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September, 1960

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Eppleton Colliery is one of three Durham pits linked together important concentration scheme being carried out by the Durham Division of the National Coal Board. The scheme has been concerned with concentrating their output at one new skip-winding shaft at Hawthorn where new coke ovens and a coal-preparation plant to deal with 750 tons of coal per hour have been built.

In order to achieve this concentration, an extensive system of haulage roadways has been driven to interconnect the three collieries with the new winding shaft. Coal is transported to this shaft in two-ton minecars, in sets of 24, hauled by battery locomotives.

An important feature of the scheme is the method of car spotting and car marshalling at the various loading points. Instead of the usual system employing creepers and retarders, an endless-rope method has been adopted; similar methods have been used with small mine tubs but it is believed that the system used in this scheme is the first to be successfully adopted for minecars. The first installation at Eppleton was completed in September 1959 and at Murton in August 1959.

The layout of one installation is shown in Fig. 1. Coal from two double-unit, flight-loaded faces in the Busty seam is delivered to the loading point. From the final belt conveyor coal is fed to a scraper chain and thence to a loading chute or hopper. This chute feeds coal directly into two-ton mine-cars. The chute gate is hydraulicallyoperated from the control platform, shown in Fig. 2, by an hydraulic power pack.

An Austin-Hopkinson, 15 h.p. "Pikrose" hydraulic hoist drives the endless-rope which draws the minecars under the loading chute. The hoist is the main item of equipment at the loading point and it is this driving unit which has been responsible for providing such a simple, yet efficient, spotting system. The hoist, situated near the loading chute, is shown in Figs. 3 and 4. The endless-rope extends along the locomotive track for about 300 yards with the loading point positioned about midway along its length.

Minecar loading

Trains of 24 empty cars are drawn by battery locomotives from the Hawthorn marshalling sidings to the loading point. Passing the loading point, a locomotive takes its train over a crossover off the main track on to the "loading track." The locomotive then reverses and pushes its train towards the loading chute. After the car nearest to the chute has been clipped to the endless-rope by a Smallman clip, the locomotive is uncoupled: the train is now under the control of the "Pikrose" hoist. It should be noted that the minecars are at no time uncoupled from the train. The locomotive then proceeds back along the main track to pick up a full train.

The Pikrose hoist draws the empty train of minecars under the chute, where it is filled, and then along the track to the marshalling point to await the arrival of a locomotive to draw it to the pit-bottom. As a rule, there are always two sets of minecars on the rope — one being filled and the other waiting on the "empties" side, or one waiting on the "fulls" side and the other being filled. In all, there are three sets of minecars in the circuit for this loading point, and one locomotive handles the three sets.

The Pikrose hoist

The success of such a system depends to a large extent on the versatility of the haulage engine and the degree of control which it has over the minecars on the rope. In this respect, the "Pikrose" hoist may be said to be ideally suited for the job. Manufactured by Austin-Hopkinson and Co. Ltd., the hoist incorporates a hydraulic transmission gear manufactured by Vickers-Armstrongs Limited, and marketed under the trade mark "Pikrose V.S.G." (Variable Speed Gear).

The drive consists of a constant-speed, flameproof, electric motor coupled to a "V.S.G." pump unit (pressure controlled) which delivers oil at pressure, through a control valve to the hydraulic motor, the output shaft of which is coupled to the reduction gearing of the hoist proper.

The pump is a pressure-controlled unit and will deliver its maximum capacity up to and including a pre-determined pressure setting. Any increase in the working pressure above the predetermined setting will cause the pump to reduce capacity, and capacity will vary inversely proportional to the pressure rise until at maximum pressure the pump delivery is zero, whilst maintaining maximum pressure on the system.

Since the fluid h.p. is a product of the capacity times pressure it follows that at zero capacity the fluid h.p. is zero and the input h.p. is that required to drive the pump at full speed plus leakage. Similarly, if the control valve is open in either direction when this condition applies, then maximum pressure is applied to the pistons of the hydraulic motor giving maximum torque at no speed.

The control valve is of the open-centre, four-way type, specially developed for hoist control. The open centre feature ensures that with the valve in midposition, oil is circulated from the pump through the valve to the oil supply tank, the pressure being only that required to force the oil through the valve and the two short pipe lines, viz., pump to valve and valve to tank.

