In order to provide ready access to each filter, a part of the vaulting near one side is elevated and made cylindrical in shape, making an inclined runway from the sand-level to a door the threshold of which is 6 inches above the level of the overflow.
Fig. 4.
This sand-run is provided with permanent timber runways and with secure doors.
Fig. 5.—Entrance to a Filter.
The manholes of the filters are provided with double covers of steel plates to exclude the cold. The covers also exclude light. When cleaning the filters, light can be admitted by removing the covers. Supports for electric lights are placed in the vaulting, so that the filters can be lighted by electricity and the work of cleaning can be done at night, and in winter under heavy snow, without removing the covers. The electric lights have not yet been installed.
The regulator-houses, the entrances to the sand-runs, and all exposed work are of pressed brick with Milford granite trimmings and slate roofs. The regulator-houses have double walls and double windows and a tight ceiling in the roof, to make them as warm as possible and to avoid the necessity of artificial heat to prevent freezing.
Fig. 6.