In a usual hydraulic system, there are two networks of tubes; one contains high pressure hydraulic fluid and the other low pressure.
One or a few engines drive pumps, which move hydraulic fluid from low pressure network of tubes to high pressure network of tubes. Hydraulic machines as motors, pumps, compressors, presses, electric generators, etc. take fluid in high pressure network and pass it to low pressure network and use pressure difference to perform their work.
When hydraulic machines change speed of their operation, conflict arises between volume of fluid movement through them and volume of fluid movement through pumps driven by engines. Often, engines cannot adjust quickly enough and this could lead to pressure waves in the system of tubes.
To protect the system, special compensating elements should be included into it. There are two types of candidates for such compensators and it is desirable to use them both, because they offer complementary capabilities.
One is a reciprocating electric generator combined with electric battery, which it feeds. Energy stored in the battery could be used, as needed, particularly to start the system. The generator starts automatically, when pressure in the system exceeds some high level and stops, when it drops below some low level. Unfortunately, when battery is full, this “safety valve” cannot be used.
The other is a reciprocating pump used to pump air into a special tank, where compressed air is kept – an air compressor. It starts and stops the same way electric generator does. However, compressed air from the tank could be vented, when pressure in it exceeds safety limit. Compressed air has its own uses, for example for air conditioning.
There are a few types of machines especially suitable to be used with hydraulic transmission.
One is various reciprocating pumps pumping liquid, gas (compressors), etc., which are driven by reciprocating hydraulic motors (pumps in reverse, hydraulic motors takes energy from the Transmission). Hydraulic presses are another example. Turbines could be used, where rotation is needed.
Energy producers (engines driving pumps) are turned on and off as needed. Speed of pumping of the transmission fluid is controllable. Cost of reciprocating pumps, compressors and motors is low. They are quiet, reliable and cost of their maintenance is low.
When tubes of transmission are not movable after they are installed, the system could be made leak proof. This could be achieved in a building, in a settlement, in an airplane or in a ship.
Alexander Liss 7/9/2019; 7/16/2019