This section is from the book "A Treatise On Architecture And Building Construction Vol4: Plumbing And Gas-Fitting, Heating And Ventilation, Painting And Decorating, Estimating And Calculating Quantities", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
General Remarks. The requirements of a good trap are: (1) that it shall entirely and effectually prevent the passage of any air or gas from the waste pipe backwards into the house; (2) that it shall be so constructed that it can be readily cleaned; (3) it should clean itself on all ordinary occasions.
Round-pipe traps are usually of the same diameter throughout, and they freely pass nearly everything that can get into them, but they are very liable to become useless through the removal of the water which seals them, by siphonage or evaporation.
The bottle trap can seldom be emptied or siphoned, and as it contains a large volume of water, it will withstand evaporation for a longer time than other traps. It will clog easier than a round-pipe trap, but is quite as easily cleaned by removing the screw plug, which is provided for that purpose. The same depth of seal forms a more effectual barrier against the back flow of gas in a bottle trap than in a round-pipe trap.
Traps for outdoor service, to receive surface water from courts, areas, roofs, etc., should have a deep seal, from 8 inches to 1 foot, according to the warmth and length of the dry seasons.
Check-valves should not be used in place of traps, because they are very liable to be prevented from closing properly by the lodgment of refuse, such as strings, rags, paper, etc., between the valve and its seat.
All traps should have a cleaning hole. The screw plug which is used to close the hole should be of such shape and size that a wrench can be applied to it firmly and safely. Large traps, such as used for drains, should have a hand-hole and a suitable cover. These plugs or covers must always be made both water and gas tight.
A separate trap should be placed under each bath tub, wash basin, sink, water closet, or urinal, and one trap should be attached to each set of laundry tubs. Traps should be set as close to the fixtures as possible. A trap should be placed in each main drain so as to disconnect the house pipes from the sewer. A trap should not be placed at any point where it will check the free circulation of air through the drainage system.
115. To prevent the back flow of water from sewers, etc. into basements or areas, a back-water trap should be employed. This allows the water to pass outward freely, but allows none to return.
A common form of back-water trap is shown in Fig. 39. This is used chiefly to drain water from the basement floors, etc., where there is danger of water backing up from the sewers. The valve is composed of a hollow copper float A, encircled by a soft rubber ring B. A rest, or stop, E for the float is attached to the brass valve seat G by four arms. These arms also act as guides to lead the valve to its seat when the sewage water rises in the drain pipe D, and buoys up the valve. When the water falls in D, the float will fall from its seat and descend with the receding water until it reaches its stop, as shown, when it will be again open for surface water. A bell-shaped casting C, suspended from the perforated cover F, dips into water and forms a seal to prevent drain air from entering the building.
116. Refrigerators should have a trap on the waste pipe. The object of the trap is to allow the waste water to pass out, and to prevent the cold air from escaping also. The cold air is heavier than the air at ordinary temperatures, and it settles at the bottom of the chamber. If there is any hole open, the cold air will flow out very much as water would, and the result is a waste of ice. The trap also prevents the entrance of bad air or dust. Cooling rooms for butter and cold storage must be carefully guarded in this respect.
Ample facilities for cleaning the traps must always be provided, because they frequently choke with the sawdust which accompanies the ice.
The waste pipe should not be directly connected to a drain, or sewer pipe, but should discharge into some clean place where it can be watched, and where there is no bad air. The utmost cleanliness must be preserved at all points about refrigerators or cold-storage rooms.
117. Rain-water leaders, if connected to the drains, must be provided with traps, having a seal so deep that the water in them will not evaporate sufficiently to unseal them during long spells of dry weather. These traps must be secured against frost. They are usually placed in the cellars.