Why do most wb's/ztr's use 2 hydro pumps?

Discussion in 'Lawn Mowing' started by instyle, Oct 15, 2007.

  1. instyle

    instyle LawnSite Senior Member
    from Canada
    Messages: 380

    I just seen scag uses 2 10cc pumps to control the wheel motors? Why use two seperate 10cc pump instead of using 1 20cc pump and an open circut.
    Also, what type of pump are most (orbit,piston,axial)?
    what kind/size of wheel motors do they use?

    I have a quick trac and there is only one pump so i can't figure out why have two.
  2. MJLsLawnCareNmoreLLC

    MJLsLawnCareNmoreLLC LawnSite Senior Member
    Messages: 840

    You still have 2 pumps essentially. It has a daul unitized pump (2 pumps in one unit).
  3. rodfather

    rodfather LawnSite Fanatic
    Messages: 9,501

    Larger the pump, the greater the hp you need plus it will slow you down on hills as well.
  4. Pumper

    Pumper LawnSite Member
    Messages: 116

    You could do it with one pump and just split/control the flow with valves. The problem with this is the cost of the valves would be more than the second pump. It is also much easier to have seperate pumps for repair and replacement. Having said that, the pump you have is actually 2 pumps in one housing. You have two 10cc axial piston rotating groups. Each one is independently controlled to provide flow and pressure to the individual wheel motors (which is a gerotor hydraulic motor).
  5. mowtech

    mowtech LawnSite Senior Member
    Messages: 252

    The only type of pump that I am aware of that is used in zero turn mowers are axial piston pumps. The advantage of this type of pump is that speed control can be accomplished easily by changing the angle of the swash plate which determines the length of stroke of the pistons hence output flow and speed. This swash plate can also be rotated such that it is flat or perpendicular to the pistons hence providing zero flow and zero output speed. It can be further rotated to reverse flow. This fairly simple design provides smooth speed change along with smooth reverse.

    There are two pumps because each side of the machine requires independent control to provide the zero turn operation i.e. directional control is accomplished by varying the speed and direction of each drive wheel independently. The pumps provide the individual control. Non-zero turn mowers such as out front rear steer units or hydrostatic garden tractors do only use one pump because the pump is only providing speed and forward reverse. The steered wheels provide the directional control.

    Most wheel motors used on zero turn motors are of the geroller design (not gerotor, a gerotor has no rollers). These are low speed high torque. The advantage is that they can be easily matched to the pumps providing the speed reduction required hydraulically as opposed to gear reduction. This is cost effective. Wheel motors on zero turn mowers generally have a displacement in the range of 12 to 24 cubic inches per revolution.

    As stated, the Quick Trac has two pumps in one housing. The disadvantage of this is the possiblity of cross contamination when one pump or motor fails.

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