Learning How Drain Plumbing Functions

Written by Adrianna Noton Sunday, 24 April 2011 03:03

When water passes through fixtures, the functions to allow waste water, also called white or bad water, to discharge. If it comes in, it must go back out. For a drain-waste-vent system to work correctly all basic elements must be present. Common rules must be observed when either installing or repairing these systems.

When water passes through fixtures, the functions to allow waste water, also called white or bad water, to discharge. If it comes in, it must go back out. For a drain-waste-vent system to work correctly all basic elements must be present. Common rules must be observed when either installing or repairing these systems.

As water enters by means of supply lines, it is pressurized. For this reason it flows evenly throughout the whole system, even moving uphill. When it exits as waste, it moves by the force of gravity, and will not travel uphill. For that reason the line must have a pitch, of 1.25 inches (3.175 cm) per foot (30.78 cm), which creates an angle that allows it to flow freely.

The pipe must be of sufficient diameter so that waste flows easily through it without clogging. As a rule it should be at least half the diameter of the fixture, and not less than 1.25 to 2 inches (3.175 to 5.08 cm). For showers the minimum should be 2 inches (5.08 cm) and with toilets a minimum of 4 inches (10.78 cm) should be observed.

These lines are made of several possible materials. Today ABS plastic, cast iron, or copper are common. Some older homes still use lead.

The lines must not only allow a free exit of water but they must not allow sewer gas to come into the home from below. This is accomplished with a trap. This is a curved section which will hold a small quantity of water, which is prevented by gravity from escaping. By looking beneath a bathroom sink, just such a trap can be observed. A P trap is seen with a line exiting into the wall, or a S trap will be noticed if the line exits through the floor.

This water in the trap will seal the line, preventing gas from passing through. As additional water is run through the fixture it will replace this water leaving the same amount again in the end. If a fixture is not used for an extended time this water will evaporate out allowing gas to rise into the home.

The last element needed for the proper functioning of the system is a vent. Each fixture drain requires a vent exiting either directly through the roof, or by means of a common stack. Several purposes are served by this. Gasses are thus allowed to exhaust from the home. Oxygen can enter the system which aids with the aerobic digestion of the sewage, and the build up of slime or corrosion of the pipes is lessened.

Lastly it normalizes air pressure between the system and the ambient outside pressure. When water moves down the pipe air must be able to be drawn in behind or it will drag the water out of the trap, and gas will be able to enter the home. Also, if not vented, pressure within the Drain Plumbing Toronto can increase to a point where gas and sewage can force their way through the trap water, into the house.