14-09-2013, 04:01 PM
Hydraulic and Pneumatic Systems
Hydraulic and Pneumatic.ppt (Size: 1.91 MB / Downloads: 377)
Advantages of hydrostatic drives
Simple method to create linear movements
Creation of large forces and torques, high energy density
Continuously variable movement of the actuator
Simple turnaround of the direction of the movement, starting possible under full load from rest
Low delay, small time constant because of low inertia
Simple overload protection (no damage in case of overload)
Simple monitoring of load by measuring pressure
Arbitrary positioning of prime mover and actuator
Large power density (relatively small mass for a given power compared to electrical and mechanical drives)
Robust (insensitive against environmental influences)
Hydraulic fluids - tasks
They have the following primary tasks:
Power transmission (pressure and motion transmission)
Signal transmission for control
Secondary tasks:
Lubrication of rotating and translating components to avoid friction and wear
Heat transport, away from the location of heat generation, usually into the reservoir
Transport of particles to the filter
Protection of surfaces from chemical attack, especially corrosion
Hydraulic Fluids
Sucking air with the pump happens but is by proper installation avoidable.
The oil is quickly into solution during the increasing pressure.
Air bubbles come to oil mostly so that with decreasing pressure the air „goes out of solution”.
At high pressure, the volume of the dissolved air is much more than the volume of the liquid.
When the pressure drops the air leaves the solution suddenly but the dissolution happens gradually.