The space occupied by indoor swimming pools is generally not fully used. In winter swimming pools are often closed. In some instances, attempts are made to remedy this uneconomic use by building up a heavy scaffolding from the bottom of the bath and laying a floor on it flush with the surrounds, so that the whole surface is available as seating accommodation for a concert or as a dance floor. The changeover thus made is, however, a slow and costly process and to cover in such an enormous pool as that in the new exhibition building at Earl's Court, London, would involve a forest of supports, needing a long time to erect and dismantle and occupying valuable storage space when not in use.
This pool is probably the largest of its kind in the world. It measures 195 feet by 95 feet and occupies a large portion of the central hall. The engineer was, therefore, set to work to design a movable steel floor which could rapidly be raised to the level of the surrounding floor, thus making the whole of the area available for exhibition displays. The lowest illustration below shows the floor at its swimming pool level, that is, with a shallow end, a gradual slope into deep water and a still deeper section for high diving. The floor consists of three sections, each 95 feet by 65 feet and weighing altogether 720 tons. If required, any of the sections can be raised 5 feet above the surrounding floor, to form a large stage. Each section is raised and lowered by two hydraulic rams shown at A. The rams do not carry the floor when it is stationary, the load being then taken on the stilts C. The stilts are formed with projections on either side at the different levels required. The projections bear on pivoted chocks on the solid foundation on which the whole weight is thus carried. The chocks are tilted out of the way to give free passage to the stilts when the floor is being raised or lowered. Steadying rollers and other devices take any lateral stress off the rams.
Movement of the two right-hand sections is carried out when the floors are horizontal; these sections have to be tilted to the correct slope for the bottom of the pool by the small hydraulic rams E. Here again the weight, when the floor is at rest, is not taken by the rams but by the jointed struts N. These function in much the same way as the struts for keeping up the hood of an ordinary perambulator. The steel floor has a granolithic covering (I) to match the floor of the central area and the connexion between the deep section and the others is made by a fold of rubberized canvas G. Sliding connexions are fitted all round the edges of the sections as shown at H in the inset on the left. The rams are controlled from a room below floor level and behind one of the walls of the bath. The work was carried out by the London Hydraulic Power Company.