Fibreglass Wet Wells
One-piece FRP wet wells for sewage and stormwater pump stations, made to your project drawings and delivered with the pipework fitted.
What is a wet well?
A wet well is the chamber of a pump station that receives the incoming sewage or stormwater and holds the submersible pumps. Flow builds up in the well until it reaches the pump start level, the pumps lift it into the pressure main, and they stop again at the stop level. The same structure is often called a pump pit or pump well.
A Mullaly wet well is made from fibreglass (FRP) in one piece in our factory, with a solid wall from top to bottom. It arrives on site with the pedestals, guide rails and internal pipework fitted to the approved drawings, ready to lift into the excavation.
Most projects suit a combo pump station, where the wet well and valve chamber are one unit. A separate wet well is used where a larger diameter is needed, or where transport limits rule out taking a combo to site. It is then paired with a stand-alone valve pit.
Wet well sizes
| Model | Diameter | Depth |
|---|---|---|
| ME150 | 1.5m | 2m to 14m |
| ME180 | 1.8m | 2m to 14m |
| ME200 | 2.0m | 2m to 14m |
| ME250 | 2.5m | 2m to 14m |
| ME275 | 2.75m | 2m to 14m |
| ME300 | 3.0m | 2m to 14m |
| ME375 | 3.75m | 2m to 14m |
Deeper wet wells are available on request, and larger diameters are engineered to project. The WSAA appraisal (PA 1020) covers external diameters from 1.2m to 4m.
Fibreglass wet well features
WSAA appraised
Mullaly FRP sewage pump stations hold WSAA product appraisal PA 1020 (Issue 4, valid to 20 April 2031) and are designed to WSA 04-2022 (Version 3.2).
Corrosion resistant
Vinyl ester resin resists the corrosive gases and chemicals in sewage, so the wet well needs no internal coating or liner.
Watertight
A one-piece, factory-made wet well does not rely on sealants applied on site to be watertight.
Fitted out in the factory
Pedestals, guide rails and pipework are fitted before delivery, so less work is done inside the well on site.
Divided chambers
A wet well can be built with an internal dividing wall. At Innes Estate a 1.2m high wall formed two separate pump chambers.
Low maintenance
Smooth walls reduce scum build-up and resist abrasion from suspended grit.
Design and drawings
Each wet well is designed by a registered practising composite engineer as a stand-alone unit for the internal and external loads on its site. Flotation is countered by external ballast, and the ballast calculations to counter hydrostatic uplift are supplied with the installation instructions. Any load on the roof is taken by a reinforced concrete slab spanning the well.
Before manufacture we send CAD fabrication drawings for your approval. They show the layout, a description and location of every fitting and connection, and all levels. A detailed specification for the fit-out pipework is available on request.
Access covers can be aluminium, with lockable hinged lids and safety grates to AS 1664, for pedestrian areas, or ductile iron Class B, Class D or Class G. Class D covers are designed for vehicular traffic.
For the hydraulic side of sizing a wet well, see our pump station design guide.
How a wet well is installed
- 1
Delivered fitted out
The wet well arrives in one piece with pipework, pedestals and guide rails in place.
- 2
Lifted into the excavation
It is craned into the prepared hole and levelled. At Sydney Airport this took under an hour, on reclaimed land with constant wet hole conditions.
- 3
Ballast and backfill
Ballast is placed to the calculations supplied with the installation instructions, then the hole is backfilled.
- 4
Connect pumps and power
The crew connects the external pipework and electrical work and installs the pumps.
Wet wells for sewage and stormwater
The same fibreglass wet well is used for sewage pump stations, where the structure must resist corrosive gases and hold wastewater with no leaks, and for stormwater pump stations, where grit and silt in the flow make abrasion resistance useful. Where a sewage pump station also needs emergency storage, Mullaly makes underground fibreglass storage tanks covered by the same WSAA appraisal.
Wet well projects
- Innes Estate, Townsville (2007). An RPEQ certified 4.0m diameter, 8.5m deep wet well with a 1.2m high dividing wall forming two pump chambers, in sandy ground next to a creek. Read the project.
- Lotus Glen SPS upgrade, Townsville (2014). An RPEQ certified 3.75m diameter, 9.03m deep wet well with a separate valve pit, beside a creek with water and rock on site. Read the project.
- Sydney Airport waste dump (2019). A 3.0m diameter, 5.0m deep wet well and valve pit combo with two 100mm discharge Homa pumps. Read the project.
Wet well questions
What is the difference between a wet well and a pump station?
The wet well is the chamber that holds the liquid and the pumps. The pump station is the whole installation: wet well, pumps, valve pit, pipework and controls.
Is a pump pit the same as a wet well?
Yes. Pump pit and pump well are other names for the wet well that holds the pumps.
When should I use a separate wet well rather than a combo?
When the project needs a larger diameter than suits a combo unit, or when transport limits rule out taking a combo pump station to site. The wet well is then paired with a separate valve pit.
How deep can a fibreglass wet well be?
The standard range is 2m to 14m deep. Deeper wet wells are available on request.
Can a wet well go in wet ground?
Yes. Mullaly wet wells are designed for a wide range of site conditions, and the ballast calculations supplied with the installation instructions counter hydrostatic uplift.
Downloads
- Fibreglass pump station technical data sheet (PDF)
- Wet well and pump station installation guidelines (PDF)
For CAD drawings or ballast calculations, contact our team.
Download the pump station brochure
Enter your email and the brochure opens straight away. We will also email you the link.
Request a wet well quote
Send us your specification or drawings and our team will come back with a design and quote. We reply to every enquiry within 2 business days.
Or call 02 4964 8270 or email sales@mullaly.com.au