This document discusses various hydraulic actuators and control components. It begins by describing different types of hydraulic cylinders including single acting, double acting, double rod, tandem, and telescopic cylinders. It then discusses cylinder cushioning and mounting. The document next covers various directional control valves including check valves, pilot operated check valves, 3/2 valves, 4/2 valves, and 4/3 valves. It provides details on the construction and operation of each. Finally, the document discusses flow control valves including pressure relief valves and compound pressure relief valves.
application of Direction control valve in automatic transmissionZIYAD AMBALANGADAN
This document discusses directional control valves and their application in automatic transmissions. It begins by defining directional control valves as valves used to control the direction of fluid flow in hydraulic circuits. It then classifies valves based on their construction, number of ports, switching positions, and actuation mechanism. Examples of poppet and spool valves are described. Applications of directional control valves in automatic transmissions include using them to direct fluid flow to engage or disengage clutches based on vehicle speed. In conclusion, directional control valves are used to distribute hydraulic energy and control the start, stop, and direction of pressurized fluid flow.
This is complete description of Hydraulic Accessories used consisting
1.Hydraulic Reservoir or tank- construction, mountings, Design
2.Heaters & coolers- Types
3.Sealing- introduction, classification, each type with diagram, materials, seal selection factors,
4.Piping- intro, sizing of pipe, Pipe Schedules, Threads, Fittings, materials, connectors,
5. Hoses- materials, selection criteria,
6. Accumulators- types, information of each type with diagram,
7. Hydraulic fluids- properties, types
8. Filters- types, specifications, materials
I hope you find this useful.
please comment if have any questions and like this.
ME 6021 - HYDRAULICS AND PNEUMATICS / UNIT II - HYDRAULIC SYSTEM AND COMPONENTSSANTHOSH00775
This document provides an overview of hydraulic systems and components. It discusses various types of hydraulic pumps including centrifugal, gear, vane, piston and axial flow pumps. It also describes hydraulic actuators like cylinders and motors. Finally, it covers control components such as directional control valves, pressure control valves and flow control valves.
This document outlines the objectives and units of a course on hydraulics and pneumatics. The objectives are to provide students with knowledge of fluid power applications in industry and an understanding of hydraulic and pneumatic components. The five units cover fluid power principles, hydraulic pumps, actuators and controls, hydraulic circuits and systems, pneumatic systems, and troubleshooting applications. Unit 1 discusses fluid properties, Pascal's law, and types of hydraulic pumps like gear, vane, piston and screw pumps.
Electro hydraulic system Components and their operationSrichandan Subudhi
After this presentation you will be knowing:
1.What are DCVs, its type and their uses
2.About Check Valves and pilot controlled check valves
3.What are solenoid actuated valves and their operation
4.What are proportional solenoid valves and their operation
5.Servo Valve Operation
6.Servo Valve Connector
The major components of a hydraulic system are:
1. A prime mover such as an engine or electric motor that provides mechanical power.
2. A pump that is driven by the prime mover to pressurize the fluid and convert mechanical energy to fluid energy.
3. Control valves such as pressure, flow, and directional valves that control the flow and direction of pressurized fluid.
4. Actuators that convert pressurized fluid power into mechanical motion or force.
5. A piping system that carries pressurized fluid between components and back to the reservoir.
The document discusses different types of hydraulic cylinders and rotary actuators. It describes single acting cylinders that work in one direction, double acting cylinders that work in both directions, and telescopic cylinders for large strokes or limited spaces. It also covers properties of cylinders, calculations, buckling checks, and cushioning cylinders at the end of strokes. Rotary actuators discussed include vane, piston, and limited angle types.
This document discusses pneumatic and electro-pneumatic systems. It covers the objectives of studying these topics which are to provide knowledge of fluid power applications in industry and an understanding of pneumatic components. The document then describes various pneumatic system elements like compressors, filters, regulators, lubricators and valves. It also explains the properties of air and perfect gas laws. Finally, it discusses pneumatic circuits and the cascade method for designing circuits.
The document summarizes key concepts in hydraulics including:
1. Hydraulics uses liquids to transmit force via Pascal's law, where pressure is transmitted undiminished throughout a confined liquid.
2. Key components include pumps to pressurize fluid, cylinders to convert hydraulic power into mechanical motion, and control valves to direct fluid flow.
3. There are different types of hydraulic systems, pumps, cylinders and valves that are suited to various applications and pressure requirements.
Hydraulic cylinders are linear actuators that convert hydraulic pressure into mechanical force and motion. There are several types of cylinders including single-acting, double-acting, and telescopic cylinders. Single-acting cylinders produce force in one direction only, while double-acting cylinders can produce force in both extension and retraction using ports on both sides of the piston. Telescopic cylinders extend in stages to provide a long stroke length and short retracted length. Cushioning devices are often used on cylinders to control the rate of deceleration and prevent shock at the end of the piston stroke.
The document provides an overview of basic hydraulic principles and components. It explains that hydraulics involves using pressurized liquids to transmit power and describes the three main sections of a hydraulic system: the drive section which includes cylinders and motors, the energy control section with valves, and the power supply section with pumps, reservoirs and other components. It then discusses key hydraulic concepts like Pascal's principle and displacement transmission. Finally, it outlines different types of hydraulic pumps including gear, vane and screw pumps as well as filters, coolers and other components.
