Presentation on theme: "1 of 69 MECH1300 Chapter 3 – Hydraulic Pumps Topics Pump Flow and Pressure Pump Drive Torque and Power Pump Efficiency Pump Types Pressure Compensated."— Presentation transcript:
1 of 69 MECH1300 Chapter 3 – Hydraulic Pumps Topics Pump Flow and Pressure Pump Drive Torque and Power Pump Efficiency Pump Types Pressure Compensated Pumps Cavitation and Aeration Symbols Pump Specifications
2 of 69 MECH1300 Hydraulic Power Unit Relief Valve
3 of 69 MECH1300 Basic Pump The basic operating principle that moves fluid through a pump is similar in all pumps –Enlarging the volume of a chamber allows fluid to enter the pump –Reducing the chamber volume moves fluid to the system –Inlet and discharge valves or ports control fluid movement through the pump
4 of 69 MECH1300 How Pumps Work In a rotary pump, the pumping action is produced by revolving components In a reciprocating pump, the rotating motion of the pump input shaft is changed to reciprocating motion, which then produces the pumping action
5 of 69 MECH1300 Basic Pump Increasing the size of the pumping chamber moves fluid into the pump
6 of 69 MECH1300 Basic Pump Reducing the size of the pumping chamber forces fluid into the system
7 of 69 MECH1300 Basic Pump The maximum pressure developed in a hydraulic system is determined by: –Resistance to fluid flow in the system –Force the prime mover can exert The output flow rate of a hydraulic pump is determined by: –Volume of the pumping chamber –Operating speed of the prime mover
8 of 69 MECH1300 Path of least resistance: –If there is no force (load) on a cylinder there is no pump pressure! What will happen to cylinders A & B when power is applied to the pump? Cylinder A Dia. = 4” with a load of 2000 lbs Cylinder B Dia. = 8” with a load of 4000 lbs Pump Cylinder A Cylinder B Pressure
9 of 69 MECH1300 Cylinder A Dia. = 4” with a load of 2000 lbs 1.Area = 12.566 in 2 2.P= F/A = 159.2 psi Pump Cylinder B Dia. = 8” with a load of 4000 lbs 1.Area = 50.27 in 2 2.P= F/A = 79.57 psi Cylinder A Cylinder B Cylinder B moves first until it is fully extended and then Cylinder A extends
12 of 69 MECH1300 Pump Drive and Torque Power Prime mover supplies input power to the pump by driving the pump shaft at a rotational speed. Pressure on the pump resists rotation. Prime mover must generate enough torque to turn the shaft against the resistance.
25 of 69 MECH1300 Pump Classifications Hydraulic pumps can be classified using three basic Characteristics: –Displacement –Pumping motion –Fluid delivery characteristics
26 of 69 MECH1300 Displacement relates to how the output of the pump reacts to system loads –Positive-displacement pumps produce a constant output per cycle –A non-positive-displacement pump has large internal clearances Allows fluid slippage in the pump Results in varying flow output as system load varies Displacement Pump
27 of 69 MECH1300 Positive-displacement pump Displacement Pump
28 of 69 MECH1300 Non-positive-displacement pump Displacement Pump
29 of 69 MECH1300 The basic pumping motions used in hydraulic pumps are: –Rotary Gear pumps are rotary pumps –Reciprocating Piston pumps are reciprocating pumps Pumping Motion Classifications Reciprocating piston movement
30 of 69 MECH1300 Hydraulic pumps are classified as either fixed or variable delivery –Fixed-delivery pumps have pumping chambers with a volume that cannot be changed; the output is the same during each cycle –In variable-delivery designs, chamber geometry may be changed to allow varying flow from the pump Fluid Delivery Classifications
31 of 69 MECH1300 Gear pumps are fixed-delivery pumps Fluid Delivery Classifications
32 of 69 MECH1300 Piston pumps may or may not be variable-delivery pumps Fluid Delivery Classifications
33 of 69 MECH1300 Variable Displacement Pumps http://www.mekanizmalar.com/variable_displacement _piston_pump.html
34 of 69 MECH1300 Variable Displacement Pumps http://www.mekanizmalar.com/variable_displacement _piston_pump.html
35 of 69 MECH1300 Pump Selection When selecting a pump for a circuit, factors that must be considered are: –System operating pressure –Flow rate –Cycle rate –Expected length of service –Environmental conditions –Cost
36 of 69 MECH1300 Pump Design, Operation, and Application Gear pumps: –positive- displacement, –fixed-delivery, –rotary units –external or internal gear teeth configurations
