Mention hydraulics, and most people think of heavy-duty oil-powered pistons. But it doesn’t take a professor of etymology to realise that the technology’s first successful medium was water, and until Jenney’s invention of the hydraulic oil system in 1906 water-based hydraulic systems had enjoyed centuries of dominance.
Now, with companies increasingly concerned about safety and the environmental impact of oil-based hydraulic systems, water is enjoying a resurgence as a hydraulic medium.
The first well-documented uses of water as a power-transmitting medium appear in the late 1700 with UK inventor Joseph Bramah patenting the water hydraulic press in 1795. Water remained an accurate and economic means of transmitting power until the end of the 19th century. Electrical power offered engineers a means of accurate control and a large power supply over long distances and in 1906 the first oil hydraulic system was introduced.
The advance of electrohydraulic controls and the invention of the electrohydraulic servovalve led to a great advance in technology for oil-based hydraulic systems. However, water-based hydraulic systems have never completely gone away, and the great advantage of using a harmless medium has seen such systems enjoy continued uses as varied as the food processing and nuclear power. Water has a great number of factors in its favour. It’s environmentally friendly and clean, doesn’t pose a fire risk, and its cost in terms of initial fill, replacement, storage and disposal is practically zero.
However, problems with lubrication require specialised designs for components with moving parts such as pumps, motors and valves and so on. Issues such as corrosion, algae and cavitation erosion – where violent gas bubble formation causes rapid component wear – have all held the technology back.
Now, thanks to improvements in material properties and an increased demand for water-based systems, systems are available that claim to overcome many traditional drawbacks.
Tony Markham, managing director of the Hull-based Water Hydraulics Company, said the biggest drawback of water hydraulics is high cost. ‘This is down to the corrosive properties of water, plus the fact that you also have to introduce some kind of lubricant – you’re looking at an expensive component,’ he said.
Markham added that while a number of companies supply equipment that operates on water as the hydraulic fluid, its design is generally borne of the equivalent oil industry standards, featuring comparatively expensive material specifications and tighter manufacturing tolerances. The result is an expensive product that restricts water hydraulics to the niche application where contamination or fire risk are the major considerations and cost is not the over-riding criterion. However, Markham claimed that, assisted by a DTI Smart Innovation Award, Water Hydraulics has reduced this cost differential. The company has launched a range of valves that offer pressure and flow control. Janus Control valves give directional flow and pressure control for system pressures up to 200 bar, making them ideal, said Markham, not just for water but any corrosive low-viscosity fluid.
The operating principle is a hydrostatically balanced face valve that mimics a spool arrangement. Functions not commonly seen in a single valve can now be supplied. A bolt-on pilot-operated check in both single and double-acting versions is available for load-holding applications.
The design is said to be very tolerant of fluid contamination. The sealing forces generated by the operating pressure produce sub-micron clearances that restrict entry of contamination to the bearing interfaces. Direct valve actuation via solenoid, pilot, hand and spring ensures that contaminants cannot clog or destroy designed pressure balances. The ability to generate appropriate actuation forces without small pilot feed galleries ensures that contamination or scale build-up will not affect the actuation of the valve.
The valve can also be configured to offer pressure control in terms of relief, reducing, unloading and overcentre. A major feature is that the section that controls the pressure differs from the surface that offers the seal. The efficiency of the valve is not affected even if the specially selected materials are eroded due to exceptionally high fluid velocities.
Manifold versions containing both pressure and flow control functions are available for volume applications, which offers a further cost reduction and minimises the use of expensive fittings and pipework.
Note: Fluid power giant Danfoss has introduced the Nessie range of pumps, power packs, valves, motors and cylinders which use tap water as the hydraulic medium.