| 摘要 |
<p>A pressure regulating valve (60) is located in the connecting line (50) between two hydraulic fluid chambers (21, 41) in two hydraulic devices, along with the operating devices (63, 65) for the valve. The operating device detects the pressure in the first chamber and opens the valve if this pressure is greater than a pre-determined value representing the maximum load which can be applied to the lifting cable, so that the first hydraulic device (20) allows a lifting cable guide (17) to move in order to reduce the cable length, whilst hydraulic fluid is allowed to flow out of the chamber at the given pressure. A sensor (30) is used to detect the load on the top cable (5) supporting the jib (3) and this sensor is connected to the pressure regulating valve, which is opened if this load exceeds a pre-determined value, so that the first hydraulic device allows the lifting cable guide to move, whilst hydraulic fluid is allowed to flow out of the chamber at the given pressure. The first hydraulic device is connected to the movable lifting cable guide and to the jib or crane frame (2). A second hydraulic device is connected to a hydraulic fluid source so that a constant pressure is maintained inside the second chamber. The two chambers have a variable volume.</p> |
