| 摘要 |
<p>A multiple speed hoisting system has a first fluid circuit, with a maximum effective cross-sectional area for hoisting heavy loads at low speed, and a second fluid circuit, with a smaller effective cross-sectional area for hoisting lighter loads at higher speed. These circuits are separately actuated by a valve that is responsive to a regulating means for selectively positioning the valve. A pressure operated control, that is in flow communication with the second fluid circuit, automatically cancels the influence of the valve regulating means; in response to a predetermined pressure level in the second fluid circuit, and allows the valve to revert to a position actuating the first fluid circuit. Undesirable oscillations within the system between the pressure operated control and the valve regulating means are avoided. In a preferred embodiment of the invention, a pressure switch is the pressure operated control, a solenoid that is actuated by a manual control switch forms the regulating means for selectively positioning the valve, and a relay is provided to stabilize the electrical control circuit, thereby prevent hunting between the pressure switch and the solenoid controlled valve. -la-</p> |
