Hydraulic Pumps

1
Hydraulic Pumps
2
Pump Objectives

• 1. Explain the difference in Positive and
  Non-positive displacement pumps.
• 2. Explain the difference in Fixed displacement
  and variable displacement pumps.
• 3. Describe the three major types of pumps.
• 4. Explain the difference in the two types of
  gear pumps.
• 5. Explain the difference in the two types of
  vane pumps.
• 6. Describe the difference in the two major types
  of piston pumps.
• 7. List the ways in which pumps are sized.
• 8. List possible sources of problems with pumps

3
Sizing and Selecting the Right Pump

• Main factors
• Fixed or variable
• Pressure psi (Max) 100 to 4000 psi
• Horsepower (HP)
• HP (GPM x system pressure in PSI) / 1714 x
  Pump efficiency
• HP GPM x PSI X .000583
• Displacement or volume (cubic inches GPM)
• GPM (Cubic Inches / minute) / 231 Ex. 462
  GPM / 231 2
• These are both a function of surface area in pump
  
• However displacement can be affect by input speed
  of pump
• Other factors to consider
• RPM (1800 or 3600)
• Direction of rotation (CCW)
• Inlet or outlet size
• Mounting
• Shaft size

4
Pump Efficiency
Actual output (GPM) ------------------Theoretic
al Output (GPM)

• Volumetric Efficiency
• Example
• Theoretical 10 GPM, actual 9 GPM
• What is the volumetric efficiency?

9--- .9 x100 90 10
5
Example 2

• For example, a hydraulic pump with a
• theoretical output of 100 GPM, and
• an actual output of 94 GPM
• at 5000 PSI and 120 SUS
• is said to have a volumetric efficiency of 94 at
  5000 PSI and 120 SUS.

6
What is the significance of volumetric efficiency?

• As a hydraulic pump wears in service, internal
  leakage increases and therefore the percentage of
  theoretical flow available to do useful work
  (volumetric efficiency) decreases. If volumetric
  efficiency falls below a level considered
  acceptable for the application, the pump will
  need to be overhauled.

7
Pump Efficiency

• Mechanic Efficiency is the Overall Efficiency
  compared to Volumetric Efficiency . Difference
  due to wear and friction
• Overall Efficiency is the ratio of power output
  to mechanical power input of the pump (HP input
  compared to HP output)

8
Pump Problems

• Too much pressure rated at 2000 operated at
  something over that for long periods of time.
• Heats the fluid
• Wears bearing
• Wear
• Contaminates Causing wear
• Where do they come from?
• External -- How do they enter? Loose lines,
  rusty cylinder with worn wiper seal, fill cap,
• Internal wearing of parts, bad fluids (wrong
  viscositywrong type), heat,

9
Pump Problems

• How does contamination affect a hydraulic pump?
• Particle contamination accelerates wear of
  hydraulic components. The rate at which damage
  occurs is dependent on the internal clearance of
  the components within the system, the size and
  quantity of particles present in the fluid, and
  system pressure.
• Particles larger than the component's internal
  clearances are not necessarily dangerous.
  Particles the same size as the internal
  clearances cause damage through friction.
  However, the most dangerous particles in the long
  term are those that are smaller than the
  component's internal clearances.
• Particles smaller than 5 microns are highly
  abrasive. If present in sufficient quantities,
  these invisible 'silt' particles cause rapid
  wear, destroying hydraulic pumps and other
  components.

10
Pump Problems

• Fluids lack of fluid, wrong fluid type, wrong
  viscosity, hot fluid, cold fluid
• Cavitation
• Seal failure

11
Pump comparison. Gear, Vane and Piston

• See text