1.A6.4 PRINCIPLES FOR THE SELECTION OF LIFTING APPLIANCES

Hand operated chain hoists are self-sustaining lifting mechanisms which provide an easy means of manually raising loads with acceptable operative effort. In the case of the larger capacities, they may be intended and arranged for more than one operative. Most chain hoists are designed for vertical lifting operations where the load is positioned directly below the hook although some are designed for use at an angle. They may be used in association with girder trolleys to move suspended loads along suitable tracks, e.g. runways.

The lower capacities are ideal for general use whilst the larger capacities are suitable for less frequent operations. Due to their comparative light weight and ease of installation, they are often used for temporary applications. They are also ideal for applications where no power source is available and are commonly used for maintenance purposes, in general workshops and storage areas where a lifting facility is required.

All modern hand operated chain hoists have a brake mechanism which makes them self-sustaining. However, some old types were not self-sustaining and these types are no longer considered suitable for use.

Some national standards require hand operated chain hoists to have load limited devices fitted.

For specific guidance on the selection and safe use of hand operated chain hoists see SECTION 3 - HAND OPERATED CHAIN HOISTS of this code.

Hand operated chain lever hoists are a self-sustaining lifting mechanism which offers a simple means of raising loads manually through short distances. They are arranged to operate in any position, making them suitable for applications where some pulling may be involved. They may be used in association with girder trolleys to move suspended loads along suitable tracks, e.g. runways.

Hand operated lever hoists are ideal for applications requiring frequent re-positioning. They are often used for short lifting applications, in maintenance work, in the erection of structures and positioning of machinery and other plant.

For specific guidance on the selection and safe use of hand operated lever hoists see SECTION 4 - HAND OPERATED CHAIN LEVER HOISTS of this code.

Machines which use a gripping action to haul a wire rope may be used for both lifting and pulling applications. They are self-sustaining and offer fixed position lifting facilities.

The wire rope passes through the machine and can be stored on a special coiler separate from the machine. This makes them ideal for applications calling for extremely long lifts. They are frequently used for maintenance and construction work. A special version of this type of machine is available for people-carrying applications and they are often used for access and rescue applications.

For specific guidance on the selection and safe use of lifting and pulling machines using a gripping action on the wire rope see SECTION 5 - LIFTING AND PULLING MACHINES USING A GRIPPING ACTION ON THE WIRE ROPE of this code.

Power operated hoists are available in a wide range of designs and capacities. They may be used in association with girder trolleys to move suspended loads along suitable tracks, e.g. runways.

Power operated hoists are self-sustaining. Whilst they may be used for temporary or permanent applications, some designs are only intended for permanent installations. They are widely used throughout industry for general and specific lifting operations, offering quicker operation and less operative fatigue than with manual equipment. Power operated hoists are ideal for repetitive lifting operations, such as on production lines, where long lifting heights are necessary or applications requiring heavy loads to be handled.

For specific guidance on the selection and safe use of power operated hoists, see SECTION 6 - POWER OPERATED HOISTS of this code.

Self-sustaining winches are often used in association with pulley blocks. They offer a means of lifting or pulling loads.

Winches may be built into structures or arranged in association with diverter pulleys to operate on their own. However, it should be noted that they offer a fixed-point lifting arrangement. They can be arranged to occupy less headroom than either hand operated hoists or power operated hoists, and the operative may be remote from the load. They are therefore ideal for use in confined spaces.

The range of designs and intended duties of winches is probably more diverse than with any other type of lifting mechanism. They are often used on construction sites, on vehicle mounted lifting arrangements, in theatres as well as fixed position lifting requirements in factories and stores. A type of winch, known as the suspended mounting hand operated winch or pole hoist, is available for people carrying applications.

For specific guidance on the selection and safe use of winches used for lifting purposes see SECTION 7 - WINCHES USED FOR LIFTING PURPOSES of this code.

