Pilot Tube Flowmeter

                                         Application where the steam mains are large insertion flowmeter is used. Local velocity is large pipe is measured using insertion flowmeter. They are designed to be inserted through an opening in an pipe, usually through an gland assembly. Using insertion flowmeter one size will fit variety of pipe sizes and also the cost is reduced. The position for the measuring device in the fluid profile is critical.

In the simple pitot tube, the upstream aperture faces into fluid. This causes a pressure to build up within this tube as a result of the fluid velocity. This pressure is referred as total pressure. By means of an aperture on the downstream side of the tube it is also possible to measure the pressure in the pipe called the static pressure. It is then possible to calculate the local velocity with respect to the difference between the total and static pressure, as measured in the normal fashion by an external DP cell.

The simple pitot tube has the drawback of a need to ensure that it is sited correctly to measure the average flowrate across the cross sectional area of the pipe.

Advantage:

1. Small in size

2. Inexpensive

3. One size can be used for variety of pipe.

Disadvantage 

1. Foreign material in a fluid can easily clog pitot tubes and disrupt normal reading.

2. Low pressure drop