| 摘要 |
A pneumatically operated hoist includes 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 as 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 or regulating air flow to and from the motor 15. Known such hoists of this type are slow in lowering light loads or too fast in lowering heavy loads safely. According to this invention the control means incorporates 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.
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