As mentioned above, hand operated chain hoists, hand operated lever hoists and power operated hoists are often used in association with travelling girder trolleys. Whilst not themselves a lifting mechanism, trolleys enable the lifting mechanism, together with its suspended load, to be moved along suitable tracks such as runways. They may be separate from the lifting mechanism, which may be suspended by its top fitting to the trolley load bar, or built into the mechanism as an integral item.

For specific guidance on the selection and safe use of travelling girder trolleys see SECTION 8 - TRAVELLING GIRDER TROLLEYS of this code.

Jacks are placed under the load, when the floor or other base on which it stands is capable of sustaining the imposed loading.

Some loads lend themselves to being jacked rather than slung and lifted. Often jacks are used to lift loads a short distance to enable lifting accessories to be attached, which in turn will then be used with other lifting appliances to perform the final lifting operation. Jacks are also commonly used in applications where the load has to be lowered into its final position, such as plant installation.

It is important that jacks are used only on floors or supporting members capable of withstanding the force exerted by the jack base when the load is raised. This is usually on a smaller area than the contact area of the load and therefore greater stresses are imposed. Care must be taken to avoid hidden hazards, such as underground pipes, drains or cables, and the use of floor spreader plates should always be used if the assessment highlights a need to distribute the force over a larger surface area. A wide range of types and designs of jack is available to suit varying applications.

For specific guidance on the selection and safe use of jacks see SECTION 13 of this code.

Where an application requires only a simple suspension point to permit a load to be lifted and lowered and a suitable suspension point or building member is not available, the use of tripods or shearlegs may be an appropriate option. These are particularly suited to temporary applications where a low-cost facility is required. They provide a fixed suspension point from which a lifting mechanism can be supported.

They are usually constructed from tube or light sections and have three, or occasionally four, legs which hinge from the top where the suspension point is provided. Alternatively, they may have provision for a winch to be mounted on the legs with a top sheave over which the rope passes. They are free standing and the legs may have feet or points at their bases.

No specific guidance is given in this code and the manufacturer’s instructions should be sought and followed. It should be noted however that they are suitable for vertical lifting and lowering only as any sideways movement of the load may cause them to become unstable and/or become effectively overloaded due to the increased stresses caused by angular loading. To avoid the danger of inadvertently overloading the legs, it is important that the legs are correctly spread. Safety chains, or similar devices, are often fitted so that the legs are held in the correct position when erected. Under no circumstances should they be altered without the manufacturer’s specific approval.

Where repeated lifting and movement along the same path is required and for general lifting duties, runways fitted with a lifting mechanism incorporating a trolley provide a suitable permanent facility. Runways may form part of the building structure, be built onto the building members or be built into self supporting structures. They may also be used for fixed position lifting when fitted with a beam clamp or suspension eye, (e.g. over lift shafts) but such arrangements are suitable for vertical lifting and lowering only.

Runways may be constructed from standard rolled steel sections or from special purpose tracking. They can be made to any length to suit the application and/or building and may be straight, curved or made to form a continuous loop. The height to the underside of the track will of course depend on the building or supporting structure and the capacity will depend on the size of track section, nature and position of supports. As runways are often custom built, suppliers usually carry out a site survey and will advise on the most suitable design for specific applications.

For specific guidance on the selection and safe use of runways seeSECTION 11 - RUNWAYS of this code.

As an alternative to a permanent runway installation, where an occasional application calls for both lifting and limited movement of the load in a single plane, a mobile supporting structure may be considered. They are ideal for use where there is no runway or the application does not justify a permanent installation. They are, in effect, a runway mounted on its own free-standing supporting structure. Whilst the structure itself is portable, and is usually mounted on wheels or castors for ease of positioning, they are generally unsuitable for movement under load. They are intended to be positioned over the load which can then be raised, moved along the track and lowered.

