Improved flow control devices at storm-water storage facilities will allow greater use to be made of the available storage volumes. In consequence, it will be possible to reduce the size and capital cost of new storm-water storage facilities, or substantially improve the hydraulic protection provided by existing facilities.
The objectives of this project are:
• to consider the transfer and development of existing ‘constant flow’ technology into the UK sewer environment;
• to identify/design passive and self-regulating devices suitable for testing;
• to assess the comparative performance and economics of improved flow control devices;
• to provide advice and guidance on the development and use of improved flow control devices.
Over the next 10 years the UK will spend billions of pounds in the provision of storm-water storage facilities. This could be significantly reduced if improved hydraulic control devices could be developed or identified.
Three possible constant flow devices were physically tested. These were a “Floating Pipe”, a Self-Regulating Valve and a HydroSlide. Testing indicated the HydroSlide could deliver a near constant flow regardless of upstream head.
Analysis of storage requirements for an orifice, a vortex control and a constant flow control device was undertaken. Storage requirements using an orifice are constant regardless of head. Vortex flow control devices usually offer no significant cost savings over an orifice and at low heads require a greater volume of storage. However, they do have the advantage of a large outlet diameter compared to an orifice designed to pass the same flow at the design head. Constant flow control devices require 10% less storage at heads below 1.2m and between 15-45% less storage with heads greater than this.
Outlets with a diameter of less than 300mm should be avoided where possible, as they are prone to blockage. Vortex flow controls should be used where the flow is less than 100 lls with heads above 1.5m. Orifices should be used with flows above 100 1./s with design heads of less than 1.5m. Constant flow control devices are most economically and practically favorable for flows above 200 11s with design heads of greater than 1.5m.
It is recommended that the HydroSlide’s performance is monitored in a live combined sewer. The spreadsheet model should be used as an initial assessment of the potential for capital cost savings in detention tanks. Constant flow control devices should be used where the outlet is greater than 300mm. At low flows, vortex flow control devices are favourable due to the size of their outlets.
A selection criteria was established to select flow control devices that could deliver a constant flow regardless of upstream hydrostatic head. A world-wide literature search was undertaken to identify devices that met the selection criteria. Five possible devices were selected for detailed theoretical analysis. After consideration, two were discounted as they failed to meet the objectives of this project. Three possible devices, the Floating Pipe, the Self-Regulating Valve and the HydroSlide were selected for physical testing as they displayed the majority of the selection criteria. A programme of physical testing for three devices was carried out. Performance curves for the tested devices were derived and cost comparisons were made against an orifice and a vortex control device. The results indicated that cost savings of up to 45% could be made by using a constant flow control device. Design guidelines for such devices and a worked example for the selection of devices are included. Conclusions and recommendations from this study for the future use of the flow control devices are given.