Sewerage System Comparisons:
Gravity, Vacuum or Low Pressure Pumps

Gravity	Vacuum	Low pressure
POWER REQUIREMENTS
Electricity required only at the Pump Station, and a number of pump stations may be required to service a single Catchment.	Power is required only at the Pump Station, so a back-up generator can be supplied if required. A single pump station is usually all that is required to cover a large area, thus reducing overall power costs versus gravity. Pumps only run on average 3 hours per day so power use is lower than alternative systems.	Grinder pumps require power at each unit. The panel is usually installed on the side of the house and power paid by the homeowner. Existing houses may need to upgrade electrical mains and power board. Some pumps require constant power. Systems that require transfer pump stations will require high total power use.
CONNECTIONS
No restrictions on connections	Usually 4-6 homes are connected to a single collection pit, though larger flows from a gravity area can be accommodated into a multiple collection pit. Hotels, schools and high flow areas can be serviced.	One pump is required per house. If the house is large or commercial flows anticipated then a larger capacity pump may be required. Camping grounds and high flow situations are not recommended.
EXFILTRATION
A broken pipe will go unnoticed for many months and the depth of the gravity lines will make detection difficult and expensive to repair.	Since vacuum is maintained within the mains at all times there is no chance of exfiltration of sewage. Operators are immediately alerted of a leak in the main due to longer vacuum pump run times and the leak can quickly be found and repaired.	As all pipework is under pressure then a break in the pipe will lead to large exfiltration. Not suitable in environmentally sensitive areas.
INFILTRATION
Broken pipe can go unrepaired for long periods allowing stormwater to enter the system. This increases Treatment costs and power use.	As it is a vacuum tight system, infiltration cannot occur.	As it is a pressurized system infiltration cannot occur.
MAINTENANCE
Low initial costs but high long term costs due to multiple pump stations and deep gravity mains. As all services are usually on public property accessibility is not a problem.	If service is required a single operator takes on average 10-15 minutes to complete any service required. No special equipment is required. Parts costing less than $20/year required for the interface valve. As all services are on public property accessibility is not a problem. 10 Year warranty is supplied	Most callouts require the pump to be lifted out. An electrician is needed to be part of the service team. Access is difficult as all equipment is on the homeowner’s property. One Year warranty only supplied for certain components. Sand and Grit will cause faster wear on the grinder cutters. If it is in a high flow situation some parts may require annual change.