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Article Excerpt
Pumps, motors
by Chad Elmore and Michelle EauClaire
Part Two of OEM Off-Highway's trip through the mobile hydraulic circuit.
Although it worked fine for its era, you could say Buckeye Traction Ditcher Co.'s wheel trencher was in search of a heart in the 1920s. Once the tracked machine followed the Yellow Brick Road to Emerald City, it would have asked the man behind the curtain for a pump. Trenchers would eventually be given that component -- the heart of today's hydraulic system -- and that's one of the reasons several early mechanically driven trenchers are now spending their retirement years parked in a central Iowa field.
On those early trenchers, the energy that moved the tracks and the rear-mounted trenching wheel was directed from the prime mover (in this case an early Caterpillar gasoline engine) through a complex array of chains, cables, shafts and gears. Each of the rusty gears on the trenchers in Iowa was designed for a specific purpose.
In actual application the exposed gears were noisy and consumed much of the power they were transmitting. Open to collect dirt and grit, the gears broke teeth and grabbed operator's clothing. Wire-rope traveled through pulleys to lower the trenching wheel into the ground. The cables made the rear of the trencher look like the tangled mess of downed power lines. In those early days, machine design was restricted by what the gears, chains and cables were required to do and by their design limitations.
Descendants of the Buckeye trencher would get the strength and versatility of a hydraulic system. Today, hydrostatic transmissions help propel tracked trenchers while motors help the digging wheel slice through tough ground conditions. When off-highway equipment was finally given a heart, the positive displacement rotary pump, individual job demands began to dictate machine design rather than the components.
The pump uses mechanical energy from the engine to push fluid through the system. The pressure in the system comes from resistance due to a load on a linear (January issue) or rotary actuator. Rotary actuators, or...
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More articles from OEM Off-Highway
The changing face of the distributor.(Department), February 01, 2008
Fundamental change forfluid control.(Department), February 01, 2008
Protect your own tools.(Editor's Notebook), February 01, 2008
A systems approach to smooth steering.(Department), February 01, 2008
BIG, STRONG and RELIABLE.(Department), February 01, 2008
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