Introduction to hydraulics and pneumatic by Varun Pratap SinghVarun Pratap Singh
Download Link (Copy URL):
https://sites.google.com/view/varunpratapsingh/teaching-engagements
This file contains basic information about hydraulics and pneumatic systems.
This document discusses pneumatic systems and their components. It covers the basics of pneumatic systems including common components like compressors, filters, dryers, receivers, control valves and actuators. It also discusses the gases used, advantages and disadvantages of pneumatic systems, applications, electro-pneumatic controllers and system diagrams. Hydraulic systems are mentioned but not described in detail.
The document outlines objectives for understanding fundamental hydraulic principles, reading hydraulic diagrams, and operating hydraulic systems safely and reliably. It discusses advantages like automatic lubrication and precise motion control. It explains Pascal's law of fluid pressure transmission and fundamental principles like flow determining speed. It provides an overview of key hydraulic components like reservoirs, filters, pumps, valves, actuators and their functions. It also covers important concepts like cleanliness levels, contamination sources, and best practices for fluid handling and storage to prevent system contamination.
This document discusses low cost automation using pneumatic systems. It begins with an overview of automation and pneumatics, explaining that pneumatics can provide low cost automation solutions through reducing labor costs, machine investment costs, and increasing productivity. The document then covers various pneumatic components and applications, advantages and disadvantages of pneumatics, pneumatic standards, classifications of pneumatic elements, and examples of pneumatic circuits.
The document discusses the fundamentals of hydraulic systems. It defines hydraulics as the study of liquids in motion and at rest and how they are used to transmit power through liquids. Key points include:
- Hydraulic systems use liquids to multiply forces and torques without needing gears or levers, allowing high forces over long distances.
- Pascal's law describes how pressure is transmitted equally in all directions throughout a confined liquid.
- Hydraulic fluids are used to transfer energy while lubricating components and remaining functional over a wide temperature range.
- Common applications include heavy machinery, manufacturing equipment, vehicles, ships and aerospace systems.
Pneumatic circuits:
Basic pneumatic circuits, Development of single Actuator Circuits, Development of multiple Actuator Circuits, Cascade method for sequencing
This document discusses the fundamentals of fluid power systems including hydraulics and pneumatics. It covers topics such as the basic principles of hydraulics including Pascal's law, types of hydraulic fluids and their properties, hydraulic components like pumps, actuators and control valves. It also discusses pneumatic systems, fluid logic control, applications of fluid power systems in various industries and troubleshooting of hydraulic and pneumatic circuits. The document appears to be part of a course curriculum on hydraulics and pneumatics.
Directional control valves are used to control the direction of fluid flow in hydraulic circuits. They contain ports for fluid to enter and exit, and can be classified based on their construction, number of working ports, switching positions, and actuation mechanism. Common types include poppet valves and spool valves. Directional control valves find application in automatic transmissions, where they control fluid flow to engage and disengage clutches or change gear ratios based on vehicle speed. Proper selection and application of directional control valves is important for efficiently distributing hydraulic power in automotive and industrial systems.
Applications for Pneumatic Controls. Pneumatic systems are used in many places in our everyday world, including train doors, automatic production lines, mechanical clamps, and more. A pneumatic system uses air that is compressed in order to transmit and control energy.
The document discusses pneumatic systems and components. It describes how pneumatic systems use compressed air to transmit power and operate cylinders, valves, and other components. Some key advantages of pneumatic systems mentioned include being fast, easily transportable, variable speed and pressure, and clean operating. Common applications described are industrial robots, machine tools, brakes on vehicles, and dental/medical tools. The document also provides details on various pneumatic components like cylinders, valves, connectors, and their functions.
3 valve shafts pneumatics and hydraulicsaman520305
Control valves determine the direction and flow of fluid in hydraulic circuits. There are three main types: directional control valves, pressure control valves, and flow control valves. Directional control valves include check valves, shuttle valves, and multi-way valves which control fluid flow paths. Pressure control valves such as relief valves, sequence valves, and pressure reducing valves maintain safe pressure levels. Flow control valves regulate fluid flow rates and actuator speeds. Proper use of control valves is important for safe and efficient operation of hydraulic systems.
Lecture 8Cylinders & open and closed circuitJavaid Toosy
The document describes open and closed loop hydraulic systems used to raise and lower loads using hydraulic cylinders. It explains how a pressure regulating valve is used to prevent excessive pressure build up when the pump is deadheaded. It provides details on the components and operation of hydraulic cylinders, including the cylinder barrel, piston, piston rod, seals, and different cylinder designs like tie rod and welded body cylinders. The pressure regulating valve helps maintain a safe pressure level between its cracking and full flow pressures.
This document discusses spool actuation methods for directional control valves. It begins by introducing the three main types of valves: directional control valves, pressure control valves, and flow control valves. It focuses on directional control valves, which determine the fluid flow path. There are two main types of spools: sliding and rotary. Spool actuation can be manual, mechanical, solenoid, hydraulic, pilot-operated, electric, fluidic, or indirect. Common actuation methods include manual handles, linkages, solenoids, and applying a pilot pressure signal. Directional control valves provide advantages such as being innovative, versatile, compact, and reliable.
