On a Thursday evening Exsel Pumps Limited received an urgent enquiry for assistance from one of its key Customers. Apparently, a vital underground sewage main had collapsed with a danger of overspill of raw sewage into the surrounding area and out to sea. Exsel immediately mobilised a team of engineers and pumping equipment from its local depot and stayed all night to ensure that an emergency system was installed and operating. Initially this involved seven Betsy 6 inch diesel pumps capable of handling raw rag-laden sewage and 700 metres of hose.
Once the initial emergency was under control a full assessment of the situation was made in the light of day, including input by Exsel’s engineers. It became apparent that the damage caused by the collapsed main and certain storm conditions could overwhelm the pumps put in place overnight. It was critical to put another solution in place as soon as possible.
Within hours trucks were loaded with a 16 inch submersible pump and inverter drive control room with over 500 metres of 500mm diameter flanged steel pipework. The equipment was delivered such that work could commence overnight and into the weekend to construct an emergency pumping station with a capacity of 1700 l/s (6120 m3/h).
It was established that the collapse was the main incoming pipe between a large seven meter deep underground concrete construction collection chamber and the main sewage treatment works. The collapsed sewage main threatened to leak a large volume of untreated sewage into the surrounding area and contaminating the outfall of treated sewage back out to sea.
The underground collector offered the best location for the emergency pump installation but accessing the collector was in itself a major operation. The whole site was covered with thick undergrowth and tons of earth. After removal of the undergrowth and earth, the specialist equipment was used to cut and access in the 60cm thick reinforced concrete roof of the collector. The first pump to be installed was a Hidrostal 116K-SS, 140 kW immersible pump.
This unit was controlled by an inverter which automatically adjusted the speed and therefore the flow of the pump in accordance with the incoming flow.
At the same time a steel flanged discharge pipe of 500mm diameter and 100 meters long was laid between the Hidrostal pump in the collector to a temporary discharge point in an undamaged section of the sewage line leading to the treatment plant.
To meet the potential peak capacity a second pump installation was required. To avoid weakening the roof structure of the collector further, the Exsel project site engineer decided to utilise a Hidrostal H12K-HD surface mounted electrically driven dry prime unit with electronic vacuum system and suction pipe. The second pump unit had to discharge to a second discharge point over 400 metres away and was also inverter controlled.
This caused further complications as the pipe run had to go past the main entrance of the treatment works. Exsel overcame this by building a pipe-bridge over the entrance to continue to allow regular traffic including HGV vehicles to pass unhindered.
The efforts of Exsel’s engineers were greatly appreciated by the customer and end user. The timely execution of a technical solution together with the professional manner in which Exsel responded to this emergency avoided a potentially major environmental incident.
Exsel continued to monitor the equipment with SMS technology to ensure rapid response in case of any issues. The SMS provided alarms for pump failure and high level but the quality of the equipment and the installation was such that no issues were encountered over the weeks in which the equipment was installed.