Bypass flowmeters are often termed rotary shunt flowmeters. The device is basically an orifice plate, with a bypass tube providing a parallel flow through a small tube wheel. The design is such that the orifice plate provides enough restriction to flow to induce a proportional flow through a bypass. The speed of the rotation of the turbine is therefore proportional to the flowrate through the main orifice plate. The turbine is connected by gear to a mechanical counter to give a total flow readout.
Advantages:
Relatively low cost giving a simple means of indicating total flow.
Disadvantages:
- Accuracy is moderate but density compensation is not normally available.
- The flowmeter is calibrated for a specific line pressure. Any steam pressure variation will lead to inaccuracies in readout.
- It is difficult to indicate the rate of flow.
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