Various types of mobile supporting structures are available, and designs range from heavy duty supporting structures intended for permanent erection to light duty fold away designs intended for one off lifting operations. The former are often used in workshops and yards and the latter are ideal for maintenance purposes. Capacities vary with the design and it is necessary to consult the manufacturer to establish the available range.

For specific guidance on the selection and safe use of mobile supporting structures see SECTION 12 - MOBILE SUPPORTING STRUCTURESof this code.

Where lifting and movement of the load in all planes is required, consideration should be given to the use of bridge and gantry cranes, which includes light cranes systems. These range from small moving beams with hand chain hoist arrangements to massive bridge structures which incorporate specially manufactured crab units. They are ideal where repeated lifting and movement of loads anywhere within the area of coverage is required.

Bridge and gantry cranes run on tracks, which may be fixed to the building structure or form a self-supporting structure. In other cases, the crane bridge may be supported on a moving supporting structure which runs on rails which are floor mounted. These are known as gantry or portal cranes. A version of the gantry crane, known as the semi-portal crane has one end of the crane bridge supported on a raised track whilst the other end is supported by a leg, usually in the form of an ‘A’ frame, which runs on a floor mounted track.

Bridge and gantry cranes are most commonly used in large workshops where loads have to be transported from one area to another, in assembly plants, in storage areas and warehouses, in outdoor applications such as stockyards and applications where other forms of moving loads may prove costly or be impracticable.

As a wide range of designs is available and cranes are usually custom built from standard components, suppliers should carry out a site survey and advise on the most suitable design for specific applications.

For specific guidance on the selection and safe use of overhead travelling cranes see SECTION 2 - ELECTRIC BRIDGE AND GANTRY CRANESof this code.

Bridge and gantry cranes are generally high cost capital items and for many general applications the cost cannot be justified as the utilization will not warrant the expenditure. In these cases, or where the use of an bridge or gantry crane is impracticable, consideration should be given to the use of slewing jib cranes.

Slewing jib cranes offer a moving runway onto which a lifting mechanism may be fitted to give lifting and limited movement in all planes. The jib arm is cantilevered on a pivot which enables it to slew. Loads may then be lifted and moved to any position within the arc of coverage. They may be mounted onto suitable building columns, walls or similar structures or be built into their own self-supporting column.

They are ideal for use in applications where loads may require to be swung out over the edge of loading docks, buildings and similar operations. They are also widely used in machine shops to lift items in and out of machine tools or on and off work benches etc. and in this context, they are often used to supplement bridge or gantry cranes.

Slewing jib cranes are usually custom built from standard components to suit specific applications. Suppliers will usually carry out a site survey and advise on the most suitable design for specific applications.

For specific guidance on the selection and safe use of slewing jib cranes see SECTION 10 - SLEWING JIB CRANESof this code.

The simplest form of manual operation associated with lifting appliances is by pulling or pushing, either directly pushing on the load or appliance or by pulling on a rope or cord and is usually confined to the travel motion. This is the cheapest method of manual operation and calls for the greatest operative effort. In most cases this requires the operative to be in direct contact with the load and care must be taken to avoid the dangers of uncontrolled loads that can result from careless operation. A clear working area is therefore required to enable the operative(s) to manoeuvre and measures should be in place to ensure the operative is not in the load travel path.

Girder trolleys and appliances with built in trolleys, bridge and gantry cranes and slewing jib cranes are all available with push/pull travel operation.

Reciprocating lever operation is used on hand operated lever hoists, lifting and pulling machines which use a gripping action on the wire rope, most jacks and certain lever operated winches. The necessary effort is kept to acceptable levels by the use of gears or linkages, but this depends on the design of the appliance and varies greatly. In most cases, the velocity (or movement) ratio is high and therefore the operative must move the lever a great many strokes to obtain relatively short movements of the load. This results in a slow operation.

