HYDRAULIC POWER
TRANSMISSION
Physical Science Applications in Agriculture Lesson B4–7 • Page 1
Student Learning Objectives. Instruction in this lesson should result in
students achieving the following objectives:
1 Identify the components of a hydraulic system and explain its operation.
2 Determine the efficiency of a hydraulic power system.
3 Calculate the actual and ideal mechanical advantages of a hydraulic system.
4 Explain the common uses of hydraulic systems on agricultural machines.
Anticipated Problem: What are the basic components of a hydraulic system and the role
each component plays in the system?
I. Hydraulics is the science of liquid in motion. Air is compressible but liquids cannot be
compressed. A system that uses oil or another type of liquid is known as a hydraulic
system. A basic idea behind any hydraulic system is that when a force is applied at one
point, the force is transmitted to another point using an incompressible fluid. The fluid is
usually an oil and the force usually multiplied during the process.
A. Basic to any hydraulic system are: 1) a pump, which creates pressure for the system,
and 2) a rotor or cylinder, which transfers the hydraulic energy back into mechanical
energy in the form of rotary or linear motion. The cylinder in this lesson consists of a
disposable syringe to transmit the energy. Also, the system involves: 3) lines, which
transfer the hydraulic energy from the pump to the rotor or cylinder and return the energy
to the pump, 4) a reservoir to store a supply of fluid, and 5) valves to control, or direct,
the fluid and its movement. All the components make up the hydraulic circuit that
completes the loop.
B. Pressure may be defined as the potential energy of a fluid power system. Applying
pressure to some unit area develops force. Pressure is calculated by dividing the force by
the area. Applying a pressure of ten pounds to one square inch area of a plunger in a
hydraulic cylinder will exert a pressure of ten pounds on each square inch of the system.
1. Pascal’s Law states that pressure exerted at any point on a confined static liquid is
transmitted with equal force on equal areas at right angles to all surfaces.
2. The scientific definition for work involves using a force to move an object. In
hydraulics force and work are inversely proportional, meaning one must be sacrificed
for the other in the system.
3. In a hydraulic system involving two pistons, when one piston is six times larger than
the other piston, a force applied to the smaller piston will appear six times greater on
the larger piston, but the smaller piston will have to travel six times farther in travel
distance.
Anticipated Problem: How is the efficiency for a hydraulic system calculated? What
factors affect the efficiency of the system?
II. The efficiency of a system is usually calculated by comparing the output to the input
of the system. In a hydraulic system, efficiency is determined by dividing the actual
mechanical advantage by the ideal mechanical advantage and multiplying the result by
100 to obtain a percentage of efficiency.
A. Efficiency of the hydraulic system in the experiment can be affected by various
factors, the most obvious being friction.
B. If the weights providing the force are not properly placed and the force does not push
directly straight down on the hydraulic piston, additional force can be exerted
horizontally between the plunger and cylinder wall. This outward force will increase the
effort needed to lift the resistance and reduce the efficiency, because the actual
mechanical advantage will be decreased.
Anticipated Problem: How is actual mechanical advantage and ideal mechanical
advantage calculated for a hydraulic system?
III. Ideal mechanical advantage is the theoretical advantage that the system would have
if there were no outside influences or limitations such as friction of the fluid or the
plungers against the walls of the syringe or hydraulic piston. Ideal advantage assumes
that there is no air present in the system and there are no fluid leaks as well.
A. Ideal mechanical advantage in a hydraulic system is determined by dividing the area
of the larger piston by the area of the smaller piston. Area of the piston is calculated by
squaring the diameter of the piston, multiplying by pi (3.14) and dividing by 4. Area is
reported in square units such as square inches or square centimeters.
B. Actual mechanical advantage is the actual advantage gained when all these
limitations and factors are considered by comparing the loads placed on the system.
Actual mechanical advantage is determined by dividing the resistance force by the effort
force. The resistance force is the object(s) attempting to be moved by the hydraulic
system.
Anticipated Problem: What uses exist in the agriculture industry for hydraulics?
