Variable Area Flow Meter Disadvantages

Variable Area Flow Meter Features

• A variable area flow meter uses a float for determining flow rate. A tapered vertical tube houses a float. Fluid or gas enters the tube's bottom opening. This small entryway leads to the float, which the fluid or gas pushes against. Measured gradations on the tube's exterior show users the measured flow rate based on the float's position inside the tube. The fluid or gas exits the tube through a larger opening on top.

Positioning

• One main disadvantage of a variable flow meter is its positioning. The tapered tube must be vertically mounted for the float to work with gravity's influence, as well as the moving fluid or gas. Some metering applications, such as those in limited laboratory spaces, may not have the room for a vertical flow meter. The user must determine if a variable area flow meter can be positioned correctly in a specific area for the best accuracy.

Float Matching

• An additional disadvantage is the flow meter's float. The float must be matched with the fluid or gas being measured. Each fluid or gas has a specific gravity, or density ratio. The float's weight and density must be calculated and calibrated to the specific gravity value of the fluid or gas. This calibration process ensures accurate metering during use.

Reading Accuracy

• Another disadvantage of a variable area flow meter is reading the float's positioning. Depending on the tube's diameter, it may be difficult to see the float within the moving fluid or gas, affecting the measurement accuracy. In addition, the tube's shape creates a parallax error. One view of the float may differ from another view at a different position around the tube. Many flow meter applications try to reduce these errors by using magnetic floats on the tube's exterior for easier measurement viewing.