SEWER SEWER PIPING DESIGNPIPING DESIGN

Sewer piping differs from water piping, in Sewer piping differs from water piping, in that sewer pipes are not under pressure. The that sewer pipes are not under pressure. The function that takes place inside sewer pipes is at function that takes place inside sewer pipes is at ambient atmospheric pressure, and the influence ambient atmospheric pressure, and the influence of gravity.of gravity.

Sewer pipes drain because they are installed Sewer pipes drain because they are installed on a slope and fluids flow downhill. The slope of on a slope and fluids flow downhill. The slope of sewer lines is a consideration because most sewer lines is a consideration because most effluent floats, and slow movement of the drain effluent floats, and slow movement of the drain allows solids to flow unobstructed. But if the flow allows solids to flow unobstructed. But if the flow is too rapid, larger solids tend to tumble, and is too rapid, larger solids tend to tumble, and become a potential for clogging a drain pipe. become a potential for clogging a drain pipe. Ideally, a horizontal sewer drain is never more Ideally, a horizontal sewer drain is never more than half full. than half full.

Drain lines that must traverse excessive Drain lines that must traverse excessive height in a short lateral distance are installed with height in a short lateral distance are installed with vertical drops rather than excessive slope.vertical drops rather than excessive slope.

Drain pipes are installed so the slope is Drain pipes are installed so the slope is consistent from the location of the fixture that is consistent from the location of the fixture that is farthest from the entrance into a public drain, or farthest from the entrance into a public drain, or to some suitable disposal.to some suitable disposal.

For this reason, the slope of drain pipes is For this reason, the slope of drain pipes is critical to their efficiency. If a drain from a critical to their efficiency. If a drain from a fixture in an intermediate area in a system is fixture in an intermediate area in a system is installed lower than the consistent point in the installed lower than the consistent point in the drain system, effluent will collect in the low drain system, effluent will collect in the low areas, and the system will not drain well.areas, and the system will not drain well.

flow

In addition to consistent slope, it is a requirement of the plumbing code for all turns in direction of piping be done with 45 degree fittings in the direction of flow, rather than 90.

This facilitates the movements of slow moving solids through a drainage system.

CROSS SECTIONCROSS SECTIONTHROUGH SINKTHROUGH SINKOR LAVATORYOR LAVATORYDRAIN AND VENTDRAIN AND VENT

Without a vent forWithout a vent forsupply of air tosupply of air toreplace fluid in replace fluid in the drain, siphonthe drain, siphonaction would pullaction would pullthe fluid out ofthe fluid out ofthe trapthe trap

Non-integral trap

Non-integral

trap

A vent provides a path to

Expel toxic sewer gas to

The atmosphere

Blowout – Public - Loud Siphon Jet – Residential - Quiet

WATER CLOSETS - Types of Discharge

The “seal” area in the diagrams indicate the integral trap. Because of the water that remains in the bowl, sewer gas is blocked from coming into the room .

The sizing of pipe for drainage is far less The sizing of pipe for drainage is far less complex than that for water piping, as there is no complex than that for water piping, as there is no pressure involved, no rate of flow of water, and pressure involved, no rate of flow of water, and distance makes a difference only in that enough distance makes a difference only in that enough slope must be available to accommodate the slope must be available to accommodate the drainage.drainage.

Three charts are pertinent to drainage.Three charts are pertinent to drainage.

The first chart lists the fixture unit value for The first chart lists the fixture unit value for fixtures, which are not quite the same as for fixtures, which are not quite the same as for water supply fixture units.water supply fixture units.

The next chart shows the size of non-The next chart shows the size of non-integral traps. A non-integral trap is a drain from integral traps. A non-integral trap is a drain from a fixture to a building drain line, such as the a fixture to a building drain line, such as the drain mechanism beneath the lavatory in the drain mechanism beneath the lavatory in the bath room or beneath the sink in the kitchen. bath room or beneath the sink in the kitchen. Non-integral means that the drain is not part of Non-integral means that the drain is not part of the fixture.the fixture.

An example of an integral trap is a water An example of an integral trap is a water closet or a urinal, which have their own traps, closet or a urinal, which have their own traps, because of the way they are made.because of the way they are made.

The third chart is the one related to The third chart is the one related to determining the collective size of drain pipes in a determining the collective size of drain pipes in a system. The fixture unit values of each unit system. The fixture unit values of each unit determines the size of each segment of pipe in the determines the size of each segment of pipe in the system that serves the fixtures. system that serves the fixtures.

The logical sequence for determining pipe size The logical sequence for determining pipe size is first to draw a plan of the building, showing all is first to draw a plan of the building, showing all the fixtures that are to be installed. A line that the fixtures that are to be installed. A line that represents the drain pipe is drawn to connect the represents the drain pipe is drawn to connect the fixtures, which extends out of the building to an fixtures, which extends out of the building to an available drain deposit, such as a municipal sewer available drain deposit, such as a municipal sewer system.system.

Beginning at the “high” end of the system, Beginning at the “high” end of the system, the fixture unit value for each segment of pipe is the fixture unit value for each segment of pipe is shown. Then from the following chart, the size of shown. Then from the following chart, the size of drain pipe is found. drain pipe is found.

The far left column indicates drain pipe The far left column indicates drain pipe diameter. Notice the top of the chart shows diameter. Notice the top of the chart shows various degrees of slope for drain pipe. For this various degrees of slope for drain pipe. For this course, use the column that allows for a slope of course, use the column that allows for a slope of ¼” per foot. The numbers in the body of the chart ¼” per foot. The numbers in the body of the chart are total fixture units allowed by the pipe sizes for are total fixture units allowed by the pipe sizes for the slope given. the slope given.

scratch

Remember that a Water Closet requires a 3” Remember that a Water Closet requires a 3” drain, and you cannot install more than two drain, and you cannot install more than two Water Closets on a 3” drain. A drain line that has Water Closets on a 3” drain. A drain line that has more than two water closets must be a minimum more than two water closets must be a minimum of 4” diameter, regardless of how many fixture of 4” diameter, regardless of how many fixture units it supports. units it supports.

The next slide shows the drainage plan for The next slide shows the drainage plan for the residence that was used to calculate water the residence that was used to calculate water supply. Realize that the drainage plan is to supply. Realize that the drainage plan is to determine pipe sizes for what is called “rough determine pipe sizes for what is called “rough plumbing,” which is that part of drainage that is plumbing,” which is that part of drainage that is installed below the floor and in walls. The installed below the floor and in walls. The smallest pipe generally used in rough plumbing is smallest pipe generally used in rough plumbing is 2” diameter.2” diameter.

Finish plumbing, or “trim” is the parts of the Finish plumbing, or “trim” is the parts of the plumbing system one can see, beneath cabinets, plumbing system one can see, beneath cabinets, under fixtures, etc., and is made of materials of a under fixtures, etc., and is made of materials of a better finish for appearance and ease of cleaning. better finish for appearance and ease of cleaning.

1

tubbath

CO

lav

7

wc

13

13

1water heater

autowash

shr

wc

22

sink85

lavatory

1

7

CO

204Water Closet

Lavatory

Water heaterAuto Washer

Kitchen SinkBath TubShower

121

322

DRAINAGE FIXTURE UNITS

The next sessions will include plumbing The next sessions will include plumbing waste for fixtures that are stacked more than two waste for fixtures that are stacked more than two story, and the method for determining vents and story, and the method for determining vents and size of vents. size of vents.