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Sanitary Drainage Systems - Volume Flow

Calculate expected volume flow load in sanitary drainage systems.

The theoretical total load for a sanitary drainage system can be calculated by adding loads for every fixture in the system. Due to intermittent use of the fixtures - this method in general adds up to unrealistic high values for the main drainage lines.

• realistic - or expected - total load is always lower than theoretical total load

Expected total load for sanitary drainage systems should instead be estimated by using empirical equations like

qet = k ( Σqn )1/2                                (1)

where

qet = expected total drainage load (gpm, l/s)

k = system coefficient describing the nature of the system

Σqn = total theoretical load - all fixtures summarized (gpm, l/s)

Note that the minimum expected total load can never be less than the load from the largest fixture.

The system coefficient compensates for the nature of the system. For systems serving large groups of people where the use is intermittent, like

• hotels
• hospitals
• schools
• theaters
• wardrobes in factories
• etc

the coefficient - k - should be in the range 0.5 - 0.8. Closer to 0.8 for smaller systems with fewer fixtures and closer to 0.5 for larger systems with many fixtures.

For more ordinary systems where consumption patterns are more continuously, like

• homes
• offices
• nursing homes

the coefficient - k - should be in the range 0.3 - 0.6. Closer to 0.3 for larger systems with many fixtures and closer to 0.6 for smaller systems with few fixtures.

Example - Sanitary Drainage System Hospital

If the theoretical total load from fixtures in a smaller hospital adds up to 50 l/s - the expected total load can be estimated to

qet = 0.7 (50 l/s)1/2

= 4.9 l/s

Assuming this is a smaller hospital the coefficient is set to 0.7.

Related Topics

• Sanitary Drainage Systems - The purpose of the sanitary drainage system is to remove effluent discharged from plumbing fixtures and other equipment.

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Temperature

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Length

m
km
in
ft
yards
miles
naut miles

Area

m2
km2
in2
ft2
miles2
acres

Volume

m3
liters
in3
ft3
us gal

Weight

kgf
N
lbf

Velocity

m/s
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ft/min
ft/s
mph
knots

Pressure

Pa (N/m2)
bar
mm H2O
kg/cm2
psi
inches H2O

Flow

m3/s
m3/h
US gpm
cfm

3 30