This means that the electric motor is running in the light load condition when the hoist is not being used and circulating the oil giving the maximum radiation cooling. The valve spool is spring centred so that release of the control handle causes the hoist to stop. This handle functions as a Dead Man’s handle, i.e., failing to safety.

Movement of the control valve lever in either direction from mid-position will close the open centre by-pass and admit pressure oil to either port of the hydraulic motor depending on direction of rotation required. The opposite port to that being supplied with pressure oil is connected to the return line. Regulation of the valve is such that any output speed can be obtained from inching, creep to full speed in either direction, and is free from all steps, being infinitely variable.

The hydraulic motor differs generally from the pump end in so far that it is usually of a fixed capacity and therefore absorbs a fixed volume of oil per revolution.

Spring loaded brakes are provided which are applied automatically when pressure oil is taken off the hydraulic motor. The brakes are taken off by hydraulic rams when pressure oil is fed to the hydraulic motor. This again ensures failure to safety.

The advantages claimed for the above system may be summoned up under the following headings:—

One of the great features of this type of transmission is the possibility of producing extreme variations of output by merely varying the type of spring fitted to the automatic control, and for this reason it is impossible to give a machine a standard "rating" since that rating would only apply to one particular control spring.

The control valve of the haulage gear is springloaded into an upright position, giving, in this position, a hydraulic lock on the drum, which means completely 100 per cent. braking. This lever has a movement of approximately 10 deg. either forward away from the central position, or backwards from the central position, and this represents forward and reverse movement of the drum, but it should be clearly understood that the movement of the lever in either direction is progressive, and gives manual speed control. If it is held firmly in the maximum position, then the automatic feature of the speed control is in operation, and the rope-speed will vary in terms of the load, that is to say, if the load is doubled the rope-speed will be halved, and vice versa from zero up to the desired maximum of the particular gearbox fitted to the machine. This speed control and automatic feature, of course, apply equally in forward or reverse, and if the handle is suddenly released it will fly back to the neutral position and will impose the automatic hydraulic lock. It will be seen, therefore, that normal brakes do not operate unless there is a failure of electric current or a failure of hydraulic pressure through a burst pipe or for any other reason.

Loading control

As shown in Fig. 1, the haulage engine house is located near the loading point. A Teleflex cable is connected to the control lever of the hoist and this runs to a lever on the loading point control platform. The loading point operator thus controls the loading chute gate and the movement of minecars with two levers conveniently placed to give a clear view of the complete loading operation. Only two men are therefore required at this loading point — the operator on the control platform and a man to clip and unclip the sets of minecars on to the rope.

The particular loading point described here works on a level grade. The loading point at present handles 900-950 tons per day from two faces plus dirt from the recaunching of the two mothergates. It will eventually handle 1,300 tons per day, but could handle more.

General

In the Hawthorn scheme, 16 loading points will be incorporated using the Pikrose hoist; 13 of these have been installed and work is proceeding on the finishing off of roadways in connection with these loading points and preparation of the remainder. In all cases the layout is such that the loading point is kept away from the main line track thus allowing loading points inbye to receive a steady flow of minecars. The loading point described here is placed about 20 feet below the trunk conveyor level, due to the difference of seam and loco road level at this point.

Where possible in the scheme, advantage has been taken of the seam gradients with relation to the haulage roads, to bring the seam conveyor road above the loading point to minimise excavation work and lifting conveyors, and to give a smooth flow of coal to the loading point, curved chutes being used to minimise breakage.

Men travelling to and from the faces in the South Busty seam, cross the track by a footbridge at the loading point and so keep the track clear at all times.

When comparing this type of car spotting system with the other more conventional types for minecars, some of the advantages which can be claimed are:—

Underground traffic is controlled by a signalling system designed and installed by the Signal and Colliery Engineering Division of the Westinghouse Brake and Signal Co. Ltd. A detailed description of this traffic control system will be given in a future issue of this journal.

Acknowledgments

For permission to publish this article we are indebted to Mr. S. W. Potts, General Manager, No. 2 (Mid-East Durham) Area, Durham Division, National Coal Board, and we would very much like to express our thanks to Mr. G. W. Day, Assistant Group Manager (Planning), and to Mr. M. Copeman, Austin-Hopkinson and Co. Ltd., for their assistance in its preparation.

Drawings and Photographs accompanying the article