NR NR/L2/SIG/11774/SR0001IB ISSUE 1 PDF

Introduction

When a run-through occurs, the train forces the open switch closed and the closed switch open. This causes the lock arm to stretch (Figure G1) and the permanent way stretcher bars/brackets to become distorted (Figure G2). In very severe cases, the pivot pin on the switch rail bracket may also bend.

If a run-through is suspected, the lock arm should be removed and examined for distortion between the centre of the pivot pin bush and the locking face. This dimension varies according to the type of lock arm. The latest supplies of lock arm have a straight line engraved on the outer face, which in the event of a run-through should appear 'bent'. If a replacement lock arm is used for comparison, check the correct type (A, B, C, D, E or F) is used. Applications of the different lock arms are as shown below:

Type A: All leads other than below (202mm)

Type B: Double slips (Inner switches) (200mm)

Type C: 1 in 7½ and flatter switch diamonds (233mm)

Type D: 1 in 5½ to 1 in 7½ switch diamonds (260mm)

Type E6: UIC 54/113A plain leads (252mm)

Type F6: Flat bottom inclined 110A or 113A With Mk 2 equipment. (212mm)

When the distorted lock arm is removed, use a chisel to mark the pivot pin bush and the locking face of the lock arm to prevent it being re-used.

If a run-through is confirmed, it is not sufficient to change the lock arm and check the lock gauge. During virtually all 'run-throughs' on Clamplocks, the stretcher bar is distorted although it may not appear so. This causes the switch opening to be reduced, and in time may lead to a premature open switch detection failure. Further damage can occur to the stretcher bar brackets which will cause the switch rail to appear crippled. It may therefore be necessary to renew or reset these brackets, as crippled switches will cause regular point failures.