With a closed loop system, the pumps stroke on demand and do not produce any pressure when there is no demand unlike an open loop system. There are no valve bodies, no heat buildup and your pumps have a very easy life compared to the open loop system in an excavator. PLM use hydraulic filtering on the pressure side and the low pressure side of each circuit to ensure only clean oil gets to the components. If you filter only on the low pressure leg, the oil must run through the entire system before it reaches the filters. Essential to the life of the components is temperature. PLM provides a massive hydraulic oil cooler completely separated from the engine radiator. Engine In order to get high line speeds you need horse power. The plms are designed to haul up with full load at 250 ft per minute. Hoisting down is 350 ft per minute. PLM uses any engine maker requested by the customer but the standard is Cummins or Cat. Engine size is chosen such that with all functions running simultaneously at full demand, only 75% of the engine power is utilized. You never run short on power. Slew Bearing PLM uses exclusively Rothe Erde slew bearings with particular features specified by PLM. The bearings are chrome vanadium hardened race with oversize rolling elements and massively oversized capacity. When your machine has its first major overhaul at 40,000 hours, the slew bearing will still be good for another 40,000. The design life for the slew bearing is 1000,000 cycles at full capacity. Automatic Lubrication PLM cranes come standard with automatic lubrication systems to ensure that as the machine is working, all components are receiving grease. All rotating components receive grease, including the head sheaves and slew bearing.

Sheaves PLM build their own head sheaves of nodular ductile iron with hardened tread. the hub is bushed with aluminium bronze. Sheave diameter is 48 inches. Operator's Cab and Controls The operator's cab is raised hydraulically and can be adjusted to suit the operation. The cab is very spacious, is heated, air conditioned, cd player, insulation , overpressure and the best driver's seat you can imagine. Glass is tinted and the interior of the cabin is painted with light absorbing colors to reduce reflection. The crane operates with two joysticks. The right joystick opens and closes the clam and controls hoist and lower. The left joystick controls swing and luff. To open the grab, the operator shifts the right joystick to the right of neutral. The closing winch then pays out until the clam is open. The winches then stop automatically. The operator cannot overpay. To lower down with clam open, the joystick is shifted to the top right corner. The clam opens automatically and both winches pay out. To close and hoist up, the joystick is shifted to the bottom left corner. The first thing that happens is that the closing line hauls in until the the clam is closed. The holding line then hauls until it is carrying 40% of the load. The closing line then hauls until it is carrying 60%. All this happens automatically in a split second without participation of the operator. The two winches then haul together. for the operator, The control is simple. top right corner to open and pay, bottom left to close and haul.

Wire Ropes With duty cycle cranes people generally use low quality ropes. This is because most ropes fail due to mechanical damage. PLMs use the best quality ropes available. Because the drums are single layer and the risk of overpaying and crossing wires over is minimal, mechanical damage is generally not the determining factor in rope life. Ropes will eventually fail by fatigue, not abrasion. Normally you can expect to replace the boom hoist rope every 2000 hours and the winch ropes every 1000 hours. Camera System PLM provides a camera and tv monitor located in the operator's cab to give the driver a view of the winch drums at all times. He can determine at a glance if the ropes are laying properly on the drums. Undercarriage Undercarriage components are Cat. Hydraulic independent track drives are provided with Mannesman Rexroth motors and Lohman final drives. The plm undercarriage will last for decades without any attention and is built to travel daily like an excavator. The crawler side frames are bolted or pinned to the center frame. The side frame and carbody construction is very simple and rugged, built for decades of pounding. Clamshell Bucket PLM evaluates your application and supply a clam that suits your needs. The clam shown below is a 21yd environmental clam on a PLM 2025 crane handling gypsum.

Environmental Features PLM cranes are designed to retain all fluids inside the machinery house which is designed as a saveall. If a hose breaks or component fails, loss of pilot pressure is detected and the system immediately shuts down. Any oil that is lost is retained inside the machinery space. You never need to worry about oil nor fuel spills into the water nor onto the ground. These cranes have hundreds of thousands of operating hours in very sensitive environments with no incidence of contamination of the sea and are built for sea and harbour service Construction of the Upper The upper is a one piece heavy weldment with massive side girders. The weldment is constructed completely, including the boom hinges, winch mountings and slew bearing mounting flange and is then line bored and machined. This type of construction is exclusive to PLM and ensures that when the crane is working hard, all components are maintained in perfect alignment. This is absolutely necessary to achieve the long life needed in a duty cycle crane. Liftcrane Mode PLMs are dual mode cranes. A selector switch is located in the operator's cab to switch from clamshell to liftcrane. In liftcrane mode, the two hoisting drums lock together and the right joystick loses the ability to move the drums independently. If you want to clam in the morning and then switch over to lifting steel coils or magnet, the changeover takes only moments.

Corrosion Protection Steel fabrications are blasted with steel grit to near white metal with a very deep blasting profile. They are then coated with zinc epoxy followed by two coats of epoxy anti-corrosive. A final polyurethane top coat is added. This system is suitable for service on the sea and is standard on all PLM cranes. The photo below shows a PLM 3520 on a 41,000 dwt ship on the North Atlantic. Parts and Service PLM cranes use standard parts supplied by Mannesman Rexroth, Cat, Cummins, and others. There are no parts specific to PLM machines. The part numbers included in the PLM manuals are the original equipment maker's numbers, not PLM numbers so you can buy your parts off the shelf almost everywhere in the world. PLM stock parts for a complete crane of every size at their factory in the Netherlands and have sales, parts and service located in North America in Manheim Pennsylvania at Crane Specialists Inc. and Aring Equipment Ltd in Butler Wisconsin.

Summary If we go back to the original question, should I use a crane or an excavator for my barge unloading operations, the answer depends on the scale of your operation and your lifetime expectations. an excavator is not suitable if risk of oil spill in the water is a problem if the reach is more than about 50 feet if the barge is more than a 15 feet below the dock level if you are moving more than 1200 t/day if you need to stockpile material. if you have long range plans Fuel consumption is high, environmental risk is high, the machines will not last last more than 5 or 6 years, they are expensive to buy, and are not suitable if you expect anything bigger than a 4yd bucket without going to a very large machine. On the plus side, the excavator is easy to operate, will last for the first year or two with very little problems, and will achieve good results for small operations. For less money, better fuel economy, greater capacity, and much longer life, you can buy a 4-rope duty cycle crawler crane. For large scale operations, the PLM 2020 on crawlers with 10yd clam for wet sand is able to achieve more than 1000 tph and instantly converts to liftcrane or magnet crane. This makes a much better choice than an e-crane , is half the cost, twice as useful and is mobile. The PLM 80 is comparable in capacity to a Manitowoc 3950 and the PLM 65 is comparable to a Bucyrus Erie 88b. The PLM 40 and 50 replace a Komatsu 750 excavator. These machines will revolutionize your thinking as soon as you sit in the operator's seat.