Fixing a Pair of Loose Hinges
Customer:U.S. Army Corps of Engineers (USACE)
Location:Poe Lock at Sault Sainte Marie, Michigan, USA
Forget about a screwdriver—we’re not talking here about repairing screen door hinges. Think of a double-door pair where each of the doors is 60 feet wide, 40 feet tall, and weighs in the area of 140 tons, and a single “hinge” can weigh considerably more than a ton.
The “doors” we’re talking about here are the gates of the Poe Lock at Sault Sainte Marie, Michigan. The Poe is the largest of the four “Soo” locks, which are said to be among the busiest in the world, passing an average of 8,000 vessels per year.
The locks, part of the St. Marys Falls Ship Canal connecting Lake Superior with the lower Great lakes, compensate for a 21-foot difference in water levels. They are operated and maintained by the U.S. Army Corps of Engineers (USACE). The Poe Lock, rebuilt in 1968, is 1200 feet long, 110 feet wide, and 32 feet deep.
The “doors” of these locks are called miter gates because when closed they form a slight “V” rather than a flat plane. When the lock doors are closed and the water level behind them is raised, the doors face well over a million pounds of force from the water, and the miter design helps to withstand the force.
On massive “doors” like these, how do you tell when the “hinges” are becoming worn? Much like an ordinary door, you monitor for looseness. “The miter ends of the gates had developed vertical movement. While the top bearing had been serviced at about 10-year intervals, the bottom bearing was the original,” says Kevin Sprague, Chief of Lock Operations.
Each leaf of a miter gate is suspended from two bearings.
The upper bearing is called a “gudgeon pin,” and it functions much like the wrist pin on a piston. The lower bearing, called a “pintle bearing,” carries the weight of the leaf as well as lateral forces. The pintle bearing is formed of cast steel in the shape of a hemisphere.
In spite of their massive size, these bearings aren’t crude. For example, the pintle ball and socket (bushing) are finished to a 16 microinch finish over the contact area.Bearing Service“We replaced the pintle and pintle bushing, re-bored the gudgeon bearing, and tested and repaired the bottom girder web,” explains Kevin Sprague. The overall project required about 10 weeks to complete, from de-watering the lock to re-watering it. A challenge was that the work had to be done during winter months. The busy locks operate for about nine months of each year, then typically close January through March, when the lakes are iced-up. That’s when the work had to be done. A degree of weather protection was provided by a huge “tent” erected over the work area. Drawing on their USACE expertise, the Corps’ crew prepared in advance by building two bridges with rails and pre-building the tent. When the time came to start the work, the giant tent was rolled over the lock gate. On-site boilers delivered several million Btu/hr of heat, but it was a cold job nonetheless. Michael Patterson, engineer for Enerpac, manufacturer of the hydraulic equipment used to lift each gate leaf for the bearing service comments, “Outside temperatures were in the 2–9 F range during our site visit.” Raising each 140-ton gate leaf to service its bearings involved a balancing act as well as heavy lifting. Although the leaf is 60 feet wide and 40 feet tall, it is only 6 feet thick. Accurate, reliable lifting was required to avoid having the gate get out of position or even topple over.
The USACE addressed the lifting requirements by selecting an Enerpac Synchronous Lifting System. The “Sync Lift” system was configured from off-the-shelf components, the only customization being programming of the system’s digital controller. Kevin Sprague explains that in the past, gate lifts
were done using manual control of lifting cylinders. That was a very tedious process involving constant checking of measurements. In addition, he points out that safety is a concern in lifting a tall, thin, heavy structure. The system incorporates pilot-operated check valves, so that “If there’s a hose failure, the system locks up,” says Mr. Sprague. The Sync Lift system delivered far better accuracy, consistency, and safety than manual control methods. Each cylinder was accompanied by a stroke position sensor that continuously fed data to the digital controller. With a view toward other applications in the future, the Corps purchased double-acting cylinders with 200 ton capacity and 12-inch stroke, fitted with saddles. The cylinders incorporate locking rings for extra safety. For hydraulic power, the Corps chose a highly portable 7.5 hp electric pump As an extra safety precaution, horseshoe shims were inserted at lift increments.
Although the Sync Lift System could have accurately raised each gate leaf in a matter of minutes, nobody wanted to take any chance of dropping one of these monster “doors,” so the Corps took a conservative approach and spread each lift over one work shift, raising a leaf in 0.2-inch increments In addition to all parts of the lift system performing flawlessly in spite of the cold operating environment, the Sync Lift feature provided peace of mind by eliminating the possibility of human error in controlling the lift.
A Practice Run
USACE personnel turned out to be above-average in their ability to absorb the details of the Sync Lift system. “We’re comfortable with hydraulics, because we have so much hydraulic equipment,” comments Kevin Sprague.
After receiving training by Enerpac engineers, the USACE crew decided that an excellent place for a “practice run” with the Sync Lift system would be to lift the work barge stationed at the lock gate. The cribbing beneath the barge had shifted and semi-toppled. Corps personnel set up the Sync Lift system using five of the 200-ton jacks, lifted the barge and renewed the cribbing.
The Bottom Line
The Synchronous Lifting System provided a high level of accuracy, consistency, reliability, and safety under harsh
working conditions. How harsh? One indicator is the numerous highly instrumented cars with anufacturer plates to be found in this locale. It turns out that some auto manufacturers favor this region as cold weather testing grounds.
Rob Faragher is North Central Area Manager of Field Sales for Enerpac (www.enerpac.com) and Corey Reynolds is an Integrated Solutions Applications Engineer. Illustrations: USACE.