Rotometers
Rotometers are flowmeters named for the rotating float which functions as the meter's indicating element. Rotometers are typically used to measure low flow rates and are an economical method of indicating and controlling gas and liquid flow for several applications. Rather than using a constant restriction area and a variable pressure differential, rotometers use a variable restriction and a constant pressure differential to measure flow. Typically, rotometers are used to measure smaller flows and the reading is usually done locally, although transmission of the readings is possible. Rotometers consist of a float that moves vertically through a slightly tapered tube. As fluid enters the bottom of the rotometer, the float is forced upward until the force is balanced by gravitational forces. Most rotometers are made of glass with markings on the outside so that flow readings can be taken visually.
Rotometers may be designed to measure the flow rate of single or multiple streams. They are also available in many variations, including gas and metal tube versions. The selection of the appropriate rotometer for a particular application requires attention to a few key details. These include which gas will be used, the required flow rate, the number of streams to be measured, and whether a metering valve is included. Rotometers are advantageous due to the simplicity of the device and the constant pressure drop they offer. Also, rotometers do not require straight pipe runs for installation, so installation can be performed almost anywhere. Rotometers are favorable for their versatility, accuracy, and ease of use.