Hydraulic operating system
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United States of America Patent
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-
Aug 10, 1999
Issued Date -
N/A
app pub date -
Jul 30, 1997
filing date -
Feb 1, 1995
priority date (Note) -
In Force
status (Latency Note)
Importance
Abstract
A hydraulic operating system has a cylinder which is actuated to raise, hold or lower a load against the force of gravity. An electromagnetic 3/2 valve connects a working chamber of the cylinder to a hydraulic reservoir when not energized, and permits flow from a pump to the working chamber when energized. A non-return valve prevents flow from the working chamber to the pump when the valve is energized. A three position switch operates an electric control unit to raise, lower or hold the load in an intermediate position. When holding in an intermediate position, the control unit constantly energizes the valve during a first period, after which the control unit intermittently energizes and deenergizes the valve so as to lower the load in stepwise fashion during a second period.
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