In certain cases subsoil-water finds its way through the walls or floors into cellars. The insertion of a gully in the cellar floor for carrying off such water is certainly not a sanitary method. This purpose should be accomplished by a proper system of subsoil-drains outside the building.

There are many districts where, by reason of their contiguity to tidal rivers, or through being situated in areas which are liable to sudden and rapid flooding', the basements become submerged. To meet these difficulties, special appliances must be used for keeping out the back-water which such sudden rises will cause in the main sewer. Where the branch-drain is connected to a brick sewer, the junction-block should be fitted with a galvanized -iron flap-valve, hung to swing freely and to close truly. To get this most accurately, a cast-iron ring 3hould be shrunk into the block, having its outer face ground; and the face of the meeting portion of the valve should also be ground. The shape of these valves is shown in Fig. 357. Another form of valve made to secure effectual closing is the balance-valve, shown in Fig. 358. This is hung inclining inwards to the branch, and is kept in that position by the counterpoised balance-weight. The small amount of water trickling down a cellar drain at ordinary times may hardly be sufficient to keep the valve open, hence a stoppage with accumulation of deposit may take place.

In the case of areas like that shown in Fig. 355, and situated in the front of the house, nothing could be better than Couzens's gully-trap for preventing backwater, two forms of which are given in figs. 359 and 360. The action in each case is automatic. Any back pressure of water in the trap shown in Fig. 359 raises the copper ball against an india-rubber seating, thus making an effectual seal; and should the water evaporate, as is sometimes the case in dry weather, the ball lowers on to the bottom seating, and prevents the rising of sewer-gas, provided that the ball fits perfectly. In the trap shown in Fig. 360 there is a door with a weighted lever, which allows the water to pass through into the gully, and closes automatically, thus preventing the back flow of water, and the rising of sewer-gas.

Fig. 359   Section of Couzen's Gully trap with Copper Ball for preventing Back water.

Fig. 359 - Section of Couzen's Gully-trap with Copper Ball for preventing Back-water.

Fig. 357. View of Swing nap valve, and Section of Flap.

Fig. 357.-View of Swing nap-valve, and Section of Flap.

Fig. 358.   View and Section of Balance Flap valve

Fig. 358. - View and Section of Balance Flap-valve.

Fig. 358   Section of Couzens's Gully trap with weighted Door or Valve for preventing Back water.

Fig. 358 - Section of Couzens's Gully trap with weighted Door or Valve for preventing Back-water.

In cases where the whole of the drainage system is below flood or tide level, and therefore subject to baek-water, Dyer's valve can be advantageously used, and may l>e fixed immediately below the intercepting trap. Access may be had to it by lengthening the manhole and forming a small additional chamber. The valve can be arranged for any desired fall or for a dead level. Fig. 361 shows one of these valves fixed in a chamber, one side of the valve being partly removed to show the suspended ball. The tide or flood when flowing up the drain enters the out-go branch, and floats the ball, which, as the water rises, approaches the inlet, and finally beds itself upon the seating, thus effectually closing the orifice and preventing the water entering the building. Consequent upon this action, the greater the amount of water-pressure there is behind, the more completely sealed the trap becomes. By reason of the arm being always slightly inclined towards the inlet-branch, there is no danger of the ball sticking with the arm vertical, or of its being moved the wrong way. When the water subsides, the ball falls with it, unsealing the inlet, and leaving a clear passage.

Fig. 362 shows Couzens's ball-trap interceptor. The action is automatic, and any back pressure of water raises the copper ball against an india-rubber seating. The access holes are covered with iron covers bedded in suitable materials, and secured to the tire-clay with brass screws; they are therefore perfectly gas and water tight. These interceptor-traps can be used either with or without inspection-chambers; if without, an access-shaft should be carried up from the large opening as shown by the dotted lines.

Often basements are at such a depth relatively to the depth of the sewer, that it is impossible to drain them satisfactorily by gravitation, or they may even be actually deeper than the sewer. The impossibility of providing an outlet for the drainage prevents the fullest use being made of such basements, and in business premises in towns this is a very serious drawback to their letting value. By the adoption of a very simple arrangement, known as Adams's Patent Sewage-Lift, all Itasements may be drained, and the sewage lifted from then automatically into the public sewer. This system is shown in Fig. 363, end the working of it is as follows: - The low-level sewage peases outside the building into an underground chamber (placed in a convenient position for access), where it enters a cylinder by gravitation, passing a flap-valve which prevents its return when the air-pressure is applied This pressure is obtained from an air-cylinder placed on a higher level in any convenient position in the same or other building. An automatic Hush-tank is fixed above the air-cylinder, and is fed by water from the service-main or bath-waste. The inflow may be regulated by hand or by a float on the sewage, so that none is wasted. As soon as the tank is full, its eon-tents are discharged from the fall-pipe into the air-cylinder, displacing the air therein, which passes by a small air-pipe to the forcing-cylinder containing the sewage to be lifted, and there exerts a pressure sufficient to raise it through the rising main into the puolic sewer. It is necessary, in order to secure the requisite pressure, that the Hush-tank should be at a height above the air-cylinder equal to or in excess of tin-height of maximum lift, but if it can conveniently be placed higher than this, less water is required to operate the lift, as a larger volume of air is carried down with the falling liquid, which answers the same purpose, and in this way as much or even more sewage can be raised than there is liquid falling. When the forcing-cylinder is empty the air-cylinder will lie full of water, but the latter is immediately withdrawn by a syphon attached, and air again passes in, to be again expelled at the next discharge. The water thus withdrawn may be stored in a tank as shown, and again used for flushing the closets in the basement or for other purposes, or may be run off by a pipe connected to the overflow from the tank, which discharges into the chamber for raised sewage. This pipe will require to be disconnected from the chamber by an intercepting trap and airinlet, with a trap below the tank and a vent-pipe to the external air. If clean water only be used for flushing, it need not be wasted when discharged from the air-cylinder, but conveyed to any point where required for use.

Fig. 361   Dyer's Valve for preventing Back water

Fig. 361 - Dyer's Valve for preventing Back water.

Fig. 362   Section of Couzen's Ball trap Interceptor for preventing Back water

Fig. 362 - Section of Couzen's Ball-trap Interceptor for preventing Back-water.

Fig. 363   Adam's Automatic Seweage  Lift.

Fig. 363 - Adam's Automatic Seweage -Lift.