What happens to fluid pressure on the upstream side of a restriction in a pipe?

The fluid pressure on the upstream side of a restriction in a pipe does not actually increase; it decreases instead. When a fluid flows through a pipe and encounters a restriction, such as a narrower section, the velocity of the fluid increases to maintain the conservation of mass. According to Bernoulli's principle, as the fluid velocity increases, the static pressure decreases on that side of the restriction.

Understanding this principle is crucial in many applications, such as in flow measurement and control in industrial processes. In practical terms, this means that if you were to measure the pressure of the fluid right before it enters the restricted area, you would find it lower compared to the pressure in a wider section of the pipe leading up to the restriction, demonstrating that the pressure decreases due to the flow dynamics at play.