THE SIGNAL BOX

OVERSEAS

HARPERS INSTRUMENTS
DESCRIPTION AND METHOD OF WORKING
Córas Iompair Éireann

prepared by Andy Boal

Harpers one-wire two position block instruments are still used on some CIE lines; these are the instructions for their operation.

Diagram of Harpers instruments

The dial of the instrument is divided into two parts—one part being for the Up Line, and the other for the Down Line. There are two Miniature Semaphore Arms—the upper one coloured Red, and the lower one White.

Under the dial is a circular glazed opening in the instrument case through which lettering upon a rotating indicator is displayed, the three following inscriptions appearing in succession:-

  1. On Green background - "Train Off, but Section Blocked" (The normal position)
  2. On White background - "All Clear"
  3. On Red background — "Train on Line"

Each instrument is fitted with a plunger, the depression of which causes a bell or gong to sound in the signal box at the opposite end of the section to which the instrument applies.

The indicator is moved to the required position by a knob immediately below the opening. When the indicator is placed to "All Clear" and the plunger is pressed in, the lower (white) arm on the dial above it, and also the upper (red) arm of the instrument at the signal box in rear are lowered. When the indicator is placed to "Train on Line" and the plunger is pressed in, the lower (white) arm on the dial above it, and also the upper (red) arm of the instrument in the signal box in rear are raised.

When the indicator shows "All Clear", and the lower (white) arm is lowered, it indicates that a train has been allowed to approach from the signal box in rear.

When the upper (red) arm is lowered, it indicates that a train has been accepted by the Signalman at the signal box in advance and constitutes the authority for the clearing of the section signal.

When the indicator shows "Train on Line", and the upper (red) arm is raised, it indicates that the section is occupied by an approaching train or permission has been given by the Signalman in rear for the fouling of the clearing point, or occupation of the line outside the home signal or outer home signal, where provided.

At certain signal boxes, the block instrument is controlled by a track circuit in rear of the respective home or outer home signal. In such cases the Is Line Clear signal cannot be acknowledged to the signal box in rear with the indicator in the "All Clear" position until the track circuit is clear of vehicles. Should the track circuit fail, a similar situation will arise and the Signalman must act in accordance with Regulation 25 of these Regulations.



Comments about this article should be addressed to John Hinson