It is the only practical system for all mine shafts - inclined, compound, and vertical. It had served the mining industry since its inception with great success until it came to be challenged by the friction (Koepe) hoist in the 1950s. Great depths in metal mines especially in gold mines had resulted in the design and installation of conical and cylindro-conical hoists before World War II but the high installation costs, high moment of inertia of the drums which had reached massive properties of 10.7 m in diameter, the doubtful overall saving in power costs, and the development of multi-layer coiling on drums have ruled out their use as mine hoists. Today, the conventional parallel cylindrical drum hoist is the only type which is still used both above and below ground.
Parallel Cylindrical Drum Hoists
The parallel cylindrical drum hoists may be classified depending on:
Number of drums used
- Single-drum hoists, and
- Double-drum hoists (i) with one drum clutched, and (ii) with two drums clutched.
Number of ropes used
- Single-rope drum hoists, and
- Blair multi-rope hoists.
Methods of drive
- Geared-drum hoists, and
- Direct-driven drum hoists.
Single-drum hoists
These are used in smaller shafts as service or production hoist for single or two-compartment hoisting with or without balance rope. In single-compartment hoisting, either a single unbalanced cage may be used or a cage/skip in counterbalance with a counterweight while in two-compartment hoisting, two cages/skips are used in counterbalance.
A single-drum unbalanced hoist is suitable for small installations, often used for sinking shafts. The drive motor draws considerable energy from the supply when hoisting the loaded conveyance and returns some of it when lowering the empty conveyance. It may be used as a small service hoist when the cost of additional shaft section and guides required for a counterweight or second conveyance cannot be justified. A good proportion of the cost of the drive is in the control equipment. By means of a two-speed gearbox, the hoisting speed can be reduced to 1 m/s for man-riding.
As a service or production hoist with cage/skip in counterbalance with a counterweight, a single-drum hoist can efficiently serve one or more levels, since the location of the counterweight at any time is not important. As a production hoist with cages/skips in counterbalance, the single-drum hoist is best used for single-level hoisting. By designing the counterweight as a service skeleton cage, service facilities can be provided at no extra cost. The peak power required is less than that required for an equivalent unbalanced hoist.
Double-drum hoists
These are normally designed with either one or two clutched drums.
The double-drum hoist with one drum clutched and a cage in counterbalance with a counterweight can be used as a service hoist for serving several levels efficiently, as quick adjustment of rope can be facilitated. It can be used as a production hoist with two cages/skips in balance for one level or multi-level operation.
The main advantages claimed for double-drum hoists with both the drums clutched are that, if something happens in one of the two compartments, the hoist can operate in the other compartment to raise or lower men and supplies, and also that they facilitate rope changing. This hoist is particularly favoured in metal mines.
With continual two-compartment hoisting from more than one level, the use of balance rope is useless, as operation from levels other than for which designed is only possible with an out-of-balance hoist. Also, the use of the balance rope would prevent clutching to the different levels, as the dividers between the compartments would foul the loop of the balance rope. The other disadvantages of a balance rope are: increase in tension of main (head) rope due to vibrations of balance rope; oscillation of the loop during acceleration and deceleration; difficulty of changing the ropes; increase in the weight of the conveyance as well as conveyance suspension gear; and necessity of a guided tail sheave to compensate for variation in effective diameter in a multilayer-coiled drum for deep shafts. In the gold mines of South Africa, a few double-drum hoists with balance ropes had been installed in the past because of the restriction imposed by the power peak demands.
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