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Plumbing Basics


Your home's supply and drainage system must always be two distinct subsystems, with no overlapping. At the fixtures (bridges between the two systems), the air admitted by the vent stack and vent pipes keeps the traps sealed and prevents sewer gases from backing up through the drains. See more plumbing pictures.
©2006 Publications International, Ltd.

 

Plumbing follows the basic laws of nature -- gravity, pressure, water seeking its own level. Knowing this, you can understand its "mysteries" and make dozens of fixes to your home's plumbing system. You can save yourself time, trouble, and money!

The plumbing system in your home is composed of two separate subsystems. One subsystem brings freshwater in, and the other takes wastewater out. The water that comes into your home is under pressure. It enters your home under enough pressure to allow it to travel upstairs, around corners, or wherever else it's needed. As water comes into your home, it passes through a meter that registers the amount you use. The main water shutoff, or stop, valve is typically located close to the meter. In a plumbing emergency, it's vital that you quickly close the main shutoff valve. Otherwise, when a pipe bursts, it can flood your house in no time. If the emergency is confined to a sink, tub, or toilet, however, you may not want to turn off your entire water supply. Therefore, most fixtures should have individual stop valves.

Water from the main supply is immediately ready for your cold water needs. The hot water supply, however, requires another step. One pipe carries water from the cold water system to your water heater. From the heater, a hot water line carries the heated water to all the fixtures, out-lets, and appliances that require hot water. A thermostat on the heater maintains the temperature you select by turning the device's heating elements on and off as required. The normal temperature setting for a home water heater is between 140 degrees F and 160 degrees F, but 120 degrees F is usually adequate and is also more economical. Some automatic dishwashers require higher temperature water, though many of these have a water heater within them that boosts the temperature another 20 degrees F.

Drainage Systems

Some sink traps have a clean-out plug that enables you to clean the trap without having to remove it from the drain.
Some sink traps have a clean-out plug that enables you to clean the trap without having to remove it from the drain.
©2006 Publications International, Ltd.

Whether your home is on a sewer or septic system, the systems within your home are essentially the same. Drainage systems do not depend on pressure, as supply systems do. Instead, waste matter leaves your house because the drainage pipes all pitch, or angle, downward. Gravity pulls the waste along. The sewer line continues this downward flow to a sewage treatment facility or a septic tank.

While the system sounds simple, there's more to it, including vents, traps, and clean outs. The vents sticking up from the roof of your house allow air to enter the drainpipes. If there were no air supply coming from the vents, wastewater would not flow out properly and the water in the traps would need to be siphoned away.

Traps are vital components of the drainage system. You can see a trap under every sink. It is the curved or S-shape section of pipe under a drain. Water flows from the basin with enough force to go through the trap and out through the drainpipe, but enough water stays in the trap afterward to form a seal that prevents sewer gas from backing up into your home. Every fixture must have a trap. Toilets are self-trapped and don't require an additional trap at the drain. Bathtubs frequently have drum traps, not only to form a seal against sewer gas but also to collect hair and dirt in order to prevent clogged drains. Some kitchen sinks have grease traps to collect grease that might otherwise cause clogging. Because grease and hair are generally the causes of drain clogs, traps often have clean-out plugs that give you easier access to remove or break up any blockage.

Since a drainage system involves all of these components, it is usually referred to as the DWV: the drain-waste-vent system. If water is to flow out freely and waste is to exit properly, all components of the DWV must be present and in good working order. Examine the pipes in the basement or crawl space under your house to help you understand the system better.

Supply and Drainage Subsystems

Fixtures should have individual supply shutoff valves so that you don't need to close the main shutoff to make repairs at the fixture.
Fixtures should have individual supply shutoff valves so that you don't need to close the main shutoff to make repairs at the fixture.
©2006 Publications International, Ltd.

The supply and drainage subsystems are two distinct operations, with no overlapping between them. There are bridges between the two, however, and the bridges are what make the plumbing system worth having. In plumbing jargon, any bridge between the supply and drainage systems is a fixture.

Toilets, sinks, and tubs are fixtures. In addition, an outside faucet is a fixture and so is a washing machine. All devices that draw freshwater and discharge wastewater are fixtures, and all are designed to keep the supply and drainage systems strictly segregated.

Some fixtures have individual supply shutoff valves so you don't need to close the main shutoff to repair them. It's a good idea to make sure everyone in the family knows the location of the main shutoff valve in your house as well as how to use it. You may want to tag the main shutoff valve so anyone can easily find it.

Before you embark on any plumbing repairs, always turn off the water supply to the fixture or the main shutoff. In addition, check with your local plumbing code official before you add or change any pipe in your house. You will learn what is allowed and what is prohibited and whether or not a homeowner is allowed to do his or her own work. If you get the green light, you can save yourself a lot of money by doing your own repairs.

©Publications International, Ltd.