Directional control valves (DCVs) determine the path of fluid flow in hydraulic systems. There are several types of DCVs classified by fluid path, design characteristics, control method, and construction of internal moving parts. DCVs include check valves, shuttle valves, two-way valves, three-way valves, and four-way valves. DCVs can be actuated manually, mechanically, with a solenoid, or with a pilot signal. The simplest DCV is a check valve, which allows uni-directional flow. A poppet check valve uses a spring-loaded poppet to control flow direction, while a pilot-operated check valve uses a pilot signal to control flow in the
The document provides information about basic hydraulics. It discusses hydraulic components like pumps, filters, coolers and heaters. It explains how hydraulics works using principles like Pascal's law and the transmission of power and displacement. Diagrams show hydraulic symbols and circuits. Hydraulic pumps are described in detail, including gear pumps, vane pumps, screw pumps and piston pumps. Key specifications for different pump types are also provided.
The document provides an overview of hydraulic cylinders, including their types, construction, operation, ratings, formulas for application, features, and installation/troubleshooting. It describes the main types of cylinders like ram, single acting, telescopic, spring return, and double acting cylinders. It covers cylinder construction details, actuation, mounting, ratings based on size and pressure, formulas to calculate speed, flow and force. It also discusses features such as seals, cushions, stop tubes, ports, and limit switches. The document concludes with guidelines for cylinder installation and troubleshooting.
The document discusses various types of hydraulic actuators used to convert fluid pressure into mechanical motion or force. It describes linear actuators like cylinders, which can be single-acting, double-acting, telescopic, or tandem cylinder designs. Rotary actuators and semi-rotary actuators are also discussed briefly. The main focus is on hydraulic cylinders, their components, operating principles, forces involved, and examples of force and power calculations.
This document provides information on various types of actuators, including solenoids, valves, cylinders, hydraulics, pneumatics, and motors. It describes how solenoids, solenoid valves, cylinders, and motors function. Hydraulic and pneumatic systems are compared, with pneumatics providing smaller forces at higher speeds but being less stiff, while hydraulics provides large forces but at lower speeds. Symbols for components like valves and cylinders are shown. The document also discusses considerations for selecting valves and provides examples of pneumatic and hydraulic circuits.
This document discusses hydraulic circuits used in hydro power plants. It describes how changing the flow through movable guide vanes can increase or decrease the megawatts generated by adjusting the vane angle. This is achieved using a hydraulic circuit called a speed governor. The document then summarizes the main components of hydraulic circuits including valves, pumps, filters, accumulators, actuators, accessories and connecting pipes. It provides examples of different hydraulic valve types including directional control valves, pressure control valves and flow control valves.
- Hydraulic actuators like cylinders are used to convert fluid pressure into mechanical motion or force. Single-acting cylinders produce force in one direction while double-acting cylinders can produce force in both directions.
- Directional control valves include check valves, two/four-way valves, and shuttle valves. They control the direction of fluid flow. Pressure control valves like relief valves limit system pressure while flow control valves regulate fluid flow rate and actuator speed.
- Properly selecting and using hydraulic components like actuators, valves, and linkages allows fluid power systems to efficiently control mechanical processes.
This document provides an overview of a course presentation on hydraulic and pneumatic control design. Specifically, it discusses directional control valves, including classifications based on fluid path, design characteristics, control method, and construction of internal moving parts. It describes common directional control valve types like check valves, shuttle valves, two-way valves, and more. It also discusses actuating devices for directional control valves and provides examples of applications using check valves.
Babic components of hydraulic & pneumatic systemswakurets_21
The document discusses the basic components and applications of hydraulic and pneumatic systems. It describes the main types of hydraulic and pneumatic actuators including linear actuators like cylinders, and rotary actuators like motors. It also explains the different types of valves used in hydraulic and pneumatic circuits including directional control valves, flow control valves, and pressure control valves. The purpose and basic operation of common valve types are provided like poppet valves, spool valves, needle valves, check valves, and relief valves.
Pneumatics: Shuttle, Twin pressure, Quick Exhaust, Time Delay, FRLAbhishek Patange
The document discusses various components used in pneumatic systems including logic gates, valves, and FRL units. It begins with explanations of shuttle valves and twin pressure/dual pressure valves that can function as OR and AND logic gates respectively. Various valves are then discussed such as time delay valves, quick exhaust valves, and their applications. Speed control methods and the stick-slip effect in pneumatics are also covered. Finally, the construction and working of the main components of an FRL (filter, regulator, lubricator) unit are explained in detail with diagrams.
An actuator is a motor that converts energy into motion. Hydraulic actuators use pressurized fluid to move a piston inside a cylinder. This provides precise linear motion. Common types include single-acting cylinders, which move in one direction, and double-acting cylinders, which can move in both directions. Hydraulic actuators are used widely in industrial and vehicular applications due to their strength, precision of movement, and ability to produce high torque.
The document discusses different types of valves and pumps used in pipelines. It describes plug cock valves, globe valves, gate valves, diaphragm valves, quick opening valves, and check valves. For pumps, it covers reciprocating pumps and their components. Reciprocating pumps work by using a piston inside a cylinder that moves back and forth to suck and discharge liquid. Rotary pumps are also discussed, specifically gear pumps which are a type of positive displacement rotary pump.
