The Mechanical Handling and Storing of Material

COAL TIPS OR HOISTS 5r9 to the axle of the platform, not rigidly, but by means of volute springs to reduce the impact. The truck is allowed to move into a position in which its centre of gravity is on the water side of the centre of the platform. The weight of the load causes a pressure in the cylinder b of about 300 lbs. to the square inch. The pressure in the accumulator is, however, only about 255 lbs. The valve is now opened, and as there is a difference in the pressure of cylinder and accumulator of 45 lbs. to the square inch, the weight of the truck pushes the ram into the cylinder, thereby lowering the platform, and the truck begins to discharge. During the tipping process the centre of gravity of the truck alters its- position in such away as to increase its leverage. I he momentum of the load does^ however, decrease as the load of the truck is getting less. At the angle of 45 the platform and truck have reached their The speed of the descent can be regu- lated by throttling the communication between hydraulic piston and accumu- lator by means of lever c, which is closed altogether as soon as the lowest position is reached. The coal as it leaves the truck falls into a shoot which forms an extension to the platform, the sides of which, to prevent waste, are somewhat higher than the truck. The end of the shoot can be so adjusted as to let the coal fall gently into the ships or barges which are to be loaded. As the load on the ram f be- comes less towards the end of the opera- tion, the pressure is reduced to about 210 lbs. When the valve is now re- opened the surplus pressure in the accumulator is sufficient to raise the platform into its original position. The valve is manipulated by a lever c over the accumulator on that part of the structure which is not movable. From maximum travel, at which the latter is empty. Fig. 725. Cross Section of Tip at Dortmund. the same spot a second lever can be used which actuates another valve, which allows the water to escape from the cylinder b to the open, in case the load in the truck should not be sufficiently heavy to force the water out of b into the accumulator. As the momentum decreases during the tipping process, the valve must be closed almost immediately after the platform has begun to descend in order to economise the pressure in the accumulator. Finally, there is a safety valve which opens automatically in case of extreme pressure in cylinder B through the valve having been closed too soon. 1 his valve admits the water into the accumulator. The plant is provided with a hand pump, which is used when the cylinder and accumulator are first filled, and also to replenish any loss through leakage, and also in cases where the cylinder b has to be relieved into the open as stated above. A mixture of glycerine and water is used in the apparatus to prevent freezing. It takes five men to manipulate the tip. One operates the valve and lever c, two are placed in the shoot and go up and down with it to regulate the discharge by means of two small winches, whilst two push the trucks on to and off the platform.