Input data

Flow

Output data

Minimum Parshall size

k minimum

n minimum

Velocity gradient of the minimum size

Intermediary Parshall size

k intermediary

n intermediary

Velocity gradient of the intermediary size

Maximum Parshall size

k maximum

n maximum

Velocity gradient of the maximum size

Description

Given the flow, selects the Parshall size. In some cases, it indicates up to three possibilities. It shows the values for k and n of the equation $𝑄=𝑘⋅𝐻^𝑛$ , for each case (metric units), as well as the corresponding velocity gradient.

Parshall dimensions table

W (in or ft)	W (cm)	A	B	C	D	E	F	G	K	N
1”	2.5	36.3	35.6	9.3	16.8	22.9	7.6	20.3	1.9	2.9
3”	7.6	46.6	45.7	17.8	25.9	38.1	15.2	30.5	2.5	5.7
6”	15.2	62.1	61	39.4	40.3	45.7	30.5	61	7.6	11.4
9”	22.9	88	86.4	38.1	57.5	61	30.5	45.7	7.6	11.4
1’	30.5	137.1	134.4	61	84.5	76.2	61	91.5	7.6	22.9
1,5’	45.7	144.8	142	76.2	102.6	91.5	61	91.5	7.6	22.9
2’	61	152.3	149.3	91.5	120.7	91.5	61	91.5	7.6	22.9
3’	91.5	167.5	164.2	122	157.2	91.5	61	91.5	7.6	22.9
4’	122	182.8	179.2	152.5	193.8	91.5	61	91.5	7.6	22.9
5’	152.5	198	194.1	183	230.3	91.5	61	91.5	7.6	22.9
6’	183	213.3	209	213.5	266.7	91.5	61	91.5	7.6	22.9
7’	213.5	228.6	224	244	303	91.5	61	91.5	7.6	22.9
8’	244	244	239	274,5	340	91.5	61	91.5	7.6	22.9
10’	305	274.5	260.8	366	475.9	122	91.5	183	15.3	34.3

Source: AZEVEDO NETTO, J. M. de; FERNANDEZ Y FERNANDEZ, Miguel. Manual de hidráulica, 9.ed. São Paulo: Blucher, 2015.

Note:

The value of velocity gradient must be verified through hydraulic calculations. It was obtained using the following expression::

G = 1000⋅ \frac{𝑄^{0.7}}{𝑊^{1.2}}

Source: (Vianna, Marcos R. Hidráulica aplicada às estações de tratamento de água. 6. ed. Belo Horizonte: Bloom, 2019);

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