This document provides an overview of hydraulic cylinders, including their types, construction, operation, ratings, formulas for application, features, and installation/troubleshooting. It describes the main types of cylinders like ram, single acting, telescopic, spring return, and double acting cylinders. It also discusses cylinder construction, actuation, mounting, ratings based on size and pressure, formulas to calculate speed, flow, force and pressure. Key features like seals, cushions, ports and limit switches are explained. Guidelines for cylinder selection, installation and troubleshooting are provided.
Hydraulic Pumps, Motors and Actuators:
Construction, working principle and operation of rotary & reciprocating pumps like Gear, Vane, Generated-Rotor, Screw, Axial Piston, Radial Piston, Pump characteristics, Linear and Rotary Actuators, Hydrostatic Transmission Systems. Selection of components for applications
This document discusses different types of hydraulic linear actuators. It describes single-acting actuators which can extend in one direction via hydraulic pressure and retract via gravity or a spring. Double-acting actuators can extend and retract via hydraulic pressure supplied to either end of the cylinder. Common types include cylinders with piston rods on one or both sides. The document also outlines the basic components of a hydraulic system including a pump to pressurize hydraulic fluid, valves to control fluid flow, piping to transport fluid, and a cylinder where fluid pressure is converted to linear motion.
Similar to Hydraulics & pneumatics (AU) Unit-II (20)
Introduction And Differences Between File System And Dbms.pptxSerendipityYoon
An introduction to file systems and a database management system. This document provides a free powerpoint presentation about the differences between a file system and database management system. Advantages and disadvantages of file system and database management system.
The Control of Relative Humidity & Moisture Content in The AirAshraf Ismail
To many of us Relative Humidity (RH%) & Moisture Content (g/ kg) are confusing terms & we often don't know which one of them to choose in order to highlight our "Humidity" issues!
This post is to briefly address the definition of Relative Humidity, Moisture Content , Moisture Load Sources & Humidity Control Hazard!
1. DEE 1203 ELECTRICAL ENGINEERING DRAWING.pdfAsiimweJulius2
This lecture will equip students with basic electrical engineering knowledge on various types of electrical and electronics drawings, different types of drawing papers, different ways of producing a good drawing and the importance of electrical engineering drawing to both engineers and the users.
By the end of this lecture, students will be to differentiate between different electrical diagrams like, block diagrams, schematic diagrams, circuit diagrams among others.
If we're running two pumps, why aren't we getting twice as much flow? v.17Brian Gongol
A single pump operating at a time is easy to figure out. Adding a second pump (or more) makes things a bit more complicated. That complication can deliver a whole lot of additional flow -- or it can become an exercise in futility.
Distillation basic knowledge is given in this PPT for the vapour liquid equilibrium in which we can understand the basic knowledge for the separation of the two miscible liquid which is being separation by the vapour temperature is it separated by the more related to this again the structure of structure
2. OBJECTIVES: L T P C
3 0 0 3
To provide student with knowledge on the application of fluid power in process,
construction and manufacturing industries.
To provide students with an understanding of the fluids and components utilized in
modern industrial fluid power system.
To develop a measurable degree of competence in the design, construction and
operation of fluid power circuits.
HYDRAULICS AND PNEUMATICS
3. UNIT II
HYDRAULIC ACTUATORS AND CONTROL COMPONENTS
Hydraulic Actuators: Cylinders – Types and construction, Application, Hydraulic
cushioning – Hydraulic motors - Control Components : Direction Control, Flow control
and pressure control valves – Types, Construction and Operation – Servo and Proportional
valves – Applications – Accessories : Reservoirs, Pressure Switches – Applications –
Fluid Power ANSI Symbols – Problems.
HYDRAULICS AND PNEUMATICS
4. HYDRAULIC ACTUATORS
Hydraulic cylinders (also called linear actuators) extend and retract a piston rod to
a push or pull force to drive the external load along a straight-line path.
HYDRAULICS AND PNEUMATICS
5. HYDRAULIC ACTUATORS
Hydraulic motors (also called rotary actuators) rotate a shaft to provide a torque to
drive the load along a rotary path.
Pumps perform the function of adding energy to the fluid (on the fluid) of a
hydraulic system for transmission to some output location.
Hydraulic cylinders and hydraulic motors do just the opposite. They extract
energy from the fluid (by the fluid) and convert it to mechanical energy to perform
useful work.
HYDRAULICS AND PNEUMATICS
7. SINGLE ACTING CYLINDER:
The simplest type of hydraulic cylinder is the single-acting design.
It consists of a piston inside a cylindrical housing called a barrel. Attached to one
end of the piston is a rod, which extends outside one end of the cylinder (rod end).
At the other end (blank end) is a port for the entrance and exit of oil.
A single-acting cylinder can exert a force in only the extending direction as fluid
from the pump enters the blank end of the cylinder.
Single acting cylinders do not retract hydraulically. Retraction is accomplished by
using gravity or by the inclusion of a compression spring in the rod end.
