Vertical spinning tunnel

Vertical spinning tunnel built between 1948 and 1955.

MATERIALS: the tunnel is constructed of pre-formed steel plates.

PLAN: the vertical spinning tunnel (VST) is circular on plan.

It is attached on its south-west side to a large rectangular building which formerly accommodated the offices and laboratories. Adjoining this building on its south-east side is the former machine hall which is square on plan. Neither of these two buildings are included in the listing.

EXTERIOR: the VST consists of a vertical steel pressure-shell in the form of a cylinder approximately 24.4m high and 13.7m in diameter. It is divided into sections by regularly spaced, full-height ribs. A cylindrical column attached to the south side is the lift shaft to the motor room which also contains an emergency staircase. Two beams project from the top of the building which act as supports for an external hoist used for lifting bulky electrical equipment to the motor room. This is glazed all round with a wide horizontal band of vertical metal-framed windows.

INTERIOR: the vertically placed working section of the tunnel is approximately 9m high and, circular in cross-section, has a diameter of 4.6m, forming in effect a tube within a capsule. There is a catch net below the working section onto which the model could be landed as the tunnel speed was reduced upon shutting down, and another above to prevent an escaping model reaching the fan. The original electric motor mounted above the tunnel, accessed via the original metal open tread staircase, has been replaced in the early C21, although parts of the original laminated teak blades of the fan are kept on site. Positioned in between the outer wall of the tunnel and the working section are a series of small rooms, including the observation room, which are closed by pressure-tight doors of similar design to those used in submarines.