Hydraulic hooklift hoist
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[edit] PRESSURE & FLOW
Hydraulic Oil Pressure = Capacity
Turning up the system's pressure will equate to greater lifting capacities. However, all hooklift hoists come preset from the factory. Doing this will most likely result in system failure, due to overloading and void any remaining warranty.
Flow Rate = Cycle Speed
Increasing the engine speed will allow for faster hoist operation. Use caution, as extended periods of engine reving (above 1,500 RPM) may damage the system and/or pump.
High-Pressure/Low Volume Systems
This was the original approach used by early European models and is still widely used today. This setup appeals to chassis with space restraints, allowing for use of the smaller piston pump and smaller hydraulic reservoir. These systems operate between 4,000 PSI to 5,800 PSI.
Low-Pressure/High Volume Systems
As the concept entered the North American market, it evolved, offering an alternative hydraulic solution. This setup is ideal for operators who require the ability to share the hoist's hydraulic system with other hydraulically powered devices, like spreaders and water tanks. The system typically uses the larger gear pump and larger hydraulic reservoir. Even though tagged as a low-pressure system, it actually operates under medium pressures. These pressures range from 2,000 PSI to 3,500 PSI.
For a quick lesson in hydraulics, visit the Gates Corporation website for Hydraulics 101 or Wikipedia's Hydraulic Machinery.
[edit] JIB
Articulating Jib
This is an a-frame/tilting design and is controlled by a single hydraulic cylinder. It can be used with a single rear pivot section or a dual rear pivot section. When extending the cylinder, this design pushes the container/body up and back, exiting the rear locks. When retracting the cylinder, this design pulls and the container/body forward and down, entering the rear locks.
Sliding Jib
This is a single arm design (tube inside a tube), also controlled by a single hydraulic cylinder. It too can be used with a single rear pivot section or a dual rear pivot section. When extending the cylinder, this design pulls the container/body forward, entering the rear locks. When retracting the cylinder, this design pushes the container/body rearward, exiting the rear locks. The sole reason behind this design was to allow for weight transfer while remaining in the rear locks.
[edit] REAR PIVOT SECTION
Single Rear Pivot
This is the simpler of the two rear pivot designs. In this design, every function operates off a mid-mount pivot point, typically located in front of the rear axle. This design does not offer traditional dumping capabilities, but rather a dump-n-drag style dump. To enter dump mode, it must exit it's rear locks.
Dual Rear Pivot
This is the more complex of the two rear pivot designs. The different manufacturers vary when implementing this design feature. The key behind this design is that it does offer traditional dumping capabilities by pivoting at the rear of the hoist, as seen with traditional dump trucks. If entering dump mode from a transport position, it remains in its rear locks when dumping. If entering dump mode after transferring weight, it may or may not be locked down in its rear locks. Consult manufacturer for more details.
[edit] REAR LOCKS
Prong Style Rear Locks
These locks offer container/body engagement of up to 7". They can be located on the hoist so they are positioned to the inside or outside of the container/body long rails. This design allows for little, if any, weight transfer while the container/body remains inside the rear locks.
Slide Through Style Rear Locks
These locks offer container/body engagement of up to 50", depending on hoist model and manufacturer. They can be located on the hoist so they are positioned to the inside or outside of the container/body long rails. This design allows for extensive travel/weight transfer while the container/body remains inside the rear locks.
[edit] LIFT/DUMP CYLINDER(S)
Single Lift/Dump Cylinder Design
The single lift/dump cylinder design is featured in both single pivot and dual pivot designs. Its offered as a way to help reduce unit costs. It will dump, but use caution when dumping at near max dump angles on uneven ground.
Dual Lift/Dump Cylinder Design
The dual lift/dump cylinder design is also featured in both single pivot and dual pivot designs. It does increase unit costs, but was introduced to help improve load handling stability when dumping on uneven ground.
[edit] COUNTERBALANCE VALVES
Counter-balance valves, also called load holding valves or over-center valves, are normally located between a directional control valve and the outlet of a vertically mounted actuating cylinder that must support weight or be held in position for a period of time. The counter-balance valve serves as hydraulic resistance to the actuating cylinder.
Remote Mounted Outside Cylinder
Remote mounting the counterbalance valve outside the cylinder is the more cost effective of the two designs found in hooklift hoists. The only potential drawback to this design is during the dump cycle, should large or heavy debris come in contact with it, knocking it off or rendering it useless.
Built Directly Into Cylinder
This design eliminates falling debris as a safety issue in both traditional dump trucks and hooklift hoists entering dump cycle. It's an advance over remote mounting.
Internal or External, both designs are highly effective when improving load handling safety. Given a loss in pressure on the retract or extend side, the counterbalance valve locks the cylinder in-place, avoiding a potential free fall while in the dump cycle.
[edit] JIB LOCKOUT VALVE
This feature is not used by all hooklift hoist manufacturers. Those who use it are intentionally rendering the jib cylinder inoperable during the dump cycle. It's main purpose is to prevent the driver from being able to pull the wrong lever while in the dump cycle. This valve is typically found between the jib cylinder and the hydraulic reservoir.
