Ships from all over the world travel through the Panama Canal every day. In a single year over 14,000 vessels on international voyages, representing approximately 4% of world trade, pass through this famous waterway.
In 1998, the Panama Canal Authority decided to accelerate its mission to upgrade the Canal to meet projected demand increases, as well as to modernize cumbersome mechanical systems and streamline operation and maintenance. One key area identified for upgrade in the $700 million project was the waterway's trademark lock operating system, which was in need of a complete overhaul of its antiquated mechanical design.
In addition to widening of the Gaillard Cut and an increase in the towboat fleet, the modernization effort sought to bring the lock system's mechanical elements, which dated back to the early 1900s, into the 21st century to meet a projected 20% increase in traffic. As part of this effort, Bosch Rexroth Corp's Industrial Hydraulics business unit was awarded a multiyear contract to manufacture new hydraulic systems for the Panama Canal locks' miter gates.
Hydraulic Drives for Lock Operation
The Panama Canal constitutes a 50-mile-long connection between the Atlantic and Pacific Oceans. Winding through one of the narrowest and lowest areas of the isthmus' long, mountainous terrain, the Canal crosses the Continental Divide at an elevation 85 ft above sea level, which is the normal operating level of Gatun Lake, although it can be filled close to 88 ft in elevation. The Canal runs northwest to southeast, with the Atlantic entrance 33.5 miles north and 27 miles west of the Pacific entrance. The average ship requires about 10 hours to travel through the Canal.
A ship may enter from the Atlantic, for example, and sail from Limon Bay at the Cristobal Harbor sea level breakwater to Gatun Locks. It would then be raised 85 ft to Gatun Lake by three lock chambers. The water used to raise and lower vessels in each lock comes from Gatun Lake by gravity through a system of main culverts that extend under the locks from the sidewalls and the center wall. From Gatun Lake the ship would travel 23.5 miles to the north end of Gaillard Cut, at 85 ft above sea level, to the Pedro Miguel Locks. At these locks the vessel is lowered 31 ft into Miraflores Lake. A mile further south, the vessel enters Miraflores Locks and by two lock chambers is lowered another 54 ft to the Pacific Ocean level.
As each ship is raised and lowered in the 110 ft wide by 1,000 ft long lock chambers, it is sealed within the lock on either end by miter gates. Rising stem valves and cylindrical valves are then activated to change the water level, either lifting or lowering the vessel to the next water level ahead. (Miter gates are shown here in closed position, with water out of the chamber.)
Previously, all of the miter gates, rising stem valves, and cylindrical valves had mechanical drives since their inception in the early 1900s. However, over the last six years, Bosch Rexroth has systematically replaced the antiquated mechanical drives of the miter gates with hydraulic drive systems -- effectively improving lock efficiency and functionality and streamlining daily operations and maintenance.
To date, Rexroth has provided replacements for all of the mechanical units that open and close the lock miter gates with hydraulic drives. Each system includes custom hydraulic power units using Rexroth AA4VSO pumps, custom manifolds, stainless steel tanks, piping, and safety and instrumentation items, plus customized hydraulic cylinders with base mounting attachments -- all of which focus on the key criteria of simplified operation and maintenance.
A component of the hydraulic solution, the AA4VSO axial piston variable displacement pump with 125 ccs and EO2 hydraulic displacement control supplies stepless displacement control via a proportional valve with electrical feedback of the swivel angle. The pump is a swashplate design for open circuit operation, and its flow is proportional to the input speed and displacement. The pump is also infinitely variable with adjustment of the swashplate angle, and it supplies a continuous operating pressure of 5,100 psi.
Unique features of the cylinders employed by each gate system are their Ceramax® and CIMS (Ceramax® Integrated Measuring System) technologies. Ceramax® is a proprietary ceramic coating applied by a plasma spray process to the cylinder's rod to enhance the rod's corrosion resistance. CIMS is a highly reliable, failsafe, and accurate stroke measuring system that works with Ceramax as a position feedback device. Advantages of CIMS include unlimited stroke length, accuracy, ease of interfacing, and the ability to replace or service while the cylinder is installed. (Each cylinder is operated by one power unit, like the one shown here.)
A Complete Turnkey Solution
One condition for replacement of the old mechanical drives, according to Rexroth systems engineer Louis Prieto, was that the new hydraulic cylinder assemblies conformed to the original mounting pads on the miter gates and construction footprint on the concrete floor. In addition to hydraulic power units and cylinders, Rexroth supplied the associated electronic controls, including the central control systems, data acquisition, and data logging for all lock operating machinery.
Furthermore, for a complete turnkey system, Rexroth also supplied and assisted with the installation of all interconnecting piping. On another application at the canal, Rexroth supplied hydraulics for a large number of locomotive winch drives, which are used to guide the ships safely through the locks by providing stable positioning to avoid accidental damage to the ships and the locks. (Shown here, the hydraulic cylinder is mounted to the cardanic ring, which was designed to adapt to the existing footprint.)
"The specially designed and manufactured control system, including PLC, Ethernet, and fiber optics, has become the backbone of the complete lock operating machinery," explained Prieto. "The PLC-based control system communicates via fiber optic technology with a backup Ethernet link. It's all part of the central data system."
Previously, the control sequence used handles for each lock station. This required the operator to reach and manually turn handles until the lock was at the appropriate position. Now, with the hydraulic upgrade, the operator controls the lock from one station, eliminating the need to manually turn the control handles. As a result, there is also a reduction in the manpower required in the control room. Operators can also monitor performance, allowing for maximum operating efficiency and streamlining data acquisition for preventive maintenance.
Benefits of the Upgraded System
"The hydraulic technology has generally reduced the maintenance requirements, inventory stock, and operations downtime," said Carlos G. Patterson, Panama Canal project engineer program coordinator for the Locks Division and leader of the design and implementation team of the Machinery and Control Systems Conversion. "It has also increased the level of technical knowledge among engineers and technicians."
Prieto agrees. "Today, unlike before, there is the ability to schedule maintenance, such as changing filter elements during a regularly scheduled outage," explained Prieto. "Furthermore, the hydraulic cylinder requires no regular maintenance." (The hydraulic cylinder is attached to the miter gate. Bosch Rexroth's black Ceramax piston rod coating, seen here, helps alleviate friction and protect against corrosion.)
To date all 80 of the Panama Canal's miter gates are working well with Rexroth hydraulics and controls, which have successfully delivered the increased reliability and reduced downtime sought by the Panama Canal Authority.
"Since the conversion to hydraulic technology, the canal has consistently improved its throughput," adds Patterson. "Although this is a result of a combination of several changes or improvements, the hydraulic technology has been an important contribution."
The Authority and Rexroth are currently working to upgrade vehicular gates by converting the old mechanical drives to hydraulic drives similar to those for the miter gates.