IV. Examples of hydraulics exist everywhere in the world, and agriculture is no exception
when it comes to uses of hydraulics. From log splitters in your backyard to gigantic
machines we see on construction sites, hydraulic equipment is amazing in strength and
agility.
A. In construction zones, we see hydraulically operated equipment in the form of
bulldozers, shovels, cranes, forklifts, and bulldozers. Another common piece of
equipment at construction sites and agricultural facilities is the skid/loader using
hydraulics to rotate the bucket, lift the bucket, and to raise and lower the bucket.
B. Large dump trucks usually have one cylinder or two to lift the bed. These cylinders
telescope, which gives them a large range of motion for dumping loads, such as rock or
grain. Even the brakes in our automobiles use hydraulics.
HYDRAULIC POWER TRANSMISSION
Part One: Matching
Instructions: Match the word with the correct definition.
a. Pressure
b. Pascal’s law
c. Work
d. Force
e. Efficiency
_______1. The application of forces in direct contact.
_______2. The ratio of output of a system to input of the system.
_______3. Strength or energy exerted causing motion or change in direction.
_______4. Pressure exerted on a liquid is transmitted with equal force on equal areas at right
angles to all surfaces.
_______5. Movement occurs when the force is applied to an object.
Part Two: Fill-in-the-Blank
Instructions: Complete the following statements.
1. __________ is the science of liquids in motion.
2. __________ is compressible while liquids are not compressible
3. Smaller diameter piston results in _________ force needed to move larger diameter piston and
larger diameter piston will move less distance.
4. Larger diameter piston results in __________ force to move smaller piston and the smaller
piston will travel greater distance.
5. __________ equals 3.14 × diameter × diameter ÷ 4.
6. Force = __________ × area.
7. In a hydraulic system, the __________ provides the pressure.
Illinois Physical Science Applications in Agriculture Lesson B4–7 • Page 8
Part Three: Multiple Choice
Instructions: Write the letter of the correct answer.
_______1. _____ Law defines how a hydraulic system operates and the relationship between
pressure, area, and distance.
a. Boyle’s
b. Ohm’s
c. Pascal’s
d. Edison’s
_______2. _____ may be defined as the potential energy of a fluid power system.
a. Pressure
b. Work
c. Force
d. Distance
_______3. When power is transmitted hydraulically, _____ are used as the carrier of the power.
a. belts
b. fluids
c. gases
d. gears
_______4. By exerting 20 pounds on a one square inch cylinder, the resulting force on a five
square inch cylinder will be _____ pounds.
a. 200
b. 100
c. 50
d. 4
_______5. Theoretical advantage that a system would have if there were no limitations such as
friction is called:
a. Efficient mechanical advantage
b. Ideal mechanical advantage
c. No mechanical advantage
d. Actual mechanical advantage
Part Four: Short Answer
Instructions: Answer the following statements.
1. Identify the major components of a hydraulic system.
2. Explain the difference between ideal mechanical advantage and actual mechanical advantage.
Illinois Physical Science Applications in Agriculture Lesson B4–7 • Page 9
Assessment
Illinois Physical Science Applications in Agriculture Lesson B4–7 • Page 24
TS–A
Technical Supplement
HYDRAULIC POWER
TRANSMISSION
1. What are the basic principles of hydraulics?
Fluids under pressure are widely used in systems that transmit and control power.
When the fluid is air or any other gas, the system is identified as a pneumatic system. A
system that uses oil or another type of liquid is known as a hydraulic system. These
two types of systems are combined into a common system called fluid power.
Basic to the hydraulic system are: 1) a pump, which creates pressure for the system,
transferring mechanical energy into hydraulic energy, and 2) a rotor or cylinder, which
transfers the hydraulic energy back into mechanical energy in the form of rotary or
linear motion. Additionally, the system usually involves 3) lines, which transfer the
hydraulic energy from the pump to the rotor or cylinder and returning the energy to
the pump, 4) a reservoir to store a supply of fluid, and 5) valves to control, or direct, the
fluid and its movement.
2. What is Pascal’s Law?
A liquid has no definite form but takes the shape of its container. Similarly, a gas has
neither form nor a definite volume. It, too, takes the shape of the vessel or container.
