A pressure sewer system uses small-diameter pipes and grinder pumps installed at each home. The sewer lines are buried just below the ground and follow the contours of the land ("up and down" hills or a constant grade across flat land, for example).

The grinder pump station collects all of the wastewater from the home and grinds it into slurry. The wastewater is then pumped to a wastewater treatment plant or system, a gravity manhole, a larger sewer main or to a septic system.

Ecoflow utilise the Probability Method for Pressure Sewer Design. This method is well accepted, flexible, and appropriate in the vast majority of applications. There are more pressure sewer systems design and operating around the world that utilise the probability method than all the other methods combined.

The probability method (also often referred to as the simultaneous operations method) uses a statistical approach that is based on empirical data. The model provides that, given a total population of pumps, there is a maximum number of pumps that will be operating simultaneously.

When the probability method is used in conjunction with the E/One progressive cavity grinder pump (that outputs a relatively consistant flow rate regardless of the network pressure), a system designer is able to accurately calculate the flow by multiplying the flow rate from an individual pump by the total number of simultaneous operations.

Once the flow is known, the pipe network can be sized to balance the total dynamic head (TDH) on the pump, the velocity in the pipeline, and the retention time. TDH should be minimised, velocity should be kept above 0.6 m/s, and retention time should be minimised.

The design process includes the following steps:

1. Collect information: Project layout showing location of connections (scaled); contour information; discharge location

2. Sketch a proposed pipe network layout: Flow should generally always head towards the discharge; no loops

3. Create zones designations where flow changes: More pumps operating simultaneously; and where two branches connect

4. Perform hydraulic calculations. Determine optimal pipe sizes to balance head, velocity, and retention time.

5. Optimize the design as required

Ecoflow offers a no-cost preliminary design service to help users evaluate the feasibility of a pressure sewer for a project. Contact us for help.

**Note: While more sophisticated methods of pressure sewer design are available (like Dynamic Modeling), it is Ecoflow’s experience that Dynamic Modeling rarely results in meaningful optimisation. The Probability Model and the E/One Progressive Cavity Grinder Pump together result in a resilient and forgiving solution that reduces risks for system designers, system suppliers, installation contractors, operations and maintenance teams, and ultimately the end users.

The typical pipe size between the grinder pump station and the property boundary is 40mm.

The common rising main size will vary depending on the system hydraulics (number of pumps connected, distance, elevation, etc.). Typical rising main sizes vary from 50mm to 225mm.

Ecoflow recommends high density polyethylene (HDPE).

HDPE is commonly used in water and wastewater applications and has demonstrated to be robust and resilient.

The most common pipe used in pressure sewers in New Zealand is PE100 SDR11.

Ecoflow recommends that combination air/vacuum valves be utilised in the pipe network.

Air/vacuum valves, air release valves and combination air valves prevent the concentration of air at high points within a system. This is accomplished by exhausting large quantities of air as the system is filled and by releasing pockets of air as they accumulate while the system is in operation and under pressure. Air/vacuum valves and combination air valves also prevent a potentially destructive vacuum from forming.

Air/vacuum valves should be installed at all system high points and significant changes in grade. Combination air valves should be installed at those high points where air pockets can form.

Most infrastructure design standards include guidance on valve use and placement. Contact Ecoflow for any help.

It depends. Ecoflow typically designs pressure sewer systems up to a maximum of 56 meters of total dynamic head. That means a single E/One pump can pump over and over a 56 meter hill or several kilometers in a straight line. However, the reality is that there are often other considerations when understanding if an application will work.

Ecoflow can help answer these questions - just contact us for help!

Also - there are a couple short video resources from E/One that may provide some assistance. Check them out here.

If the alarm turns off after a few minutes and does not turn on again, the grinder pump should be OK. Check regularly to ensure that the grinder pump is operating and the alarm is not on.

If the alarm turns on and off repeatedly or turns on and stays on, call an authorised service center (like Ecoflow) for service. Discontinue water use to avoid causing a backup or overflow.

Look on your alarm panel for a service sticker with a phone number.

A typical single family home uses less than 700 litres of water per day. The E/One will use between 9 and 20 kWh per month (60-240 kWh per year). Check your utility bill for the cost per kilowatt hour in your area. For example, if you pay 11 cents per kilowatt hour: $0.25 KWh x 120 KWh = $30.00 per year cost of electricity to operate the E/One pump.

It depends on the ownership model of the pressure sewer system. The ownership model is typically dictated by the local council or water authority.

When systems are publicly owned, the council or water authority is responsible for the costs to maintain the grinder pumps. This has economic and logistic benefits.

When the systems are privately owned, the grinder pump stations are owned by the individual property owners. Costs to operate, maintain, and replace the systems are the responsibility of the property owner. This model is easier for the council but may result in unexpected expenses for the homeowner - similar to when other household appliances require maintenance.

Ecoflow are specialists in the products from Environment One Corporation (E/One). E/One invented the concept of pressure sewers in the 1960s and continue to be the global market leaders and innovators.

Ecoflow may not have the expertise to service or repair systems from other suppliers. However, Ecoflow may be able to help you retrofit your system to be compatible with E/One grinder pumps. Contact us for more details.

Most standards or design guidelines recommends the pressure sewer system achieves a minimum periodic velocity of 0.6 meters per second. This is generally accepted around the world as the minimum velocity to promote "self-scouring" or self-cleaning of the inside of the pressure sewer pipe network.

The velocity is determined by considering the number of grinder pumps which will be operating simultaneously (and therefore the flow) and selecting an optimal pipe size that will balance the pressure or head of the pump whilst accomplishing the minimum velocity.

A properly operating system should not smell. If you can smell the system, something may be wrong and it might be best to have a service technician check it out.

One exception may be if the system has not been used for a long period of time (4+ weeks). It is possible that the retained wastewater in the system may have gone septic. You usually won't notice until you return and start using water again. If that's the case, the odour will typically disperse after a short period of time with regular water use.

If you are leaving for an extended period of time, it's best to flush the system with clean water (e.g. fill a bath) before departing. Also - it's best to leave power on to the system even if you plan to be gone for a period of time.