This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
There is also a slight drop at the outgo of the trap, which gives it the cascade motion, similar to Stidder's. The "Loco" intercepting trap is shown in Fig. 178, Where the drains have an equal fall, and it ii desired to change the levels, instead of adopting the system for this purpose shown in Fig. 339, page 448, a modified form of this trap may be used, with a deflector bend fixed as shown in Fig. 373.
Fig. 370 - Section of Winser's Villa Detector trap, with Shafts for Sweeping and Air-inlet, etc.
Fig. 371. - Siagg's Intercepting Trap.
Fig. 372-Section of "Loco' Intercepting Trap.
Intercepting traps for fixing in manholes are designed upon the same general principles, the shape of the inlet being slightly altered to suit the brickwork and the channel in the bottom of the manhole, Instead of the band-hole for inspection being placed verti-cally upwards, it is inclined and carried forward so as to clear the wall of the manhole, and afford ready access to the drain. Fig. 374 shows the ordinary type of manhole-interceptor, known as the "Beancliff". Slagg's quick-motion trap, previously referred to, has also been improved by the addition of an inspecting arm, which enables it to be built into a manhole. Another trap designed upon very similar lines is called the "Improved Kenon Trap", Fig. 375, the shape at the throat being changed from circular to ovoid with the object of getting an improved scour from the sewage during its passage through the trap. Green's Patent "Stopless" Trap possesses practically the same features. Mr. John Jones has recently intro-«luced a patent stopper for the clearing-arm of intercepting traps. Fig. 376 will give a good idea of its merits. The frame of this stopper is cemented into the-socket of the cleansing-arm, and the closing or stopping plate is securely fixed in position by means of a simple lever, and when closed is absolutely air-tight. The strongest back-pressure will not blow it out. A chain is attached to the end of the lever, and carried up to the under side of the manhole-cover. Should the trap by any means get choked, and the inspection-chamber gradually fill with sewage, all that is required is to take off the manhole-cover and give a slight pull to the chain; this releases the stopping-plate, and leaves the cleansing-arm open to take away the accumulated soil. These stoppers can be made to fit the arm of any interring trap If it is preferred to have an entirely closed channel in the manhole, a closed intercepting: trap may be used. Fig. 377 is a section of a manhole showing the "Waverley" trap with raking eye to the sewer for purposes of inspection, and a fresh-air inlet-shaft brought up to the surface clear of the manhole. This trap has been in use for some time in Scotland, and has so far given every satisfaction. Another trap on practically similar lines, but made entirely in one piece, is shown in Fig. 378, and is known as Syke's Interceptor.
Fig. 373. - Section showing Change of Level by means of "Loco" Trap and Bend.
Fig. 374 - Section of "Beancliff" Intercepting Trap for Manhole.
Fig. 375 - -Improved " Kenon " Intercepting Trap.
Fig. 376. - Jones's Patent Stopper or the Clearing-arms of Intercepting Trapa.
Wherever it is decided to use an intercepting trap at the foot of a soil-pipe, a slightly-modified form will have to be adopted. Brown's and Stidder's trap are very suitable for the purpose, but either of these requires a special tapering eye-piece for the air-inlet, so as to allow the air-space between the bars of the grating to be equal in sectional area to the sectional area of the soil-pipe itself. Mr. Hellyer has devised a trap which carries out this principle in a very workman-like manner. Another very excellent soil-pipe trap is shown in Fig. 379, the top part being Hanged to receive an iron frame (secured by screws through the flange of the socket), in which the grating is hinged and provided with a lock, so that any authorized person can open it. This trap is made, as shown in the drawings, for outside soil-pipes, and also to receive soil-pipes from ground-floor w.c.'s. Another form of soil-pipe interceptor is shown in Fig. 380, known as Green's Patent, the trap possessing the novel features shown in the cross sections, and the hopper, being loose, can be turned in any direction.
The fourth paragraph of the Model By-law 66 prescribes that all waste-pipes from sanitary appliances within the house, with the exception of waste-pipes from the slop-sinks, must discharge in the open air over a channel leading to a trapped gully grating at least 18 inches distant. The reason for fixing arbitrarily a definite space in the open air between the end of the waste-pipe and the gully grating is not sufficiently understood or appreciated. It has t>een the custom hitherto for the waste-pipe to be fixed so that the open end rests upon the gully grating, or in many cases it is inserted into the gully below the grating. It is well known that even above the water-line there may be an accumulation of offensive matter upon the sides of the gully, the gases from which will freely pass up the waste-pipe into the house, and although there may be traps upon the waste-pipes inside the house, they are not a sure prevention against the inroad of gases. We have already seen from Dr. Fergus's experiments that gases can be absorbed by the water standing in the trap, and given off inside the house. Many gullies which are used to receive the discharge of waste-pipes, are from their shape and dimensions liable to hold a great amount of filth, and, from the way in which they are fixed, this filth escapes and penetrates into the surrounding ground and into the wall. Others have also a most imperfect water-seal, often not exceeding 3/4 inch in depth, which is easily lost by evaporation, so that odours from any accumulation caused by defective joints in the branch drains will freely escape into the house.
Fig. 377 - " Waverley" Closed Intercepting Trap axed in Manhole.
Fig 378.-Section of Syke's Interceptor In Manhole.
Fig. 379 -Two Forms of Trap For foot of Sod-pipe.