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Hydraulic Pumps and Motors Explained for Hydraulic Power Systems
- 1. PUMPS AND MOTORS STUDENT: NGUYEN VAN THANH ST. ID: 1613121 CLASS: CK16KCTN INTRUCTOR: TRAN NGUYEN DUY PHUONG HYDRAULIC POWER SYSTEM ANALYSIS _CHAPTER 8_
- 2. Hydraulic Pumps The pump is the heart of the hydraulic system. The pump is the generating force of the hydraulic system, it creates the flow of fluid which supplies the whole circuit. Pumps convert mechanical energy to hydraulic power
- 3. There are two broad classifications of pumps: 1. Positive Displacement Pumps 2. Dynamic Pumps Hydraulic Cylinder Electric Motor T x ωV x I Hydraulic Pump P x Q Hydraulic Motor F x v T x ω Hydraulic Pumps
- 4. Hydraulic Pump and Motor Inlet Outlet Pump Housing Drive Gear Idle Gear Drive Gear Motor Housing Inlet Outlet Idle Gear A pump drives its fluid, while the motor is driven by its fluid.
- 6. 1. Dynamic (nonpositive displacement) pumps. This type is generally used for low-pressure, high-volume flow applications. They are not capable of withstanding high pressures they are of little use in the fluid power field. Normally their maximum pressure capacity is limited to 250—300 psi. This type of pump is primarily used for transporting fluids from one location to another. The two most common types of dynamic pumps are the centrifugal((impeller) and the axial flow (propeller) pumps.
- 7. Dynamic Pumps Centrifugal pump Axial Flow pump
- 8. They are not suitable for handling viscous fluids, and thus are not suitable for use in hydraulic applications. Dynamic pumps are typically used for low pressure, high volume flow applications. Unlike positive displacement pumps, dynamic pumps are not self priming. This is because large clearance between the rotating part and the stationary housing does not allow a suction pressure to occur at the inlet port when the pump is turned on. Centrifugal pump Axial Flow pump Dynamic Pumps
- 9. Positive Displacement Pumps A positive displacement pump increases the pressure of the fluid by trapping a fixed amount of fluid into a cavity then reducing the volume of the cavity be mechanical means. As the volume of the fluid inside the cavity is reduced, its pressure is increased, allowing it to be forced against the higher pressure in the pipe
- 10. Positive Displacement Pumps Positive displacement pumps can be classified by the type of mechanical motion of its internal elements that produces the volume change in the liquid. The motion may be reciprocating or rotary. There are essentially three basic types: ◦ 1. Gear Pumps External gear pumps Internal gear pumps Lobe pumps Screw Pumps ◦ 2. Vane Pumps Unbalanced Vane Pump (Fixed or variable displacement) Balanced Vane Pump (Fixed Displacement Only) ◦ 3. Piston Pumps Axial Design Radial Design
- 11. Some kind of pumps
- 12. GEROTOR PUMPS Gerotor pump operation is similar to internal gear pump operation, with the inner rotor having one less gear tooth than the outer rotor.
- 13. PISTON PUMPS - BENT AXIS Bent-axis piston pumps operate in the same manner as an axial piston pump, but rather than the swash plate being at an angle, the pistons and piston block are at an angle.
- 14. SCREW PUMP In a screw pump, three precision ground screws meshing within a close fitting housing deliver non pulsating flow quietly and efficiently. The screw pump is an axial flow positive displacement unit. The two symmetrically opposed idler rotors act as rotating seals, confining the fluid in a succession of closures or stages.
