...Except that with Arrow brakes, losing air pressure causes the brake to
open. In most Arrow brake calipers, there is a steel frame with a pair of brake shoes that 'float' within the frame. Between the shoe and the caliper there is an airbag, two airbags per caliper, one on each side. A leaf spring pulls the shoe back from the center of the caliper (away from the brake fin) while the airbags inflate to push the shoes together. A spool valve is used to operate this...with the valve in the "A" position, air flows from the pressure tank to the airbag. With the valve in the "B" position, air vents from the airbag. Presumably, a solenoid is used to move the valve to the "B" position, and a pressure switch can kill power to the solenoid when the pressure drops below a preset level. The problem is that if the hose that blows is the one between the valve and the caliper, then the airbag can vent no matter what the valve is doing, and the caliper fails. If the valve is positioned at the caliper, eliminating that potential failure, the airbag will vent on attempted application due to the loss of an air pressure source, and the caliper will fail.
Again, the solution to that problem is redundancy. It appears that on Intamin's system they had a similar situation, but they lacked the redundancy in the air supply line, so when the supply line failed, all of the calipers failed instead of only one.
The part that bothers me about it is that at Darien Lake, the brake calipers are counterweighted to remain closed in the absence of air pressure. I don't see why at New England the calipers apparently didn't close; this implies that air pressure is required to move the caliper in either direction on that system.
--Dave Althoff, Jr.
