• A Pipe elbow used as a liquid flow meter is known as an Elbow meter.

• Flow rate ismeasured bydeterminingthe differentialpressure developedbetween theinnerand outer radii of the bend by means of two pressure tapslocated midway on the bend.

• It is based on the principle that when fluid flows through an elbow, it exerts centrifugal force on the inside of the pipe wall, creating a pressure differential between the inner and outer radii of the elbow.

• The pressure taps in the elbow measure this differential pressure, which is proportional to the density of the liquid times the square of its velocityand inversely proportional to the elbow's radius.

• In most cases, one tap at the 45° point is enough, as in the figure but an additional tap at the 22.5° point may also be used.The size of each of the two taps should not exceed one-eighth of the pipe diameter.

• Elbow meters are used when lack of space prohibits use of most other flow meters, which require long and straight pipe.