Fibreglass pump stations: 10 years experience in New Zealand
Annual Conference
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Pump stations constructed in fibreglass have been successfully used for handling municipal and industrial wastewater for ten years in New Zealand. This paper reviews these experiences, and the engineering details that have contributed to this success.
The engineering properties of fibreglass are well known. Fibreglass is a flexible material with strain to failure of 2%. Yield strength and ultimate strength are the same. Design safety factors of three to ten are used, so that the design point is well away from the yield point. This design gives good resistance to sudden shock loads, such as earthquakes.
The service life of a fibreglass pump station is dependent on the chemical resistance of the resin. Isophthalic polyesters are used in municipal pump stations, and vinyl ester resins are used in industrial chemical pump stations where chemical concentrations and temperatures are higher. Both resins are resistant to hydrogen sulphide gas. The 50 to 100 year design life required in municipal wastewater networks is achieved by fibreglass. When properly engineered and constructed, fibreglass has an indefinite life in these applications.
Fibreglass pump stations achieve engineering benefits because they are fabricated, assembled, and fitted out in a factory so that on-site work is minimised. Factory ‘butt and strap joints’ are easily done and quality assured, and this eliminates future leaks and infiltration. Bases are moulded with sloping sides to optimize pumping and minimize solids settling. Pump hold-down bolts are factory fitted; with anchoring plates located outside the pump station. These are captured in concrete on installation to ensure pump security. The weight of backfill on a factory fitted anti-flotation ring provides the required anti-flotation force. The lightweight of fibreglass reduces transport and installation costs.
Case histories are presented of a variety of installations, including municipal stations and one in a dairy factory handling CIP wastes. Four of the pump stations reviewed endured the Christchurch earthquakes of 2010/11.
LCC (life cycle cost) analysis shows that fibreglass pump stations have the lowest cost over a 100-year life. Whilst costing more at the time of initial purchase, the installed cost can be similar or less than conventional concrete pump stations. Further during the 100 year period, the fibreglass pump station needs minimal maintenance whereas others would need maintenance and replacing, or at the very least re-coating, on a regular basis.