Water hydraulics
The water hydraulics , also clear water hydraulics , is the forerunner of the oil hydraulics . Water hydraulics was used especially in forging presses as early as the 19th century (e.g. weapon smiths). At this time, a powerful hydraulic system was not available.
The historical development of water hydraulics has had a decisive influence on oil hydraulics. 2/2-way valves, suction and filling valves have their origins in water hydraulics.
Advantages and disadvantages
advantages
- As a fluid medium , water is not flammable.
- Clear water (drinking water) instead of oil is environmentally friendly.
- Clear water reduces operating costs; There are no precautions to be taken for oil leakage (oil separator). There are no storage and disposal costs for hydraulic fluids.
- Line resistances are significantly lower with water than with oil, which can improve the efficiency.
- With water, the return line can be omitted, comparable with pneumatic systems.
- Because of its lower compressibility, water has better control properties .
- In heavy industry (forging presses, extrusion press, etc.), pressure accumulators can be used to reduce or avoid power consumption peaks.
disadvantage
- Water has a significantly low viscosity , so the pumps and valves of the oil hydraulics cannot be used. Plunger pumps with special seals convey the pressurized water and seat valves control the press function
- the low viscosity leads to greater leakage flows and thus to a lower degree of efficiency.
- Valves from the oil hydraulics with their gap seals have too great a leakage and thus erosion on the valve edges. The known slide valves as well as proportional and servo valves cannot therefore be used in water hydraulics
- Water-hydraulic systems are made entirely of high-quality stainless steels and are therefore comparatively expensive in terms of acquisition costs
- Water is prone to cavitation due to the high vapor pressure .
- In heavy industry (forging presses, extrusion press, etc.) as well as in underground coal mining, emulsion (water with 2 to 5% oil, emulsifiers, biocides and possibly anti-corrosion agents) is used.
- In rare individual cases, biocides must be added to water cycles.
- due to the higher compression rate, there is a risk of water hammer
- The freezing point of the water is zero degrees Celsius at ambient pressure. Correct operation at sub-zero temperatures cannot therefore be guaranteed without further measures.
Web links
History of water hydraulics from the provider of Wasserhydraulik Krisch-Dienst GmbH