Hydraulic hooklift hoist
PRESSURE & FLOW
Hydraulic Oil Pressure = Capacity
All hooklift hoists are preset, at the factory, to achieve intended lifting capacity. Turning up the system's pressure will increase lifting capacity, but adjusting or tampering with hoist's pressure settings may result in system failure (extreme overload) and most likely void manufacturer's 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 hydraulic 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. This may not be the ideal approach if planning to share the hoist's hydraulic system with other hydraulically powered devices. These systems operate between 4,000 to 5,800 PSI.
Low-Pressure/High Volume Systems
As the concept entered the North American market, it continued it's evolution, 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. This system typically operates with 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 to 3,500 PSI.
For a quick lesson in hydraulics, visit the Gates Corporation website for [http://www.gates.com/brochure.cfm?brochure=2901&location_id=3439 Hydraulics 101] or Wikipedia's Hydraulic Machinery.
This is an a-frame design (tilting), 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, engaging the rear locks.
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, engaging the rear locks. When retracting the cylinder, this design pushes the container/body rearward, exiting the rear locks. This design allows for weight transfer while remaining in the rear locks.
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, the system must exit its 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 (up against the cab), all hoist (regardless of manufacturer) remain in their rear locks when dumping. If entering dump mode after transferring weight (overloaded), the hoist may or may not remain in its rear locks. Consult manufacturer for more details.
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. Depending on all design elements, this style has the potential to allow for extensive travel (weight transfer) while the container/body remains inside the rear locks.
Single Lift/Dump Cylinder Design
The single lift/dump cylinder design is featured in both single pivot and dual pivot designs. It helps reduce unit cost and still offers true hooklift capabilities. While in dump, heed manufacturer warnings when dumping at near max dump angles while 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.
[http://www.hydraulic-equipment-manufacturers.com/hydraulic-pressure-control-valve.html 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 of Cylinder
Remote mounting the counterbalance valve outside the cylinder is the more cost effective of the two designs found in hooklift systems. The only potential drawback to this design is during the dump cycle, should large or heavy debris come in contact with the valve housing, knocking it off or rendering it useless.
Integral - Built Directly Into Cylinder
This design eliminates falling debris as a safety concern 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 for improving load handling safety during a loss in pressure. Should a loss in pressure result, the [http://home.wxs.nl/~brink494/balklep_e.htm counterbalance valve] locks the cylinder in-place, avoiding a potential free fall while in the dump cycle.
JIB SAFETY 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. Its main purpose is to prevent the driver from being able to pull the wrong lever while in the dump cycle. This valve is typically located near the middle to rear of the hoist and plumbed between the jib cylinder and the hydraulic reservoir.
BUSHINGS & LUBRICATION
Bronze Bushings & Grease Zerks
Bronze bushings used with grease zerks have been around for decades. The soft bronze bushing does require frequent greasing to achieve maximum life expectancy, but is designed as a wear item that can be replaced. Its biggest asset is its 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. Failure to grease as instructed could result in an expensive refurbishing effort.
Permanent Lubricated Bushings
Permanent lubricated bushings 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. It is also possible to drill these out and outfit them with a grease zerk at a later time.
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, a hoist generally lifts (off the ground) and dumps the same max capacity. However, there can be exceptions to the rule when dealing with shorter than desired wheel bases.
Understand there is no standardized rating system in the hooklift industry. Some design for best-case, some for middle of the road and others for a worst-case scenarios.
Best Case Scenario
Capable of achieving max lift capacity (off the ground), only when using the shortest recommended body length. Capable of achieving max dump capacity, only when using the longest recommended body length.
Capable of achieving max lift capacity (off the ground) with either the shortest or mid-range (recommended) body lengths. Capable of achieving max dump capacity with either the longest or mid-range (recommended) body lengths. This tends to be the most common method for hoist capacity ratings.
Worse Case Scenario
Capable of achieving max lift capacity (off the ground) with all recommended body lengths. Capable of achieving max dump capacity with all recommended body lengths.
Along with container lengths playing a factor in achieving rated capacities, so do hook heights. This is especially true, as dual hook heights become more common place. Some hoists offering dual hook heights may require the taller hook height to achieve max lift and dump capacities. Others with ratings built around the lower hook height are typically capable of lifting greater capacities than posted rating may suggest. Consult the manufacturer for complete details on posted capacity ratings.
There are three possible cab control options; cable, air or electric. Cable controls (least expensive) 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 expensive) come as dash mounted switches. With dash mounted switches, it's either on or off, feathering the load is not an option.
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 do not have made design adjustments in the hook head itself and/or in the rear locks, eliminating the need for such a device.
Some manufacturers utilize proximity switches (electronic control boxes) to indicate you've entered a particular phase of a cycle, finished a phase of the cycle or that something is wrong with the system. Manufacturers who use them will mount them in a variety of locations throughout the hoist. When activated, a red warning light and/or alarm will sound in the cab.
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 steeper load angles than that of the longest bodies intended for use with a particular hoist. Also chassis frame height plays a big factor in this equation. The lower the chassis frame height, the lower the load angle and vise versa.
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.
BELOW GRADE REACH
This is the distance the hook head travels below the lifting bar on the container. This distance can vary greatly from hoist-to-hoist and manufacturer-to-manufacturer (ranging from 1" to 24"). 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.
• 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.
• 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 an 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.
HOOKLIFT HOIST MANUFACTURERS
• [http://www.americanrolloff.com/ American Roll-off] - made in USA.
• [http://www.dalby.fr/ DALBY] - made in France.
• [http://www.amplirollusa.com/ Ampliroll] - made in France.
• [http://www.galbreath-inc.com/ Galbreath/Wastequip] - made in USA.
• [http://www.hiab.com/ Multilift] - made in Finland.
• [http://www.palfinger.com/palfinger/3235_EN.524D4616555903?pdb_gber_id=6 Palift] - made in France.
• [http://www.stellarindustries.com/ Stellar/K-PAC] - made in USA.
• [http://www.swaploader.com/ SwapLoader] - made in USA.
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