A trap is a loop or water seal placed in a pipe to prevent the gases from the drain or sewer from passing up through the waste pipes of the fixtures into the rooms. A common form made up of cast iron pipe and known as a "running trap" is shown in Fig. 29. A trap of this form is placed in the main drain pipe of a building outside of all the connections to prevent gases from the main sewer or cesspool from entering the building. A removable cover is placed on top of the trap to give access for cleaning.

The floor trap shown in section in Fig. 30 is made both of brass and of lead. It is commonly used for kitchen sinks and is placed on the floor just beneath the fixture. It is provided with a removable trap screw or clean-out for use when it is desired to remove grease or sediment from the interior. Fig. 31 shows a common form for lavatories, which consists simply of a loop in the waste pipe. These are usually made of brass and nickle plated when used with open fixtures. A trap for similar purposes is shown in Fig.. 32 and 33.

Fig.. 34 and 35 show a form known as the centrifugal trap on account of the rotary or whirling motion given to the water by the peculiar arrangement of the inlet and outlet. This motion carries all solid particles to the outside and discharges them with the water, thus keeping the trap clear of sediment. Where there is likely to be a large amount of grease in the water as in the case of waste from a hotel or restaurant it becomes necessary to use a special form of separating trap to prevent the waste pipes from becoming clogged. A grease trap designed for this purpose is shown in Fig. 36. Its action is readily seen as the fatty matter will be separated, first by dropping into a large body of cold water and then being driven against the center partition before an outlet can be gained. The grease then rises to the surface where it cools and can then be easily removed as often as necessary.

Sometimes a cellar or basement is drained into a sewer which is liable to be filled at high tide or from other causes and a special trap or check must be used to prevent the cellar from becoming flooded. Such a trap is shown in Fig. 37. When water flows in from below, the float rises, and the rubber rim pressing against the valve seat prevents any passage through the trap; the cut shows the valve closed by the action of high water. Tanks or cisterns for flushing closets or other fixtures are usually made of wood and lined with zinc or copper. These are generally placed inside a finished casing. A common form is shown in Fig. 38. The arrangement of valves for supplying water to the tank and for flushing the fixtures is shown in Fig. 39. The large float or ball cock regulates the flow of water into the tank from the street main or house tank. When the water in the tank falls below a certain level the float drops and opens a valve, thus admitting more water, and closes again when the tank is filled. The closet is flushed by pulling a chain attached to the lever at the right which opens the valve in the bottom of the tank and admits water to the flushing pipe. In this form the valve remains open only while the lever is held down by the chain, the weight on the other end of the lever closing the valve as soon as the chain is released. Another form which is partially automatic is shown in Fig. 40. When the chain is pulled it raises the central valve from its seat and allows the water to flow down the flush pipe until the tank is nearly empty. When empty, the strong suction seals the valve which remains closed until the chain is again pulled. In this type of valve a single pull of the chain is sufficient to flush the closet without further attention.

A purely automatic flushing device is shown in Fig. 41.

Traps 1000235

Fig. 29.

The chain in this case is attached to the rim of the seat so that when it is pressed down, the valve in the compartment at the bottom, connecting with the flush pipe is closed and at the same time communication is opened between the two compartments. When the pull on the chain is released the valve connecting the flush pipe is opened and the opening between the compartments closed so that the water in the lower portion of the tank flows through the flush pipe into the closet automatically, and when empty no more can be admitted until the lever is again pilled down and the valve in the partition opened.

Traps 1000236

Fig. 30.

Traps 1000237

Fig. 31.

Traps 1000238

Fig. 32.

Traps 1000239

Fig. 33.

Traps 1000240

Fig. 34.

Traps 1000241

Fig. 33.

Traps 1000242

Fig. 36.

Traps 1000243

Fig. 37.