As commonly used in vertical transportation appliances, hydraulic crane plays a significant part.
During the process of lifting, commodities are lifted by drum propelled by rotation of hydraulic motor.Different in lifting hydraulic system of various types, the basic design idea of different factories is the
same. Lifting hydraulic system generally consists of electrical machine, oil pump, safety valve, change
valve, pressure gage, balanced valve, motor or hydraulic cylinder, pipeline and some other components.
Electrical energy can be transferred into hydraulic pressure energy by motor drive hydraulic pump and
then into mechanical energy drive load by motor or hydraulic cylinder propelled by control valve. With
general adoption of bidirectional meter out regulative system, hydraulic system can control commodity
ascension and descension speed effectively. Hydraulic lock or speed limit lock is launched within the oil
way so as to guarantee that hydraulic cylinder can stay in any position at any time during operation in
avoidance of the danger of commodities’ self-descension due to instantaneous power cut or the tripping of
air switch. Security settings of overload protection and hydraulic pressure should be launched in
hydraulic system[4-5]. The setting pressure of relief valve should be no greater than 110%of working
pressure the system specified and the pressure specified by the system should be no greater than the
setting pressure specified by hydraulic pump. Working pressure of relief valve should be adjusted before
lifting operation and should be restricted within the maximum allowable working pressure. A Hydraulic
lifting system is shown in the following figure.