🔍 Key Concepts

• Submerged tube evaporator operation and purpose of the automatic dump (divert) valve • Typical maximum salinity of distillate allowed for potable water on marine evaporators, usually expressed in grains per gallon (gr/gal) or parts per million (ppm) • Relationship between salinity limits and protection of the freshwater tanks and users

💭 Think About

• Which choice best represents a realistic upper limit for salinity in potable/distilled water used on ships? Think about human use and machinery needs. • How does the automatic dump valve protect the system when salinity becomes too high—would it act at a very low threshold or allow more contamination before dumping? • If 1 grain per gallon is a relatively salty concentration, what fraction of that would still be considered “distilled” or “fresh” for marine standards?

✅ Before You Answer

• Compare these values to typical potable/distilled water standards: is 0.10–0.25 grains per gallon a tight control range or a very loose one? • Remember that the dump valve is designed to prevent brine carryover into the freshwater system—so the setpoint should be at a level where contamination is just beginning to become unacceptable. • Double‑check any rules of thumb you know: roughly 1 grain per gallon ≈ 17 ppm—use that to estimate how many ppm each answer represents and which range is most appropriate for distilled water.