🔍 Key Concepts

• How different types of pressure gauges operate (single pressure, dual pressure, positive vs negative) • The meaning of positive pressure (above atmospheric) and negative pressure (vacuum/below atmospheric) • Which gauge types are typically used on systems where you must see vacuum on one side of zero and pressure on the other

💭 Think About

• Which type of gauge scale must cross through zero so it can indicate both vacuum (negative) and pressure (positive) on the same dial? • Does a differential, duplex, or simplex gauge necessarily show readings on both sides of atmospheric pressure, or do they usually show separate pressures or a difference between them? • Think about boiler and pump systems: which gauge is commonly used to see suction (vacuum) and discharge (pressure) on a single pointer and dial?

✅ Before You Answer

• Identify which term specifically implies a gauge that reads pressure relative to atmospheric, on both sides of zero • Confirm which gauge name is commonly associated with boiler service for showing vacuum and pressure on the same dial • Eliminate any gauges that read two separate pressures or the difference between two pressures rather than a single pressure that can be either positive or negative