🔍 Key Concepts

• Trace the flow path from inlet to outlet and note which chambers around each disc are at inlet pressure vs outlet pressure. • Understand how a double-ported (double-disc) globe valve uses two discs to either balance hydraulic forces or use pressure to assist motion. • Relate pressure acting surface (upper vs lower face of each disc) to whether forces on the stem cancel (hydraulic balance) or add (hydraulic assist).

💭 Think About

• For the top disc, which side (upper or lower) is directly exposed to the incoming high-pressure flow from the left? Do the same for the bottom disc. • If inlet pressure pushes the top disc one way and the bottom disc the opposite way, what does that do to the net force on the stem? If both push the same way, what does that suggest? • Look at the cavities above, between, and below the discs: which of those spaces appear to be in open communication with the inlet passage and which with the outlet passage?

✅ Before You Answer

• Verify which faces of the discs are surrounded by the shaded region marked as inlet flow and which are surrounded by the outlet side. • Check whether the areas that see inlet pressure on the two discs are opposite each other along the stem (tending to cancel) or oriented in the same direction (tending to add). • Confirm whether the design goal of this type of control valve, as drawn, is usually to keep the stem force small and independent of line pressure (hydraulic balance) rather than to use line pressure as an assist.