- 15. Pump Efficiencies η A v T Qactual flow rate produced by the pump theoretical flow rate produced by the pump Q = = Pump Type ηv (%) Gear Pump 80 – 90 Vane Pump 82 – 92 Piston Pump 90 – 98
- 16. Mechanical Efficiency Δ η ω Δ ω η ω ω η T m T T T T m A A A A A m PQpower produced by pump assuming no leakage power delivered to the pump T PQ T T T T T Theoretical torque required to operate the pump actual torque delivered to the pump = = = = = = η η ω η ω η ω η η η o A o A A A T o T A A A T o T A A o v m actual power produced by pump actual power delivered to the pump PQ T PQ PQ PQ T Q PQ Q T = = = ´ = ´ = Overall Efficiency
Hinweis der Redaktion
- many different types of pumps exist to assist fluid movement in a variety of systems an external gear pump uses two gears rotating against each other to provide fluid movement one gear is driven by a motor connected to a shaft this is called the drive gear because it is driven by a motor and it in turn meshes with and drives the movement of the second gear as the gears rotate away from each other and come out of mesh they create an expanding volume on the inletside of the pump this creates a vacuum at the inlet port allowing fluid to flow into the pump then fluid flows into the cavities and is trapped by the gearteeth as the gears rotate a flow path is created around the outside of each one fluid trapped in the slots between teeth is carried around and discharged into the cavity with the outlet port meshing of the teeth in the center of the pump seals the outlet port from the inlet port no fluid passes between the gears the advantages of external gear pumps are their high speed and pressure relatively quiet operation and that their design accommodates a wide variety of materials disadvantages include bushings in the liquid area can become worn and that they have fixed end clearances internal gear pumps are exceptionally versatile this type of pump has one inner gear which is inside a second outer gear the inner gear has a shaft driven by a motor and has teeth that protrude outward the outer gear has teeth that protrude inward toward the center of the pump as the inner gear rotates it meshes with and moves the outer gear liquid is trapped in the gear spaces and carried from the inlet to the discharge a stationary crescent-shaped divider separates the intake and discharge portions of the fluid advantages of internal gear pumps are a smooth and almost pulseless flow and slightly more horsepower for its size disadvantages are its higher cost limited size range low to moderate pressure ratings and few sources of manufacture a rotary vane pump is a positive displacement pump that consists of vanes mounted to a rotor the veins are on an off center drive shaft as the shaft rotates the variable-length veins slide in and out to maintain contact with the pump housing the tension in the veins is maintained by either springs or hydraulic pressure as the veins rotate they create chambers of varying sizes within the pump fluid enters at the largest chamber as the vanes rotate and retract the chambers get smaller forcing fluid to exit through the discharge port the advantages of vane pumps are that they can handle low viscosity fluids at relatively higher pressures can dry run for short periods and develop a good vacuum their disadvantages include complexity and their unsuitability for both high pressure and high viscosity fluidspiston pumps come in many different forms a swashplate is a device used to translate the motion of a rotate shaft into the reciprocating motion of a piston swashplate piston pumps have a rotating shaft connected to a cylinder block containing Pistons which are pressed against a stationary swash plate that sits at an angle to the cylinder as the shaft rotates the Pistons move against the swashplate causing them to reciprocate within the piston block the pistons create a vacuum that forces fluid in during half a revolution and expels fluid during the other half on the intake stroke a spring ensures the Pistons pull back and maintain contact with the swashplate causing fluid to fill the empty cavity left behind on the discharge stroke the angle of the swashplate forces the Pistons back inside the piston block and discharges the fluid the greater the slant on the swashplate the further the pump Pistons move and the more fluid they transfer piston pumps in general are manufactured with closer internal fits than other pumps this means that internal slippage can be less so that they operate with reasonable efficiency at pressures both too high or too low for the operation of other pumps radial pumps are designed so the Pistons stroke in a direction at right angles to the shaft the pistons are arranged like wheel spokes around a cylinder block with an eccentric central cam mounted on a drive shaft as the shaft rotates the cam moves towards the Pistons forcing them down into the cylinder block and discharging the fluid as the cam moves away Springs help retract the piston and cause the intake stroke check valves ensure that fluid only enters the inlet ports and only exits the outlet ports radial piston pumps have a low noise level very high loads at low speeds and high efficiency hand pumps are used when a source of power is not available or where the extra expense of a power pump isn't warranted for example they are used on shop presses and other portable equipment service standby pumps and serve as sources of emergency power hand pumps are always of piston type and are usually constructed with a piston working between two check valves you double-acting hand pumps are more efficient allowing fluid to both enter and discharge on both strokes of the piston moving the pump handle in either direction allows fluid to be drawn in from the reservoir and discharged via the outlet ports check valves in all locations prevent fluid backflow