HYDRAULICS AND PNEUMATICS
8. DOUBLE ACTING CYLINDER:
In this double-acting cylinder design, the barrel is made of seamless steel tubing,
honed to a fine finish on the inside.
The piston, which is made of ductile iron, contains U-cup packings to seal against
leakage between the piston and barrel.
The ports are located in the end caps, which are secured to the barrel by tie rods.
HYDRAULICS AND PNEUMATICS
9. DOUBLE ROD CYLINDER:
In a double-rod cylinder, the rod extends out of the cylinder at both ends. For such
a cylinder, the words extend and retract have no meaning.
Since the force and speed are the same for either end, this type of cylinder is
typically used when the same task is to be performed at either end.
Since each end contains the same size rod, the velocity of the piston is the same
for both strokes.
HYDRAULICS AND PNEUMATICS
10. TANDEM CYLINDER:
Tandem cylinder is used in applications where a large amount of force is required
from a small diameter cylinder.
Pressure is applied to both pistons, resulting in increased force because of the
larger area.
The drawback is that these cylinders must be longer than a standard cylinder of
larger flow rate than a standard cylinder to achieve an equal speed because flow must
go to both pistons.
HYDRAULICS AND PNEUMATICS
11. TELESCOPIC CYLINDER (Double Acting):
The telescopic cylinder contains multiple cylinders that slide inside each other.
They are used where long work strokes are required but the full retraction length
must be minimized.
One application for a telescopic cylinder is the high-lift fork truck.
HYDRAULICS AND PNEUMATICS
13. CYLINDER CUSHIONING:
Double-acting cylinders sometimes contain cylinder cushions at the ends of the
cylinder to slow the piston down near the ends of the stroke. This prevents excessive
impact when the piston is stopped by the end caps.
As shown, deceleration starts when the tapered plunger enters the opening in the
cap. This restricts the exhaust flow from the barrel to the port.
During the last small portion of the stroke, the oil must exhaust through an
adjustable opening.
The cushion design also incorporates a check valve to allow free flow to the
piston during direction reversal.
HYDRAULICS AND PNEUMATICS
14. CYLINDER MOUNTING: illustrated in Fig.
This permits versatility in the anchoring of cylinders. The rod ends are usually
threaded so that they can be attached directly to the load, a clevis a coke, or some other
mating device.
The following benefits are obtained
1. Free range of mounting positions
2. Reduced cylinder binding and side loading
3. Allowance for universal swivel
4. Reduced bearing and tube wear
5. Elimination of piston blow-by caused by misalignment
HYDRAULICS AND PNEUMATICS
18. DIRECTION CONTROL VALVES
CHECK VALVE (One directional flow control valve):
Simplest type of direction control valve is a check valve.
It is a two-way valve because it contains two ports.
The purpose of a check valve is to permit free flow in one direction and prevent
any flow in the opposite direction.
Fig showing the internal operation of a poppet check valve. A poppet is a
specially shaped plug element held onto a seat by a spring.
Fluid flows through the valve in the space between the seat and poppet.
A light spring holds the poppet in the closed position. In the free-flow direction,
the fluid pressure overcomes the spring force at about 5 psi.
If flow is attempted in the opposite direction, the fluid pressure pushes the poppet
(along with the spring force) in the closed position. Therefore, no flow is permitted.
HYDRAULICS AND PNEUMATICS
19. DIRECTION CONTROL VALVES
CHECK VALVE (One directional flow control valve):
The higher the pressure, the greater will be the force pushing the poppet against
its seat. Thus, increased pressure will not result in any tendency to allow flow in the
no-flow direction.
Fig shows the graphic symbol of a check valve along with its no flow and free-
flow directions.
Graphic symbols, which clearly show the function of hydraulic components (but
without the details provided in schematic drawings), are used when drawing hydraulic
circuit diagrams.
Note that a check valve is analogous to a diode in electric circuits.
HYDRAULICS AND PNEUMATICS
21. DIRECTION CONTROL VALVES
PILOT OPERATED CHECK VALVE
A second type of check valve is the pilot-operated check valve.
This type of check valve always permits free flow in one direction but permits
flow in the normally blocked opposite direction only if pilot pressure is applied at the
pilot pressure port of the valve.
In the design, the check valve poppet has the pilot piston attached to the threaded
poppet stem by a nut.
The light spring holds the poppet seated in a no flow condition by pushing against
the pilot piston.
The purpose of the separate drain port is to prevent oil from creating a pressure
buildup on the bottom of the piston.
The dashed line represents the pilot pressure line connected to the pilot pressure
port of the valve.
Pilot check valves are frequently used for locking hydraulic cylinders in position.
HYDRAULICS AND PNEUMATICS
25. DIRECTION CONTROL VALVES:
3/2 VALVE
Three-way directional control valves, which contain three ports are typically of
the spool design rather than poppet design.
A spool is a circular shaft containing lands that are large diameter sections
machined to slide in a very close fitting bore of the valve body. The radial clearance
between the land and bore is usually less than 0.001 in. The grooves between the lands
provide the flow paths between ports.
These valves are designed to operate with two or three unique positions of the
spool. The spool can be positioned manually, mechanically, by using pilot pressure, or
by using electrical solenoids.
