Case Studies - PAC Enviro

Storm & Effluent Flow Control System

Storm & Effluent Flow Control System Northern Ireland


Our client required new stand-alone control systems and associated hardware to control two small effluent to sewer flow control systems that would operate to site-specific parameters.

The requirement was to restrict the daily effluent discharged at each site while ensuring that the discharge limit permitted set by the local environment agency was not exceeded.

All data was required to be logged and trended within the clients on site Building Management System (BMS) for record keeping.


Site 1

An effluent flow control system was installed on the first site to limit the maximum daily discharge of 1.2m³ per day (i.e. 1200 litres per day). This was achieved by restricting the effluent discharge to 50 litres per hour while ensuring enough velocity and flow to ensure the outlet didn’t block and thus ensuring self-cleaning of the outlet pipework.

In the event that the maximum flow is reached before the hour had elapsed the flow control actuator closes and thus prevents effluent flowing through the system. After the initial time period and permitted totalised flow limit had passed, the actuator re-opens and another 50 litres will be allowed to flow out during the next period available.

In the event of flooding and the inline storm tank is at capacity a high level probe within the tank triggers an alarm, the actuator opens and remains open until the water level within the tank drops sufficiently preventing any premature spill.

Site 2

On the second site the maximum daily volume of effluent discharge permitted was 22.8m³ per day (22,800 litres per day). This was achieved by using an inline flow meter to measure the flow and a modulating actuator to restrict the flow to 950 litres per hour.

A dedicated overflow outlet was installed within the storage tank to prevent the chamber from flooding by using the new control functions along with the data available from an ultrasonic level controller and a V-Notch Weir to monitor the effluent flowing from the overflow at the time of a storm event. Trending and logging of the time and duration of the event is relayed to the clients BMS for regulatory and record purposes.

Control Panel and HMI

PAC Enviro’s highly skilled in-house design & build team developed the specific controls required that enabled our client to have a tailor-made control panel specific for each site. Our client’s objective was to make the system simple and user-friendly.

The HMI on the MCC displays a simple visual of the system which indicates key information including plant status, current flow meter reading, valve position and flow totals over a period of 30 days. The alarm history is also recorded.


Upon completion of the M&E installation, the systems on both sites were commissioned, tested, demonstrated and signed off with our client.

Operation and Maintenance manuals (O&Ms) were produced and tailored to the client’s requirements and included certification of all instruments/controls/drawings/maintenance requirements and site witness documentation for all aspects of the projects.

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