Hydraulic machinery
One drawback, compared to machines using gears and shafts, is that any transmission of power results in some losses due to resistance of fluid flow through the piping.
[2][clarification needed] Because it produced superior results, the hydraulic press eventually displaced the steam hammer for metal forging.
[3] To supply large-scale power that was impractical for individual steam engines, central station hydraulic systems were developed.
Hydraulic power was also used for elevators, to operate canal locks and rotating sections of bridges.
A fundamental feature of hydraulic systems is the ability to apply force or torque multiplication in an easy way, independent of the distance between the input and output, without the need for mechanical gears or levers, either by altering the effective areas in two connected cylinders or the effective displacement (cc/rev) between a pump and motor.
A hydraulic circuit is a system comprising an interconnected set of discrete components that transport liquid.
The approach of describing a fluid system in terms of discrete components is inspired by the success of electrical circuit theory.
Just as electric circuit theory works when elements are discrete and linear, hydraulic circuit theory works best when the elements (passive components such as pipes or transmission lines or active components such as power packs or pumps) are discrete and linear.
This usually means that hydraulic circuit analysis works best for long, thin tubes with discrete pumps, as found in chemical process flow systems or microscale devices.
[4][5][6] The circuit comprises the following components: For the hydraulic fluid to do work, it must flow to the actuator and/or motors, then return to a reservoir.
Disadvantages: The pump cannot be utilized for any other hydraulic function in an easy way and cooling can be a problem due to limited exchange of oil flow.
To keep down the oil temperature, the system pressure during transport must be lowered, meaning that the minimum displacement for the motor must be limited to a reasonable value.
Recent technical achievements for the converter transmissions have improved the efficiency and developments in the software have also improved the characteristics, for example selectable gear shifting programs during operation and more gear steps, giving them characteristics close to the hydrostatic transmission.
The inch function affects the preset characteristics for the 'hydrostatic' gear ratio versus diesel engine rpm.
The cylinder areas, motor displacements and mechanical torque arms must be designed to match load pressure in order to bring down the power losses.
System type (3) gives the advantage that activated functions are synchronized independent of pump flow capacity.
The flow relation between two or more activated functions remains independent of load pressures, even if the pump reaches the maximum swivel angle.
This feature is important for machines that often run with the pump at maximum swivel angle and with several activated functions that must be synchronized in speed, such as with excavators.
They are powered by an electric motor or an engine, connected through gears, belts, or a flexible elastomeric coupling to reduce vibration.
Tolerances are very tight in order to handle the high pressure and avoid leaking, spools typically have a clearance with the housing of less than a thousandth of an inch (25 μm).
The reservoir is also designed to aid in separation of air from the fluid and also work as a heat accumulator to cover losses in the system when peak power is used.
Some designs include dynamic flow channels on the fluid's return path that allow for a smaller reservoir.
Examples of accumulator uses are backup power for steering or brakes, or to act as a shock absorber for the hydraulic circuit.
In some factories where food is prepared, either an edible oil or water is used as a working fluid for health and safety reasons.
In addition to transferring energy, hydraulic fluid needs to lubricate components, suspend contaminants and metal filings for transport to the filter, and to function well to several hundred degrees Fahrenheit or Celsius.
Filters are an important part of hydraulic systems which removes the unwanted particles from fluid.
Metal particles are continually produced by mechanical components and need to be removed along with other contaminants.
[9] This arrangement is more expensive, since the filter housing is pressurized, but eliminates cavitation problems and protects the control valve from pump failures.
This location is relatively insensitive to blockage and does not require a pressurized housing, but contaminants that enter the reservoir from external sources are not filtered until passing through the system at least once.
Another disadvantage of hoses is the shorter life of rubber which requires periodic replacement, usually at five to seven year intervals.
