servo valve coloring book

The Electrohydraulic Servovalve Coloring

Book

Rosamond Dolid, PMP®

MTS Systems Corporation

© 2010

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AcknowledgementsThe CAD rendering and drawings were contributed by Nathan Milner and Kristin Haag, undergraduate mechanical engineering students at the University of Minnesota. Content review was provided by Professor Will Durfee, Department of Mechanical Engineering, University of Minnesota.

Permission to reproduce photographs was granted by MTS Systems Corporation and by Moog Inc.

Support for this project was provided by MTS Systems Corporation and by the Center for Compact and Efficient Fluid Power, an NSF Engineering Research Center.

For information on this project, contact the author, Roz Dolid at [email protected].

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About this book

This purpose of this book is to facilitate understanding of a basic electrohydraulic servovalve. This is not a guide to valve design, nor does it provide proprietary information regarding design or manufacturing of valves. The primary audience for this book is degreed engineers working in the fluid power industry who may not have received a fluid power education or who may not be familiar with servovalves. Versions of this book have been used to train newly hired engineers at MTS Systems Corporation since 2007.

The underlying concept of this book is that the act of coloring components helps your brain to fully understand where those components are located and how they contribute to the operation of the valve. The inspiration to use coloring as a means to understand complex ideas is “The Anatomy Coloring Book” by Kapit and Elson, which has long been used by medical school students to deepen their understanding of how the human body works. So, grab your colored pencils or crayons and get started!

Twelve colors are sufficient to complete this book, by re-using each color once. Twenty-four colors are enough for every item to have its own color throughout the book. Colored pencils are a better choice than crayons or markers. Use the same color for the same part throughout the book as much as possible –this allows the color itself to be a memory trigger for the part it is associated with.

For the first part of the book, which covers servovalvecomponents, choose distinct colors for adjacent parts. Later, when coloring in the oil flow paths, color represents a pressurestate. Choose a color sequence that shows pressure level in an order that makes sense, for example a light spectrum sequence of red, orange, yellow, green, blue, purple.

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Introduction: What is a Servovalve?

An electrohydraulic servovalve is a device that takes an electrical current and turns it into hydraulic flow which can then create linear, rotational, uni-directional or reciprocating mechanical motion.

Servovalves were invented during the late 1940’s for military use. In the 1960’s MTS Systems Corporation began using servovalves in displacement and force controlled test equipment. There are several types of servovalves, including the flapper nozzle style 4-way valve, which is presented in this book.

Two stage MTS valve built by Moog, Inc

Three stage MTS valve, withtwo stage Moog valve used asthe pilot stage

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First Stage: Armature assemblyA. Permanent Magnet (2)B. Wire Coils (2)C. Armature AssemblyD. Upper Pole PieceE. Lower Pole Piece

F. Ferrous Core or ArmatureG. Flexure TubeH. FlapperJ. Feedback WireK. Nozzles

The first stage of an electrohydraulic servovalve converts the input electrical current signal into a hydraulic flow.

Armature Detail

A B

C

D

E

F

G

H

J

K

C

K

BB

A

F F F

F

H

C

C

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First Stage: Flapper-Nozzle Interaction

Null

Activated

Use the same color for these parts as on the previous page.Notice that the flapper on the activated valve is closer to the nozzle on the left, which throttles the flow running through theleft nozzle.

KK

KK

G

H

G

H

G

G

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Second Stage: Components

J. Feedback WireL. SpoolM. FilterN. Fixed OrificeO. Variable Orifice

L

M

N

J

Notes: 1. Use brown or black for the filter2. The variable orifices in this view are closed so there is no space to color. Pages following will reveal the orifices.

M

MM

N

L L L L L

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Second Stage: Spool Features

Q. The wider portions of the spool are called lands.R. The precision machined edges that define the variable orifice openings are called metering edges. Only two metering edges are visible in this drawing.

R

Q

QQ

Q

R

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Second Stage: Variable Orifices

When the valve is activated by a command signal, some of the variable orifices open while others remain closed. The arrows indicate the direction of oil flow through the open orifices.

When the valve is in its null position, all of the variable orifices are closed. There is a small amount of leakage through this type of valve even in the null position, which must be taken into account when sizing a system for an application.

O. Variable orifice

O

OO

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Full Valve: Oil Pressures – Null Position

S. Supply pressureT. Filter pressure

U. Spool pressureW. Working pressure

Y. Return pressure

Color in the pressure legend accordingto the colors used in the picture

S S

SS S

T T T T

U

U

U U

Y

Y

Y

Notes: 1. Color the filter brown or black2. Working pressures are equal so

there is no flow to the next device (actuator or spool)

W

W

W W

W

W

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Full Valve: Oil Pressures – Activated Position

Notes: 1. Color the filter brown or black2. Use the same color for variableorifices as previous pages

S. Supply pressureT. Filter pressure

U. Higher Spool pressureV. Lower Spool pressureW. C1 working pressureX. C2 working pressure

Y. Return pressure

Color in the pressure legend accordingto the colors used in the picture

S S

S

S

S

T T T T

U

U V

V

W

W

W

X

X

X

Y

Y

Y

O. Variable Orifice

O

O O

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Full Valve: Oil Flows

Using one color, draw the path of an oil particle traveling through the valve when the valve is in the null (top) and activated (bottom) positions, remembering that there are four different pathways for an oil particle to travel through when the valve is activated.

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Servovalve Parts

1. Spool2. Nozzle3. Fixed Orifice4. Tubular Filter5. Disc Filter

1

2

34

5

Courtesy of MTS Systems Corporation

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Torque Motor Armature Assembly

1. Upper and lower pole pieces2. Permanent magnet3. Electromagnet coil4. Feedback wire


1

2

3

4

15

Torque Motor Assembly

1. Torque motor armature assembly with signal connector

2. Permanent magnet3. Electromagnet coil4. Armature/flexure tube/flapper/feedback wire

assembly

1

2

3

4


16

Three Stage Servovalve

1. Torque motor armature assembly2. 2nd stage spool3. Manifold block (porting between 2nd and 3rd

stage spools)4. 3rd stage spool

1

2

34


17

Servovalve and Hydraulic Piston Actuator


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References

1. Dolid, R., "What Makes a Bicycle? A Coloring Activity to Teach Basic Mechanical Concepts”presented at the 2006 ASME International Mechanical Engineering Congress and Exposition, November 5-10, 2006, Chicago, IL.

2. Kapit, W. and L. Elson, The Anatomy Coloring Book, 3rd ed., Benjamin Cummings, 2002.

3. Merritt, H.E., Hydraulic Control Systems, New York, John-Wiley & Sons, 1967.

4. Moog Inc., “Electrohydraulic Valves, a Technical Look”, http://www.moog.com/media/1/technical.pdf.

5. Wang, D., Dolid, R., Donath, M. and Albright, J., “Development and Verification of a Two-Stage Flow Control Servovalve Model”, presented at the 1995 ASME International Mechanical Engineering Congress and Exposition, November 12-17, 1995, San Francisco, CA.

servo valve coloring book

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