Regarding the Capabilities of Safeties-In Conjunction with Rope Brakes/Added degree of Redundant-Safety.

When considering Retarding Forces the following can occur:-

* As a Summary the Safety Retarding Forces can produce a maximum stopping distance of approx 0.35 gravitational acceleration

* When evaluating Free-Fall a retardation is IMPRESSED upon a freely-falling Lift Car and an acceptance test must be carried out, it is assumed that after the Governor Trips the lift car could be --Driving = 2.4 to 4.3 times normal when Overspeeding--when free-wheeling: = 1.96 to 4.3 times normal--when stopped:= 1.02 to 4.3 times normal.

* It is assumed that the governor tripping speed is 25% greater than rated speed, the lift car would continue to increase during the time taken to activate the Governor and Safety System, it  could occur at 25 per cent greater than governor speed.The resulting distance the car falls necessitates a stop at -0.215 x gravitational acceleration.

To Conclude an ANALYSIS would show that in extreme cases it is possible to stop the lift car and when Retardation occurs when STOPPING and the ROPES are still INTACT the maximum permissible Retardation of a free falling Lift Car reduces and the PIT buffer Striking Speed is 115 per cent or rated speed. Since High Speed Lifts in excess of 4 metres per second reduced stroke Oil Buffers one uses such a System of Stopping, the analysis then shows that in an Emergency Terminal speed is LIMITED by a device and an Additional Height is needed to slow the Lift Car down. At high speeds when the Safeties apply a low coefficient of friction is effective.

This is taken from a Generic Article in Elevator World by George W. Gibson - From - John Irwin C. Eng. M. I. Mech. E. of 22 Princess Court, Queensway, London W2 4RB.

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