Figure shows the flow paths through a three-way valve that uses two positions of
the spool. Such a valve is called a three-way, two-position directional control valve.
The flow paths are shown by two schematic drawings (one for each spool
position) as well as by a graphic symbol (containing two side-by-side rectangles). In
discussing the operation of these valves, the rectangles are called as "envelopes."
HYDRAULICS AND PNEUMATICS
27. DIRECTION CONTROL VALVES:
4/2 VALVE
Figure shows the flow paths through a four-way, two-position directional control
valve.
Observe that fluid entering the valve at the pump port can be directed to either
outlet port A or B.
The following is a description of the flow paths through this four-way valve:
1. Spool Position 1: Flow can go from P to A and B to T.
2. Spool Position 2: Flow can go from P to B and A to T.
HYDRAULICS AND PNEUMATICS
30. DIRECTION CONTROL VALVES:
4/3 VALVE
Figure shows the flow paths through a four-way, three-position directional control
valve.
They are mainly 4 types:
1. Manually Actuated Valves
2. Mechanically Actuated Valves
3. Pilot-Actuated Valves
4. Solenoid-Actuated Valves
HYDRAULICS AND PNEUMATICS
31. DIRECTION CONTROL VALVES:
4/3 VALVE (Cont…)
1. Manually Actuated Valves :
Figure shows a cutaway of a four-way valve. It is manually actuated.
Since the spool is spring loaded at both ends, it is a spring centered three-position
directional control valve, Thus, when the valve is unactuated (no hand force on lever),
the valve will assume its center position due to the balancing opposing spring forces.
The graphic symbol of this four-way valve also shown.
In the graphic symbol that the ports are labelled on the center envelope, which
represents the flow path configuration. Also the spring and lever actuation symbols
used at the ends of the right and left envelopes. These imply a spring-centered,
manually actuated valve.
It should be noted that a three-position valve is used when it is necessary to stop
or hold a hydraulic actuator at some intermediate position within its entire stroke
range.
HYDRAULICS AND PNEUMATICS
32. DIRECTION CONTROL VALVES:
4/3 VALVE (Cont…)
1. Mechanically Actuated Valve :
Figure shows a four-way, spring offset valve that is mechanically rather than
manually actuated.
This is depicted in the cutaway view, with the spool end containing a roller that is
typically actuated by a cam-type mechanism.
Note that the graphic symbol is the same except that actuation is depicted as
being mechanical (the circle represents the cam-driven roller) rather than manual.
HYDRAULICS AND PNEUMATICS
33. DIRECTION CONTROL VALVES:
4/3 VALVE (Cont…)
1. Pilot Actuated Valve :
Directional control valves can also be shifted by applying air/oil pressure against
a piston at either end of the valve spool.
As shown, springs (located at both ends of the spool) push against centering
washers to center the spool when no air/oil is applied.
When air/oil is introduced through the left end passage, its pressure pushes
against the piston to shift the spool to the right. Removal of this left end air/oil supply
and introduction of air through the right end passage causes the spool to shift to the
left. Therefore, this is a four-way, three-position, spring-centered, air pilot-actuated
directional control valve.
In the graphic symbol, the dashed lines represent pilot pressure lines.
HYDRAULICS AND PNEUMATICS
34. DIRECTION CONTROL VALVES:
4/3 VALVE (Cont…)
1. Solenoid Actuated Valve :
A very common way to actuate a spool valve is by using a solenoid as illustrated
in Figure.
When the electric coil (solenoid) is energized, it creates a magnetic force that
pulls the armature into the coil. This causes the armature to push on the push pin to
move the spool of the valve.
Solenoids are actuators that are bolted to the valve housing as shown.
Like mechanical or pilot actuators, solenoids work against a push pin which is
sealed to prevent external leakage of oil.
There are two types of solenoid designs used to dissipate the heat created by the
electric current flowing in the wire of the coil.
1. Air gap solenoids 2. Wet(oil) pin solenoids
HYDRAULICS AND PNEUMATICS
37. COMPOUND PRESSURE RELIEF VALVE: (Pilot Operated)
A compound pressure relief valve (which is normally closed) is one that operates
in two stages. As shown in Figure, the pilot stage is located in the upper valve body
and contains a pressure-limiting pop pet that is held against a seat by an adjustable
spring.
The lower body contains the port connections. Diversion of the fuel pump flow is
accomplished by the balanced piston in the lower body.
The operation is as follows: In normal operation, the balanced piston is in
hydraulic balance. Pressure at the inlet port acts under the piston and also on its top
because an orifice is drilled through the large land.
For pressures less than the valve setting, the piston is held on its seat by a light
spring. As soon as pressure reaches the setting of the adjustable spring, the poppet is
forced off its seat.
This limits the pressure in the upper chamber. The restricted flow through the
orifice and into the upper chamber results in an increase in pressure in the lower
chamber.
HYDRAULICS AND PNEUMATICS
38. COMPOUND PRESSURE RELIEF VALVE :
This causes an unbalance in hydraulic forces, which tends to raise the piston off
its seat. When the pressure difference between the upper and lower chambers reaches
approximately 20 psi, the large piston lifts off its seat to permit flow directly to the
tank.
If the flow increases through the valve, the piston lifts farther off its seat.
