Welcome to the Frequently Asked Questions (FAQ page). Below, we have tried to answer the most common questions visitors to our Web site may have. If you find that your question is not answered on this page, please email us dennis@trueflow.co.uk or call us during [BUSINESS HOURS] at 01656 880922.
Q1. Many instrument suppliers claim an accuracy of much better that 8% so why is the accuracy requirement difficult to meet.?
A1. Instrument inaccuracy is only one part of the jigsaw that makes up the overall uncertainty value. Measurement structures also introduce an uncertainty, due to the limitations of the construction, or due to the formulae used to establish the depth to discharge relationship. Other errors such as the zero setting or the errors in depth measurement can introduce further uncertainty that has to be included in the overall uncertainty calculation.
Q2. Do we have to measure flow rates at the final effluent discharge point.?
A2. The procedures allow the discharger to choose the location for flow measurement as long as it meets specific requirements. The measurement location must represent the daily discharge through full treatment and on to final effluent. The measurement location must take into account storm overflows and returns, together with process returns and any imported flows.
Q3. If Magflow meters are provided with a certificate of calibration showing an accuracy of better than 0.5% over the selected range, why are they not used more extensively.?
A3. Because many existing works are designed around flumes or v-notch installations there is a reluctance to abandon these installations in favor of a magflow meter. It can also be difficult to find suitable locations where the pipe work can be arranged to ensure that the meter remains full at all times. When the pipe work can be modified to accommodate a magflow meter, then this type of meter can offer significant cost savings in terms of installation cost and ongoing maintenance requirements. When installed in accordance with the manufacturers recommendations accuracy of better than 1% is achievable. The meters can offer a wider flow range than flumes and v-notches and are the only instruments that can effectively measure the flow rates for WwTW’s at the lower end of the population range.
Q4. How will the continuing accuracy of measurement be maintained.?
A4. Part of the MCERTS requirement is for a quality management system (QMS) to cover important aspects of effluent flow measurement. The manual will include specifications for the procurement, installation, calibration and ongoing maintenance for all measurement sites. The manual will need to demonstrate to the auditor that the accuracy of the measurement system can be maintained for the lifetime of the audit. If the auditor feels that the QMS is inadequate and the accuracy requirements may be compromised then the site may not achieve certification.
Q5. Where can I find further information on the EA’s flow policy requirements.
A5. Further information on the EA’s policy is detailed in two documents “Water Quality Consenting Standard - Flow Measurement of Discharges” and “Water Quality Consenting Guidance - Flow Measurement of Discharges.