Many will have experienced the situation where a lift table is set to a specific height, they have gone home for the evening, and when returning in the morning they find that the lift table has dropped a significant height from the position they had left it in the night before. Drift, or vertical creep, is defined in Pentalift’s Glossary of Terms as the following: Drift – the action of a lift platform slowly lowering on its own, usually due to slight internal hydraulic leaks (through valves) or inability of a brake to hold a motor. The current applicable standard for fabrication of industrial scissor lifts is ANSI MH29.1:2012. In Section 4, Responsibilities of Manufacturers, element 4.7, MH29.1 states that drift “shall not exceed 0.5 percent of the maximum vertical travel of the platform over a period of 15 minutes under full load at any position of the platform. All hydraulic systems will experience drift unless they are mechanically prevented from doing so.
So what can be done if the application requires that the table does not drift? There are valves that can be added to the hydraulic circuit that will help minimize the drift. Adding solenoid holding valves will definitely help minimize the vertical creep. Adding a manual Water, Oil, Gas valve, or WOG valve will provide the ability to manually shut off the flow of fluids which will do an even better job of minimizing the drift. With that said, there is no hydraulic method alone that will completely eliminate drift. The simplest and only method to truly ensure zero drift is to have mechanical stops that can be dropped in and prevent the table from lowering. Other solutions would really be compensating for the drift rather than preventing it, using limit switches and logic relay to sense when the table lowers and for the power unit to automatically momentarily activate and raise the table back to the same position, although this is much more complicated and expensive. Contact your Pentalift Sales Representative for more information.