However, this compresses only the light spring, and hence very little override occurs.
Compound relief valves may be remotely operated by using the outlet port from
the chamber above the piston.
For example, this chamber can be vented to the tank via a solenoid directional
control valve.
When this valve vents the pressure relief valve to the tank, the 20-psi pressure in
the bottom chamber overcomes the light spring and unloads the pump to the tank.
HYDRAULICS AND PNEUMATICS
40. FLOW CONTROL VALVES
Pressure Regulating Valve : (Pressure Reducing Valve)
A second type of pressure control valve is the pressure-reducing valve.
This type of valve (which is normally open) is used to maintain reduced pressures
in specified locations of hydraulic systems.
It is actuated by downstream pressure and tends to close as this pressure reaches
the valve setting. Figure illustrates the operation of a pressure-reducing valve that uses
a spring-loaded spool to control the down stream pressure.
If downstream pressure is below the valve setting, fluid will flow freely from the
inlet to the outlet.
Note that there is an internal passageway from the outlet, which transmits outlet
pressure to the spool end opposite the spring.
When the outlet (downstream) pressure increases to the valve setting, the spool
moves to the right to partially block the outlet port.
HYDRAULICS AND PNEUMATICS
41. FLOW CONTROL VALVES
Pressure Regulating Valve : (Pressure Reducing Valve) (Cont…)
Just enough flow is passed to the outlet to maintain its preset pressure level.
If the valve closes completely, leakage past the spool could cause downstream
pressure to build up above the valve setting.
This is prevented from occurring because a continuous bleed to the tank is
permitted via a separate drain line to the tank.
Figure also provides the graphic symbol for a pressure-reducing valve. Observe
that the symbol shows that the spring cavity has a drain to the tank.
HYDRAULICS AND PNEUMATICS
43. FLOW CONTROL VALVES
Unloading Valve:
An additional pressure control device is the unloading valve.
This valve is used to permit a pump to build pressure to an adjustable pressure
setting and then allow it to discharge oil to the tank at essentially zero pressure as long
as pilot pressure is maintained on the valve from a remote source.
Hence, the pump has essentially no load and is therefore developing a minimum
amount of power.
This is the case in spite of the fact that the pump is delivering a full pump flow
because the pres sure is practically zero.
This is not the same with a pressure relief valve because the pump is delivering
fuel pump flow at the pressure relief valve setting and thus is operating at maximum
power conditions.
Figure shows a schematic of an unloading valve used to unload the pump
connected to port A when the pressure at port X is maintained at the value that satisfies
the valve setting.
HYDRAULICS AND PNEUMATICS
44. FLOW CONTROL VALVES
Unloading Valve: (Cont…)
The high-flow poppet is controlled by the spring-loaded ball and the pressure
applied to port X. Flow entering at port A is blocked by the poppet at low pressures. The
pressure signal from A passes through the orifice in the main poppet to the topside area
and on to the ball.
There is no flow through these sections of the valve until the pressure rises to the
maximum permitted by the adjustable set spring-loaded ball. When that occurs the
poppet lifts and flow goes from port A to port B, which is typically connected to the tank.
The pressure signal to port X (sustained by another part of the system) acts against
the solid control piston and forces the ball farther off the seat. This causes the topside
press sure on the main poppet to go to a very low value and allows flow from A to B with
a very low pressure drop as long as signal pressure at X is maintained.
The ball reseats, and the main poppet closes with a snap action when the pressure at
X falls to approximately 90% of the maximum pressure setting of the spring-loaded ball.
Figure also includes the graphic symbol of an unloading valve.
HYDRAULICS AND PNEUMATICS
46. FLOW CONTROL VALVES
Sequence Valve :
The sequence valve, which is designed to cause a hydraulic system to operate in a
pressure sequence. After the components connected to port A have reached the adjusted
pressure of the sequence valve, the valve passes fluid through port B to do additional
work in a different portion of the system.
The high-flow poppet of the sequence valve is con trolled by the spring-loaded
cone. Flow entering at port A is blocked by the pop pet at low pressures. The pressure
signal at A passes through orifices to the topside of the poppet and to the cone.
There is no flow through these sections until the pressure rises at A to the
maximum permitted by the adjustably set spring-loaded cone. When the pressure at A
reaches that value, the main poppet lifts, passing flow to port B.
It maintains the adjusted pressure at port A until the pressure at B rises to the
same value. A small pilot flow (about 1/4 gpm) goes through the control pis ton and
past the pilot cone to the external drain at this time.
HYDRAULICS AND PNEUMATICS
47. FLOW CONTROL VALVES
Sequence Valve :
When the pressure at B rises to the pressure at A, the control piston seats and
prevents further pilot flow loss.
The main poppet opens fully and allows the pressure at A and B to rise to higher
values together. Flow may go either way at this time.
The spring cavity of the control cone drains externally from port Y, generally to
the tank. This sequence valve may be remotely controlled from vent port X.
Figure also includes the graphic symbol for a sequence valve.
The pilot line can come from anywhere in the circuit and not just from directly
upstream, as shown.
HYDRAULICS AND PNEUMATICS
52. FLOW CONTROL VALVES
Counter Balance Valve :
The purpose of a counterbalance valve is to maintain control of a vertical hydraulic
cylinder to prevent it from descending due to the weight of its external load.
