Sundstrand Series 20 Hydraulic Controls
April 19, 2021
Control speed and direction is carried out by the movement of a single Control Lever from a neutral lay out. The pump swashplate is spring loaded to neutral position to make sure there is a positive neutral. The swashplate is fitted with two opposed single acting Servo Cylinders to move the swashplate and vary the pump displacement. Pressurizing one of the cylinders while debilitating the other will move the swashplate from its neutral position. To get the reverse direction from neutral, the other cylinder is pressurized and the other is depleted. Oil is pointed to the preferred servo cylinder by the control valve which is turned on by a signal from the operator thru the control lever or from the swashplate and its feed back linkage system. If the circuit pressures tend to overcome the swashplate – servo piston preset position, the feedback linkage connecting the swashplate to the control valve will turn on the control valve and give enough pressure to the servo piston and help the swashplate in its position preset by the operator. The control valve is spring centered and takes in enough under lap to open both the servo cylinders to drain when the control lever is in neutral. The lets the servo cylinder centering springs to move the swashplate to the zero stroke position giving a positive neutral.
There are several types of controls:
Displacement, pressure override, etc. to give the drive the best outcome for the application needed.
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