turning the valve rotates the ball inside. When the face with the hole faces the piping, the fluid passes through, and when the face is on its side, the fluid is shut off.

Bore Difference

-

Full bore

Standard Bore

Reduced Bore

Nominal size (pipe) and ball

Identical

Ball inner diameter is one size smaller than nominal diameter

Ball I.D. at least 1 size smaller than nominal diameter

Flow loss

Almost none

Increase

Considerable increase

Size of structure

Large

Medium

Small (space saving)

 

Globe valve

The inside of the valve has a two-layer structure, and the fluid is controlled by a conical valve that moves up and down at its passage point. Due to its structure, resistance is high, but the flow rate is adjustable and the opening/closing torque is high.

グローブバルブ グローブバルブ

 

Gate valve

Controls fluid by sliding vertically against the piping. It is not suitable for flow control, but is used for flow and shut-off operations.

ゲートバルブ ゲートバルブ

 

Butterfly valve

Like ball valves, butterfly valves control fluid by rotating inside the valve. The difference is in the shape of the valve. Butterfly valves do not have a hole in the valve and regulate flow by adjusting the gap between the valve and the piping.

バタフライバルブ バタフライバルブ

 

Needle Valves

By turning the handle on the valve, the valve moves vertically up and down to control the fluid. This is the same shutoff method as a gate valve, but the needle valve can adjust the flow rate.

ニードルバルブ ニードルバルブ

 

Check valve (check valve)

A valve that prevents backflow. Like a valve in a human blood vessel, it opens in one direction but not in the opposite direction. They are used in one-way piping.

チェックバルブ(逆止弁) チェックバルブ(逆止弁)

 

Diaphragm valve

Diaphragm valves control fluid by actuating a valve called a diaphragm. Diaphragm" means a diaphragm, and fluoroplastic or rubber is used. It is very airtight and can be used for delicate fluids, but it is not suitable for use under high pressure.

ダイヤフラムバルブ

 

Solenoid Valve / Electric Valve

These valves are operated by the force of electromagnets and are characterized by extremely fast response speed. On the other hand, this type of valve is not suitable for water volume control, and is often used for either flowing or shutting off water.

電磁弁・電動弁

 

Select by Nominal Size

The A and B nominal sizes are used to express the size of piping, with the A nominal size converted to meters and the B nominal size converted to inches, but these are unique to Japan and not accepted in the global standard. It may sound a bit complexbut 1 inch = 25 millimeters is considered as the standard. In the yardage system, there is no unit smaller than 1 inch, so numbers smaller than 1 inch are written in fractions with the denominator being 8.

There is no relationship between the B designation and millimeters below 1 inch. 6A (millimeter), for example, is strictly speaking 0.234 inches, which is 23/100, or approximately 2/10, while the B designation is 1/8. B designation is a rule and needs to be memorized. The nominal diameter is only a standard for differentiating pipes, and while it is as close as possible to the inside diameter, it is not the same.

 

A designation

B designation

Reading (BU)

Outer diameter (JIS)

6

1/8

1 bu

10.5mm

8

1/8(2/8)

2 bu

13.8mm

10

3/8

3 bu

17.3mm

15

1/2(4/8)

4 bu

21.7mm

20

3/4

6 bu

27.2mm

25

1(8/8)

inch

34mm

32

1-1/4

inch 2 bu

42.2mm


The reason why 1/4 is called 2 minutes and 1/2 is called 4 minutes (bu) is because it is the number of numerators when the denominator is divided into 8.

 

Select by Material

Valves are made of a variety of materials depending on the application.

Carbon steel castings for high temperature and high pressure (SCPH2)

This material has high hardness, tensile strength, and impact resistance, and is used in high-temperature, high-pressure plants.

 

Ductile iron castings (FCD-S)

With the same level of hardness as copper and excellent cost performance, demand for this material has been rapidly increasing in recent years.

 

Bronze (CAC13A)

The oldest material, made by adding tin, lead, and zinc to copper.

 

Brass (C3771)

Known generally as brass, this material has excellent workability and corrosion resistance.

 

Stainless steel castings

This material has excellent corrosion and heat resistance, but is expensive, so it is a material of choice where it is used.

 

Select by fluid used

Valves are items used to control the movement of materials in piping. Liquids and gases that pass through the piping are called fluids, and valves should be selected according to the fluid.

 

Fluid

Valves are used for water pipes through which hot water and water pass. Gate valves and butterfly valves are often used.

 

Gas

Butterfly valves and globe valves are suitable for controlling gas and air.

 

Selection by Connection Method

When selecting a valve, it is necessary to pay attention to the connection method.

 

Flange type

A gasket is placed between the connecting surfaces of the valve and secured with bolts. This is the most versatile connection method and is used regardless of pressure or diameter.

フランジ形

 

Screwed type

This connection method is used for water pipes of 50A or less. The most important feature of this connection method is that it is cost-effective because it requires only threading of the connection surface. This connection method is often used for low-pressure and low-size pipes.

ねじ込み形

 

Welding type

This is a method in which the pipe and valve are fixed by welding. There are two types of connection methods: socket-weld (plug-in type), which is generally used when the valve diameter is 2 inches or smaller, and butt-weld (butt-weld type), which is suitable for a wide range of sizes.

差し込み型
plug-type

突き合わせ型
butt joint

 

Points to consider when selecting a valve

Check the following items when selecting a valve.

  • Operating pressure (Mpa)
  • Valve body material (to match the fluid to be used)
  • Nominal size of piping

 

Summary

Valves must be selected according to the purpose for which they are to be used and the fluid to which they are to be applied. There are many types of valves, and they have different strengths and weaknesses depending on the fluid they are good at handling and the pressure to which they are adapted. It is important to understand the characteristics of valves and select the right product for the intended use.