Vacuum drainage systems | Archive Titles

Table 1: The differences between conventional and vacuum drainage systems
Parameter	Conventional (gravity)	Conventional (pumped)	Vacuum
Pipe size (mm)	Branches 32-100 Stacks 100-150	Branches 32-100 Stacks 100-150	Discharge from valves 32-50 Service connection 38-90
Pipeline gradient	To a fall	To a fall	Flexible arrangements, with minimal gradients or sawtooth profile. Vertical upward flow sections ‘lifts’ can be used
Maintenance requirements	Negligible, only after abuse or blockage	Regular planned servicing of pumps and interface units	Regular, planned servicing of pumps and interface units
Energy requirements	At time of installation	At time of installation and throughout lifetime of building	At time of installation and throughout lifetime of building
Retrofit or extension of system within building	May be difficult to accommodate pipework and falls	May require additional pumps	Flexible layout makes installation simple
Water consumption	7·5 litre flush wcs	7·5 litre flush wcs	N/A
Low water consumption wcs	6 litre flush wcs	6 litre flush wcs	1·5 to 3 litre flush vacuum toilets
Loading of sewerage system	Dependent upon appliances installed	Dependent on pumping rate	Discharge from forwarding pumps can be times to coincide with low flow periods

Table 2: advantages and disadvantages of vacuum drainage systems
Advantages	Disadvantages
Low installation costs	High component costs
Environmentally safe	Mechanical components – possibility for failure
Electrical power only required at vacuum station	Skilled design, installation and maintenance required
Always self cleansing	Regular maintenance required
No possibility of vermin in pipe lines	Standby facilities required
High turn around time – no need for cistern to refill for subsequent flushes	Require area for situation of vacuum tanks and vacuum generation equipment
High water velocities prevent deposits in pipework	High velocity water may cause transient plumbing noise
Minimise risk of leakage
Can use small diameter lightweight pipes which can be installed without a continuous fall
Vertical lifts are possible
Ability to easily separate grey and black water
Possible water saving technique if vacuum toilets are used