Fig. 36.
CLOSED RECEIVER.
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Fig. 37.
CLOSED RECEIVER.—LONGITUDINAL SECTION.
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The Closed Receiver.
—Next we will turn our attention to the closed receiving apparatus used at all terminal stations where the pressure in the tube is considerably above the pressure of the atmosphere, so much so that the tube cannot be opened to allow the carrier to pass out without an annoying blast of air and a high velocity of the carrier. This apparatus is similar to the receiver used in the sub-post-office of the Philadelphia postal line, but contains several modifications and improvements tending towards simplification. Fig. 36 shows it in elevation, and Fig. 37 in longitudinal section. As in the open receiver just described, the air from the tube A is deflected through slots B into a branch pipe, C, that conducts it from the receiving apparatus to the sending apparatus and return tube. The carriers arrive from the tube A, pass over the slots B, where the air makes its exit, and run into an air-cushion, D. This air-cushion is a tube about twice the length of the carrier, closed at one end, and supported upon trunnions. When the carrier has been brought to rest, this closed section of tube is tilted by the movement of a piston in a cylinder to an angle that allows the carrier to slide out; the tube then returns to its original position. If the end of the air-cushion was closed perfectly tight the carrier, after coming to rest, would rebound and might be caught in the joint between the stationary and movable parts of the apparatus, when the air-cushion tube tilted. To prevent the rebounding of the carrier a relief-valve, E, has been placed in the head of the air-cushion tube. It is held closed against the normal pressure in the tube by a spiral spring, but the excessive pressure created by checking the momentum of the carrier opens the valve and allows a little air to escape through the passage F and pipe G, down the pedestal H, to the atmosphere. When the air-cushion or receiving tube D is tilted to discharge a carrier, the circular plate I covers the end of the main tube. In order to prevent carriers sticking in the receiving tube when it is tilted, and to insure their prompt discharge, the pipe J is provided. In the tilted position of the receiving tube, the end of this pipe coincides with the end of the main tube, from which it receives air to hasten the discharge of the carrier. A check-valve, K, prevents the air from flowing backward in this pipe when a carrier is being received in the air-cushion chamber. The opening of this check-valve can be adjusted by a screw, thereby regulating the speed of ejection of the carrier.
Fig. 38.
INTERMEDIATE STATION RECEIVING AND TRANSFER APPARATUS.
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