The Comprehensive Flowmeters Resource

Rotameters – VA Meters

A rotameter is a common type of industrial flowmeter that is used to measure the flowrate of a liquid or gas. It consists of a tapered tube with a float inside. Rotameters work in a simplistic way: fluid raises the float when it passes through the tapered tube. Probably the simplest way to visualize how a rotameter works is to turn to phenomena we see in everyday life. We could use a water fountain with a flow going upwards and placing a tennis ball on the waterspout tells us how fast the water is flowing by how high the tennis ball will rise. Of course, we are going to have a problem balancing the ball but if we were to place a tube over the waterspout, the balancing issue is solved. 

Once someone understands the basic principles of this particular flowmeter type, it is easier to spot in a factory setting. The above image uses something called a Bobbin (which is actually a weighted piece) which moves up and down according to flow rate. 

A typically common designed of rotameter is consist of a tapered metering tube with flow going down to up and through the device. The bobbin is the resistance piece which moves higher according to higher flow. The graduations or markings on the device correspond to the flow rate. Rotameters are often use as a visual means of recognizing flow rate although some variations of them are designed with mechanical/electrical outputs.  In addition, a flow controller such as a needle valve can be manufactured integrally with rotameter to control flow manually by hand. In this case the rotameter has now become a flow controller or regulator. 

Someone might be asking why rotameters are also called variable area flow meters. The reason is that part of the flow meter’s operation is based on a principle of varying area. The tapered tube increases the area for the liquid or gas volume so that a wider flow range can be covered. In fact, the generic name for this type of meter is should actually VA Meter (V=variable, A=Meter) but at this point it would not be fair if we did not mention that the term rotameter became so popular because of a company called Rota (Deutsche Rotawerke GmbH) now owned by Yokogawa.

Types of Rotameters

Rotameters come in several varieties, and each has unique properties. There are several types of rotameters, including flanged armored rotameters, low-cost sight and rate indicators, and glass tube flow meters.

Flange Armored Rotameters

The flange armored rotameters have several different connection sizes, including ASME, DIN, and JIS numerous threaded fittings and flange variants to offer for versatile installations, widely used as a mechanical indicator alternative that do not require power, which lowers installation costs and makes it an affordable option for measuring flow in potentially hazardous areas.

Glass Tube Flow Meter

A glass tube rotameter is a type of low-cost rotameter that is normally used in many general applications. 

Why use a rotameter?

Rotameters are extremely popular in almost in every industry. They are easy to use, easy to understand and often easy to replace. Several manufacturers have taken a further step to produce rotameters in different styles and with different options. 

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