Control valves

Control Valves

How to Select Control Valve?

 Control Valves Are Mainly used to Control

• pressure

• Flow

Pressure Control Valves are again classified as below

•  Pressure Reducing Valves 

• Pressure Sustaining Valves(Upstream & Down Stream)

• Both Pressure sustaining And Reducing (Up on Customer Request)

Flow Control Valves are used to controls the over flow & Under Flow to the water reservoir

• Float control Valve (Controls the Min. flow to reservoir)
• Altitude Control Valve (Controls the Max.flow to reservoir)

How Control Valve Works:

For Example Pressure Reducing Valves

 Automatically reduces a higher inlet pressure to a constant lower outlet pressure. The valve consists of a main valve and Actuator. Slight changes in downstream pressure acts on topside of control diaphragm (spring and Diaphragm type Actuator) causing main Valve to counteract pressure changes and hold a constant outlet pressure.

The Actuator will reduce the upstream pressure to a constant downstream pressure regardless of the change in flow rates/or inlet pressure. The pilot Actuator is a Normally Open valve that senses the downstream pressure.

Types of Actuators:

·         Spring And Diaphragm

·         Pneumatic Actuator

·         Electric motor Actuator

·         Electro-hydraulic Actuator

    In this Published Document we are Considering Spring and diaphragm type actuator only.

    In the Next Post we are clearly discoursed other type of actuators and how they function 

    with the Main valve. You can see various pictures of actuators in Pages.

Spring and Diaphragm Actuator:

Pneumatic Actuator:

Electric motor Actuator:

Electro-hydraulic Actuator:

How Spring And Diaphragm Actuator Works with Pressure 

Control Valve?

    Consider a Control valve of Inlet Pressure P1 is used for Pressure Reducing Purpose to P2, below shown image is a Sectional View of a spring and Diaphragm Actuator Which is connected to the main valve As a Pilot Control Circuit.

      INLET of Spring and diaphragm actuator is directly connected to an Upstream Pressure P1 which is Equal to the pressure of diaphragm chamber in Main Valve.

      OUTLET is connected to downstream side of Main valve, The Pressure Setting Screw 8 is used to set Required Downstream pressure P2.

    In top chamber spring force as acting Downwards against water force by a Helical Spring 14.

    If there is a requirement of water in downstream side Seat 6 remains open fully to enter water in the Bottom chamber. In this condition Water Force Effected by INLET Pressure is greater than the Spring Force.

    If there is no Requirement of water in Downstream Side, water of pressure P2 is filled in Bottom Chamber Which is acting against spring force upwards. 

    This Upward movement of spring 14 is directly connected to the Seat by the help of Yoke 3 is closes the inlet orifice.in this condition OUTLET Pressure is Acting against the Presetting Spring Force.

Next Publisher topics:

• ·         What is Cv and Fv
• ·         How to Select right Control for given Pressure and Cv
• ·         Spring Force calculation
• ·         Actuator Force Calculation