In the case of mechanical jacks, the required effort to raise a load can be high. Part of the mechanical advantage is obtained by the length of the lever bar which can be as long as 2 metres. The space required by the operative(s) must be carefully assessed. Lever operation usually requires the operative to be directly adjacent to the load.

Hand chain operation, where the operative pulls on a chain which turns a drive wheel, is used on hand chain hoists, girder trolleys, bridge and gantry cranes and for the slewing motion on jib cranes. The necessary effort is kept to acceptable levels by the use of gears but varies greatly with the design of the appliance. As with lever operation, the velocity (or movement) ratio is high and therefore the operative must pull a considerable length of chain to achieve comparatively short movements of the load. This results in a slow operation. In most cases hand chain operation requires the operative to be directly adjacent to the load.

The use of rotating handles is almost exclusive to winches. Although now rare, hand-wheel drives may also occasionally be used on some types of jack and to drive the slewing motion on jib cranes. In order to keep the required effort to acceptable levels, very high gear ratios are employed. This calls for the operative to revolve the handle or hand-wheel a great number of times to move the load very short distances and the resulting operation is slow. In the case of winches, they can usually be arranged so that the operative is remote from the load. In the case of jacks, the operative is directly adjacent to the load.

Electricity is the most common form of power used with lifting appliances. It is used on hoists, winches, trolleys and cranes to provide power for both lifting and travelling or slewing motions. Although examples of DC supply appliances still exist, AC supply is considered to be the norm. Most types of electric power operated lifting appliances are available for three phase operation. Single phase and low voltage hoists and winches are available in the lower capacities and some types of vehicle winches are available for battery operation.

Pneumatic power operation is used on hoists, trolleys, winches and some cranes. It is less efficient and more difficult to carry to the appliance than electricity. For this reason, it is less common in general use than electricity, but it has many advantages making it more suitable for certain applications.

Hydraulic power is the least common form of power operation associated with lifting appliances, usually being restricted to special purpose equipment and to some types of winch. The hydraulic pressure is obtained by means of an electric or petrol/diesel driven unit. It has many similarities to pneumatic power, the main difference being that where air is allowed to exhaust to atmosphere, oil is kept within a sealed system.

Petrol or diesel driven motors are used to power mobile cranes, winches, crawler cranes, telescopic handlers, kerb handler, etc. thereby providing a means of power operation where no other power source is available. One of the main disadvantages of petrol and diesel engines is the production of toxic fumes. They are therefore only suitable for use in outdoor applications or where very good ventilation is assured.

Various methods of supplying power to electric power operated appliances are available and, to some extent, the method selected depends on the specific application. Although variations exist, the main electric power feed systems are:

Bare wire conductors were very common in the past, but they are now considered unsuitable for new installations due to the inherent danger to personnel. They may still be found on older installations. In these cases, their continued use should be investigated, and an assessment made of the risk, e.g. they may be safe by virtue of their position. Where any doubt as to their safe use exists, they should be changed to an alternative system.

All of these systems permit movement of the appliance. Fixed-position, permanently installed appliances can of course be wired directly to the supply and trailing cables, with plugs, can be used for temporary fixed position equipment.

It should also be noted that the power feed system must include an earth as the practice of earthing through trolley wheels is no longer considered acceptable. In addition, in the case of a three-phase supply system, the earth must not be used as a neutral. If required a separate neutral conductor must be included.

Bare wire conductors were at one time the usual method of supplying power both along the gantry and across the crane bridge. The conductors were tensioned between insulated anchor points at each end and supported at intervals by insulated brackets. The connection to the conductor was usually by a conducting wheel or shoe which travelled under the wire, lifting it from the insulated supports as it passed.

This system has the disadvantage that the conductors are exposed. Although usually safe by virtue of their position, in time the wire will break and fall whilst still live. The consequences are then a matter of luck but can obviously be serious. This can be addressed by additional guards, but they can make the system difficult to maintain and it is likely to be more economical to replace the system. Because of the potential dangers, bare wire conductors are no longer considered acceptable and any remaining systems should be reviewed in the light of current legislation.

