🔍 Key Concepts

• Thermostatic expansion valve (TXV) power element function and how its bulb pressure acts on the diaphragm to open the valve • Balance of forces on the valve: bulb pressure vs. spring pressure vs. evaporator (equalizer) pressure • What happens to bulb pressure and diaphragm force if the power element loses its refrigerant charge

💭 Think About

• Look at the illustration and trace which force actually pushes the valve pin open when the system is operating normally. If that force disappears, which direction will the spring push the valve member? • Consider what the external equalizing line does: does it help open the valve, help close it, or just help sense evaporator pressure at the outlet? • In a fail condition with no bulb pressure, would the system designer normally choose to risk flooding the evaporator/compressor, or to risk losing cooling capacity?

✅ Before You Answer

• Verify which side of the diaphragm the bulb/power element pressure is on and which side the spring pressure is on in the drawing. • Confirm whether the equalizer line adds opening force, closing force, or only provides a pressure reference under the diaphragm. • Decide, based on the force balance, whether the valve port and pin move toward more open or more closed when bulb pressure goes to zero.