Copyright Goodheart-Willcox Co., Inc.
140 Hydraulic Systems for Mobile Equipment
Today’s electronic controls can also be used to reduce cylinder shock
loads. Construction wheel loaders use programmable kick-outs. The operator
accesses the programmable option in the machine’s monitor. The operator
places the bucket in the desired position then presses the monitor’s key to have
the bucket “kicked out” once it reaches that set position. Kick-out is a term
used to indicate that the cylinder has stopped moving. A kick-out can be set
for the lower position and the raise position. The monitor can have several
other features allowing the operator to set the kick-out for a specifi c work tool
being used, such as pallet forks or bucket. The kick-out can be set for tilting, or
curling, the bucket as well.
The machine’s ECM determines the cylinder’s position through a sensor.
As the cylinder reaches the end of travel, the ECM will slow the cylinder by
varying the electronically controlled DCV.
A cylinder stroke can be mechanically limited. A stop tube is sometimes
placed inside a cylinder, which limits the overall stroke of the cylinder. See
Figure 6-23. Stop tubes are sometimes used when a cylinder has a long rod,
and the rod has a tendency to buckle or bend. The stop tube will prevent the
rod from fully extending.
Agricultural implements frequently use an external depth stop that con-
sists of an aluminum clamp that fi ts around the cylinder’s rod. See Figure 6-24.
These types of depth stops are readily available at farm equipment stores.
The clamps are available in a variety of thicknesses and are used to adjust the
individual wings on implements. The clamps are easily installed and can be
quickly removed from the cylinder.
Cylinder Speeds
A cylinder’s speed can be calculated if the cylinder’s area is known and the
quantity of oil fl ow into the cylinder is known. The speed is measured in feet
per minute (ft/min), feet per second (ft/sec), or meters per second (m/sec). The
speed of a cylinder is computed by multiplying the fl ow rate times a factor, and
dividing that product by the cylinder’s area:
Speed (ft/min) = (Flow (gpm) × 19.25)/Area (in2)
Speed (ft/sec) = (Flow (gpm) × 0.3208)/Area (in2)
Speed (m/sec) = Flow (lpm) × 0.167)/Area (cm2)
If a cylinder was supplied a 20 gpm of oil, and if the cylinder had an area
of 7.07 in2, the cylinder would extend at a rate of 54 feet per second. A factor
Figure 6-23. Stop tubes can be installed inside a cylinder, limiting the cylinder’s overall stroke.
Stop tube