Job Sheet 1 Introduction to Fluid Power Fluid Power Basics Fluid power relies on a hydraulic system to transfer energy from a prime mover, or input power source, to an actuator, or output device (Figure 1-1). Flow in a hydraulic system is produced from a positive displacement pump rather than a centrifugal pump. There are three important 1. Flow makes it go. In order to have movement in a hydraulic system, the actuator must be 2. the actuator. 3. there is less volume to displace when the cylinder retracts. The cylinder rod occupies space, thus diminishing the volume to be displaced. Prime Mover A Actuator B Rod series and contribute to total system pressure. Pascal s law forms the basis for understanding the relationship between force, pressure, and undiminished in all directions and acts with equal force on equal areas and at right angles to them. Festo Didactic Inc. 88394-20 1
Force=Pressure Area Pressure= Force Area Force Area= Pressure Figure 1-2. Pascal s Law. actuator. The effective area of the cylinder piston is the area available for force generation. Pressure that is not used to provide work is called pressure drop, or resistive pressure. added to the overall system pressure requirements. a hydraulic system because it serves as a lubricant, a medium for the transfer of heat and advantage in the transmission of force. Fluid Cooler wall an the piston acts as a sealant because of its low viscosity. transfers energy from the input side generally non-compressible. Using a positive displacement pump, energy is transmitted from the prime mover (input passes through the conductors and components, certain considerations are required to ensure 2 Festo Didactic Inc. 88394-20
Velocity Viscosity increases, its viscosity decreases. Petroleum-based Water glycol require special bearings when using water glycol. Synthetic are typically not compatible with most common seal components. Environmentally friendly spill. through hoses and components is called the hydraulic circuit. Festo Didactic Inc. 88394-20 3
has risen to its target value, the accumulator charging valve switches the pump to circulation. the pressure in the accumulator drops by 10%, the charging valve switches over and the In case of excessive temperature, a cooling fan is activated. The fan switches off once the temperature decreases. Should the hydraulic fluid overheat, or if the hydraulic fluid level in the tank is too low, both motor-pump units are switched off. If the power unit is equipped with a heating system, the control system switches are either activated or de-activated to keep the hydraulic fluid at a constant temperature. between the housing and the rotating teeth of the gears, where it travels around the housing Outlet 4 Festo Didactic Inc. 88394-20
The rotating portion of the pump, or rotor, is positioned off-center of the cam ring, or housing. are thrown out by centrifugal force and contact the ring, or housing, to form a positive seal. port. A Outlet B than atmospheric pressure. The other half is subjected to full-system pressure, resulting in side loading the shaft while under high-pressure conditions. To compensate for this, the ring is canceled out by equal, but opposite, forces on the other side. Since the forces acting on the shaft are balanced, the shaft side load is eliminated. Flow is created in the same manner suction cavities rather than one of each. Constant-volume, positive-displacement vane pumps used in industrial systems are commonly of the balanced design. in its degree of angle. With a vertical swash plate, no displacement occurs because there is no Festo Didactic Inc. 88394-20 5
barrel as it follows the angle of the swash plate. rotation, the piston moves out of the cylinder barrel and generates an increasing volume. In the other half of the rotation, the piston moves into the cylinder barrel and generates a decreasing output is measured in gpm. maintaining compensated pressure at the outlet of the pump. Of the three types of hydraulic pumps discussed (gear, vane, and piston), only the vane and piston may be pressure-compensated. Actuators The actuator is the interface component that converts hydraulic horsepower back into a hydraulic motor, which provides rotating motion. 6 Festo Didactic Inc. 88394-20
Cylinders are linear actuators. This means that their output force, or motion, is a straight line. Cylinders convert hydraulic power into linear mechanical power and perform tasks such as pushing, pulling, tilting, and pressing. and is used in applications where stability is needed on heavy loads. on the opposite end (Figure 1-8). They are designed so that they are retracted by a load or a device, such as an internal spring. A System Pressure B The is the most commonly used cylinder in mobile hydraulics (Figure 1-9). Pressure can be applied to either port, providing power in both directions. Outlet A B in applications where it is advantageous to couple a load to both ends, or in applications where equal speeds are needed in both directions. Festo Didactic Inc. 88394-20 7
WARNING! must be taken during their operation. Failure of the cylinder (Figure 1-10), its parts, its mounting, its connections to other objects, or Unanticipated or uncontrolled movement of the cylinder or connected objects Falling of the cylinder or objects it supports Fluid escaping from the cylinder, potentially at high velocity Possible consequences of piston rod failure or separation of the piston rod from the piston may Piston rod and/or attached load thrown off at high speed detachment from the piston rod. Motors to turn a resisting object by means of a shaft. pushes on the internal surface area of the motor, developing torque. Resistance from the load 8 Festo Didactic Inc. 88394-20
Exhaust Flow System Pressure or bi-directional. They are instantly reversible and can absorb severe shock loading without over the relief valve. 1-12). Gear Motor should be torque, which is the turning effort or rotary force generated at the motor shaft. Festo Didactic Inc. 88394-20 9
of a hydraulic motor is the volume of oil required for the motor shaft to turn one 3 /r) in SI units, or in cubic inches per revolution (in 3 /r) in English units. Large displacement motors usually have The amount of torque generated at the shaft of a hydraulic motor is directly proportional to the motor displacement and system pressure at the motor inlet. The formula for calculating the theoretical torque Torque Torque ( lbin. ) ( Nm. ) Displacement x essure In3 Pr r = 2π ( / ) ( psi) Displacement x essure cm3 Pr r = 2πx1000 ( / ) ( kpa) The resistance of the load connected to the motor shaft determines the amount of system pressure developed at the motor inlet and, therefore, the amount of torque generated at the The amount of power generated by a hydraulic motor is equal to the torque developed at the Power ( hp) Power ( W) Torque lb In x Speed = 63025 (. ) ( rpm) TorqueNm x Speed = 954. (. ) ( rpm) The actual amount of power generated by a hydraulic motor is less than the theoretical value inside the motor. 10 Festo Didactic Inc. 88394-20
rate while its output force, or torque, is a function of pressure. affecting the torque output. Conversely, increasing the system pressure available to a motor increases the torque output capability without affecting the rotation speed. Table 1-1 shows the used to convert measurements of displacement and torque from SI units to English units, and vice versa. Cubic centimeters per revolution (cm 3 /r) X 0.061 = Cubic inches per revolution (cm 3 /r) X 16.387 Cubic centimeters per revolution (cm 3 /r) X 8.85 Pounds inches (lb.in, lbf.in) X 0.113 Festo Didactic Inc. 88394-20 11
hydraulic unit. Use the information provided in the Information Sheet to respond to these questions. Flow in a hydraulic system is produced from a. a centrifugal pump. b. a positive displacement pump. c. pressure drop. d. load-induced pressure. hydraulic system because it serves as a a. lubricant. b. medium for the transfer of heat and energy. c. sealant. d. with most common seal components, and are used when applications a. Petroleum-based b. Water glycol c. Synthetic d. Environmentally friendly Festo Didactic Inc. 88394-20 13
Which of the following converts hydraulic power into linear mechanical power, and performs tasks such as pushing, pulling, tilting, and a. Pressure-compensated hydraulic pumps b. Piston pumps c. Gear motors d. Cylinders Which of the following is the interface component that converts a. b. Piston pumps c. d. Unbalanced vane pump Name: Date: Instructor approval: 14 Festo Didactic Inc. 88394-20