The world of water hydraulics
Original article date: June 2000
Don’t overlook water hydraulics, even though they form just a small part of the total market. The BFPA has published a new technical guideline
The hydraulics industry uses a wide range of fluids – mineral and vegetable oils, emulsions, polyglycol or chemical solutions and synthetic esters. Among these are water and water-based fluids. Although these form a relatively small part of today’s fluid power market, their importance cannot be underestimated. Partly because of this, the British Fluid Power Association has published a new technical guideline.
Water-based hydraulic fluids are often defined as those having a viscosity equal to or less than 5 centistokes. This is deemed to be the level at which normal oil-hydraulic components may not function or which may give an unacceptable service life. Where fire resistance, product contamination and environmental issues are important, then the use of water hydraulics can come into its own. The steel, copper and aluminium industries, food processing, paper, pulp and wood chipboard manufacture, offshore, mining, power generation, nuclear and even the automotive industries are all significant users of this technology.
Water has low viscosity and low compressibility characteristics that make it an excellent transmitter of energy in a hydraulic system. In common with most hydraulic fluids, additives are often used to improve certain properties of water and to control bacterial growth.
Water is readily available and naturally recycled, almost eliminating fluid purchase, storage and purchase costs. It doesn’t wear out either! Fluid additive suppliers and water companies can advise on disposal of high water-based fluids, some of which can be disposed of down the drain. Note, however, that spillage and leakage directly into water courses and rivers may infringe environmental laws.
Water hydraulics is constantly finding its way into new applications. This is a result of technical development in recent years, resulting in new ranges of products becoming available that look and perform like their counterparts in oil hydraulics. Manufacturers now produce axial piston pumps with SAE flanges, directional control valves with CETOP interfaces and even electro-hydraulic proportional controls.
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Mixing it with oil and water |
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| Liquid | Mineral Oil | Water | Comment |
| Kin ematic Viscosity at 50 degC (cSt) | 15-70 | 1 | Reduced pressure losses Tolerances/sealing is more critical |
| Density at 15degC | 0.87-0.90 | 1 | Increased risk of cavitation |
| Vapour pressure at 50 degC (bar) | 10-8 | 0.1-0.5 | Increa sed risk of cavitation |
| Compression Modulus E (N/mm?) | 1.6 x 10-9 | 2.4 x 10-9 | Improved system stiffness |
| Thermal conductivity at 20degC (W/mK) | 0.11-0.14 | 0.598 | More effective heat removal Reduced cooler size |
| Max working temperature range (degC) | -20 to +90 | 3 to 50 | Precautions needed for frost Enlarged cooler capacity |
| Flash point (degC) | 210 | n/a | No fire risk at all |
| Ignition Point (degC) | 301-360 | n/a | No fire risk at all |
| Corrosion Protection | Good | Poor | Components must be made of corrosion-resistant materials Possible precautions needed during long standstill periods |
| Environmental Impact | High | None | Fewer problems concerning pollution |
| Relative cost | 100 | 0.02 | Cost saving |
| Storage Costs | Some | None | Cost saving |
| Disposal Costs | High | Negligible | Cost saving |
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Fire-resistant fluids in common use |
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| Type | Composition | Water Content |
Viscosity Grade (cSt) |
Working Temp degC |
Supplied as |
| HFAE | Oil in water emulsion | >95% | 1 | +5 to 50 | Concentrate (add to water) |
| Oil in water emulsion with thickener |
>80% | 10,15,22,32,46 | +5 to 50 | Pre-mixed | |
| HFAS | Chemical solution in water | >95% | 1 | +5 to 50 | Concentrate (add to water) |
| HFB | Water in oil emulsion | >40% | 46,68,100 | +5 to 50 | Pre-mixed |
| HFC | Polymer solution | >35% | 22,32,46,68 | -20 to +50 | Pre-mixed |
| Water glycol | <80% | 22,32,46,68 | -2 0 to +50 | Pre-mixed | |
| HFDR | Synthetic fluid phosphate ester | 0 | 15,22,32,46,68,100 | -20 to +70 Short term 150 |
Pre-mixed |
| HFDU | Other synthetic fluid free from water | 0 | 15,22,32,46,68,100 | -20 to +70 Short term 100 |
Pre-mixed |
- British Fluid Power Association
June 2000