Squeeze Brakes

Most descenders generate the friction by bending the rope around the surface of the descender. The change in direction generates a normal force that generates friction that is nicely approximated by the well-known snubbing formula. But what if we want to eliminate the bend? There has been a lot of interest in that idea, leading to the development of squeeze brake descenders. A control systems theorist might immediately recognize that this would lead to instability, and that is exactly what the experimenters found out.

Squeeze brakes have a straight rope path. They obtain their friction by compressing the rope between two plates, and not by snubbing. Standing in the drop zone under the rappeler with the idea of providing a bottom belay won’t work with a squeeze brake. Without snubbing, adding tension below the brake does not provide more friction and does not slow the rappeler – in fact, it tends to do the opposite. Similarly, using one’s braking hand does not better below a squeeze brake than it would above the brake.

I’m not going to discuss their history here, instead referring the reader to Kirk MaGregor’s 1986 article “Squeeze Brakes Up to 1982” in Nylon Highway #22. Kirk was one of several who tried a basic squeeze brake, and in his own words found, “Its speed fluctuated randomly over a wide range as it moved down the ropes, making accidents likely.” Others had similar experiences. Most people abandoned the squeeze brake idea after Sara Corrie’s severe, near-fatal accident in 1978. Cavers at the 2023 NSS Convention who were present for the accident told me that she was using a Musicbox or something very similar. If you want to try squeeze brakes, please first modify your will to leave all your assets to me.

Image	ID	Device ↓	Description	Acquired	Weight ↓	Height ↓	Width ↓	Thickness ↓	Std. volume ↓
	464	Mar-Mex Escapeline	Squeeze brake with horn, extruded sides, soft anodized, plastic knob	John E. Weinel, Inc., 1985	383	75	104	93	725
	3056	Storrick - MacGregor Squeeze Brake	2 Al-side plates /w control crank & spring, nutcracker handles, cable connections	Gary Storrick, 2021	1454	305	155	59	2780
	3254	Storrick - Adams Fire Escape Device	2 Al side plates, U-shaped rod hinge/eye,  control screw on swinging gate	Gary Storrick, 2023	670	147	83	75	920
	3260	Storrick - Rabelos Detachable Fire Escape Device	2 hinged Al side plates,  control screw on swinging gate, hook on rear plate, D-ring eye	Gary Storrick, 2023	757	185	82	102	1546
	3331	Storrick - Rabelos Fire Escape Device	Block /w broached rope hole, pressure block, control screw.	Gary Storrick, 2023	404	77	97	26	194
	3252	Storrick - Zachariasen Musicbox	Squeeze Brake, 2 Al side plates /w pressure platelever, control screw on swinging gate	Gary Storrick, 2023	622	222	80	60	1069
	3251	Storrick - Zachariasen Son of Musicbox	Squeeze Brake, 2 Al side plates /w sliding pressure plate, pressure spring, control screw, bar /w eye, 2 QR pins	Gary Storrick, 2023	1113	159	124	70	1375

SqueezeBrakes.php/20230926
© Copyright 2023, Gary D. Storrick, All Rights Reserved.