Seawater-driven pump eliminates pressure hose connections

Sea trials of a new pump/motor patented by Hytar of Tampere were successfully completed in a Norwegian fjord last year. The unit, which is targeted at both topside and subsea applications, may be the first water-hydraulic system capable of handling seawater for power transmission. According to Hytar's Jorma Terava, more development work is needed for offshore applications, but "we hope to have a fixed-pump version finished by mid-1997", with a fixed motor available early next year.

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The Hytar water hydraulic pump/motor.


Sea trials of a new pump/motor patented by Hytar of Tampere were successfully completed in a Norwegian fjord last year. The unit, which is targeted at both topside and subsea applications, may be the first water-hydraulic system capable of handling seawater for power transmission.

According to Hytar's Jorma Terava, more development work is needed for offshore applications, but "we hope to have a fixed-pump version finished by mid-1997", with a fixed motor available early next year.

The new unit, which uses identical parts to function either as a pump or motor, is a modular, swash plate, axial piston-type machine, displacement of which can be adjusted during assembly between 13-40 cu cm/rev. It is designed for use in open or closed systems, and either submerged or in air in hazardous environments.

In subsea applications, no fluid reservoir is necessary since water is taken directly from the surrounding sea, filtered, used and then discharged. Therefore the need for pressure hoses or umbilical connections to an offshore platform is eliminated.

According to Hytar, water offers other advantages as a hydraulic medium. Its low viscosity results in high flow-rates, high energy transmission rates and fast reaction to control signals. Also, water costs less than hydraulic oils and is safer to the environment. Furthermore, it is readily available, and storage and disposal is simpler and inexpensive. It also presents no fire risk.

Development of the new pump/motor arose from joint research between Hytar, Tampere University of Technology and various manufacturers. This was coordinated under the Eureka programme.

Both pump and motor handle can cope with operating pressures up to 3,000 psi. In pump mode, the unit handles flow rates up to 54 liters/min. and is rated up to 19kW, according to the displacement selected. As a motor, it handles up to 871 liters/min., giving torque output up to 100Nm with a power rating of up to 21kW. The motor's nine-piston design ensures high starting torque and silent running. Fibre-reinforced polymers and coatings, previously developed for outer space application, also allow water to be used to lubricate all moving parts.

The standard water pump/motor weighs 25 kg and is equipped with a 30mm drive shaft. Options include motors with a double shaft or with extra heavy-duty axial bearings, and also an integral booster pump. A variable-displacement version of the pump/motor is also under development.

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