With a coiled cable (Figure 1.A6.4.6.3-1 ) the supply cable is coiled in the manner of a tension spring giving an extension ratio of approximately 3 to 1. This system is suitable for short travel distances only due to the sag in the cable. Not only will a hanging loop of cable be a potential hazard, but cable sag causes a drag on the trolley which, in the case of push/pull units, can pull the trolley back along the runway track. By positioning the cable in a central position, double the length of coverage may be achieved. Coiled cable may be used on curved runway tracks.

With a festooned cable (Figure 1.A6.4.6.4-1 ) system, the supply cable is looped along a taut wire or ‘C’ rail running parallel to the runway track. Small sliding hangers or trolleys, from which the cable is suspended, allow it to move freely back and forth whilst maintaining the power supply. The cable may be of circular or flat-form construction, the latter being the most common. Taut wire systems are limited to lengths not exceeding 30 metres due to sag in the support wire and are only suitable for use in straight runs. They are however ideal for dirty and dust laden environments. ‘C’ rail systems are not limited in the same way. They are therefore suitable for longer runs and some types are suitable for applications which include bends. However, they are unsuitable for use in areas where a build-up of dust or other deposits can form in the rail. Both types are limited by the space required to house the bunched-up cable when the appliance is at the end of the runway track.

Festoon conductors have the advantage that the electrical connection is permanent and does not depend upon a sliding shoe which will require maintenance. However the disadvantage is that they are limited in length because space is required to accommodate the loops when bunched close. They are often used to supply the power across the bridge of electric bridge and gantry cranes and are suitable to supply power along short runway tracks.

There are several distinct variations of this type, but they all work by storing the power supply cable on a drum and paying it out to allow movement. Some incorporate a spring to reel in the cable. When the cable reeling drum is positioned high up, the spring also provides sufficient tension to hold the cable in a shallow loop which can keep it clear of people and obstacles. This system is limited by the size of the drum and, as the cable is always under tension, it exerts a pull on the trolley which can, in extreme cases, cause the travel to be arrested or even cause the appliance to be pulled back along the runway track. However, incorporation of a swivel mounting, or a fairlead enable them to be positioned centrally and double the length served. Cable reeling drums may be used on curved runway tracks.

Another variation is most commonly used to supply power to portal cranes. These are usually mounted on one of the crane legs and lay the cable into a trough on the ground as the crane moves and cable is paid out. A power drive incorporated into the drum winds the cable back when the travel direction is reversed. These reeling drums can be quite large and accommodate a considerable length of cable. Also, as the cable is not in any significant tension, they can service a long crane track.

In this system (Figure 1.A6.4.6.6-1 , Figure 1.A6.4.6.6-2 ) a linear conductor is enclosed within a protective insulating cover which has a narrow opening on the underside. A sliding shoe connects with the conductor through this opening. For a three phase power supply, four conductors are required, one for each phase and one for the earth.

This system has the advantage of being able to supply power along an almost unlimited length. Because of this it is very suitable for supplying down shop power. Whilst some voltage drop will inevitably occur with long lengths, it can be countered by connecting the supply at the mid point or in extreme cases, at several points along the length.

A variation of this type is the shrouded conductor system in which the required number of conductors are enclosed within a single insulating shroud. This type has all the advantages of the individual insulated conductor and is also more compact.

These systems are unsuitable for use in certain environments, e.g. those that would require flame proofed or explosion proofed equipment. They are ideal for long travel distances and may be used on curved runway tracks.

