Determining Pump Flow - Rice Irrigation

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Soil and Water Management
Rice Irrigation - Determining Pump Flow

A good method of determining pump discharge is to use an inline flow meter. Many irrigation equipment dealers handle flow meters and can provide cost and proper installation information. Proper installation is very important to assure accurate readings and good service from the flow meter. A portable flow meter can be used to monitor the flow of more than one pumping plant. Most flow meters can be equipped with a totalizing dial that records the total quantity of water pumped. This provides useful water management information that can also be used to document irrigation water requirements.

If a flow meter is not available, the discharge rate can be estimated by the plumb bob method described in the following section (Figure 1 and Table 4).

Figre 1. Drawing of pump on how to measure pump flow.

When the water discharges from a vertical riser, the flow rate can be estimated with a vertical measurement. However, the accuracy is usually very poor because of the difficulty in obtaining a good measurement of the vertical height. A more accurate measurement is usually obtained if a hydrant is installed on the riser creating a horizontal discharge. A joint of pipe inserted in the hydrant stabilizes the flow and makes the plumb bob method possible.

Table 4. Pump Flows Calculated from Yardstick and 8-inch Plumb Bob Measurements
Length (L)	Inside Diameter of Pipe (D) - Inches
Inches	4"	5"	6"	7"	8"	9"	10"	11"	12"	13"	14"
4	64	100	144	196	256	324	400	484	476	676	784
6	96	150	216	294	384	486	600	726	864	1014	1176
8	128	200	288	392	512	648	800	968	1152	1352	1568
10	160	250	360	490	640	810	1000	1210	1440	1690	1960
12	192	300	432	388	768	972	1200	1452	1728	2028	2352
14	224	350	504	686	896	1134	1400	1694	2016	2366	2744
16	256	400	576	784	1024	1296	1600	1936	2304	2704	3136
18	288	450	648	882	1152	1458	1800	2178	2592	3042	3428
20	320	500	720	980	1280	1620	2000	2420	2880	3380	3920
22	352	550	792	1078	1408	1782	2200	2662	3168	3718	4312
24	384	600	864	1176	1536	1944	2400	2904	3456	4056	4704
26	416	650	936	1274	1664	2106	2600	3146	3744	4394	5096
28	448	700	1008	1372	1792	2268	2800	3388	4032	4732	5488
30	480	750	1080	1470	1920	2430	3000	3630	4320	5070	5880
32	512	800	1152	1568	2048	2592	3200	3872	4608	5408	6272
34	544	850	1224	1666	2176	2754	3400	4114	4896	5746	6664
36	576	900	1296	1764	2304	2916	3600	4356	5184	6084	7056

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Soil and Water Management Rice Irrigation - Determining Pump Flow

Soil and Water Management
Rice Irrigation - Determining Pump Flow