What is the maximum +/- differential pressure?

• A. -0.5 to 8.7 PSI
• B. 0 to 9 PSI
• C. -1 to 9 PSI
• D. -0.2 to 8.8 PSI

Answer: (A)

Differential pressure is the difference between the pressures on the two sides of a device. The maximum +/- differential pressure is simply the range of this difference that the device is designed to tolerate in either direction.

For this case, the specified range is -0.5 to 8.7 PSI. That means the device can handle up to 8.7 psi of positive differential (upstream pressure higher than downstream) and up to 0.5 psi of negative differential (downstream pressure higher than upstream) without issues. The asymmetry reflects a design where forward pressure drops are more tolerable than reverse ones, often due to seals, flow paths, or internal components that prevent reverse flow.

Other ranges either omit any negative differential, allow a larger negative value, or shift the bounds in ways that don’t match the device’s actual tolerance, so -0.5 to 8.7 PSI best represents the true maximum +/- differential.