rotor meter water flowmeter

The Rotor Flowmeter, also known as rotary flowmeter or  rotary meter, is a device that measures the volumetric flow rate of fluid in a closed tube .

 The rotometer belongs to a class of meters called variable area flowmeters, which measure the flow rate by allowing the cross-sectional area through which the fluid travels to vary, causing a measurable effect.

A rotormeter consists of a tapered tube, typically made of glass with a float (a shaped weight, made of either anodized aluminum or ceramic), inside which is pushed up by the pull force of the flow and pulled down by gravity. The drag force for a given cross section of fluid and float is a function of flow rate squared only, see drag equation.

A rotometer requires no external power or fuel, it uses only the inherent properties of the fluid, together with gravity, to measure the flow rate. 

A rotameter is also a relatively simple device that can be mass produced from cheap materials, allowing for its widespread use.

Since the flow passage area increases as the float moves up the tube, the scale is approximately linear.

Clear glass is used, which is highly resistant to thermal shock and chemical action.

The rotor flowmeter is used in small pipe diameter and low flow rate. Commonly used instrument caliber 40-50mm below, the smallest caliber to 1.5~4mm. Suitable for measuring low flow rate, small flow rate and liquid.

For example, diameter 10mm below the nominal pipe diameter of the full flow of glass tube rotor flowmeter, flow rate only in 0.2~0.6m/s between, or even less than 0.1m/s; Metal Rotor Flowmeter and diameter greater than 15mm glass tube rotor flowmeter slightly higher, flow rate in 0.5~1.5m/s between.

Most rotameter flowmeters do not have an upstream straight section requirement or require a low upstream straight section. 

The rotameter has a wide range of flow rates, typically 10:1, down to 5:1, and up to 25:1. The output of the flow detection element is approximately linear.