Hydraulic hooklift hoists are mounted on heavy duty truck

Truck

A truck or lorry is a motor vehicle designed to transport cargo. Trucks vary greatly in size, power, and configuration, with the smallest being mechanically similar to an automobile...

s to enable hauliers to change out flatbeds

Flatbed truck

A flatbed truck is a type of truck which can be either articulated or rigid. As the name suggests, it has an entirely flat, level 'bed' body with no sides or roof...

, dumpster bodies

Dumpster

A dumpster is a large steel waste receptacle designed to be emptied into garbage trucks. The word is a genericized trademark of Dumpster, a American brand name for a type of mobile garbage bin...

, and similar container

Shipping container

A shipping container is a container with strength suitable to withstand shipment, storage, and handling. Shipping containers range from large reusable steel boxes used for intermodal shipments to the ubiquitous corrugated boxes...

s. Primarily used in conjunction with tilt frame bodies and specialised containers, generally designed for the transportation of materials in the waste

Waste

Waste is unwanted or useless materials. In biology, waste is any of the many unwanted substances or toxins that are expelled from living organisms, metabolic waste; such as urea, sweat or feces. Litter is waste which has been disposed of improperly...

, recycling

Recycling

Recycling is processing used materials into new products to prevent waste of potentially useful materials, reduce the consumption of fresh raw materials, reduce energy usage, reduce air pollution and water pollution by reducing the need for "conventional" waste disposal, and lower greenhouse...

, scrap

Scrap

Scrap is a term used to describe recyclable and other materials left over from every manner of product consumption, such as parts of vehicles, building supplies, and surplus materials. Unlike waste, scrap has significant monetary value...

 and demolition

Demolition

Demolition is the tearing-down of buildings and other structures, the opposite of construction. Demolition contrasts with deconstruction, which involves taking a building apart while carefully preserving valuable elements for re-use....

 industries.

The system employs a series of hydraulic ram

Hydraulic ram

A hydraulic ram, or hydram, is a cyclic water pump powered by hydropower. It functions as a hydraulic transformer that takes in water at one "hydraulic head" and flow-rate, and outputs water at a higher hydraulic-head and lower flow-rate...

s to hook, lift and hoist the container onto the chassis

Chassis

A chassis consists of an internal framework that supports a man-made object. It is analogous to an animal's skeleton. An example of a chassis is the underpart of a motor vehicle, consisting of the frame with the wheels and machinery.- Vehicles :In the case of vehicles, the term chassis means the...

 of the truck. There are several configuration options, and strict guidelines which must be followed to ensure that the container is secured on the truck in transit.

Load Capacity

Lift and dump capacities of hydraulic hooklift hoists typically range from 8000 to 68000 lb (3,628.7 to 30,844.3 kg). Generally a hoist is capable of lifting (off the ground) and dumping (onto the ground) the same maximum capacity, although there can be exceptions where short wheel bases are involved.

The ratio of container length to chassis length is a factor in achieving rated load capacity. This ratio determines the load angle, and all hooklift hoist systems indicate a recommended range of body lengths, typically 3 – difference in length between the container and the chassis. Container bodies shorter than the recommended length produce substantially steeper load angles, and consequently lower load rating, than those of the longest bodies intended for use with a particular hoist.

Chassis frame height is also important, as the lower the chassis frame height, the lower the potential load angle. A combination of low chassis with the longest recommended body lengths offers the best case.

Finally, hook height has an effect, as a taller hook height achieves a greater lift and dump capacity.

Hydraulic system

Hydraulic machinery

Hydraulic machines are machinery and tools that use liquid fluid power to do simple work. Heavy equipment is a common example.In this type of machine, hydraulic fluid is transmitted throughout the machine to various hydraulic motors and hydraulic cylinders and which becomes pressurised according to...

 

The hydraulic operating pressure of all hooklift hoists are preset at the factory to achieve the intended lifting capacity for the design application. The original approach used by early European models, still widely used today, was a high pressure / low volume system. This setup suits chassis with space restraints, allowing for use of a smaller piston pump

Axial piston pump

An axial piston pump is a positive displacement pump that has a number of pistons in a circular array within a cylinder block. It can be used as a stand-alone pump, a hydraulic motor or an automotive air conditioning compressor.-Description:...

 and a smaller hydraulic reservoir. Such systems operate between 4000 to 5800 psi (27,579 to 39,989.6 kPa).

The North American market developed low pressure / high volume systems, which allowed operators to share the hoist's hydraulic system with other hydraulically powered devices. These systems typically operate with a larger gear pump

Gear pump

A gear pump uses the meshing of gears to pump fluid by displacement. They are one of the most common types of pumps for hydraulic fluid power applications. Gear pumps are also widely used in chemical installations to pump fluid with a certain viscosity...

 and larger hydraulic reservoir. Operating pressures range from 2000 to 3500 psi (13,789.5 to 24,131.7 kPa).

Jib system

There are two common types of jib system, each controlled by a single hydraulic cylinder

Hydraulic cylinder

A Hydraulic cylinder is a mechanical actuator that is used to give a unidirectional force through a unidirectional stroke. It has many applications, notably in engineering vehicles.- Operation :...

. Both systems can be used with either a single or dual rear pivot section.

