Designer's Corner

Truck-brake watchdog

Changes in pedal feel and travel warn automobile drivers of impending brake
problems. Pneumatically operated brakes on heavy duty trucks don't give drivers
that same tactile feedback, but this electronic brake monitor provides a visual
substitute.

The system uses a set of three discs journaled on the drum brake's S-cam shaft. One disc follows the movements of the brake's actuator/adjuster lever. Another rotates with the cam shaft. Sandwiched between them, a third, stationary disc houses Hall-effect sensors that signal an electronic annunciator if magnets in either of the two rotating discs come into range. Properly adjusted, those disc magnets trigger the panel when brake lining thickness or adjuster travel move out of safe limits.

Reese Larson, So. 530 Farr Rd. #92, Spokane, WA 99206, (509) 924-4498.


Quick clamp

A quick pull on the outer sleeve is all that's needed to release this self-locking bar clamp. To grip the bar, an annular clutch plate constrained at one sector is tilted axially by a biasing spring. Pulling the sleeve drives an internal projection against the plate opposite the constrained sector, bringing the plate into axial alignment with the bar, releasing the clamp.

Donald Lundstrom, 661 Grove St., Worcester, MA 01605.


Auto shut-off sprinkler

This fire-safety device comprises two chambers with a PTFE spool valve and a pilot valve driven by a bimetalic disc spring. Initially, supply water fills both chambers, entering the inner one by a small orifice on its upper surface. Water pressure on top of the spool coupled with the spool's weight keep the valve closed without seals.

During a fire, the disc everts, opening the pilot valve. Water flows out of the inner chamber faster than it enters through the orifice, thus reducing downward pressure on the spool. Upward pressure from water in the outer chamber then unseats the spool, dousing the fire. When the temperature falls, the pilot valve closes, and the spool valve soon follows. By lessening the risk of excessive water damage, the design may encourage sprinkler installation in homes. It is available for license.

Peter Vari, P.O. Box 452, Newtown, PA 19840, (215) 396-1948.

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