Basics of Variable Area Flowmeters

 

 

The Basics of Variable Area Flowmeters

A variable area flowmeter is designed such that the device has a cross-sectional area through which gas or liquid passes. This area changes depending on how the rate of flow changes, causing a measurable effect by which the rate of flow can be determined. In this article you will learn about where variable area flowmeters are used, and why they are best suited for those applications.

Where are Variable Area Flowmeters Used?

The typical place where you will find variable area flowmeters is in rugged industrial service. Their economical composition makes them one of the most affordable and reliable methods for measuring process liquids and gasses. They are often built with end caps that can be removed, allowing them to be easily cleaned between uses.   They can be installed quite easily. There are different sized of variable area flowmeters, also known as rotameters, available, depending on which rate of flow you intend to measure. You will find them most commonly being used in a few specific applications, such as producing polyurethane foam, in test benches for fuel flow, and in test benches for hydraulic components.

The Composition of a Variable Area Flowmeter

There are various different ways in which a rotameter could be built, but the following is a description of what might be found in an average device. To secure the end-fitting, three O-rings and an end gasket seal are set in place. The O-rings are compressed by a packing gland or frame, and this allows for a seal to take place between the tube and the fitting. Whether you want a flanged connection, or if you prefer a corrosion-resistant material, you can choose which kind of fitting will suit your needs best. You can mount the device either in-line or on a panel, thanks to the standard frame/bezel assembly. Stainless steel frames contain tapered metering tubes.

How a Variable Area Flowmeter Works

The tapered tube is typically made of a smooth borosilicate glass. Within this tube is a freely moving metering float made of a material that is compatible with the fluid to be processed. Before flow takes place, the float will remain at the bottom. Once liquid or gas begins flowing through the tube, the float will be pressed upward in proportion to the pressure created. The float will oscillate a bit as its weight reaches equilibrium with the hydraulic force. Once it reaches this equilibrium, it remains in place as long as flow rate does not increase or decrease. However, if the flow rate does increase or decrease, the position of the float will change accordingly.

Before You Order

Due to the different sizes of rotameter available, there are some things you will want to confirm before you order one. Be sure to confirm the orientation of inlet/outlet fitting. Make sure to specify the specific gravity, the minimum and the maximum flow rates, the viscosity and type of fluid to be measured, and the temperature and pressure at which it will be operating. Also make sure to calculate the water equivalent flow, and from that value determine the tube code, capacity code, and model code. Once you have done all of this, you should know which kind of variable area flowmeter you will be using.

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