In both cases, the word fluid can be applied to either the gas or the liquid because
both substances can flow. The energy of the liquid or the gas in the sealed container
can be harnesses to do useful work. In other words, it can transfer or multiply force
or energy. In electricity, voltage acts as pressure to push or force an electron from one
atom to another to create a flow of electrons which passes though a conductor to a load,
then returns to the power source. In a hydraulic system, the pressure is created by a pump
and an enclosed system of lines creating a flow of fluid through transfer devices. If
pressure is greater in any one direction, then the fluid will flow that direction. This
fact, or law of physics, is called Pascal’s Law. The law applies to all enclosed fluids at
rest, both gaseous and liquid. Under these conditions the law states that any pressure
applied to an enclosed fluid is transmitted equally in every direction without
loss. An addition, the fluid acts with equal force on all surfaces.
3. How does the multiplication of force occur in a hydraulic system?
To best understand how a hydraulic system can multiply force, one should first
understand the mechanical advantage of force. Whenever a small force is used to
create a larger force, there is a gain which is called mechanical advantage.
In a hydraulic system application such as a press or jack, a large piston and a small
piston are connected by a pipe and controlled by two valves which are designed to
allow fluid from the small piston to transfer to the large piston when compressed.
Pressure refers to the force per unit area. Work is defined as the product of a force
and the distance through which the force acts.
If both pistons of the system are of the same size, the force transmitted by one piston
is equal to the force of the other piston (Newton’s Third Law of Motion). This
proportional equilibrium with regard to the transfer of energy of the applied force
through a fluid on two pistons of the same area (in an enclosed circuit) allows an
inverse relationship between force and distance, which allows us to multiply the
force, or pressure applied, if the area of one cylinder is smaller than the area of the
other cylinder. That is, a 1,000 lb. force applied to 2 square inches equals 2,000 lbs.
of force. If the area is increased to 4 square inches, a force of 4,000 lbs. is produced
from the same 1,000 lbs. of applied force, hence the multiplication of force.
4. How does the conservation on energy apply in a hydraulic system?
In addition to flowing in any direction and applying forces equally in all directions,
fluids are used in hydraulic systems because they are said to be non-compressible
(oil will only compress approximately ½ of 1% at 1,000 psi). This is about the same
compressibility as steel. Therefore, hydraulics is an efficient means of power
transmission by the use of fluids. Because of these facts, energy is lost only through
opposition to flow from the restrictions of valves, connectors and lines which we call
fluid resistance, and the loss of energy from heat generated by the resistance. While
hydraulic systems are not 100% efficient in converting or transferring energy, they
are one of the most efficient applications of mechanical engineering found in today’s
mechanical applications of technology.
Illinois Physical Science Applications in Agriculture Lesson B4–7 • Page 26
5. Why is actual mechanical advantage less than ideal mechanical advantage?
The reason for this difference is the result of fluid resistance of the system. Opposition
is present whenever a force acts to change a motion or flow and another force is
present to oppose the original force and limit the change of motion. Fluid resistance
limits the change of motion or flow and transforms some of the energy into heat
(thermal) energy, or loss. Added to this is the loss resulting because fluids have a
varying degree of viscosity, or internal friction (drag) of once fluid particle against
another in motion. Additional losses of efficiency could result from poor connections,
gaskets, seals, fittings, or leaks. To determine the efficiency of a system, determine the
actual mechanical advantage and the ideal mechanical advantage. Once this is
determined, the efficiency can be calculated by dividing the actual mechanical advantage
by the ideal mechanical advantage and multiplying the result by 100 to obtain a
percentage of efficiency. The following example demonstrates the above law and
principles.
Actual Mechanical Advantage = Force exerted by large piston/Force exerted on small
piston
1.90 = 1,900 lbs. / 1,000 lbs.
Ideal Mechanical Advantage = Area of large cylinder/Area of small cylinder
2.00 = 4 sq. in./2 sq. in.
Efficiency (e) = Actual Mechanical Advantage/Ideal Mechanical Advantage × 100
0.95 = 1.90/2.00 or 95% Efficiency
Illinois Physical Science Applications in Agriculture Lesson B4–7 • Page 27