37 of 69 MECH1300 Pumping action of gear pumps results from unmeshing and meshing of the gears –As the gears unmesh in the inlet area, low pressure causes fluid to enter the pump –As the pump rotates, fluid is carried to the pump discharge area –When the gears mesh in the discharge area, fluid is forced out of the pump into the system Pump Design, Operation, and Application Flow outputs from below 1 gpm to 150 gpm Pressure rating range up to 3000 psi
38 of 69 MECH1300 The gerotor pump design is an internal- gear pump –Uses two rotating, gear-shaped elements that form sealed chambers –The chambers vary in volume as the elements rotate –Fluid comes into the chambers as they are enlarging and is forced out as they decrease in size Pump Design, Operation, and Application
39 of 69 MECH1300 The gerotor is a common internal-gear design Pump Design, Operation, and Application
40 of 69 MECH1300 Vane pumps are positive- displacement, fixed or variable delivery, rotary units. –Design is commonly used in industrial applications –Delivery can range up to 75 gpm –Maximum pressure of about 2000 psi Pump Design, Operation, and Application
41 of 69 MECH1300 Vane pump consists of a slotted rotor, fitted with moveable vanes, that rotates within a cam ring in the pump housing –Rotor is off center in the ring, which creates pumping chambers that vary in volume as the pump rotates –As chamber volume increases, pressure decreases, bringing fluid into the pump –As volume decreases, fluid is forced out into the system Pump Design, Operation, and Application
42 of 69 MECH1300 Pump Design, Operation, and Application
43 of 69 MECH1300 Piston pumps: –positive-displacement, fixed- or variable-delivery, reciprocating units –provide high volumetric efficiency (90%), –high operating pressure (10,000 psi or higher), –high-speed operation Pump Design, Operation, and Application
45 of 69 MECH1300 A basic piston pump consists of a housing that supports a pumping mechanism and a motion-converting mechanism –Pumping mechanism is a block containing cylinders fitted with pistons and valves –Motion converter changes rotary to reciprocating motion via cams, eccentric ring, swash plate, or bent-axis designs –Rotating the pump shaft causes piston movement that pumps the fluid Pump Design, Operation, and Application
46 of 69 MECH1300 Piston pump classification is based on the relationship between the axes of the power input shaft and piston motion –Axial Inline Bent axis Pump Design, Operation, and Application
48 of 69 MECH1300 Piston pump classification is based on the relationship between the axes of the power input shaft and piston motion –Radial have the highest continuous operating pressure capability of any of the pumps regularly used in hydraulic systems are available with operating pressure ratings in the 10,000 psi range Pump Design, Operation, and Application
49 of 69 MECH1300 A stationary-cylinder radial-piston pump Pump Design, Operation, and Application
50 of 69 MECH1300 Reciprocating Pump Design, Operation, and Application Radial
51 of 69 MECH1300 Screw pumps have pumping elements that consist of one, two, or three rotating screws –the screws rotate, fluid is trapped and carried along to the discharge of the pump –screw pumps operate at a very low noise level Pump Design, Operation, and Application
52 of 69 MECH1300 Pressure compensation reduces energy consumption Additional Design Features of Pumps
56 of 69 MECH1300 Gallons per minute is the number of gallons a pump can force into the system every minute and thus the amount of fluid flow that pump can produce. in 3
57 of 69 MECH1300 Design & Operating Considerations Cavitation is caused when inlet line pressure drops below the vapor pressure of the fluid and bubbles form –Reduces lubricity of the system fluid –Collapsing bubbles produce severe shock waves that can damage pump parts –Collapsing bubbles also produce noisy pump operation
58 of 69 MECH1300 Design & Operating Considerations
59 of 69 MECH1300 Entrained air is air suspended in fluid –Enters the inlet line through leaks on the suction side of the pump –Can produce a result similar to cavitation Design & Operating Considerations
60 of 69 MECH1300 Testing inlet line pressure can help indicate which condition exists High negative pressure (vacuum) indicates cavitation Pressure closer to 0 psi may indicate entrained air Design & Operating Considerations
