| 摘要 |
This invention relates to a pneumatically operated hoist comprising a housing 10 provided with a suspension means 12,13 for suspension of the hoist from an overhead support, a pneumatically driven motor 15 provided with a first flow passage 75 arranged for serving as a pressurized air inlet during raising of a load and an air exhaust passage during lowering of the load and a second flow passage 76 arranged for serving as an air exhaust passage during raising of the load and a pressurized air inlet during lowering of the load, a load engaging means 16,17 drivingly connected to the motor 15, and a control means 18 for regulating airflow to and from the motor 15. Known such hoists are slow in lowering light loads or too fast in lowering heavy loads safely. …<??>According to this invention the control means incorporate a flow restricting means 77,78 provided in said first flow passage 75 and arranged for restricting flow through said first flow passage 75 during lowering of the load, and a load sensitive shunt valve 41 arranged for providing a second air exhaust passage 69,70 during lowering of a load having a weight below a predetermined magnitude and for closing said second air exhaust passage 69,70 during lowering of a load having a weight greater than said predetermined magnitude whereby more efficient operation is obtained. |
