Transcript Slide 1

WATER SUPPLY PIPING FOR BUILDINGS
PLUMBING OBJECTIVE: The correct method of properly
sizing plumbing pipes.
Piped in water supply systems have become an
essential part of society. Think as you got up this morning
what it would have been like if you didn’t have water.
Perhaps you couldn’t get a drink, brush your teeth, or flush
a toilet. Indeed life would be a little different.
Thank goodness for the folks who pioneered plumbing.
It probably is the most convenient, yet most taken for
granted part of our modern technology. Truly this is a
system we don’t notice when it is there and works. But
abruptly do without plumbing, and life gets miserable.
There are two primary parts of plumbing.
Water supply piping
Piping for waste – getting rid of all that water
Supply piping has evolved with modern technology. In
the earliest times, pipe was made of wrought iron, and was
not easily worked. Piping then changed to steel, then
galvanized steel with a coating of zinc to retard rust.
Installation was difficult because pipe joints had to be
threaded and joined with fittings to make the system
water-tight.
Installation of steel piping was slow and tedious,
because lengths between fittings had to be cut exact, then
fastened together with threaded joints, one following
another in progression.
Copper pipe was developed, along with a new type of
fitting to connect joints. Pipe and joints no longer needed
to be threaded. Copper piping is joined together with brass
fittings, in a connection called a “sweated Joint.” A brass
fitting is heated with a gas torch so the material expands.
While it is still hot, the fitting easily slides over the outside
of the end of the pipe, and when it cools, the fitting
contracts against the pipe to make a tight fit. The
connection is then soldered.
Plastic piping, such as polyvinylchloride (PVC) was
developed into an economical and efficient system, but is
not suitable for water piping under pressure inside
buildings. The fittings and methods of joining are not
dependable enough to trust against a leak that might occur
inside a wall or an attic. But PVC piping is used extensively
where piping is installed outside of habitable buildings.
Within the past several years a high strength plastic
pipe has been developed that is suitable for high pressure
water systems, and is approved by most building codes.
The fittings are made of brass, and the connections by steel
crimps. The major advantage of the material is that it is
manufactured in long rolls, making installation easier
because it eliminates many joints in a system.
Another advantage is that the material for cold water
use is translucent white, and the material for hot water use
is translucent red. The pipe also comes in blue. Material is
manufactured under the name “Wirsbo-pex.” Wirsbo is a
manufacturer’s name, and “pex” is a chemical acronym for
“polyethylene cross-linked,” hence the X.
Water is transported through a system of piping by
pressure. A common pressure available from a municipal
system may be in the vicinity of 60 pounds per square inch.
In early times, the most economical way for a municipality
to provide water pressure was to raise a water tank to a
height of 100 feet or so, and the weight of the water would
cause the pressure.
Consider that water weighs 62.4 pounds per cubic foot.
Imagine a volume of one cubic foot, a block 12” x 12” x
12” high. Then divide the block into one inch x one inch
columns, each 12 inches tall. The cubic foot would consist
of 144 of these 1” x 1” x 12” columns of water.
How much would each column weigh? 62.4 divided by
144 = 0.433 pounds. Since the cross section area of one of
these columns of water is one square inch, it follows that
the weight of water transposes to 0.433 pounds per square
inch, PER FOOT OF HEIGHT.
Since unit pressure, or stress, is in terms of weight per
unit of area, and the cross section of the column is one
square inch, water pressure equals 0.433 psi per foot of
height.
So what is the pressure of a one-square-inch column of
water ten feet high? 0.433 x 10 = 4.33 pounds.
What is the pressure of a one-square-inch column of
water one hundred feet high? 0.433 x 100 = 43.3 pounds.
Say you have a vertical pipe, 2” in diameter, 10’ high.
What is the pressure at the bottom of the pipe? 4.33 psi.
What if the pipe were 4” in diameter, what would be the
pressure in the bottom of the pipe? 4.33 psi.
It doesn’t matter the volume of water per foot of height
- - - unit pressure is in pounds per square inch. If the ocean
were only one foot deep, the pressure at the bottom would
be 0.433 psi.
Pressure is the force that pushes water through a
system, from the point of origin, to the fixture that is
farthest away from the source. Available pressure
diminishes within the system for a variety of reasons; first,
it takes pressure to make the water meter work, so some of
the available pressure is used to operate the water meter.
Then, if the water piping rises in height, say from the water
meter that may be 3’ below the ground, and the pipe
extends upward to the attic space within a building, a
portion of available pressure must be used to raise the
water upward.
Then a portion of the available pressure must be used to
operate a fixture, such as a sink, lavatory, or water closet.
And finally, there is pressure lost in the system because of
friction. Water moves against the walls of the pipe, and
water movement must negotiate through bumps at fittings
and valves.
All these contribute to the reduction of pressure from
the source to a point of use.
Another aspect of properly sizing the pipes in a
plumbing system is the speed at which water moves
through the system. If water is allowed to move faster than
about 8 feet per second, the movement will cause
turbulence against the walls of the pipe, and through
fittings. Turbulence in water flow creates NOISE.
