To measure the water flow rate in closed pipelines, flowmeters, which are based on the measurement of variable pressure drop in the pipelines, as well as tap-water meters are used.

Pipelines of more than 1000 m in diameter. An ultrasonic multi-channel flowmeter RUM-1 (in Russian РУМ-1) is installed on them; they allow automatizing water supply control and remote metering of flow rate.

With pipelines of more than 400-1000 m in diameter ultrasonic single-channel flowmeters UZR-V (in Russian УЗР-В), ERIS (in Russian ЭРИС) type electromagnetic flowmeter of local velocity, and constriction flowmeters are mainly used.

UZR-V type ultrasonic flow meters are installed on pipelines of more than 400-1000 m in diameter. This flowmeter measures the difference of pulse repetition frequencies of ultrasonic vibrations directed along and opposite the stream. It consists of two piezoelectric sensors installed on the pipeline; electronic module with a rate-of-flow indicator and a meter that are mounted indoor; cable for the connection of the sensors to the electronic module.

The principle of operation of electromagnetic flowmeters based on that a magnetic field is created in the electrically conducting fluid the flowrate of which is to be measured by using an electromagnet. When running through, the fluid crosses field force lines and there, as in a moving conductor, electromotive force arises proportional to the liquid flow rate. The induced electromotive force is read off by electrodes and is transmitted by signal wires to the electronic module. The ERIS type flow meter measures the velocity at a point of the pipeline cross-section area.

Constriction flowmeters are installed on pipelines of more than 100-1500 m in diameter. They are composed of a restriction mounted on a pipeline; differential-pressure-gauge flowmeter that converts a differential pressure into a unified signal; interconnecting lines that transmit the differential pressure from the sensor to the differential-pressure-gauge flowmeter; secondary instrument receiving the unified signal and generating a measurement-data signal in an intelligible form.

An electromagnetic flowmeter of IR-61 (in Russian ИР-61) type, ultrasonic flowmeter of UZOR [in Russian] УЗОР) type, velocity flowmeters, and constriction flowmeters are installed on pipelines of less than 400 m in diameter.

There are velocity flowmeters of VD-180, SV-1, STV-100, STV-150 (in Russian ВД-180, СВ-1, СТВ-100, and СТВ-150 respectively) types. The meter operating principle is based on converting the hydraulic fluid energy into the mechanical energy on the impeller shaft.

Source: The nature and tasks of the operation of irrigation and drainage systems