Expected Loads in Sanitary Drainage Systems

Calculate expected loads in sanitary drainage systems

The total theoretical load for a sanitary drainage system can be calculated by adding all fixtures known maximum loads. Due to the nature of intermittent use the number of fixtures will unfortunate add up to unrealistic loads for the main drainage lines to handle. Realistic loads will always be far less than the total theoretical loads.

An expected load for a sanitary drainage system can be estimated using a formula like

q_et = k ( Σq_n )^1/2 (1)

where

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

k = system coefficient describing the nature of the system

Σq_n = 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 is used to compensate the calculation to the nature of the system. For systems typical 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 few 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 loads from the fixtures in a smaller hospital adds up to 50 l/s, the expected load can be estimated to

 q_et = 0.7 ( 50 )^1/2

    = 4.9 l/s

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

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