In this system, Figure 1.A6.4.6.7-1 , the conductors are encased in an articulated chain which lays in a trough. Cross bars along the length of the carrier can be opened from the outside, so that cables can be easily inserted and plugs connected. Internal separators in the carrier separate the cables. Cables can also be held in place with an integrated strain relief. Mounting brackets fix the ends of the carrier to the machine. Besides only bending in one plane due to the rigid jointed structure, cable carriers also often only permit bending in one direction. In combination with rigid mounting of the ends of the carrier, this can entirely prevent the enclosed cables from flopping in undesired directions and becoming tangled or crushed. Cable carriers are used anywhere on cranes where moving components require power, control and communication power feeds in a flexible media. Energy Chain cable carriers are quiet in operation, lightweight and provide covered cable design that can be quickly opened. They can be used in extreme conditions such as heat-resistant or clean room environments.

It has the advantage that the electrical connection is permanent and does not depend upon a sliding shoe which will require maintenance. They are particularly suitable for feeding power across the crane bridge when the chain can be positioned alongside a bridge girder avoiding the potential hazards arising from suspended cable loops. However, there is a limit to the length which they can service.

Trailing cables, with plug and socket arrangements, may be used in certain circumstances. They enable temporary installations to be made quickly and economically. Although they may be used for short travel distances, their use should be limited as it is undesirable to have long trailing mains voltage cables. The installation must take account of the possible dangers of such a system. Any trailing cable should be suitable for the conditions of service and armoured cable should always be used. When used for temporary installations, it is important that a check is made to ensure the correct phase connection prior to operation of the appliance as the polarity of sockets is not assured.

Modern electric power operated appliances are usually fitted with low voltage control as standard. However older hoists, special purpose hoists, winches and some cranes may not have low voltage control. Low voltage control may be 110 volt or less. Although it is quite common in many European countries to use mains voltage control, low voltage systems at 24 or 48 volt AC or DC, often referred to as Extra Low Voltage, are strongly recommended. Where fitted, this is the voltage at which all components of the lifting appliance control circuit function and is supplied by a transformer within the appliance.

Various types of controls are used with electric power operated appliances. In addition to controlling the hoist/ lower and travel motions and any speed variations, they may include other control functions such as emergency stop, a key switch for isolation of the appliance, etc. Further details for on control types can be found in the specific appliance sections of this code.

Pendant cable suspended handheld push button controls are supplied as standard with hoists. They are also commonly used with bridge and gantry cranes although larger cranes may be fitted with cabs with control panels, older types utilize drum controllers. Pendant control permits the operative to move position during operation whilst still remaining in close association with the load.

For some appliances, e.g. winches, direct online starters may be used. Wall mounted push buttons are suitable for some applications. These are often used for multi-station control applications and are useful in cases where the load has to be lifted through many floor levels or where loads have to be passed from one area to another as they allow the operative to be remote from the load. An essential requirement with this type of arrangement is the provision of emergency stop buttons to override all control positions until manually reset. They should be positioned so that they are easily accessible for the operatives or others who may need to use them. Emergency stop controls should be of a type that must be manually reset, thereby ensuring operatives are able to confirm the danger has passed or take remedial action before it is possible to operate the appliance again.

Non-conductive controls, e.g. infra-red, radio, etc. have become more commonplace in recent years. They are particularly useful in areas where direct access may not be possible as they permit the operative to be completely remote from the load and appliance. It is necessary to have the area scanned before introducing this type of control to ensure that no false signals will be sent or received as the result of interference with other equipment. As this type of control may be operated from any position, the control legends should clearly identify the direction of travel motions with symbols or clearly defined wording, e.g. east, west, etc. The appliance should be marked in a similar way. Such marking must be positioned so that it is clearly visible to the operative from any position.

The working capacity and operational speed of pneumatic power operated lifting appliances relies on the provision of an air supply which is at the design pressure and delivery rate. In the event of the pressure being below that for which the appliance is designed, the actual lifting capacity will be lower than that for which the appliance is rated. Equally, if the pressure is higher than intended, it may, depending on design, be possible to raise a load greater than that for which the appliance is designed, resulting in an overload situation, unless fitted with suitable overload protection. This is a danger which must be averted and this can be done by the provision of a pressure regulator in the air line near to the appliance entry port. If the air delivery rate is below that for which the appliance was designed, the operational speed will be slower than intended.

