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)
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
- wardrobes in factories
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
- 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.
The purpose of the sanitary drainage system is to remove effluent discharged from plumbing fixtures and other equipment.
Dimensions of copper tubes ASTM B306 Drain Waste and Vent - DWV.
Dimensions of Poly(Vinyl Chloride) (PVC) Sewer Pipes with belled end.
Dimensions of cast iron soil pipes.
Cleanouts provides access to the sewer for rodding.
DFU are used to calculate the drainage flow from fixtures and the required capacities of sewer service systems.
Drain pipes and vent stack sizing.
Support of Drain Waste and Vent - DWV - pipes.
Vents in draining systems protects traps against pressure differences that could cause them to siphon or blow out .
Drainage Fixture Units (DFU) connected to building drains and sewers.
Maximum Drainage Fixture Unit - DFU - loads in sanitary piping systems.
Septic systems handles waste from drain systems.
Carrying capacities of sewer and wastewater pipes - gpm and liter per second.
In sewage piping and pumping systems the fluid flow rate must be kept within certain limits to avoid operating problems.