Which device measures flow by pressure difference across a constriction?

Which device measures flow by pressure difference across a constriction?

• A. venturi meter
• B. pitot tube
• C. orifice plate
• D. rotameter

Answer: (A)

Flow is measured by converting a pressure difference produced as fluid passes through a constriction into a flow rate. When fluid speeds up through a narrower section, its velocity increases and its pressure drops; the difference between the upstream pressure and the throat pressure can be used to calculate how much fluid is moving. A venturi meter applies this by using a smooth, gradual narrowing to a throat and measuring pressures before and at the throat. This setup minimizes energy losses and keeps the relationship between pressure drop and flow rate predictable, giving accurate readings over a range of conditions. The other options measure flow differently: a pitot tube gauges velocity by comparing stagnation and static pressures in open flow and isn’t used for differential pressure flow in a piping line; an orifice plate also creates a pressure drop across a constriction but with a sharp edge that causes more energy loss and typically less accuracy; a rotameter uses the height of a float in a tapered tube, not a pressure difference across a constriction.

Flow is measured by converting a pressure difference produced as fluid passes through a constriction into a flow rate. When fluid speeds up through a narrower section, its velocity increases and its pressure drops; the difference between the upstream pressure and the throat pressure can be used to calculate how much fluid is moving. A venturi meter applies this by using a smooth, gradual narrowing to a throat and measuring pressures before and at the throat. This setup minimizes energy losses and keeps the relationship between pressure drop and flow rate predictable, giving accurate readings over a range of conditions. The other options measure flow differently: a pitot tube gauges velocity by comparing stagnation and static pressures in open flow and isn’t used for differential pressure flow in a piping line; an orifice plate also creates a pressure drop across a constriction but with a sharp edge that causes more energy loss and typically less accuracy; a rotameter uses the height of a float in a tapered tube, not a pressure difference across a constriction.