Hydraulic Power Systems
Hydraulic (Positive
Displacement) Pumps
Types of fluid pumps and motors:
Positive displacement Rotor-dynamics
Operates at relatively low Fluid transfer at relatively
flow rates and high high flow rates and low
pressures, and only used pressures
with lubricating fluids
Major aspects in the selection of
pumps and motors:
1. Cost
2. Pressure ripple and noises
3. Suction performance
4. Contaminant sensitivity
5. Speed
6. Weight
7. Fixed or variable displacement
8. Maximum pressure and flow, or power
9. Fluid type.
Mechanical principle in pump
design:
Operating speed
Pressure
Type of fluid
Requirement for providing variable displacement
control
Gear Pumps
External gear pumps and motors:
Operating ranges:
Power (1-100) kW
Pressure up to 250 bar
Speed (1000-3000) rpm
Efficiency ≥ 90%
External Gear Pumps:
Advantages:
Simplicity
Low cost
Good suction performance
Low contamination sensitivity
Relatively low weight
Design accommodates wide variety of materials
Disadvantages:
Noisy
Alternative for low noise applications:
1. Vane pumps
2. Internal gear pumps
Applications:
Common external gear pump applications include,
but are not limited to:
Various fuel oils and lube oils
Chemical additive and polymer metering
Chemical mixing and blending (double pump)
Industrial and mobile hydraulic applications (log
splitters, lifts, etc.)
Acids and caustic (stainless steel or composite
construction)
Low volume transfer or application
Internal Advantages:
Non-pulsating discharge
Excellent for high-viscosity liquids
Constant and even discharge regardless of pressure
conditions
Operates well in either direction
Single adjustable end clearance
Easy to maintain
Flexible design offers application customization
Disadvantages:
Usually requires moderate speeds
Medium pressure limitations
Applications:
Common internal gear pump applications include, but are
not limited to:
All varieties of fuel oil and lube oil
Resins and Polymers
Alcohols and solvents
Asphalt, Bitumen, and Tar
Polyurethane foam (Isocyanate and polyol)
Food products such as corn syrup, chocolate, and peanut butter
Paint, inks, and pigments
Soaps and surfactants
Glycol
Piston Pumps
Piston pumps:
Operating ranges:
Pressure up to 450 bar (for high pressure applications)
Power (100 – 300 – 1000) kW
Efficiency ≥ 90%
Note: price of piston pump = 10 times of gear pump.
Vane Pumps
Advantages:
Handles thin liquids at relatively higher pressures
Can run dry for short periods
Can have one seal or stuffing box
Develops good vacuum
Disadvantages:
Complex housing and many parts
Not suitable for high pressures
Not suitable for high viscosity
Not good with abrasives
Applications:
Aerosol and Propellants
Aviation Service - Fuel Transfer, Deicing
Auto Industry - Fuels, Lubes, Refrigeration Coolants
Bulk Transfer of LPG and NH 3
LPG Cylinder Filling
Alcohols
Refrigeration - Freons, Ammonia
Solvents
Aqueous solutions