As shown in Figure, the primary port of this valve is connected to the bottom of the
cylinder, and the secondary port is connected to a directional control valve (DCV).The
pressure setting of the counterbalance valve is somewhat higher than is necessary to
prevent the cylinder load from falling due to its weight.
As shown in Figure, when pump flow is directed (via the DCV) to the top of the
cylinder, the cylinder piston is pushed downward. This causes pressure at the primary
port to increase to a value above the pressure setting of the counterbalance valve and
thus raise the spool of the CBV.
This then opens a flow path through the counterbalance valve for discharge through
the secondary port to the DCV and back to the tank. When raising the cylinder, an
integral check valve opens to allow free flow for retracting the cylinder.
Figure also gives the graphic symbol for a counterbalance valve.
HYDRAULICS AND PNEUMATICS
54. FLOW CONTROL VALVES
Pressure Compensated Flow Control Valve:
If the load on an actuator changes significantly, system pressure will change
appreciably.
Thus, the flow-rate through a non-pressure-compensated valve will change for the
same flow-rate setting. Figure illustrates the operation of a pressure compensated
valve.
This design incorporates a hydrostat that maintains a constant 20-psi differential
across the throttle, which is an orifice whose area can be adjusted by an external knob
setting.
The orifice area setting determines the flow-rate to be controlled. The hydrostat is
held normally open by a light spring. However, it starts to close as inlet pressure
increases and overcomes the light spring force.
This closes the opening through the hydrostatic and thereby blocks of all flow in
excess of the throttle setting. As a result, the only oil that will pass through the valve is
the amount that 20 psi can force through the throttle.
HYDRAULICS AND PNEUMATICS
55. FLOW CONTROL VALVES
Pressure Compensated Flow Control Valve:
Flow exceeding this amount can be used by other parts of the circuit or return to
the tank via the pressure relief valve.
Also included in Figure is the graphic symbol for a pressure-compensated flow
control valve.
HYDRAULICS AND PNEUMATICS
58. ELECTRO-HYDRAULIC SERVO VALVE :
Figure gives a cutaway view of an electrohydraulic servo valve.
This servo valve is an electrically controlled, proportional metering valve suitable
for a variety of mobile vehicles and industrial control applications such as earth-
moving vehicles, articulated arm devices, cargo-handling cranes, lift trucks, logging
equipment, farm machinery, steel mill controls, utility construction, fire trucks, and
servicing vehicles.
The torque motor includes:
1. Coils 2. Pole pieces 3. Magnets and 4. An armature.
The armature is supported for limited movement by a flexure tube. The flexure
tube also provides a fluid seal between the hydraulic and electromagnetic portions of
the valve.
The flapper attaches to the center of the armature and extends down, inside the
flexure tube.
HYDRAULICS AND PNEUMATICS
59. ELECTRO-HYDRAULIC SERVO VALVE (Cont..):
A nozzle is located on each side of the flapper so that flapper motion varies the
nozzle openings.
Inlet-pressurized hydraulic fluid is filtered and then supplied to each nozzle
through one of the two inlet orifices located at the ends of the filter.
Differential pressure between the ends of the spool is varied by flapper motion
between the nozzles.
The four-way valve spool directs the flow from the supply pressure port to either
of the two outlet-to-load ports in an amount proportional to spool displacement.
The spool contains flow metering slots in the control lands that are uncovered by
spool motion.
Spool movement deflects a feedback wire that applies a torque to the
armature/flapper.
Electrical current in the torque motor coils causes either clockwise or counter-
clockwise torque on the armature.
HYDRAULICS AND PNEUMATICS
60. ELECTRO-HYDRAULIC SERVO VALVE (Cont…) :
This torque displaces the flapper between the two nozzles. The differential nozzle
flow moves the spool to either the right or left.
The spool continues to move until the feedback torque counteracts the
electromagnetic torque.
At this point the armature/flapper is returned to center, so the spool stops and
remains displaced until the electrical input changes to a new level.
Therefore, valve spool position is proportional to the electrical signal.
The actual outlet flow from the valve to the external load will depend on the load
pressure.
Rated flow is achieved with either a +100% or -100% electrical signal, at which
point the actual amount of rated flow depends on the valve pressure drop (inlet pressure
minus load pressure).
HYDRAULICS AND PNEUMATICS
62. PROPORTIONAL VALVE :
Proportional control valves, which are also called electro-hydraulic proportional
valves, are similar to electro-hydraulic servo valves in that they both are electrically
controlled.
However there are a number of differences between these two types of valves. For
example servo valves are used in closed-loop systems whereas pro proportional valves
are used in open-loop systems.
In servo valves, electrical current in a torque motor coil causes either clockwise or
counter-clockwise torque on an armature to control the movement of the valve spool.
On the other hand, a proportional valve uses a solenoid that produces a force
proportional to the current in its coils.
Thus, by controlling the current in the solenoid coil, the position of the spring-
loaded spool can also be controlled. This means that unlike a standard so solenoid
valve, a proportional valve can provide both directional and flow control capability in
a single valve.
HYDRAULICS AND PNEUMATICS