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.
125. Soil and vent pipes should run vertically if practicable, and if they must be run otherwise, they should be inclined not less than 1 foot in 40 feet. All bends and curves should be made of large radius. Where an offset has to be made in a soil or vent pipe, it is advisable to use two obtuse angle or eighth bends, B, B, as shown in Fig.
44. Right angle or quarter bends, as at A, should not be used for this purpose.
The Y branch A should be inclined in the direction of the flow, that is, downwards towards a soil pipe, and upwards towards a vent pipe. By inserting an eighth bend B into the Y branch, one pipe can be connected to another at right angles in a proper manner.
126. All soil pipes should extend through and above the roof. The diameter of the pipe must be increased before it passes through the roof, because the warm air and vapor which rise in it will be condensed, and in cold weather the outdoor end of the pipe will become lined with ice. The formation of ice will continue until the mouth of the pipe may be choked. By enlarging the pipe, the time required to choke it is greatly prolonged. Thus a 4-inch stack should be increased to 5 inches diameter at the roof, as shown in Fig. 46. The hub of the 5-inch piece B should extend above the roof to the extent shown or slightly lower. The opening through the roof should be made water-tight by means of the flashing F of 6-pound sheet lead. This should be extended upwards under the shingles or slates A and be securely nailed to the roof boards. The hole for the pipe C should be flanged downwards into the hub B, so that when the joint is calked with oakum and lead, a perfectly water-tight joint will be made with the flashing.
127. All branch pipes should be ventilated. This is usually accomplished by attaching a back-vent pipe to the crown of each fixture. It will relieve the pipe from accumulations of foul gas, secure a steady current of fresh air through the branch pipe, and prevent the sealing water from being sucked out of the traps by siphonage.
The separate back-vent pipes should be connected to one vent stack unless the horizontal distance to be traveled is so great that a good draft cannot be secured. Local vents must not be connected to the vent stack. Rain-water leaders should not be used for vent pipes. Vent pipes must be connected to that side of the trap which is between the seal and the soil, or drain, pipe.
128. The proper mode of connecting the vent pipe is shown at A, Fig. 47. A common, but improper, vent connection is shown at B and D in the same figure. When a large volume of water enters the trap suddenly, it will drive up into the part D, and if it carries grease, soap, or refuse with it, it will be deposited in D as shown. After a time the vent will become choked and perhaps entirely closed. If the vent pipe be attached as shown at A, the current of water will tend to create a suction and a downward current in the vent pipe, which will prevent the deposit of any grease or refuse at that point.
129. The vent pipe should be attached to the stack at such a height that, in case the waste pipe becomes choked, the waste water cannot pass through the vent pipe into the stack without filling the fixture and thus giving notice to the householder that something is wrong. It also prevents an 4-6 overflow by the discharge of waste water from the floors above. This is illustrated in Fig. 48. The kitchen sink A is connected to the waste and vent pipe stacks B and C. The waste stack is choked at the point D, and waste water from the sinks above rise in the waste branch E, half fills the sink A, then discharges into the vent pipe C; thence into the drain, to which the vent stack is connected at its base. The cause of the chokage at D is presumably oakum, driven into the pipe by a careless workman, which accumulates falling solid bodies until the pipe is entirely closed. Tea leaves and coffee refuse make the chokage water-tight.
If the back-vent branches be too low, this dangerous state of affairs may go on unnoticed, until finally the system becomes so clogged that it will at last show itself somewhere.