Other forms of gravity-type VA meters may incorporate a piston or vane that responds to flow in a manner similar to the float’s behavior. All these devices can be used to measure the flow rates of most liquids, gases, and steam. There are also similar types that balance the fluid flow with a spring rather than gravitational force. These do not require vertical mounting, but corrosive or erosive fluids can damage the spring and lead to reduced accuracy. The term rotameter derives from early versions of the floats, which had slots to help stabilize and center them and which caused them to rotate. Today’s floats take a variety of shapes, including a spherical configuration used primarily in purgemeters (which will be discussed later on). The materials of construction include stainless steel, glass, metal, and plastic. The tapered tube’s gradually increasing diameter provides a related increase in the annular area around the float, and is designed in accordance with the basic equation for volumetric flow rate: With h being constant in a VA meter, we have A as a direct function of flow rate Q. Thus, the rotameter designer can determine the tube taper so that the hei...