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IIT Basic Hydraulics Interactive Computer Based Training Course

Basic Hydraulics.pdf (Size: 3.08 MB / Downloads: 24)

COURSE INTRODUCTION

Welcome again to the IIT Basic Hydraulics Interactive Computer Based Training Course.

This course has been designed to give you a broad based understanding of the most

important hydraulic concepts. Upon completion of this course, you should understand

various basic physics laws as they apply to fluid power, as well as understand schematics

and system design. You will also study the various components found in a typical

hydraulics system and how these components function and interact with each other.

From this main menu, you can select from any of the course topics listed on the right hand

side of your screen. Although you can work through these topics in any order, we

recommend that you start at the top of the list with Fluid Power Physics and continue

through the subjects from top to bottom. These topics are presented in this order to aid in

your understanding of the material presented. While using this program, you can return to

the main menu screen at any time.

FLUID POWER PHYSICS

Introduction

After completing the lessons and exercises in this section you will better understand the

basic physics principles that govern fluid power. These principles are timeless and

understanding them well will provide you with a solid foundation on which to learn much

more about fluid power.

Energy

As we begin our study of basic hydraulics we must first recognize that fluid power is

another method of transferring energy. This energy transfer is from a prime mover, or input

power source, to an actuator or output device. This means of energy transfer, although not

always the most efficient, where properly applied may provide optimum work control.

Energy may be defined as the ability to do work.

Work:

Work is defined as force through distance. If we move 1000

pounds a distance of 2 feet we have accomplished work. We

measure the amount of work in foot-pounds. In our example, we

have moved 1000 pounds 2 feet or have accomplished 2000 footpounds

of work.

Horsepower:

Mathematically, hydraulic horsepower is expressed as follows: horsepower

equals flow, in gallons per minute (gpm), times pressure, inch-pounds per square inch

(psi), divided by 1714, a constant. In our illustration we are lifting 10,000 pounds (this is

our force) a distance of 1 foot (this is the work to be accomplished). If we lift our load in 2

seconds we have defined a power requirement. This may be expressed as hydraulic

horsepower. To lift our 10,000 pounds a distance of one foot in 2 seconds we must have a

required flow rate at a specific pressure, based on cylinder size and the pump flow

discharge. In this illustration a 10 gpm pump is required to extend the cylinder in 2

seconds. The pressure requirement to lift the 10,000 pounds is 1500 psi. Based on our

formula our theoretical horsepower requirement would be 8.75.

Torque:

Torque is twisting force. It is also measured in foot-pounds. In this illustration we

are producing 10 foot-pounds of torque when we apply 10 pounds of force to a 1 foot-long

wrench. This same theory applies to hydraulic motors. Hydraulic motors are actuators that

are rated in specific torque values at a given pressure. The twisting force, or torque, is the

generated work. A motor’s rotations per minute (rpm) at a given torque specifies our

energy usage or horsepower requirement.

Flow

Flow in a hydraulic system is produced from a positive displacement pump. This is

different from a centrifugal pump, which is not positive displacement. There are three

important principles that must be understood relating to flow in a hydraulic system.

Principle one: Flow makes it go. For anything to move in a hydraulic system the actuator

must be supplied with flow. This cylinder is retracted. It can extend only if there is flow into

port B. Shifting the directional control valve will send flow to either extend or retract the

cylinder.

Principle two: Rate of flow determines speed. Rate of flow is usually measured in gpm or

gpm. Gpm is determined by the pump. Changes in pump output flow will change the

speed of the actuator.

Principle three: With a given flow rate, changes in actuator volume displacement will

change actuator speed. With less volume to displace, the actuator will cycle faster. For

example, there is less volume to displace when we retract, because the cylinder rod

occupies space, diminishing the volume to be displaced. Notice the difference in speed

between extend and retract.