1. Chapter 12 Fluid Power

2. Objectives Upon completing this chapter, you should be able to: –Discuss some fluid power fundamentals –Explain psi, psig, psia, and inches of mercury ("Hg) –Understand how force is transmitted through a hydraulic system

3. Objectives (cont’d.) –Understand the effects of compressing air for a fluid power system –Learn how to recognize the different valves that may be used in a fluid power system –List and explain at least eight methods of valve actuation –Discuss the operation of different actuators

4. Fluid Power Fundamentals Fluid power has several advantages over mechanical power: –Ease of control –Accuracy –Ability to multiply force –Constant force –Constant torque –Instantly reversible

5. Fluid Power Fundamentals (cont’d.) Pressure: restriction against the flow of liquid –Responsive to the amount of restrictions present in that system –The total pressure will be just the amount necessary to overcome the restrictions that are present in the system

6. Hydraulics Hydraulics: the science of transmitting power through a liquid –The liquid used most commonly is hydraulic oil

7. Oil Temperature As oil is pumped, pressure will begin to rise if there are restrictions in the system –As the pressure begins to rise, the temperature of the oil begins to rise

8. Static Head Pressure The amount of pressure that is developed for every inch of rise in elevation above the point of measurement

9. Figure 12-1: Static head pressure. Delmar, Cengage Learning 2013.

10. Hydraulic Operation When pressure is applied to a fluid, the pressure is transmitted through the fluid Power in should equal power out –Except in the case where losses exist in a circuit, such as from mechanical friction and flow friction

11. Hydraulic Operation (cont’d.) The force of a piston can be calculated by multiplying the pressure times the area (F = P x A)

12. Figure 12-2: Hydraulic power is transferred through the fluid. Delmar, Cengage Learning 2013.

13. Pneumatics Pressure is created as soon as the air is compressed Pneumatic energy is often referred as “air” A pneumatic system will have a method of storing compressed air

14. Fluid Conditioners These devices include: –Filters –Air lubricators Typically installed along with a pressure regulator –Trio assembly or filter-lubricator-regulator (FLR)

15. A Vacuum Vacuum fluid power may be described as deriving its force from the weight of the atmosphere Atmospheric pressure (at sea level) is 14.7 psi Vacuum measured in inches of mercury ("Hg)

16. Figure 12-7: An example of using a vacuum to do work. Delmar, Cengage Learning 2013.

17. Valves Used in a fluid power system for one of the following purposes: –Flow control –Directional control –Pressure control Open: fluid can flow through it Closed: fluid cannot flow through it

18. Valves Many types of valves available: –Spool valves –Poppet valves –Gate valves –Ball valves –Needle valves

19. Linear Actuators Cylinders –Refers to all of the components that are housed within the cylinder, including the piston –The piston does the work because the shaft of the piston is connected to the load

20. Cylinders Single-acting –Actuated by fluid, and then returns to its original state using a spring return Double-acting –Moved by fluid in both directions

21. Figure 12-21: The single-acting cylinder principle. Delmar, Cengage Learning 2013.

22. Rotary Actuators Hydraulic and pneumatic motors are referred to as rotary actuators Rotary actuator –A device that has a rotary movement instead of a linear movement as for the cylinder

23. Flow Control Circuitry Three types of flow control circuitry are used in a linear hydraulic system: –The meter-in circuit –The meter-out circuit –The bleed-off circuit

24. Accumulators Accumulators are used in hydraulic systems to maintain pressure within the system Refer to Figure 12-27

25. Pneumatic Directional Control Circuitry The most common pneumatic control circuit - the flip-flop circuit –Uses a double-end rod, double-acting cylinder Referred to as an oscillator