In areas like West Texas, where the water contains a
large amount of particulate matter, (calcium, magnesium,
etc.) the turbulence will cause the particles to fasten
themselves to pipe walls due to a difference in electrical
charge. Over a period of time, particles build up in the pipe
and reduce the effective diameter of the pipe.
Plumbing fixtures have evolved through improvements
in design required by efficiency of use, and by some
governmental regulations with purpose of conserving water.
Plumbing fixtures; sinks, lavatories, closets, faucets,
etc., are rated by water use in terms of FIXTURE UNITS. A
fixture unit once was defined as one cubic foot of water,
but that definition has no specific meaning in sizing piping.
Fixtures defined by fixture units is a comparison of the
amount of water used – and these comparisons have led to
the development of a chart defining gallons per minute
demand, based on quantities of fixtures, and a reasonable
assumption of frequency of simultaneous use of fixtures.
In other words, the more fixtures that are installed
within a system, the less likely that all fixtures are used at
the same time. So demand in gpm is less per fixture unit as
the number of fixture units increase.
Standard plumbing fixture charts through history of use
define the amount of fixture units per fixture, based
primarily on their demand for water.
Two pages of the supplementary packet contain charts and
tables that are useful as the basic components of water
piping design.
First Chart (next slide)
Upper left gives maximum pressure required for fixtures.
Lower right gives fixture unit value for various fixtures.
Lower left gives pressure required to operate water
meters.
Upper right gives the length of a straight piece of pipe that
is equal to the amount of friction loss for various
fittings.
FIXT PRESSURE
FITTINGS
FIXTURE UNITS
WATER METER
water
flow
water
flow
water
flow
90 degree
standard ell
water
flow
water
flow
standard
coupling
inline tee
90 degree
side tee
45 degree
standard ell
water
flow
valve of
various types
STANDARD PIPE FITTINGS
( FRINGES )
GLOBE VALVE
CHECK VALVE
GATE VALVE
ANGLE VALVE
There are two charts on the opposite side:
Chart One is the conversion from fixture units to quantity
of water in gallons per minute. Notice the chart has two
double columns; one labeled at the top for
Predominantly Flush TANKS, and to the right,
Predominantly Flush VALVES.
Valve types refer to the method by which water closets
and urinals expel waste. Flush tanks are the domestic
type, like in a residence, where water for flushing is stored
in a tank at the back of the fixture.
Flush valves are the commercial type where there is no
tank, and water for flushing must all come from the water
supply pipes. This type of fixture requires more pressure
and larger pipes to flush.
Notice in the conversion chart that as the number of
fixture units INCREASE, the quantity in gallons per minute
decreases proportionately. This is simply an indication that
the more fixtures in a facility, the less likely that all will be
required to flush at the same time.
The second chart on the page is one that shows the
relationship between available water pressure in p.s.i. per
100 feet, the flow of water in gallons per minute, the flow
velocity of water, and the pipe diameter.
First, limit the flow of water to 8 ft. per second. That is
indicated by a slanted line from upper left to lower right.
Then determine the available water pressure in p.s.i.
per 100 feet from the piping layout. That will be a straight
line upward from the bottom of the chart.
Where the two lines intersect will determine if the size
of the pipe is based on available pressure, or by limiting the
velocity of water to 8 fps.
Diameter of pipe is indicated by a slanted line from
lower left to upper right, and where this pipe diameter line
FIRST intersects the pressure line or the velocity line,
READING HORIZONTALLY TO THE LEFT, will be the maximum
amount in gpm that particular pipe diameter will supply.
An example problem follows, and shows a simple step
by step procedure for determining the proper pipe size.
PLUMBING
WATER SUPPLY EXERCISE
12
fixture
units
total fixture units = 30 = 20 gpm
longest length = 90'
meter pressure loss = 9 psi
rise pressure loss
= 4.33 psi
psi
fu 12
9 gpm
total pressure loss = 28.33 psi
flow 20 fu
30 fu
Available pressure of 60 psi, minus
28.33 pressure loss = 31.67 psi
to push the water through the system.
14 gpm
31.67'
x 100 = 23.46 psi / 100'
135'
Limit the velocity of
water through the piping
to no faster than 8 feet / sec.
Using the pipe size chart 2
make a table that shows the
max. gpm for each pipe size:
pipe dia. max gpm
1/2"
3/4"
1"
1 1/4"
1 1/2"
2"
3 1/2
10
18
28
44
78
Water
Meter
30 fu
flow
system rises 10'
The available pressure in psi per 100'
gpm
8 fu
7 gpm
flow
6'
20 gpm
flow
6'
fixture pressure loss = 15
System is predominately
flush TANKS
8 10 fu
10
fixture
units
flow
20 gpm
Available
pressure =
60 p.s.i.
