Inst ToolsInst ToolsInst Tools
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Search
  • Books
  • Software
  • Projects
  • Process
  • Tools
  • Basics
  • Formula
  • Power Plant
  • Root Cause Analysis
  • Electrical Basics
  • Animation
  • Standards
  • 4-20 mA Course
  • Siemens PLC Course
Reading: Directional Control Valves Working Principle
Share
Notification Show More
Font ResizerAa
Inst ToolsInst Tools
Font ResizerAa
  • Courses
  • Design
  • PLC
  • Interview
  • Control System
Search
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Inst Tools > Blog > Control Valves > Directional Control Valves Working Principle

Directional Control Valves Working Principle

Last updated: October 14, 2019 1:09 pm
Editorial Staff
Control Valves Solenoid Valve
No Comments
Share
8 Min Read
SHARE

Directional control valves perform only three functions:

Contents
Classification of Directional Control ValvesDirectional Control Valve2-way directional control valves3-way directional control valves
  • stop fluid flow
  • allow fluid flow, and
  • change direction of fluid flow.

These three functions usually operate in combination.

Classification of Directional Control Valves

Directional control valves can be classified according to-

  • number of ports
  • number of positions
  • actuating methods
  • type of spool.

Example: A 5/2 directional control valve would have five ports and two spool positions.

Number of Ports

Ports that will be counted shall be external ports only. 5/2

Number of Positions

Including the normal and working positions which a valve spool can take there are types like two position, three position and proportional valve …

Actuating Methods

Manual, spring, electrical, pneumatic, and hydraulic.

Manually Operated

Manually operated valves work with simple levers or paddles where the operator applies force to operate the valve. Spring force is sometimes used to recover the position of valve.

Some manual valves utilize either a lever or an external pneumatic or hydraulic signal to return the spool.

Mechanically Operated

Mechanically operated valves apply forces by using cams, wheels, rollers, etc., hence these valves are subjected to wear.

Hydraulically Operated

A hydraulically operated DCV works at much higher pressures than its pneumatic equivalent. They must therefore be far more robust in nature so are precision machined from higher quality and strength materials.

Solenoid Operated

They are widely used in the hydraulics industry. These valves make use of electromechanical solenoids for sliding of the spool. Because simple application of electrical power provides control, these valves are used extensively.

However, electrical solenoids cannot generate large forces unless supplied with large amounts of electrical power. Heat generation poses a threat to extended use of these valves when energized over time. Many have a limited duty cycle. This makes their direct acting use commonly limited to low actuating forces.

Often a low power solenoid valve is used to operate a small hydraulic valve (called the pilot) that starts a flow of fluid that drives a larger hydraulic valve that requires more force.

A bi-stable pneumatic valve is typically a pilot valve that is a 3 ported 2 position detented valve. The valve retains its position during loss of power, hence the bi-stable name.

Bi-stability can be accomplished with a mechanical detent and 2 opposing solenoids or a “magna-latch” magnetic latch with a polarity sensitive coil. Positive opens and negative closes or vice versa. The coil is held in position magnetically when actuated.

Type of Spool

Spool is of two types namely sliding and rotary. Sliding spool is cylindrical in cross section, and the lands and grooves are also cylindrical. Rotary valves have sphere-like lands and grooves in the form of holes drilled through them.

Directional Control Valve

The simplest directional control valve is the 2-way valve. A 2-way valve stops flow or allows flow. A water faucet is a good example of a 2-way valve. A water faucet allows flow or stops flow by manual control.

A single-acting cylinder needs supply to and exhaust from its port to operate. This requires a 3-way valve. A 3-way valve allows fluid flow to an actuator in one position and exhausts the fluid from it in the other position. Some 3-way valves have a third position that blocks flow at all ports.

A double-acting actuator requires a 4-way valve. A 4-way valve pressurizes and exhausts two ports interdependently. A 3-position, 4-way valve stops an actuator or allows it to float. The 4-way function is a common type of directional control valve for both air and hydraulic circuits. A 3-position, 4-way valve is more common in hydraulic circuits.

The 5-way valve is found most frequently in air circuits. A 5-way valve performs the same function as a 4-way valve. The only difference is an extra tank or exhaust port. (Some suppliers call their 5-way valves, “5-ported 4-ways.”)

All spool valves are five ported, but hydraulic valves have internally connected exhaust ports going to a common outlet. Because oil must return to tank, it is convenient to connect the dual tank ports to a single return port.

For air valves, atmosphere is the tank, so exhaust piping is usually unimportant. Using two exhaust ports makes the valve smaller and less expensive. As will be explained later, dual exhausts used for speed-control mufflers or as dual-pressure inlets make this configuration versatile.