• The articulating jib, also referred to as a tilting jib, is a simple a-frame
  A-Frame
  An A-frame is a basic structure designed to bear a load in a lightweight economical manner. The simplest form of an A-frame is two similarly sized beams, arranged in a 45-degree or greater angle, attached at the top...
  
  . When extending the cylinder, the container/body is pushed up and back, exiting the rear locks. When retracting the cylinder, the container/body is pulled forward and down, engaging the rear locks.
• The sliding jib consists of a single arm, composed of a tube inside a tube. 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.

Rear pivot section

• The single rear pivot system is the simpler of the two rear pivot designs. Every function operates relative to a pivot
  Lever
  In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...
  
   point, typically located in front of the rear axle. This design does not allow traditional tip-dumping capabilities.
• The dual rear pivot system is more complex, offering the added benefit of a traditional tip-dumping capability. This is achieved by pivoting at the rear of the hoist, typically behind the rear axle.

Rear lock system

There are typically two styles of rear lock. Both styles can be located on the hoist such that they are positioned either on the inside or outside of the container/body long rails.

• The prong style rear lock offers a container/body engagement of up to 7 in (178 mm). This design allows restricted weight transfer while the container/body remains inside the rear locks.
• The slide through style rear lock offers a container/body engagement of up to 50 in (1,270 mm). This style typically allows more extensive weight transfer while the container/body remains inside the rear locks.

Lift/dump cylinder(s)

Two configurations are typical, both suitable for either single or dual pivot designs.

• The single lift/dump cylinder
  Hydraulic cylinder
  A Hydraulic cylinder is a mechanical actuator that is used to give a unidirectional force through a unidirectional stroke. It has many applications, notably in engineering vehicles.- Operation :...
  
   design reduces unit cost, retains true hooklift capabilities, but can be unstable while dumping on uneven ground.
• The dual lift/dump cylinder design, whilst increasing unit cost, improves load handling stability when dumping on uneven ground.

Safety features

A series of safety valve

Safety valve

A safety valve is a valve mechanism for the automatic release of a substance from a boiler, pressure vessel, or other system when the pressure or temperature exceeds preset limits....

s act to ensure safe operation of the system.

• Counterbalance valves, also called load holding valves or over-center valves, serve as hydraulic resistance to the actuating cylinder when the load weight is required to be held in position for a period of time. These come in two distinct configurations, both highly effective in improving load handling safety during a loss of hydraulic pressure: essentially locking the lift/dump cylinder in-place, preventing potential free fall of the load in the event of hydraulic failure.

* Remote mounted system, in which the counterbalance valve is mounted outside the cylinder. This is the more cost effective solution, but can be prone to damage.

* Integral system, in which the counterbalance valve is built directly into the main cylinder, eliminating the potential for damage by falling debris.

• Jib safety valves are not a feature of all systems, but are designed to render the jib cylinder inoperable during the dump cycle. This protects the system from damage should the operator accidentally pull the wrong control lever during the dump cycle.

• The hook latch covers the opening in the hook head, effectively securing the lift bar inside the hook head during transport and dump. It is designed to augment the rear lock system during transit

• Some systems utilize proximity switches to indicate to the operator which part of the lift/dump cycle is current, or whether there is a fault in the system. These can me mounted in a variety of locations throughout the hoist. When activated, a red warning light and/or alarm sounds in the cab.

• Below grade reach is the distance that the hook head travels below the lifting bar on the container. This distance varies between hoist systems, ranging from 1 to 24 in or 25.4 to 609.6 mm. A below grade reach of 5 in (127 mm), or greater, improves stability when working on uneven ground.

Cab controls

Cab controls can either be operated by cable, air or electricity. Both cable and air controls, in a floor mounted lever configuration, offer additional benefits in controlling the load, by feathering the controls.

• Cable controls
  Control system
  A control system is a device, or set of devices to manage, command, direct or regulate the behavior of other devices or system.There are two common classes of control systems, with many variations and combinations: logic or sequential controls, and feedback or linear controls...
  
  are the least expensive, and are commonly floor mounted levers. They are generally favored in cold weather environments.
• Air controls can be installed as floor mounted levers or dashboard mounted switches.
• Electric controls are the most expensive and only come as dashboard mounted switches. The disadvantage of these systems, is that the control is either on or off, and thus controlling the load by feathering is not an option.

Advantages

The flexibility offered by the hydraulic hooklift hoist system offers several advantages:

• Reduced licensing fees through reduced fleet size
• Ground level loading and unloading
• Exact positioning (dropping off) of containers
• Ability to get in and out of tight spaces
• Quick exchange of containers: system allows container to be lift/dropped in around 90 seconds
• Ability to engage a container up to 30º off center when picking up
• No cables to hook up, unhook or that could potentially break
• Complete in-cab operation

Disadvantages

The main disadvantages of the system are revealed on uneven ground:

• If below grade reach is small, it can be difficult to set down or pick up container
• Load handling stability, particularly while dumping, can be compromised at maximum dump angle. This is particularly the case in single lift/dump cylinder configurations
• Container lengths are fairly inflexible, as hooklift hoists are designed to carry bodies within 3 to 5 ft (914.4 to 1,524 mm) of the shortest recommended body

External links

• Diagram demonstrating different types of container arrangement: Bilitewski, B., Härdtle, G., Marek, K. (1997) Waste management p.84. Springer ISBN 3540592105.