Case Study:
Getting the Right Capacity Dock Lift

A customer reported that its 5,000-lb warehouse dock lifts were lasting two to three years, but since they were a huge improvement over other models, was very happy with them. In disbelief, since lifts last 10-15 years, the lift manufacturer requested that his team observe a week’s typical operation of the grocery chain.

At first everything seemed normal. The trucks were unloaded one pallet at a time and the pallet weights were 400 to 3,000 lb each. On the second day the milk delivery showed up. The deliveryman started to wheel off stack after stack of milk crates. He placed each stack in a row along one side of the lift. Then he started a second row and then a third. When he was done he had all of the crates stacked up on one half of the lift. He next lowered the lift and hauled them all inside. He came back out and did the same operation a second time. When finished with the full crates, he loaded stacks of empty crates on to the lift, raised them up to the truck and left.

Over the next few days no delivery had a load that weighed more than about 3,000 lb. On day five, a Friday afternoon, the milk delivery for the weekend came. A different deliveryman took the stacks of milk crates off the truck and onto the lift, just as before. On his third load the observers walked over and asked him why he was unloading so many crates at a time and on one side. His answer was not surprising: “because it is faster to only make three large trips and I need room to move.” After a quick calculation the observers noted that each load of crates that was brought to the ground was nearly 7,000 lb.

A 5,000-lb dock lift is designed to lift a 5,000-lb centered load. There is a pressure relief valve designed to bypass the system if the load is heavier than the rated capacity. If the deliverymen were trying to lift the load it would not have lifted and they would have known the load was too heavy. Since the lifts are gravity down, the loads of milk were lowered without utilizing the pump and motor. Adding to the problem was the placement of the loads: 7,000-lb loads were on three quarters of the platform. This presented the lift with a load that was much heavier than that it was designed for. Plus, the loads were offset with the majority of the weight over only one leg set.

The manufacturer suggested that the grocery chain make its lift pits deeper and go to 8,000-lb capacity lifts. The immediate response was that re-pouring the pits and larger capacity lifts would be cost prohibitive. After the manufacturer pointed out that it would take only five years to recover costs if lifts did not need to be replaced every two to three years, the chain decided to go with the 8,000-lb lifts and are now seeing 10-15 years of service life. The new and appropriate lifts paid for themselves more than twice over. The lessons learned are to size the lift for the worst-case scenario and to understand an off-centered load will affect the life of the lift. It does not matter if the weight is lifted or lowered, the lift has to be rated for the weight.