61 of 69 MECH1300 The inlet line of the pump must be carefully sized and configured to eliminate cavitation and air entrainment –Fluid velocity in the line should not exceed 4 feet per second –Lines should be no smaller than the diameter of the pump inlet fitting –Strainer and inlet line filters must not restrict fluid flow Design & Operating Considerations
62 of 69 MECH1300 Pump Flow Rate –Q (gpm) = (V * N)/231 –Q (lpm) = (V * N)/1000 Design & Operating Considerations Q – flow rate (in 3 /min, cm 3 /min) V – pump displacement (in 3 /rev, cm 3 /rev) N – drive speed (rpm) Horsepower required for a given flow rate and pressure –HP = (P*Q)/1714 –P in psi; Q in gpm; HP in hp –kW = (P*Q)/60,000 –P in kPa; Q in lpm; kW in kW
63 of 69 MECH1300 Glossary Application information –Information supplied by a manufacturer describing conditions and limits of operation in which a product may be expected to successfully operate. Axial piston pump –A hydraulic pump using a design in which the reciprocating motion of the pistons is parallel to the power input shaft.
64 of 69 MECH1300 Glossary Balanced-vane pump –A hydraulic vane pump using a design with two inlet and outlet chambers that balance the load forces on the bearings of the pump rotor shaft.
65 of 69 MECH1300 Glossary Cavitation –The formation of gas within a liquid stream that occurs when pressure drops below the vapor pressure of the liquid; may result in excessive noise and pump damage. The condition in a hydraulic pump can result from restricted inlet flow or excessive oil viscosity.
66 of 69 MECH1300 Glossary Dual pump –A design in which two pumps are built into a single case. The pumps may be rated at different pressures and flow outputs to provide additional flexibility. Fixed-delivery pump – Any hydraulic pump design that has a nonadjustable fluid delivery rate.
67 of 69 MECH1300 Glossary Gear pump –A hydraulic pump design that uses gears to move fluid through the pumping chamber of the component. Gears may have internal or external teeth.
68 of 69 MECH1300 Glossary General hydraulic horsepower –A computed figure used in hydraulic systems based on fluid flow and pressure. Equal to fluid flow weight in pounds per minute multiplied by the pressure in feet of head divided by 33,000 foot pounds per minute.
69 of 69 MECH1300 Glossary Gerotor design –A common internal-gear pump or motor design. The pumping chamber of these units has two gear-shaped elements that form varying-size chambers as they rotate.
70 of 69 MECH1300 Glossary Impeller –The rotating component of a dynamic compressor or impeller pump. Energy is increased in the fluid as centrifugal force causes flow through the unit.
71 of 69 MECH1300 Glossary Mechanical efficiency –The theoretical horsepower needed to operate a pump or compressor divided by the actual horsepower required. Non-positive-displacement pump –A pump that does not have a variable-volume pumping chamber. An impeller or other device is used to move the fluid. The inertia of that fluid movement produces pressure when flow is resisted.
72 of 69 MECH1300 Glossary Power unit –The unit in a hydraulic system that provides energy for the system, moves fluid through the system, provides a safe maximum limit of system pressure, and maintains desired system temperature and fluid cleanliness.
73 of 69 MECH1300 Glossary Radial-piston pump –A positive-displacement piston pump design in which the pistons are located in a cylinder block or housing that is perpendicular to the power input shaft.
74 of 69 MECH1300 Glossary Reciprocating pump –One of a variety of pump designs using reciprocating pistons to move fluid. The drive mechanisms vary, but a reciprocating piston moves the fluid against resistance from the system actuator.
75 of 69 MECH1300 Glossary Screw pump –A pump unit that uses intermeshing screws to form chambers that linearly move hydraulic oil through the pump. The design provides a continuous, positive displacement of the oil.
76 of 69 MECH1300 Glossary Stationary-cylinder design –A radial-piston hydraulic pump design in which a cam operates pistons located in a fixed cylinder block. Swash plate –An inclined disk in a hydraulic axial-piston pump or motor that causes the pistons to reciprocate.