Unless steps are taken to remove it, moisture will condense in the air line and in the appliance. Although the complete removal of moisture is impracticable a suitable filter/drainer should be placed in the air line to limit this. This should be positioned at a low point in the air supply line and before any coiled or spiral hoses.

Due to the self-purging nature of air motors and the associated loss of lubricant, a regular supply of lubricant is necessary. This can be provided by an oil mist lubricator. Lubricators should be placed in the air feed as near to the appliance entry port as possible.

The air supply line should be fitted with a suitable valve to enable the appliance and its associated feed to be disconnected from the air supply. Such valves are part of the feed system which is considered to start at this point.

Although the air feed system may be plumbed directly onto the air supply line, the use of bayonet connectors has advantages. They enable appliances to be more easily removed for maintenance, relocation or storage. They also permit the ready replacement of worn or damaged hoses.

There are three main methods of feeding the air supply to pneumatic appliances:

With a coiled hose, the high-pressure hose is coiled in the manner of a tension spring giving an extension ratio of approximately 3 to 1. It is normally supplied with an extended length of 3 metres, but due to stiffness and the drag imposed on the appliance, it is best suited to shorter travel distances. In the case of push/pull units, this drag can cause the trolley to be pulled back along the runway track. By positioning the coiled hose in a central position, double the length of coverage may be achieved. Coiled hose supplies are suitable for use on curved runway tracks.

With a festooned hose system (Figure 1.A6.4.7.3-1 ), the high-pressure hose is formed in a loose spiral. This is supported by a taut wire which passes through the centre of the spiral and runs parallel to the runway track. The hose is then free to slide back and forth along the taut wire. Some drag is imposed on the appliance and large hanging loops of high-pressure hose can be a possible hazard. A further limit to the length of this system is the space required to house the bunched-up hose when the appliance is at the end of the runway track. Festooned hose air feed systems are suitable for use on straight runway tracks only.

With a hose reeling drum, the supply hose is stored on a spring-loaded drum and is paid out and recovered as the appliance travels the runway track. This system is limited by the size of the drum and, as the hose is always under tension, places a drag on the trolley which in extreme cases can cause the travel to be arrested or even cause the appliance to be pulled back along the runway track. By positioning the reeling drum in a central position, double the length of coverage may be achieved. Hose reeling drums may be used on curved runway tracks.

Fixed-position, permanently installed appliances may be connected directly to the air supply line with suitable rigid tubing. However, it may be desirable to have a short flexible hose and bayonet connector feeding to the appliance to enable it to be removed for maintenance or storage.

The control of pneumatic equipment is very basic, requiring the simple opening and closing of a supply valve but this can be achieved in several ways.

The most basic method of control is the pull cord. This is the simplest option and is commonly used on pneumatic power operated hoists and trolleys. The motor control valve is fitted with a double lever arm from which the control cords are suspended. By pulling on the cord, the operative directly opens the control valve in the selected direction. An alternative to this is the twist rod control. In this case, the motor control valve stem is fitted with a twist rod. By turning the rod, the operative directly opens the control valve in the selected direction.

Pneumatic power operated winches are often fitted with lever controls. The motor control valve stem is fitted with a lever. By pulling or pushing the lever, the operative directly opens the control valve in the selected direction.

Pendant hose suspended hand held controls are available for use with hoists and winches. The hand held control houses valves which control the motions, either directly or by using air to operate the main control valve. Similar arrangements are used where remote control is necessary although these may include rigid pipe lines.

If the control is remote or utilizes a long pendant control, hose signal delay can occur resulting in over travel of the motion or a delay in commencing the operation. In some cases, electric control systems can be fitted which operate solenoid valves fitted to the appliance. These have the advantage of overcoming signal delay over long distances, but such systems may not be flame/explosion proof.

