Fig. 34.
OPEN RECEIVER.—LONGITUDINAL SECTION.
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Fig. 35. OPEN RECEIVER.—SLUICE-GATE MECHANISM.
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Referring to the longitudinal section, the apparatus is attached to the end of a pneumatic tube, A. The current of air from the tube A flows through the slots B into a pipe, C, that conducts it to a tank near the air-compressor. About the centre of the apparatus is a sluice-gate, E, that is raised and lowered by a piston in a vertical cylinder, F, located just above the sluice-gate. This piston is moved by air-pressure taken from some part of the system. When a carrier arrives from the tube A, it passes over the slots B and runs into the air-cushion D, where it comes gradually to rest. Checking the momentum of the carrier compresses the air in front of it considerably, and this excess of pressure is utilized to move a small slide-valve that controls the movement of the piston in the cylinder F, so that as soon as the carrier has come to rest the sluice-gate rises and allows the carrier to be pushed out with a low velocity on to a table. The small pipe G conducts a small portion of the air compressed in front of the retarded carrier to the controlling valve, H, seen in Figs. 33 and 35. Referring now to the section of the valve and cylinder, Fig. 35, the pipe G enters the top of a small valve-cylinder containing a hemispherical piston, I, that is held up by a spiral spring, J. This spring has just sufficient tension to hold the piston I up against the normal pressure of air in the tube. When a carrier arrives and compresses the air in the air-cushion, the excess of pressure forces the piston I down against the spring J, and moves the piston slide-valve K. This change of position of the slide-valve allows the air in the cylinder F to escape to the atmosphere through the passage L, passage P, and pipe M, while compressed air from some part of the main tube enters through the port N and passage O to the under side of the piston in the cylinder F. This moves the piston up, carrying with it the sluice-gate E.
There is just sufficient pressure in the tube in rear of the carrier to push the carrier past the gate and on to the table. As the carrier moves out it raises a finger, Q, Fig. 34, that projects into its path. Raising this finger extends the spring R, Fig. 33, and rotates the lever S, bringing the pawl T under the end of the controlling valve-stem. When the carrier has passed out and the finger Q is free to descend, the spring R rotates the lever S back to its original position, and thereby raises the controlling slide-valve, which causes the sluice-gate to close. By having the upward motion of the finger Q simply extend the spring R, and the downward motion, by the force of the spring, move the valve, we are enabled to have several carriers pass out of the tube together without having the sluice-gate close until the last carrier has passed out. If raising the finger Q moved the valve, then when the first carrier passed out, the gate would close down upon the second. Attached to the receiving apparatus and extending beyond it is a tube, U, cut away upon one side so that the carriers can roll out of it on to a table, and having in the end a buffer to stop the carriers if by any accident they come out of the tube with too much speed. This buffer consists of a piston covered with several layers of leather and having a stiff spring behind it. The whole apparatus is supported from the floor upon suitable standards, and, for an eight-inch tube, occupies a floor-space twelve feet long by two feet wide, not including the table.
This is the simplest form of receiving apparatus. Owing to conditions of pressure already explained, its use is confined principally to the pumping stations. The only care that it requires is an occasional cleaning and oiling.
