Littleport Depot

Wisbech Road, Littleport, Ely, Cambridgeshire, CB6 1RA

01353 861416



FP McCann offers a specialist design and building service for circular biological filter walls. The inherent flexibility of this well-proven system allows us to accommodate all ancillary requirements.

FP McCann’s filter beds provide low whole life costs, due to the low energy and low maintenance required by the system. Offering many advantages over ASP, Baff and Saff Treatment processes, the system uses zero energy, zero chemicals and has a very low carbon footprint.

Due to daily and seasonal temperature fluctuations, traditional brick, cast in-situ concrete and stiffly joined, freestanding filter bed structures have high levels of failure associated with the development of excessive circumferential stresses induced in the wall. During successive cycles of expansion and contraction, the passive pressures at wall/filter medium interface increase with time in a racketing manner. This failure normally occurs suddenly, although it may take years to develop and even with thorough and regular visual inspection, it is difficult to predict.

As CIRA Report 58 states: “The failure by ring tension is characterised by vertical cracks which progressively increase in width, but many years may lapse before the wall collapses.”

High Strength/High Flexibility Solutions

In designing for long-term serviceability, it is essential to understand the nature of the stress escalation. FP McCann’s filter beds incorporate a specifically designed and patented panel-to-panel connection assembly. This assembly combines the unique features of high strength (to enhance structural integrity) and high flexibility (to prevent the development of excessive circumferential stresses due to temperature variations). These failures make the assembly particularly durable and lead to a longer life.


An important aspect of this assembly system is that passive pressures are reduced to acceptable levels and do not play a critical role in the structural performance of FP McCann’s filter beds. FP McCann has extensive experience in the design and construction of filter bed retaining walls of ring tension-type. Many structures have been in service for over 40 years, with their expected lifespan much longer than this.

Patented and Reliable

FP McCann’s well-proven and patented system incorporates neoprene washers, which prevent damage arising from thermal movement and overcome the problem of failure caused by passive resistance. Used for many years by water companies and authorities nationwide, the FP McCann system not only offers total reliability but also proven value and design flexibility in the construction of new and the repair of existing filter bed walls.

Design and Installation

Utilising highly skilled and experienced installation teams, the precast units are erected to the highest of standards. FP McCann offers a full design and building service anywhere in the country.