The simplest machines are hand operated and usually it is the hand chain block which first comes to mind. But there is also the lever hoist, the hand winch and the suspended winch (also known as a pole hoist). This is effectively a hand winch mounted at the end of a tubular pole at the other end of which is a sheave and hook. The rope from the winch passes through the tube and over the sheave to the hook. The whole machine is suspended from a point above the sheave.
The range of lifting capacity for each of these machines varies considerably and may ultimately limit your choice. However, provided your application falls within the available range, the decision can be based on performance.
The main advantage of hand operated equipment in terms of performance is that the speed can be as low as the operator wishes. It is therefore very suitable for precision assembly or installation work where fine control is required. If the required height of lift is short and the operator can reach, the lever hoist can be ideal as it allows sensitive control without the risk of a hand chain getting in the way. If the operator has to stand back a little, the pole hoist offers that facility. To stand back even further, a floor or wall mounted winch can be the solution and also offer greater height of lift, although incorporating the facility to travel is more complex.
All the above can be used in conjunction with the lifting machine structures featured in previous articles in this series and also from any fixed lifting point. There is one other type of manual lifting machine which is usually used in conjunction with a fixed lifting point and that is the jaw winch. Unlike a conventional winch which winds the rope onto a drum, a jaw winch grips the rope in two pairs of jaws operated by levers, opening and closing them alternately as they move to pull the rope through the machine in a motion similar to that of a person pulling a rope by hand. The height of lift is not therefore limited by the capacity of a drum but simply by the length of the rope.
The hand chain block offers sensitive manual control coupled with a very much greater height of lift but, as already mentioned, the hand chain can get in the way. In the days when most hand chain blocks were permanently installed, the length of the hand chain was normally set to just clear the floor. This allowed the loop of chain to hang properly. These days, hand chain blocks are more usually treated as a portable lifting machine and the length chosen is the nearest standard one available. Inevitably this can result in a bunch of chain on the floor or on the load and which can present a hazard if care is not exercised. However whilst the ideal situation is for the hand chain to hang and be operated vertically, all blocks will tolerate sufficient angle for the operator to stand back a little. Indeed some are specifically designed to work with the hand chain pulled from any angle.
There are many makes of hand operated lifting equipment on the market and some manufacturers offer more than one model. There is also a wide variation in cost which to a large extent reflects a difference in quality. The quality may be a matter of the materials used. For example, a machine with a higher grade chain or an alloy body may cost more but weigh less. However it may be a matter of the quality of design, machining, finish, or tolerances between components, in which case it might affect how smoothly the machine operates or how much effort is required. These are points which need to be checked and the only sure way is to actually try out the machine before buying.
With regard to operating effort, this will be in proportion to the load lifted. Consequently, it may be advantageous to use a machine with a higher working load limit and de-rate it to the safe working load required. Do not take this de-rating too far. The brake in many hand operated lifting machines requires a minimum load to operate satisfactorily and it is advisable to avoid lifting a load of less than 10% of the working load limit.
If the lifting machine is used in conjunction with a slewing jib, runway, mobile gantry or crane bridge, then it is likely that a travel motion is required, for which purpose a travelling trolley is employed. There are three basic options: push travel, geared travel and power travel.
Push travel is the simplest. As the name implies, manual force is used to push – but on what? Often the operator pushes the load which, being suspended, swings away until the lifting machine makes sufficient angle to the track to overcome friction. At this point, the trolley suddenly jerks forward. It is not very precise and the higher the track the worse the effect. If the operator cannot get behind the load to push, it is tempting to stand in front and pull. This is potentially hazardous as the jerking motion can cause the load to swing into the operator. This sort of push travel is therefore best left to applications where the track is not too high, there is room for the operator to push without being trapped and precise positioning is not required. A useful variation of push travel which resolves some of these problems is to fit a handlebar onto the trolley. This ensures that the operative can safely push or pull the trolley directly.
A geared travel trolley is moved by means of a hand chain which drives through geared runners on one side of the trolley. It provides very good control and ease of movement even if the track is high. It has some limitations, particularly when used on a runway. Because the hand chain hangs to one side, its weight, together with the effort from the operator, tends to tip the trolley. Under light load or no load condition it would tip, with the possibility of becoming derailed, unless restrained. It is restrained by an anti-tip roller fitted to the opposite side plate and engaging with the underside of the track flange. If the track has joints with plates under the flange, the anti-tip roller will foul on them. There are other ways of joining the track but the buyer should be aware that considerable expense may be incurred if modifications are necessary to avoid this problem.
Power travel trolleys are similar to geared travel trolleys except that the drive is from a motor instead of a hand chain. They are usually only used in conjunction with power operated hoists, which will be the subject of the next article in this series.
Vitali manual chain blocks at CeMAT Asia Vitali manual chain blocks at CeMAT Asia Verlinde’s Stagemaker hand chain block Verlinde’s Stagemaker hand chain block Pfaff has refreshed its Pro range of lever hoists and manual chain blocks Pfaff Pro range The simplest machines are hand operated and usually it is the hand chain block which first comes to mind. But there is also the lever hoist lever hoist Kito CX 003 miniature chain hoist Kito CX 003 miniature chain hoist Rotzler Titan TC 3 crane winch Rotzler Titan TC 3 crane winch
