What Is a Rectangular Weir?

The compound weir consists of a rectangular weir and a triangular weir. Its advantage is that it can adapt to a wide range of flow. When the flow is small, it is actually a triangular weir, so the accuracy is higher.

The choice of weir height and weir width depends on the maximum and minimum flow. Generally, the head at the top of the weir is not less than 3cm, otherwise the surface tension and viscosity will be too large. At the same time, the head at the top of the weir should not be larger than half of the height of the weir to reduce the impact of near-current velocity.

The weir wall shall be perpendicular to the direction of incoming water and the trough.

The compound weir does not have an accurate flow calculation formula, so it can only be used after passing a calibration test.

H (Cm)	Q (L / s)	H (Cm)	Q (L / s)	H (Cm)	Q (L / s)
3.57	0.35	9.41	3.99	12.44	11.04
4.56	0.71	9.99	4.59	13.00	12.99
5.70	1.22	10.54	5.42	14.95	20.30
6.95	1.87	11.46	7.91	17.63	33.60
8.57	3.06	11.83	9.17	18.93	40.40
19.96	47.5	23.09	71.0	24.93	88.6

The basic principle of a water measuring weir is that there is a certain exponential relationship between the water head at the top of the weir and the flow, so the flow can be estimated through water depth measurement.

Water measuring weirs can be divided into triangular weirs, rectangular weirs, and compound weirs according to the shape of the weir plate.

Duplex Weir Delta Weir

Triangle weir layout

The layout of the triangular weir is shown in the figure. Generally, a triangular weir with a weir mouth of 90 ° should be used. The width of the weir groove should be 3 to 4 times the maximum head of the weir.

In the formula: Q --- flow (m ³ / min);

K --- flow coefficient;

B --- weir width (B = 0.5 ~ 1.2m);

H --- head of weir (H = 0.07 ~ 0.26mB / 3);

D --- The height from the bottom of the groove to the lower edge of the notch is D = 0.1 ~ 0.75m.

Double weir rectangular weir

Rectangular weir layout

The rectangular weir layout is shown in the figure. Generally, the water depth at the top of the weir is required to be less than or equal to 3cm to prevent the surface tension of the water flow and the viscosity of the water from being too large. At the same time, the head at the top of the weir should not be more than half of the height of the weir to reduce the impact of near-current velocity.

Rectangular weir is suitable for measuring large flow, and the calculation formula of flow is

In the formula: Q --- flow (m ³ / min);

B --- weir width (B = 0.5 ~ 6.3m);

H --- head of weir (H = (0.03-0.45b) m);

b --- notch density (b = 0.15 ~ 5.0m);

K --- flow coefficient;

D --- the height from the bottom of the groove to the lower edge of the weir mouth (D = 0.15 ~ 3.5m, bD / B²0.06). ^[1]