Experiment 2-4 Power and Work
Objectives: 1. Define the terms “power” and “work.” 2. Describe the forms of power produced by a fluid power system. 3. Calculate the horsepower being supplied by a hydraulic system. 4. Calculate the heat being generated by a hydraulic system. 5. Explain how heat is generated in a fluid power system. 6. Explain how work is performed in a hydraulic system.
Power and Work Power is defined as the rate at which energy is being generated or consumed. The most common energy form for performing work is mechanical energy. In most cases, mechanical energy is the result of another energy form being converted into mechanical energy. An example of a converted form of energy would be electrical to mechanical or in the case of a hydraulic system, electrical to fluid power. The fluid power energy is in the form of pressurized fluid which enters an actuator and pushes on a moveable member. The moveable member will push against the load because of the pressurized fluid acting on it.
Power and Work Linear and Rotary Formulas for Horsepower Linear Horsepower = Force X Speed Rotary Horsepower = Torque X Speed 63,025 63,025
Generation of Fluid Power Fluid power is generated when the pump if forced to turn by a prime mover, either a electric motor or engine. The pump forces fluid into the system and from there to the actuator to displace an internal moveable member.
Generation of Fluid Power Power Generated by the Pump HP = Flow Rate x Pressure 1714 The above formula represents an important relationship between flow, pressure, and horsepower. If you increase either flow or pressure, horsepower will increase proportionally.
Power Used The amount of power used by an actuator is determined through observation and then calculation. In other words, how much of a load is being moved and how fast. This can be determined in part by examining pressure gauges and the drop of pressure that occurs while the work is being performed.
Heat Generation In the study of fluid power, there exists a law that states energy cannot be created or destroyed but it will change form. This thermo dynamic relationship portrays an example of energy changing to the form of heat. In fact, no energy transfer system is perfect and the usual outcome of energy loss will always be in the form of heat. The amount of heat generated by a system represents, to some degree, its inefficiency. The amount of heat a system can generate may be calculated with the following information. 1 Hp = 2545 BTU/Hr. Hp = Psi x Gpm divided by 171 or BTU/Hr. = 1-1/2 x Psi x Gpm
Heat Generation An important point to make is that heat dissipation takes place where ever heat comes into contact with a cooler surface. This means that heat is being released throughout the system but primarily at the reservoir. The presence of heat indicates that energy has been transformed. With that said, keep in mind that if energy is transformed into work, such as an actuator moving a load, under normal circumstances, no heat is developed. Cylinders are nearly leak free and therefore convert nearly 100 percent of the pressurized fluid into mechanical energy. It is a mistake to associate the heat felt on a cylinder as being the product of inefficiency when it is in fact simply conducted from the oil.
Review 1. What form of power does an actuator produce? 2. What factors determine the amount of power generated by the hydraulic system? 3. How does a hydraulic or pneumatic system transmit power. 4. What causes energy loss in fluid power systems? 5. Into what form does lost energy change? 6. Calculate the amount of power required by the actuator in each of the loads applied and show your work. 7. Consider the function of the relief valve. Which of the load conditions in question 6 would waste the greatest amount of energy. 8. Why does it require more pressure to retract a load that is attached to a double acting cylinder? 9. Why is there relatively no heat produced from a cylinder when compared to the relief valve? 10. Calculate the heat potential of one hydraulic training unit in BTUs.