Following are schematic symbols for commonly used directional control valves.

2-way directional control valves

A 2-way directional valve has two ports normally called inlet and outlet. When the inlet is blocked in the at-rest condition, as shown in Figure 8-1, it is referred to as “normally closed” (NC). The at-rest box or the normal condition is the one with the flow lines going to and from it.

The boxes or enclosures represent the valve’s positions. In Figure 1, the active box shows blocked ports, or a closed condition, while the upper box shows a flow path.

When an operator shifts the valve, it is the same as sliding the upper box down to take the place of the lower box. In the shifted condition there is flow from inlet to outlet. Releasing the palm button in Figure 1 allows the valve spring to return to the normal stop flow condition.

A 2-way valve makes a blow-off device or runs a fluid motor in one direction. By itself, a 2-way valve cannot cycle even a single acting cylinder.

2-way directional control valves

Figure shows a “normally open” (NO) 2-way directional valve. Energizing the solenoid on this valve stops fluid flow.

Valve operators come in different types. Figure 3 shows a solenoid pilot operator using solenoid-controlled pressure from the inlet port to move the working directional spool. Figure 4 shows a cam-operated valve. A moving machine member usually operates this type valve.

3-way directional control valves

A 3-way valve has three working ports. These ports are: inlet, outlet, and exhaust (ortank). A 3-way valve not only supplies fluid to an actuator, but allows fluid to return from it as well.

Figures 5 through 10 show schematic symbols for 3-way directional control valves.

3-way directional control valves

Figure . Solenoid pilot-operated 3-way selector valve.

Figure depicts an all-ports-blocked, 3-way, 3-position valve. A valve of this type connected to a single-acting, weight- or spring-returned cylinder could extend, retract, or stop at any place in the stroke.

directional control valves symbols

Some 3-way valves select fluid flow paths as in Above Figure. Use a spool-type valve for this operation. Another flow condition is the diverter valve shown in Below Figure. A diverter valve sends fluid to either of two paths.

directional control valves image

Don't Miss Our Updates
Be the first to get exclusive content straight to your email.
We promise not to spam you. You can unsubscribe at any time.
Invalid email address
You've successfully subscribed !

Continue Reading

Fluid Power Systems
What happens when Fluid Flow Reversed through Control Valve?
Control Valve Air Lock Relay Working Principle
Pressure Relief Valve Principle
Working Principle of Pneumatic Actuators
Different Types of Control Valve Actuators
Share This Article
Facebook Whatsapp Whatsapp LinkedIn Copy Link
Share
Leave a Comment

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Stay Connected

128.3kFollowersLike
69.1kFollowersFollow
210kSubscribersSubscribe
38kFollowersFollow

Categories

Explore More

What is a Float Control Valve? Types, Advantages, Disadvantages
What is Motor Actuator ?
Inspection and Test Requirement of Control Valves
Introduction to Types of Valves
Globe Valve Seat and Disk
Dome Valve Working Principle
Pneumatic Control Valve Actuators
Progressive Control Valve Sequence

Keep Learning

Solving Critical Control Valve Hunting

Solving Control Valve Hunting: Instrument Troubleshooting

Plug Valve Parts

What is Plug Valve ?

electric motor actuator principle

What is a Electric Motor Actuator ?

Y Body Globe Valve

Globe Valve Body Design

Basic Configuration of Motor Operated Valve

Rotork Motor Operated Valve Basic Configuration

pilot operated relief valves

Pilot-operated Relief Valve Principle

Malfunctioning Inlet Check Valves

Malfunctioning Inlet Check Valves caused chaos at Compressor stop/trip

Valve stem travel

Control Valves Mechanical Friction Problems

Learn More

Clamp Meter

What is a Clamp Meter?

Radiometric level Principle

Radiometric level measurement Working Principle

Economics of Power Generation Objective Questions

100+ Economics of Power Generation Objective Questions and Answers

Business Skills Every Engineer Needs

Business Skills Every Engineer Needs

Electric Circuits Objective Questions

Electric Circuits Objective Questions – Set 15

Group of Induction Motors

How to Operate a Group of Induction Motors using PLC Logic?

Common Materials used in Instrumentation Cables

Common Materials used in Instrumentation Cables

Quality Control Inspector Questions

Quality Control Inspector Interview Questions and Answers

Menu

  • About
  • Privacy Policy
  • Copyright

Quick Links

  • Learn PLC
  • Helping Hand
  • Part Time Job

YouTube Subscribe

Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Welcome Back!

Sign in to your account

Username or Email Address
Password

Lost your password?