Which gauge reads both positive and negative pressures?

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

Answer: (B)

Gauges come in different types because systems can push fluid (positive pressure) or pull it (vacuum). Some gauges only read positive pressures above atmospheric, while others only show vacuum below atmospheric. A compound gauge is designed to handle both: it has scales for pressures above atmospheric and for pressures below atmospheric, so you can monitor when a line is pressurized and when it’s pulling a vacuum. That dual capability is exactly why it’s the best choice here—it provides readings on both sides of atmospheric pressure, which is essential in pump operations. The other gauges don’t cover both conditions: a standard pressure gauge reads positive pressure only, a barometer measures atmospheric pressure, and a vacuum gauge reads vacuum (negative pressure) only.