What can cause a rise in differential pressure across an orifice plate?

A rise in differential pressure across an orifice plate occurs when there is an increase in the resistance to flow within the system. When there is a restriction in pipe fittings, it creates additional pressure drop as fluid must navigate through a narrower area or around an obstruction, which increases the overall differential pressure across the orifice plate. This is because the orifice plate is designed to measure flow based on the pressure differential created by the fluid flowing through it. As restrictions increase, the pressure upstream of the orifice plate rises while the pressure downstream may decrease, leading to a higher differential pressure reading.

In contrast, factors such as increased fluid viscosity and reduced flow rate typically do not result in a rise in differential pressure across an orifice plate; instead, they can lead to different behaviors within the system. Increased fluid viscosity may create a higher friction loss, but it generally does not affect the differential pressure in the same way as a physical restriction does. Similarly, a reduced flow rate can lead to lower differential pressure readings because the driving force through the orifice is diminished. Blockages would also lead to an increase in pressure upstream, yet the scenario specifically describes restrictions which are more directly related to fittings rather than complete blockages.