Weir Tank

Our weir tank system is an ideal solution to measure the flow of water in open channels. Manufactured in rigid PVC and reinforced for additional robustness, our flow measurement weir tanks include two solid external support bands to prevent bowing and distortion, with the inlet and outlet pipes able to be fabricated to suit customer requirements.

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Weir tanks are ideal to provide both cost-effective and accurate flow measurements, using the technology of placing a fixed obstruction within the flow of effluent.

The system includes provision for a data logging flow meter housed in a weather-proof kiosk, a critical laser-machined thin plate weir, an upstream baffle and a maintenance drain-down valve. In addition, the outlet weir plate has additional supports so it remains free from any bowing or skew.

A weir tank within the field can typically see an accuracy rate of between +/-5-15% when correctly specified, installed and maintained. At SIRIS we can supply an off-the-shelf, fully compliant, regulatory flow measurement system that can be installed above or below ground.

A weir tank is not suitable for use where there is a high proportion of solids present within the effluent as these may stick to the sides of the weir system and crest and impact measurement and flow.  In addition, low extremes of temperature where ice may form can impact the accuracy of measurement of flow.

Ideal for above ground applications

Weir tanks can be useful in applications where flow is above ground and the flow of water is piped.


A fully-compliant solution with minimal on-site commissioning

Our robust and cost-effective weir tanks offer a complete solution for both above and below ground applications.

The complete system is factory-calibrated in accordance with BS/ISO standards and requires minimal on-site commissioning.

When you invest in a SIRIS weir tank we guarantee it will be pre-calibrated at our specialist workshop to ensure it meets all regulatory requirements, including MCERTS and BS/ISO 1438. This means installation is as simple as connecting the inlet and outlet pipes, powering up and switching on – making it an ideal off-the-shelf solution.

Accurate & reliable data

SIRIS weir tanks are MCERTS accredited so you can be confident that the data provided is reliable and accurate forlong-term flow measurement.

All SIRIS products are compatible with our web-based data recording software, which allows quick and easy access to your data at any time – from any location.

Design & installation

We pride ourselves in offering a bespoke service to all of our clients. Our design and installation process ensures we provide you with a cost-effective solution tailored to suit your site’s individual requirements.

V notch weir design: how does it work? When designed, installed and maintained correctly, thin plate V notch weirs provide a highly accurate solution for open channel flow measurement. In order to maintain accuracy, it's essential that V notch weir design is calculated correctly. In this guide we'll explain how V notch weirs work, their pros and cons, and the equations involved in… Read article
Guide to Critical Depth Flumes Video Simon from our Sunderland Head Office took some time to explain the basics of flumes in our guide critical depth flumes and how best to maximise use of their functionality. Using our flow measurement test rig, our instructional video guide to critical depth flumes covers: What is a flume? Common flume mistakes   Approach length… Read article

Compatibility with site systems

All SIRIS products can be used with our data monitoring software, Palette, however they are also compatible with your existing SCADA system. Our expert team is committed to working in partnership with our customers to meet their individual requirements and ensure our products fit seamlessly into each site.

Nick Richardson says...

“SIRIS flow measurement weir tanks offer an ideal off-the-shelf solution for some sites. Not only are they easy to install and set up on site but they are guaranteed to meet Environment Agency MCERTS flow requirements – giving you the peace of mind that your system is fully-compliant.”

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