The use of fibre rope is limited to low capacity manually operated winches and pulley blocks. Fibre ropes are made in a wide range of base materials, each with their own characteristics. Capacity for capacity, a larger size of rope is required than for any of the other lifting media. It is unsuitable for arduous conditions, but man-made fibres have good selective chemical resistance.

Various grades of short link chain are used with hand and power operated hoists and with lever hoists. As a general rule, capacity for capacity, short link chain is the heaviest of the lifting media. As the links are free to articulate fully, one with another, short link chain provides the most flexible lifting medium.

Appliances which utilize short link chain incorporate a pocketed load wheel over which the chain passes, and it is this which provides the means of movement. In the case of power operated hoists, where constant speed of movement for lengthy periods of time is experienced, the action of the chain passing over the load wheel can cause long load chains to oscillate. This can lead to the load swinging and, as a result, manufacturers often impose limits on the extended dimension of their equipment.

As the chain passes over the load wheel, the slack side of the chain hangs freely in a loop. This presents a hazard which, in some cases, can be avoided by the use of a purpose made slack chain collecting box, bucket or bag. It should be noted however that such devices hang below the appliance and therefore restrict the height to which some loads may be lifted.

Chain is suitable for use in most conditions although special care must be taken when selecting the grade of chain for use in chemical and acidic environments and the supplier’s advice should always be sought in these conditions. It is particularly suited to arduous conditions as the effects of wear are less onerous than with other lifting media. To improve wear characteristics, modern chains for use in power operated hoists are case hardened.

Roller chain is used with lever hoists and pneumatic power operated hoists. At one time, it was also used with electric power operated hoists and it is possible that an odd example of this may still be found.

Appliances which utilize roller chain incorporate a load sprocket over which the chain passes, and it is this which provides the means of movement. The pitch of roller chain is much shorter than that of short link chain and, as a result, the movement of the chain is much smoother than that of the latter. This makes it suitable for handling delicate loads and for other applications where this feature is desirable. Roller chain is the most rigid of the lifting media as it only articulates in one plane, making storage of the slack chain more difficult than with other lifting media. The slack chain is usually allowed to hang from the appliance, and it can therefore be an obstruction in certain applications. As a result, roller chain is normally used for shorter lifting applications than the other lifting media.

Roller chain is not suitable for prolonged use in dusty environments as deposits will easily build up in the small spaces between chain rollers.

Wire rope is perhaps the most adaptable of the lifting media. It is used on power operated hoists, winches and lifting and pulling machines which use a gripping action to haul wire rope.

In the case of winches and power operated hoists, the rope is stored on a drum the capacity of which limits the available lifting height. The movement of the rope on and off the drum is very smooth and, as a result, faster speeds of operation are possible than with other lifting media. Some designs of hoist utilize a double start drum. In this case, the bottom hook follows an upward path which is central to the drum. Others utilize a single start drum where the bottom hook moves across the drum as it travels, and this can be restrictive where close end approach, or a true vertical lift is necessary.

Various constructions of wire rope are available to suit most conditions of use and the supplier’s advice should be sought as to the most suitable for the particular application.

The use of flat woven man-made webbing is occasionally used for lifting appliances. It is mostly used on lower capacity manual and power operated hoists. Although it is less resilient to arduous conditions than the other lifting media, it does have selective resistance to chemicals and is less liable to harm delicate surfaces.

Various safety devices are used in lifting appliances to limit the amount of movement, to protect the appliance from the worst effects of overloading or otherwise protect the appliance. These may be essential to the safe use and therefore be fitted as standard or provide additional features to the safe use of the appliance and be available as optional extras. It is therefore necessary to consult the manufacturer’s specification to establish what provisions are made as standard and discuss any additional or special requirements with the supplier.