Students put the hydro in hydraulics
Photo by Tom Campbell
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Graduate student
Louis Cassens puts a revolutionary lawn mower through a trial
run near Purdue's Food Science Building. The mower uses ordinary
water in place of hydraulic fluid.
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By Steve Tally
Four Purdue undergraduates have built an industrial riding
lawn mower that's a cut above the rest.
The students have created what is thought to be the first
vehicle that uses water in all of its hydraulic systems, including power
steering, power brakes and transmission.
Recent advances in water hydraulic systems have allowed
them to perform as well as petroleum hydraulic systems. Because water
offers several environmental and economic advantages over petroleum
hydraulic fluid, the students teamed up to demonstrate that such a vehicle
is now possible.
May graduates Jason Brown of Pendleton, Ind.; Dan Sellers
of Bourbon, Ind.; and Dan Pitstick of Rensselaer, Ind., worked through
their final semester at Purdue to build the machine. Nathan Schoonover,
of Evansville, Ind., who graduated in December, also worked on the project.
Although the mower was redesigned to prove a point, it
does have a practical purpose. Mowers leak some hydraulic fluid, and
on golf courses that fluid can kill grass on greens that often cost
tens of thousands of dollars to construct and maintain.
The Jacobsen Company donated the Greens King IV mower,
a 31-horsepower, front-wheel-drive mower with three sets of gang mowers
that are raised and lowered hydraulically.
Gary Krutz, professor of agricultural and biological
engineering and the students' adviser, says water hydraulic systems
only would be practical in vehicles that use high-pressure systems,
such as heavy equipment used in construction, agriculture, forestry
and mining. (Automobiles have hydraulic brake and steering systems,
but these are not typically highly pressurized.)
Using water in hydraulic systems currently costs twice
as much as using petroleum products, but that could change as more applications
are found for water hydraulics.
"If all of the research and development were done,
all of the major companies would be using water instead of hydraulic
fluid," Krutz says. "Because the industry is in its infancy,
mass production hasn't lowered the cost. But once you start mass producing
the necessary parts from ceramic, fiber-reinforced plastic or stainless
steel, the prices will drop."
The water used in the mower isn't straight from the tap;
ordinary city water contains too many minerals and impurities and could
cause build-up and corrosion. Instead, the system uses distilled water
that has been de-ionized to remove any electrical charges that could
cause corrosion.
Corrosion also is the reason parts for water hydraulic
systems have to be made of stainless steel, plastic or ceramics. But
the more expensive parts would be worth it because using water in hydraulic
systems makes machinery more energy efficient, saving money.
The boost in energy efficiency is due to water's lower
viscosity. Viscosity is the measure of how fast a liquid flows. Water
flows up to 1,000 times faster than hydraulic fluid at normal air temperatures.
Once the machine is warmed up, water is still 10 times less viscous.
Reduced viscosity means less energy is required to push
the hydraulic fluidthrough the system, making it more efficient. By
using water instead of heavier petroleum fluid, Krutz estimates the
efficiency could be boosted at least 10 percent.
Replacing hydraulic fluid with water won't be without
problems, however. Because tighter fittings and higher quality parts
are needed to prevent leaks and corrosion, water systems are more costly.
Also, the reduced viscosity of water means that turbulence within the
system could reduce efficiency if the parts aren't engineered properly.
Contact Krutz at: krutz@purdue.edu
