. Science of railways . foot-valve offits seat, closes exhaust port D and forms a closed passage of airthrough the foot-valve and on through the admission valve Eto the top side of the large piston head T. By reason of thenow greater area of downward pressure (air pressure on bothsides of piston T and on top side only of piston U), the pistonis forced down. When the small piston head blinds port F and air cushionis formed in the bottom of cylinder until relieved by escapethrough stuffing box G. This prevents heavy jarring of thedoors in opening. To close the door—when pressure of the port on p
. Science of railways . foot-valve offits seat, closes exhaust port D and forms a closed passage of airthrough the foot-valve and on through the admission valve Eto the top side of the large piston head T. By reason of thenow greater area of downward pressure (air pressure on bothsides of piston T and on top side only of piston U), the pistonis forced down. When the small piston head blinds port F and air cushionis formed in the bottom of cylinder until relieved by escapethrough stuffing box G. This prevents heavy jarring of thedoors in opening. To close the door—when pressure of the port on pedal Cis withdrawn, foot-valve seats itself, again blocking the air atB; exhaust port D is opened, permitting a free escape of airfrom top side of large piston head T through exhaust valve Hand the piston is again forced up by the original greater areaof upward pressure in A. When the large piston head blinds port J, an air cushion isformed in the top of the cylinder until relieved by escape 702 LOCOMOTIVE Shoemaice^^ Fire Door. LOCOMOTIVE APPLIANCES. N 703
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