Valve system for preventing uncontrolled descent in fork lift trucks
US4955461A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Oct 31, 1988 |
| Grant date | Sep 11, 1990 |
| Priority date | — |
| Expiry date | Oct 31, 2008 |
Classification
- Technology area (CPC B)Performing Operations; Transporting
- CPC primaryB66F9/22
- WIPO fieldHandling
- WIPO sectorMechanical engineering
Abstract
A hydraulic lift valve system for fork lift trucks comprising a three way valve including a spool in a bore having a first neutral position, a second lift position and a third lower position. In the second lift position, the spool functions to apply fluid from a source to a cylinder for lifting the fork of the truck only after the pressure exceeds the load pressure and a predetermined value as established by a first poppet valve. Upon shifting to the third position the spool functions to permit exhaust of the fluid in the cylinder and therefore lowering the fork only after a predetermined pressure is established in a pilot valve which permits the first poppet valve to open, thereby insuring that the fork of the lift truck is not lowered unless there is a predetermined load on the fork. By this arrangement, the problem of uncontrolled descent of the fork upon engagement of the fork with an object is obviated.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.