C.G.Godfrey Limited have been the authorised distributor of Qua-vac BV’s Vacuflow® technology in the UK since 1987. In the years since they have become the countries leading contractor for the design, installation and maintenance of vacuum sewerage systems.
Clients including Anglian Water, Southern Water, Severn Trent Water and Thames Water and a number of other “blue-chip” clients have seen the company construct in excess of forty vacuum sewerage systems from inception to completion and in many cases the systems are still maintained by the company today.
New methods of construction and the operating equipment used within the systems have evolved as new technologies have been developed. Initially trenches were excavated with traditional 360° excavator’s this was quickly replaced by the use of road trenches and narrow trenching techniques, which in certain ground conditions, remains in use today. However, with the development of “no-dig” technology and in particular the progress made in improving the accuracy of directional drilling equipment the company adopted this as the principle means of vacuum main installation.
Materials such as polyethylene pipe and foam concrete were identified as means of facilitating the new construction methods, the traditional concrete vacuum collection chambers, whilst still used, have now been replaced with polyethylene units with recycled composite covers and frames on most installations. Both the 63mm and 90mm vacuum interface units are offered in the UK market, these combined with
Qua-vac’s renowned ball float activator make the Vacuflow system the most reliable vacuum system on offer today.
One scheme recently completed on behalf of Severn Trent Water and its framework partner NMCN was the Salford Priors 101A First Time Rural Sewerage Scheme.
Initial project solutions included the utilisation of conventional gravity sewers at depths of up to 7 metres and 4 No. sewerage pumping stations, necessary as a result of the areas undulating terrain.
Due to the many significant disadvantages identified with the use of a gravity sewerage system for this application a vacuum sewerage system was proposed as the most effective alternative solution.
The projects specific design encompassed approximately 3km of vacuum main, a central vacuum collection and discharge pumping station, 750m of rising main and 640m of gravity sewer capable of serving 50+ properties. Effluent is discharged at a rate of 5-6l/s into Severn Trent Waters wastewater network along School Road, Salford Priors.
Vacuflow® Technology was installed to service all properties within the catchment areas. Waste water from each property, or where possible groups of properties drains by gravity to a vacuum collection chamber sited either in the adjacent highway verge or within the property boundary, no chambers are positioned in the highway. Collection chambers are constructed from either polyethylene or precast concrete and are fitted with Hermelock B125 or D400 composite covers and are similar in size to a standard manhole.
The vacuum station is the only element requiring an electrical supply. The vacuum station is comprised of a station building containing the MCC and 2 No vacuum pumps, outside is an underground vacuum tank and pump and valve chambers within which 2 No discharge pumps, isolation and non-return valves and flow meter are housed. The systems vacuum pumps run for approximately 2 to 5 minutes per cycle.
Once wastewater reaches the vacuum station it is deposited into the vacuum tank where it is then temporarily stored until the tank reaches a predetermined level when the discharge pumps are activated and the wastewater is conveyed through a rising main and gravity sewer to the nearby sewer network on School Road, Salford Priors.
Innovation
CGG continually seek to challenge project efficiencies by employing innovative technologies.
At Salford Priors efficiencies were made to meet budget and programme constraints. To achieve these efficiencies emphasis was placed in “offsite” prefabrication. Prefabrication facilitated the opportunities for reductions in cost and programme duration, whilst also achieving greater control of product quality and eliminated elements of risk to health and safety on the project.
Numerous prefabricated components, including the fully fitted vacuum station building and foundation slab, pumping station and valve chamber were efficiently programmed for ‘just in time’ delivery to ensure only one crane visit was necessary to site the various elements.
Hermelock composite covers, either D400 or B125 rated were installed on all collection chambers, made of a polyurethane composite material reinforced with fibre glass these covers offer the following advantages;
Light weight
Not susceptible to corrosion
Watertight seal
Bolting system to lock covers
Maintenance free
Resistant to loading (EN-124 standards)
Zero scrap value
25 year guarantee
CGG’s preferred method for vacuum main installation is via directional drilling, however ground conditions on site did not permit this option therefore all vacuum mains were, where feasible, installed by the use of a road trencher which facilitated the excavation of narrow trenches, the recycling of road surfacing materials and reduced areas of highway reinstatement. A trencher is a rapid method of excavation, with levels controlled by laser, typically achieving 150-200m of trench per day.
Pipes were pre-welded and laid alongside the trench then carefully lowered in onto a sand bed, thus eliminating the need to enter the trench. A sand surround and traceable marker tape were then laid over the pipe prior to backfilling.
Foamed concrete was used to backfill trenches. Foamed concrete is a highly workable, low density material. Incorporating up to 75% of air, foam concrete is generally self levelling and self compacting thus eliminating the need for compaction and vibration. Permanent asphalt reinstatements were then undertaken.
In recent years the company’s vacuum system workload has seen increasing growth in both the maintenance of our own Vacuflow systems and the refurbishment of systems manufactured and installed by our competitors Iseki, flowvac and Rodiger.
Clients are now recognising the benefits of regular planned maintenance and the savings it produces, many now engage the company to undertake the annual servicing of their vacuum systems. Other clients Thames Water and Southern Water in particular having witnessed the operation and reliability of the Vacuflow® system have also undertaken the complete refurbishment of other manufacturers systems, with all vacuum interface units and activators replaced with new Qua-vac equipment. The new infrastructure is proving to be far more robust and reliable than the equipment it replaced and is producing better than anticipated cost benefits for them.
www.cggodfrey.co.uk
