A weir is a versatile primary flow management device that will meet the needs of most operations. If you want to get the most out of your weir, however, then it’s important that you understand how to take measurements using this device and some of the pitfalls that you may encounter.
If you’re not experienced with using a weir, it can be very easy to take your measurements the wrong way, so it’s a good idea to examine this issue very closely. Here are some of your options for taking measurements in a weir that you should consider if you wish to use this device in your system.
Never Measure at the Face
As with any flow management device, the key to taking correct readings is choosing the right point of measurement. Although it’s common to assume that you should take your measurements at the face of the weir plate, this is actually incorrect.
At a weir’s face, the water level decreases. This means that if you measure at this point, you will only get a general idea of the flow and not an actual hard measurement of the flow in your system. If you want the most accurate reading possible, you need to take your measurements upstream of the device. Measuring anywhere else means your readings won’t be as precise as you need.
Setting the Weir Correctly
Another factor to consider when measuring flow using a weir is if the crest of your weir is properly positioned. If you’re not careful about the position of your weir crest, your readings will not be accurate, and the success of your operation will be limited.
If you want your flow readings to be correct, you need to calculate your anticipated maximum head level and then position your weir crest at two times this height. Any higher or any lower, and your readings will be off.
Staff Gauge Problems
In most cases, measurements in a weir are taken using a staff gauge. Although this measurement device is very simple, you should be aware of some problems involved with these gauges.
For instance, if your weir is in an outdoor application, your staff gauge may become covered in dirt and debris, making it hard for your operator to take readings. Also, when your staff gauge is mounted on the face of the weir, it will display a much lower water level than actually exists in your system. Staff gauges mounted on weirs will give you a basic idea of water level, but the readings won’t be accurate.
Choose a Weir for Your System
As long as you keep this information in mind, taking measurements in a weir shouldn’t be that difficult, especially if you’re using a high-quality fiberglass weir from Tracom, FRP. We are one of your best resources for open channel flow management tools, and whether you want to use a weir or a flume, we can provide you with a primary device that will help your operation succeed to the fullest extent possible.
Request a weir quote from Tracom today and learn more about our line of products.
