🔍 Key Concepts

• Look at how each illustrated valve is controlled: is it a simple direct-acting valve, or a pilot‑operated valve with a separate power element? • For large capacities (50 tons and over), manufacturers usually avoid having the diaphragm directly move a large main seat; they use a pilot valve operating a larger main port. • In variable‑capacity systems, you want a valve that can modulate smoothly over a wide range of loads, not just snap open/closed like a small unit valve.

💭 Think About

• Which illustration shows a small, compact valve body more suitable for fractional‑ton or small tonnage units, and which shows a much larger body with a pilot section and main valve section? • Which design would keep the operating force on the diaphragm and power element relatively small, even though the main valve is passing a very large mass flow of refrigerant? • If the system’s capacity increases above 50 tons, what limitations would a simple direct‑acting expansion valve have in terms of diaphragm size and spring force?

✅ Before You Answer

• Identify which drawing shows two stages of control (a small pilot port plus a separate, larger main valve) rather than a single needle or seat. • Check which valve has a remote sensing bulb and power element clearly arranged to control a separate main valve in a big body casting. • Before choosing, eliminate any valves that look like small direct‑acting thermostatic expansion valves typically used on low‑tonnage or residential/commercial equipment.