The Tire Valve: A Plunger the Air Holds Shut

"This invention relates to valves, particularly to air valves for pneumatic bicycle tires". The valve A has a tubular casing D and a plunger E "one being movable relatively to the other". The casing's flange F lies inside the tyre B, and a washer G and nut H on its thread a clamp the tyre between them. "The plunger E has a conical seating face g within the casing and acting against the seat f of the latter for closing the valve." A plug I screwed into the casing guides the plunger; "A spring K within the hollow i ... acts ... against the plunger to force the latter to the closed position." A lug m in a groove k stops them turning. On the stem's threaded head M screws a handle nut N; below it a packing washer P sits in the socket. "When the valve is in closed position the nut N is screwed down tightly against the washer P", sealing both the casing and the stem. When it is open, "the nut N is screwed away from the washer and the plunger and nut can oscillate together under the action of the inflowing air and the closing action of the spring K." The pump coupling C screws onto the casing "until its internal shoulder p tightly engages the packing washer P", and the nut is small enough to pass freely within it.

Take an old inner tube. Unscrew the valve core with a core tool or pliers and find the spring, the seat and the sealing face — the same parts as Schrader's plunger, spring and seat, made smaller. Refit it. Fit the tube in a tyre, pump it with the floor pump's gauge, and count strokes to 3, 5 and 7 bar; compare with the notebook. Listen at the valve with a drop of soapy water on it for leaks.

**George H. F. Schrader** of New York filed US 505,486 on 9 February 1893; it is dated 26 September 1893. It claims a bicycle-tyre valve with a spring-closed plunger and a locking hand nut with packing. His earlier US 495,064 of April 1893 is a different valve. **Honest limits.** The tyre and pump volumes, seat size and spring force in the notebook are examples; the estimate ignores the air in the hose and the heating of the air.