1. TSM 363 Applied Fluid Power
Principle of Hydraulic Pumps

2. 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

3. It’s Powerful, What Provides the Power?

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

5. Positive Displacement Pumping

6. 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

7. 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!

8. 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

9. 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

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

11. 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

12. 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

13. 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

14. 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

15. Operation Principle of Piston Pumps

16. Needs for Variable-Displacement PumpH
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.

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

18. Operation of Variable Displacement

19. 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

20. 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