Fig. 470. - Wrought-iron Open Gutter (St. Pancras Ironworks Co.).
Fig. 471. - Covered Surface-drain.
The object of trapping is to prevent the passage of gases from the sewer back into the stable, and it will be understood that, in the attempt to attain this very essential object, the disconnection of the stable drains by this means, whatever form they may assume, should be as complete as possible. Undoubtedly the most simple and sanitary method is the surface-drain, which may be a mere open channel running from the front of the stall back-wards, or it may be provided with a movable cover, so as to admit of the necessary cleansing and prevent obstruction. The two illustrations above show the two systems of the open and covered surface-drain (figs. 470, 471).
In applying the system of surface-drainage, whether covered or uncovered, it is necessary that the floor should be inclined in such a manner as to allow a sufficient fall for the escape of the sewage. In the case of stalls the fall is necessarily from before backwards. In the box it is commonly made to converge towards the centre, to which all fluid matters are conveyed by grooves in different parts of the flooring (fig. 472), and thence, by means of an underground drain, to the outlet; but with a little ingenuity surface channels can be used in boxes as well as in stalls, and are certainly better, as a drain-inlet within the building is a possible source of danger to the animals and also to the men employed.
Fig. 472. - Brick with Drainage Channel for Stable Floor.
Various methods may be adopted, according to the size of the stable. In the case of a large one the separate channels in each stall or box run into a long channel at the foot of the stall, the outlet of which is at either end of the stable. When only two or three stalls or boxes have to be provided for, the urine may be conveyed from each by a separate channel to the outside of the stable; in fact, so long as the true principle is maintained, it is a matter of indifference how the details are arranged.
The. channels in the stables must be disconnected from the drains outside by being made to discharge over trapped gullies. The liquid passes from the channel through a short iron pipe built into the wall, and it is a good plan to fit on the outer end of this pipe a brass or iron flap hinged at the top to open outwards (fig. 473), so that, while the liquid can run out readily, the flap prevents to a large extent the inlet of more or less foul air. Two good forms of gully are shown in figs. 474 and 475, one being of cast-iron and the other of stoneware, and each having a grating at the top and a strainer below to retain solid matter. The stoneware gully has a side inlet, to which the drain from a grid under a water-tap can be connected. If the sewage is conveyed by the drains into a manure-tank, cesspool, or public sewer, aerial communication between these and the drain must be stopped by an intercepting trap, which is most conveniently placed in an underground chamber or manhole provided with an air-tight cover. The drains must be ventilated by means of a grated opening a little above the surface of the ground (for preference near the intercepting chamber), and by a 3½ or 4-inch stout pipe of lead or cast-iron fixed to the wall of the building at the highest point of the drain and carried up to such a height and in such a position as to afford a safe outlet for foul air.
Fig. 473. - Drain-pipe with Flap.
Fig. 474. - Winser's Iron Gully.
Fig. 475. - Winser's Stoneware Gully.
Stoneware pipes jointed with Portland cement and laid on a bed of concrete are commonly used for drains, but cast-iron pipes are more durable and more permanently water-tight.
In the next illustration (fig. 476) a very good method of draining by the use of underground pipes, where that system is already in use or is at any rate determined upon, is shown.
Fig. 476. - Underground Drain for Stable.
In this drawing a, a represent the walls of the stable, B, B the stable drain-pipe starting from the manhole G outside one end of the stable, and running under the stable to the manhole at the other end in which the siphon-trap c is placed. Into this drain the gullies f, f, inside the stable, discharge. The siphon contains water the level of which is shown by the interrupted lines. In theory at least the water is a barrier against the passage of foul air from the outlet drain D back into the stable pipe, as such air will take its course through the clear opening of the ventilating pipe E rather than attempt to force the guarded part of the siphon c, which protects the stable pipe. As will be seen in this drawing, the drain is ventilated through pipes passing into the manholes at either end. These manholes are covered with air-tight iron covers, and provision is made for easy access for the purpose of cleaning out the drain by means of a brush with jointed cane handle. A trap similar to c must be placed between the outlet drain and the sewer or cesspool. It is of course essential that the gullies and the drain should be kept well flushed. Automatic flushtanks are now made for fixing at the highest points of drains, and can be regulated to discharge a fixed quantity of water periodically . (say) once or twice a day. They require no attention, except for cleaning and repairs, and are useful for keeping drains clean, particularly in flat districts where the drains are laid with very little fall. The automatic flush.tanks may be supplied from an overhead rain.water tank, but a supplementary supply of water should be laid on for use in dry weather.