Under which condition will the rate of flow of a liquid through a metering orifice be greatest?

Under which condition will the rate of flow of a liquid through a metering orifice be greatest?

• A. Atmospheric pressure 14.7 PSI
• B. Unmetered pressure, 17 PSI
• C. Metered pressure 5 PSI
• D. Vacuum

Answer: (B)

Flow through a metering orifice is driven by the pressure drop across the orifice—the bigger the difference between the upstream and downstream pressures, the faster the liquid is pushed through. Among the given conditions, the largest driving pressure difference is created when the supply is at 17 psi and the downstream side is at atmospheric pressure, giving the greatest flow across the orifice. If both sides were at atmospheric pressure, there’d be almost no driving force and the flow would be minimal. A metered pressure of 5 psi provides a smaller drop, so the flow is less. A vacuum might seem to offer a large drop, but in typical metering situations the scenario with the 17 psi unmetered supply provides the strongest differential, leading to the greatest flow.

Flow through a metering orifice is driven by the pressure drop across the orifice—the bigger the difference between the upstream and downstream pressures, the faster the liquid is pushed through.

Among the given conditions, the largest driving pressure difference is created when the supply is at 17 psi and the downstream side is at atmospheric pressure, giving the greatest flow across the orifice. If both sides were at atmospheric pressure, there’d be almost no driving force and the flow would be minimal. A metered pressure of 5 psi provides a smaller drop, so the flow is less. A vacuum might seem to offer a large drop, but in typical metering situations the scenario with the 17 psi unmetered supply provides the strongest differential, leading to the greatest flow.