50'
12'
8'
Measured length of system (origin to farthest fixture) = 90'
Calculated length (measured length + 1/2 measured length) = 90 + 45 = 135'
10'
flow
8
fixture
units
In the process, two assumptions must be made, and will
be verified later in the calculation. First, a meter size is not
known until pipes are sized, so an assumed meter size must
be selected. At the water meter chart, the total gpm for
the system is known ( 20 gpm ) Find 20 gpm at the bottom
of the chart and draw a straight line upward from the
bottom. Probably the line will cross 2 or 3 slanted lines
(that indicate meter size). Select the middle one and read
to the left to see a pressure to operate the meter is 9 psi
for a ¾” meter.
Second, since pipe sizes are not known, the equivalent
length of fittings must be assumed. The equivalent length
of fittings is the addition of equivalent lengths for each
fitting that is in the pipe that extends from the source of
water to the fixture that is farthest away. Since this cannot
yet be determined, ASSUME AN EQUIVALENT LENGTH OF ½
THE MEASURED LENGTH. In this case, the measured length
is 90 feet; ½ of 90 = 45; 90 + 45 = 135’ which is the
CALCULATED length.
After subtracting the pressure loss of meter, rise, and
fixture, an amount remains as the pressure that pushes the
water through the system. But the pipe size chart needs a
number that is the available pressure per 100 feet of
length. Since an available pressure remains of 31.67 psi, it
must push the water a distance of 135 feet. So pressure per
100 feet equals (pressure / calculated length) x 100.
In this case, 31.67 x 100 = 23.46 psi/100 feet
135
On the pipe size chart, draw a line from 23.46 upward from
the bottom of the chart and stop it at the 8 fps velocity
line.
PLUMBING
WATER SUPPLY EXERCISE
12
fixture
units
total fixture units = 30 = 20 gpm
longest length = 90'
meter pressure loss = 9 psi
rise pressure loss
= 4.33 psi
psi
fu 12
9 gpm
total pressure loss = 28.33 psi
flow 20 fu
30 fu
Available pressure of 60 psi, minus
28.33 pressure loss = 31.67 psi
to push the water through the system.
14 gpm
31.67'
x 100 = 23.46 psi / 100'
135'
Limit the velocity of
water through the piping
to no faster than 8 feet / sec.
Using the pipe size chart 2
make a table that shows the
max. gpm for each pipe size:
pipe dia. max gpm
1/2"
3/4"
1"
1 1/4"
1 1/2"
2"
3 1/2
10
18
28
44
78
Water
Meter
30 fu
flow
system rises 10'
The available pressure in psi per 100'
gpm
8 fu
7 gpm
flow
6'
20 gpm
flow
6'
fixture pressure loss = 15
System is predominately
flush TANKS
8 10 fu
10
fixture
units
flow
20 gpm
Available
pressure =
60 p.s.i.
50'
12'
8'
Measured length of system (origin to farthest fixture) = 90'
Calculated length (measured length + 1/2 measured length) = 90 + 45 = 135'
10'
flow
8
fixture
units
From this little chart that is made to show the limit in
gpm of water for each pipe size, go to the plan layout and
write the sizes of pipes for each segment.
When you get to the maximum size of pipe at the
meter, notice if it is larger than the meter you assumed.
Chances are, the meter will need to be larger, which will
result in LESS pressure required to operate. So the first
assumption will be OK.
Last - - - list the types and sizes of fittings along the
pipe that extends from the meter to the farthest fixture.
Add the equivalent lengths to see if it exceeds 45’, which
was the assumption made for equivalent length of fittings.
If the added numbers are less than 45’, then the second
assumption is OK. If the number is larger than 45’, then go
back and recalculate the available pressure in psi per 100
ft., and recalculate the little pipe size chart.
PLUMBING
WATER SUPPLY EXERCISE
12
fixture
units
total fixture units = 30 = 20 gpm
longest length = 90'
meter pressure loss = 9 psi
rise pressure loss
= 4.33 psi
psi
fu 12
9 gpm
total pressure loss = 28.33 psi
flow 20 fu
30 fu
Available pressure of 60 psi, minus
28.33 pressure loss = 31.67 psi
to push the water through the system.
14 gpm
31.67'
x 100 = 23.46 psi / 100'
135'
Limit the velocity of
water through the piping
to no faster than 8 feet / sec.
Using the pipe size chart 2
make a table that shows the
max. gpm for each pipe size:
pipe dia. max gpm
1/2"
3/4"
1"
1 1/4"
1 1/2"
2"
3 1/2
10
18
28
44
78
Water
Meter
30 fu
flow
system rises 10'
The available pressure in psi per 100'
gpm
8 fu
7 gpm
flow
6'
20 gpm
flow
6'
fixture pressure loss = 15
System is predominately
flush TANKS
8 10 fu
10
fixture
units
flow
20 gpm
Available
pressure =
60 p.s.i.
50'
12'
8'
Measured length of system (origin to farthest fixture) = 90'
Calculated length (measured length + 1/2 measured length) = 90 + 45 = 135'
10'
flow
8
fixture
units
END OF FIRST DAY PLUMBING
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