The residual pressure is read on which gauge?

• A. Compound gauge
• B. Vacuum gauge
• C. Differential gauge
• D. Pressure gauge

Answer: (A)

Residual pressure is the pressure you’re delivering through the discharge side of the pump, the pressure you want to maintain to keep flow reliable. The compound gauge is used for this reading because it combines two scales in one instrument: a pressure side for positive discharge pressure and a vacuum side for suction conditions. When water is flowing, you read the residual pressure on the pressure portion of the compound gauge. The vacuum gauge measures suction-side conditions, a differential gauge shows the difference between two pressures rather than the actual discharge pressure, and a plain pressure gauge lacks the dual-scale readout that’s standard on pump panels. So the residual pressure is read on the compound gauge.