Editing Self-locking device (section)

===Inertial drum brake ascender===

[[Image:Wren_Industries_Silent_Partner.jpg|thumb|200px|right|The Wren Industries 'Silent Partner']]
To overcome these limitations, the Wren Industries 'Silent Partner' device was developed. This system has four mechanical moving parts inside a frame that is attached to a climber's sit harness and is basically an inertial [[drum brake]] with the belay rope connected to the device by tying a [[clove hitch]] around the device's drum. The Silent Partner is unique in the sense that it operates in both directions of drum rotation so it can be attached to a climber's sit harness in either position, eliminating the danger of stepping off a multi-pitch anchor point before the first runner can be placed.

[[Image:Silent_Partner_Clove_Hitch.jpg|thumb|200px|right|Illustration of a clove hitch over the 'Silent Partner']]As long as the clove hitch can feed over the drum, the rope will feed through the device. In a fall, the drum is back driven by the rope as the device slides down the rope; when the drum rotation exceeds a certain [[angular velocity]], it locks off to the frame and the increase in friction induced between the stationary drum and the rope causes the clove hitch to rapidly tighten around the locked drum to arrest the fall.

The method used to lock the drum against the device frame is by the use of two straight knurl edge discs that are thrown outwards by [[centrifugal force]] as they ride on parallel ramps milled into the drum's enclosed outer periphery. Two light return springs act as centrifugal force trips and as return springs to reset the discs when the fall load is released and the device is unlocked. A simple nylon guide is used to ensure both discs activate simultaneously to jam the discs between each drum ramp and the frame's lock ring.

While the device works quite well, it suffers from rope drag that can prematurely tighten the clove hitch, so allowance must be made to reduce the hanging weight of the rope below the device. The rope diameter and elasticity is critical for operation, as higher than normal fall forces can be generated due to the rapid locking rate, in the order of 13&nbsp;kN at runners and anchor points.