Hydraulic power transmission is a drive
or transmission system that uses hydraulic fluid under pressure to drive
machinery. The system is concerned with the generation, modulation, and
control of pressure and flow, and in general such systems include:
- Pumps which convert available power from the prime mover to hydraulic
power at the actuator.
- Valves which control the direction of pump-flow, the level of power
produced, and the amount of fluid flow to the actuators. The power level
is determined by controlling both the flow and pressure level.
- Actuators which convert hydraulic power to usable mechanical power
output at the point required.
- The medium, which is a liquid, provides rigid transmission and
control as well as lubrication of components, sealing in valves, and
cooling of the system.
- Connectors which link the various system components provide power
conductors for the fluid under pressure, and fluid flow return to tank
- Fluid storage and conditioning equipment which ensure sufficient
quality and quantity as well as cooling of the fluid.
Some of the major advantages of hydraulic
power transmission are as follows:
- Great efficiency and economy due to low friction losses and high
system reliability (efficiency is approx. 70 to 80 percent)
- Freedom of location of input and output power converters such as
prime movers, pumps, and actuators.
- Safety and overload protection by means of relief valves.
- Emergency power stored in an accumulator.
- Infinitely variable control of output force, output torque, output
speed, and actuator position.
- Extremely high output forces and force multiplication by means of the
- Low inertia and ease of shock absorption during actuator motion,
reversal, start, and stop.
- Hydraulic systems are self-lubricating and power can be diverted to