[edit] BUSHINGS & LUBRICATION
Bronze Bushings & Grease Zerks
Bronze bushings used with grease zerks have been around for many years. The soft bronze bushing does require frequent greasing to achieve maximum life expectancy, but is designed as a wear item that can be replaced. It's biggest asset is it's ability to allow new grease to be forced through the pivot joint. Doing so expels all contaminants that may have entered the pivot joint over time or during regular use.
Permanent Lubricated Bushings
Permanent lubricated bushing offer virtually maintenance free operation at the pivot joint. Unlike the bronze bushing and grease zerk combination, there is no way to expel contaminants that may have entered the system over time. It to is a wear item that can be replaced.
[edit] LIFT & DUMP CAPACITIES
You'll find that lift and dump capacities will range from 8,000 lb. to 68,000 lb. This changes from manufacturer-to-manufacturer and from hoist-to-hoist. As a rule of thumb, the hoist generally dumps the same capacity it will pick up. However, there are exceptions to the rule.
Understand there is no standardized rating system for the hooklift industry. Some design for best case, some for middle of the road and others for a worst case scenario. Best case or middle of the road have been designed around a set body length and/or particular hook height. Those using a worse case scenario have designed around the longest container (full) while being picked up off the ground and the shortest container (full) going into a dump. Consult the manufacturer on their particular rating system.
[edit] CAB CONTROLS
There are three possible cab control options; cable, air or electric. Cable controls (most inexpensive option) come as floor mounted levers. Air controls can be installed as floor mounted levers or dash mounted switches. Both cable and air controls (floor mounted lever setup only), offer the ability to feather the load. Electric controls (most costly option) come as dash mounted switches. With dash mounted switches, it's either on or off, feathering the load is not an option.
[edit] HOOK LATCHES
The hook latch was designed to cover the opening in the hook head, securing the lift bar inside the hook head during transport and dump. Some manufacturers implement this design and some do not. Those who don't have made adjustments in the hook head design itself and/or in the rear locks, eliminating the need for such a device.
[edit] PROXIMITY SWITCHES
Some manufacturers utilize proximity switches (electronic control boxes) to indicate you've entered a particular cycle, finished a particular cycle or that something is wrong with the system. Manufacturers who use them will mount them in a variety of places throughout the hoist. When activated, a red warning light and/or alarm will sound in the cab.
[edit] LOAD ANGLES
Load angles are determined by a variety of factors. All hooklift hoist systems state a recommended range of body lengths they were designed to handle. This range is typically 3' to 5' difference in length. Bodies at the shortest or shorter than recommended lengths will offer substantially greater load angles than that of the longer bodies in that same range. Also chassis frame height plays a big factor in this equation.
If loading angle is a chief concern, consider a chassis with a low-profile frame height, using the longest body lengths possible and/or consult the manufacturer for a best case scenario.
[edit] BELOW GRADE REACH
This is the distance the hook head is able to drop below the lifting bar on the container. This distance can vary greatly from hoist-to-hoist and manufacturer-to-manufacturer (ranging from 1" to 18"). 5" or greater is ideal, if working in uneven ground applications. Some hoists (by design) exceed 5" with ease. To find out exactly what the below grade reach is for a particular hoist, consult the manufacturer or check the bid specs.
[edit] ADVANTAGES
• Eliminate the need for seasonal trucks.
• Reduce licensing fees by reducing fleet size.
• Ground level loading and unloading.
• Ability to engage (picking up) a container within 30 degrees (side-to-side) off center.
• Exact positioning (dropping off) of containers.
• Able to fit in and out of tighter space than a cable hoist, due to shorter system lengths.
• Quick exchange of containers. Mount or dismount container in less than 90 seconds.
• No cables to hook up, unhook or that could potentially break.
• 100% In-cab operation.
[edit] DISADVANTAGES
• Below Grade Reach - see detailed explanation above. Use caution, as some hoists do not have ideal below grade reach. This can make it difficult to set down or pick up containers in uneven ground.
• Extras, Above & Beyond - If you want to do something unique, such as a over-the-cab ladder rack or camper, you'll need to get creative or partner with an experienced truck equipment shop who is also a talented fabricator.
• Load Angles - see detailed explanation above. Yes, it is possible that a cable hoist could offer better load angles than a hooklift hoist.
• Container Lengths - a hooklift hoist is not a cable hoist. Hooklift hoists are designed to carry bodies within 3' to 5' of the shortest recommended body.
• Load Handling Stability - while dumping, load stability can be greatly decreased at maximum dump angle. This is more prominent in the single lift/dump cylinder design.
[edit] HOOKLIFT HOIST MANUFACTURERS
• American Roll-off - made in USA.
• Ampliroll - made in France.
• Galbreath/Wastequip - made in USA.
• Multilift - made in Finland.
• Palift - made in France.
• Stellar/K-PAC - made in USA.
• SwapLoader - made in USA.
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