Basics

What is a valve ?

A valve is a device with moving mechanism that passes, stops or controls the flow of a fluid.
Such fluid control valves have been applied to various facilities including piping of a waterworks system, farm water supply, and sewage system.
A gate valve was the most popular type in the past, although it could not provide enough operability and control. However, as a recent increased demand for more efficient and optimized water use in larger-scale water supply/distribution facilities, various valves with different functions have been developed and adopted in fluid control applications.
See the types, characteristics, roles and applications of such valves as below.

Basic structures of valves

• Gate Valve

  

• Butterfly Valve

  

• Ball Valve

  

• Check Valve

  

Types of valves

Gate valve／Multi-hole variable orifice valve／Check valve／Fire Hydrant／Butterfly valve／Plug valve／Flap valve／Slide gate／Sleeve valve／Emergency Shut-off valve／Air valve／Ball valve

Usage and Features of valves

Valve actuator

Rotation or sliding of a valve disc enabled by an actuator opens and closes a valve.
From a range of actuator types, you need to select an appropriate one according to usage, type, control method, and installation environment of a valve.

Supplement

Control valves and control methods

Control methods are roughly classified into flow rate control, pressure control and level control. You need to select one of them according to an intended use of a valve.
For flow rate control, a multi-hole variable orifice valve and sleeve valve are suitable due to their high control performance.
In any case, you need to consider cavitation conditions to select a valve type.

Selecting a valve based on cavitation conditions

Select a type of control valve that can satisfy the following cavitation conditions.

Obtain the operating cavitation coefficient with the following formula.

P1 : the water pressure at upstream side of the valve.
P2 : the water pressure at downstream side of the valve.

Water hammer prevention and a valve

A pressure surge by water hammer may occur when a valve opens or closes quickly. The impact differs depending on length of a pipe, flow pressure, flow rate, etc.　To prevent water hammer, sudden change caused by opening/closing of a valve should be avoided as below to reduce pressure increase.

(1) Using a valve with high flow control performance

(2) Keeping an appropriate operation time for opening/closing.