TSM 363 Applied Fluid Power Principle of Hydraulic Pumps

Goals of this Lecture Basics of hydraulic pump Principle of Positive displacement pumping Key parameters Principles of typical hydraulic pumps Gear pumps Vane pumps Piston pumps

It’s Powerful, What Provides the Power?

Energy Flow in a Fluid Power System Energy Level ni, Ti P1 Q1 P4 Q4 vo, Fo no, To

Positive Displacement Pumping

Key Hydraulic Pump Parameters Rated discharge pressure – the maximum continuous operating pressure of a pump under normal operating condition maximum discharge pressure minimum discharge pressure (or margin pressure) maximum inlet pressure Rated speed – the speed at which the pump can continuously operate to discharge flow at the rated pressure maximum speed minimum speed

Pressure Rating of the Pump Pressure rating is the maximum pressure that should be encountered at the pump discharge port. M P T R H Pressure is determined by Load!

Power Output from a Hydraulic Pump In a hydraulic displacement pump, the power output is determined by the setting pressure and the actual output flow rate, and the pump efficiency using the equation below: Pump Power Output HPout = (Q·P)/1714 Q = flow rate, in gpm P = pressure, in psi

Delivery Capacity of a Pump In practice, the pump is rated in terms of how much fluid is supplied per unit of time, and expressed in terms of: Gallons per minutes (GPM) liters per minutes (L/min) Pump Capacity (flow rate) Q =D·n/k Q =flow rate, in GPM or L/min D =Displacement, in in3 or cc n =Pump shift speed, in rev/min k =Unit conversion constant

Example: Determination of Pump Capacity From the catalog of a hydraulic pump manufacturer, we can find the following information: Pump Delivery @ 1000 RPM & 0.641 in3/rev. Please try to determine the pump capacity: Q = D·n/K K = unit conversion constant Q = 0.641 (in3/rev) x1000(rev/min)/231(in3 /gal) K = 231(gal/in3), because 1 gal = 231 in3 Q = 2.77 (gal/min)

Commonly Used Hydraulic Pumps Vane Pumps Unbalanced vane pump Balanced vane pump Gear Pumps External gear pump Internal gear pump Piston Pumps Radial piston pump Axial piston pump

Vane Pumps Construction with a round cam ring Low cost Limited pressure capability Unbalanced hydraulic loading (side-loading) Popular with fixed displacement pumps Prevents side-loading Limited pressure range Relatively more expensive

Gear Pumps Fixed displacement only High pressure capability Unbalanced Available as single, multiple or through drive version One external gear and one internal gear fixed displacement only Unbalanced More compacted in size

Piston Pumps Pistons arranged radially in a cylinder block High efficient medium-high pressure range Rotating cylinder block (centrifugal force) Pistons parallel to axis of the cylinder block High efficient medium-high pressure range Compacted size

Operation Principle of Piston Pumps

Needs for Variable-Displacement Pump H 1,000 psi Fixed displacement pumps discharge a set volume of fluid regardless of the system requirement. An amount of excess will generate heat to the system.

Power Wasted in a Fixed-Displacement Pump Pump displacement “Corner” horsepower Pump output flow Metering point Wasted Power Relief setting Useable Power Operating pressure

Operation of Variable Displacement

Key Feature of a V-Displacement Pump Fixed Displacement Pump A fixed volume of fluids will be provided in each revolution Variable Displacement Pump The volume of supplying fluids may be change based on demands

Lecture Summary Discussed a few basic theoretical equations, and their applications in hydraulic systems: Principle of Positive displacement pumping Key parameters of hydraulic pumps Common types of hydraulic pumps The need for variable displacement pumps