The hydraulic pump motor system is used in power transmission where the conventional power transmission is not suitable, as in aircraft controls
The unconventional system – Hydraulic Pump Motor System
The conventional power transmission system of electric generator - power transmission lines – distribution system – electric motors has been in use for a very long time. In some cases however, the system has the disadvantages that cannot be accepted. The radio interference from such transmission can affect the communications from aircraft to the ground control station.
This is unacceptable condition in the aircraft navigation.
Hence alternative system of power transmission by hydraulic pump/motor system is used.
Hydraulic Pump/Motor System Advantages
The system of hydraulic pump/motor has many advantages.
1. So long as the integrity of the hydraulic pipe system is maintained there are very less chances of failure in transmission system. The possibility of failure of components in electrical system is reduced as the actual numbers of components are reduced.
2. The system is fast and easily controllable. Hydraulic systems usually are fast response systems compared to the electrical systems. The systems can be controlled from microprocessors just as the electrical systems
3. The radio interference emanating from electrical system is absent in the hydraulic system. The radio interference can be very disturbing for the communications between the ground control and the aircraft. Since communication disturbances are not to be tolerated, the hydraulic systems are used in aircrafts.
4. The radio interference can also affect aircraft controls and the electrical system is where necessary and hydraulic control used for everything else.
5. The system is far more reliable than the electrical system as there is no possibility of tripping of electrical feeders
6. The starting time of hydraulic motors is less and response is quick, making the control responsive. Quick actions are necessary in aircraft controls and hence hydraulic controls are preferred.
Hydraulic Pump Motor System Description
The hydraulic pump and motor system consists of a positive displacement pump, safety gadgets for pump against overpressure, pipe and fittings and the final actuating motors.
Hydraulic Pumps: The pumps are normally of the positive displacement types and can be geared pumps or lobe pumps. The advantage from the positive displacement pumps is the constant pressure even with increasing demand and very high reliability.
Safety devices: Safety devices have to be employed in the system to ensure that the system does not get pressurized beyond the design capacity. The positive displacement pumps can continue to supply pressurized oil and if the over pressurizing prevention devices are not installed, the lines can burst, and hence the devices. These devices can be mechanical (spring loaded safety valves, dump oil lines) or solenoid valves
Hydraulic Oil Lines: The job of these lines is just to convey oil from point A to point B. The oil lines are generally made of stainless steel as they do not corrode and are stronger for a given weight. The lines are tested for double the design pressure to make sure that the lines do not burst even under extreme conditions.
Hydraulic Motors: These motors are of turbine type and are designed to convert hydraulic energy into rotary motion. The hydraulic motors and hydraulic cylinders are the final acting elements in the hydraulic systems. The oil from these elements goes back to the hydraulic tank for reuse. Just to make sure that is has not picked up any dirt while passing from the pump to motors; the oil is filtered again before reuse.