Hydraulics Study Guide

  1. Introduction to Fluid Systems
    1. Fluid systems involve the use of fluids to transmit and multiply force.
    2. Fluids flow.
    3. When the fluid is a liquid, the system is called a hydraulic system.
    4. When the fluid is gaseous, the system is called a pneumatic system.
    5. Hydraulic fluids such as hydraulic oil are incompressible, a fluid which is as dense as it can get. The most commonly used incompressible hydraulic fluid is oil.
    6. Pneumatic fluids such as air are compressible.
    7. Hydraulic systems transmit forces from point to point through a fluid.
  2. Hydraulic Systems: The Basic Idea
    1. See the illustration Simple Hydraulic System. Click on the arrow to apply force and see how the force is transmitted.
    2. See the illustration Hydraulic Multiplication. Click on the force arrow to see how force is multiplied. Note that the area of each cylinder relates to the distance moved and the force applied.
    3. See a second explanation of Hydraulic Multiplication by reading the three paragraphs under the same animation at another site
      1. What is the realtionship between piston diameter, and distance moved?
      2. What is the relationship between piston areas and forces?
  3. How Log Splitters Work: Basic Components of a Hydraulic Machine
    1. The basic power source for the log splitter is the ____. The power source turns energy from gasoline into _____ energy which is used to drive the splitter.
    2. The engine drives the attached ____ ____. What does this device do?
    3. What is the path of the hydraulic oil from the pump and back to the pump?
    4. What is used to control the flow of hydraulic oil in the system?
    5. What device converts the force of the hydraulic oil into linear motion?
    6. Hydraulic systems have a reservoir (a tank) which holds the hydraulic oil for a time before it is used again. This allows the oil to cool and compensates for the varying amount of oil required for each part of a cycle.
  4. Scroll down to the illustration cross-sectional view of the splitter's hydraulic system. Click on the "Push" and "Pull" button to operate the handle of the control valve.
    1. Note the high-pressure and low-pressure sides of the circuit in each position.
    2. Note how the spool valve changes the path for oil flow.
    3. Note how pressure is exerted on each of the piston in the cylinder.
  5. Scroll down below the cross-sectional view to a listing of typical specifications for log splitters.
    1. How is the power of the gasoline engine typically rated?
    2. What two specifications are given for the hydraulic pump?
    3. What two specifications are given for the hydraulic cylinder?
    4. What is the rated splitting force of the machine?
    5. How is the splitting force calculated?
    6. The cylinder is a two-stage cylinder. During one stage, hydraulic fluid forces the piston shaft to extend from the cylinder. During the second stage, hydraulic fluid is used to retract the piston shaft back into the cylinder.
      1. Why is more fluid needed to extend than to retract the piston?
      2. What is the difference in the pressures and flow rates during the extension and retraction stages of this machine?
  6. Download and watch the following mpeg videos: (See Instructions)
    1. Hydraulic Shovel in Operation
    2. Pistons in Operation
  7. Large Hydrauic Machines
    1. Find the pair of hydraulic cylinders which are used to lift and lower the arm at the "shoulder" of the excavator. Find the hydraulic cylinder which operates at the "elbow." Find the hydraulic cylinder which rotates the bucket.
    2. Hydraulic cylinders operate in a linear direction. Hydraulic motors provide a rotational motion. How many hydraulic motors are on the excavator and what is their purpose?
    3. Make a table similar to the one below. Fill in information for each machine as you study it.
      Hydraulic Machine Parts and Functions
      Machine Hydraulic Cylinders Functions Hydraulic Motors Functions
      Excavator
      • 2 Shoulder
      • 1 Elbow
      • 1 Bucket
      • Lifts & lowers arm
      • Extends & retracts elbow
        • Opens & closes bucket
      • 1 Cab turret
      • 2 Tracks
      • Rotate the machine on stationary tracks
      • Drive the left and right tracks forward and backward
      Skid-Loader
      Dump Truck
  8. Go to The Operator's Seat Note the joy sticks and pedals. The controls in the cab are electrical; two joy sticks which send electrical signals and 4 pedals use either electrical or mechanical links to valves.
  9. Go to Large Hydraulic Machines. Scroll down to pictures of the valve block and high-pressure hydraulic lines.
    1. Is the valve block electrical, mechanical, hydraulic, or a combination? Explain.
    2. Special are lines used to transport hydraulic fluid to and from hydraulic cylinders and motors? How are these tubes and hoses different than ordinary tubes and hoses?
  10. Go to Tracks
    1. Describe how the tracks are driven and aligned or guided.
  11. Go to Shovel Specifications.
    1. What is the maximum psi of the pump?
    2. What is the oil flow rate?
  12. Download and observe the mpeg video Skid-Loader in Operation
  13. Skid Loaders
    1. Add to your chart the machine name, cylinders, functions, motors, and functions for the skid loader.
  14. Download and observe the mpeg video Dump Truck Operation
    1. Add to your chart the machine name, cylinders, and uniquie function of this type of cylinder.

Brake Systems

  1. Go to Master and Slaves Hydraulic System.
    1. This system employs a "master" cylinder and two "slave" cylinders. How is this system different than the hydraulic systems we have discussed so far?
  2. Go to A Simple Brake System
    1. Make a sketch of Figure 8: A simple brake system.

    Leverage and Mechanical Advantage

  3. Go to Leverage.
    1. Note that the left end of the lever (2X) is twice as long as the right end of the lever (X).
    2. Note that the distance traveled by the left end (2Y) is twice as much as the distance traveled by the right end (Y).
    3. Note that the force applied to the left end (F) produces twice as much force (2F) on the right end.
    4. Assume the left side of the lever is the input side and the right side is the output side of the lever.
      1. What is the ratio of input length to output length?
      2. What is the ratio of input distance traveled to output distance traveled?
      3. What is the ratio of input force to output force?
      4. For this type of lever, how does the direction of input force relate to the direction of output force?
      5. What is the mechanical advantage of this lever system?
      6. If a force of 10 lbs was put on the input side of the lever, what would the output force be?

    Locating the Parts

  4. Go to Master Cylinder.
    1. Identify the master cylinder above the brake pedal. Slave cylinders are located at each wheel.
  5. Go back to Simple Brake System.
    1. Identify the "master" cylinder and the "slave" cylinder.
    2. What is the mechanical advantage of the brake system diagram which you have sketched?
    3. For this type of lever, how does the direction of input force relate to the direction of output force?
    4. If the force on the brake pedal was 25 lbs., what would the force be on the master cylinder piston rod?
    5. The diameter of the master cylinder piston is 2". What is the area of the piston next to the hydraulic fluid?
    6. What is the diameter of the slave cylinder piston? What is the area?
    7. If the force on the brake pedal was 25 lbs., what would the psi be in the master cylinder?
    8. What would the psi be in the slave cylinders?
    9. What would the total force be against the piston of the slave cylinder?

Jaws of Life

  1. Spreaders
  2. Cutters
  3. Rams

Cranes

  1. How Cranes Work
  2. Parts of a Hydraulic Truck Crane
  3. In the Operator's Seat

Miscellaneous

  1. Crane-Related
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December 5, 2001