The Door Check: An Air Cushion With a Valve That Knows How Hard You Push

"A great deal of annoyance is often caused to the audience in a church, lecture-room, or theater by the slamming of doors". Norton's invention "consists in a cylinder, piston, and self-adjusting valve ... combined together, so that the quantity of air which can escape from the cylinder through the valve during the forward stroke of the piston will depend upon the force exerted": "the greater the force exercised upon the piston the less the escape of air through the valve". Cylinder C has caps c and c′. The piston rod D passes through c and is jointed to a swivel on the bracket A′ on the frame; a spiral spring E around the rod is compressed when the door opens. Cap c′ has a small central hole f with a groove f′ round it, forming a ridge f⁴, and a disk f² "made of soft leather, rubber, or like substance" with three or four slits f³. Drawn back, air enters freely through the slits; pushed forward, the disk is pressed onto the cap, "forming ... a joint more or less air-tight, according to the pressure exerted by the piston." A very small hole c² in the cylinder wall lets the door move steadily until the piston passes it, after which "the door will strike the jamb very gently." "For use on doors of ordinary size I make the cylinder of a piece of seamless brass tubing, eighteen inches long and one and three-eighths inch internal diameter."

Use a large plastic syringe as the cylinder: cut a small flap valve from rubber sheet and glue it over a drilled hole in the syringe tip so air can enter freely but must squeeze out past the flap. Fix the barrel to a cupboard door and the plunger rod to the frame with a wire link, close to the hinges; hang the door on a spring hinge. Open the door and let it go: time the closing with the stopwatch with the valve, and with the tip wide open. Then drill a tiny hole partway along the barrel, as Norton did, and watch the door run quickly until the plunger passes it and slow for the last part. Compare with a bike pump's cylinder for scale.

**Lewis C. Norton** of Boston filed US 228,776 on 2 February 1880; it is dated 15 June 1880. His claim is the door-fender of cylinder, piston, cap and a valve of hole, ridge and slit disk. He disclaims earlier fenders in which more force let more air escape. **Honest limits.** The door's mass and speed are examples, and the isothermal cushion ignores the air bleeding out through the valve during the stroke.