Globe Valve

Overview

A globe valve regulates flow by lifting a disc straight up off a horizontal seat inside a rounded, globe-shaped body. Unlike a gate valve, which is meant to be fully open or fully shut, the globe valve is built to sit at any intermediate position, so it is the default choice wherever an operator or controller needs to set and hold a flow rate. The price of that control is pressure drop: flow has to turn up through the seat and back down, an S-shaped path that costs head even when the valve is wide open.

The Valve Body forms that Z-shaped passage and holds the Plug & Seat; the Bonnet bolts on top and carries the stem out of the pressure boundary. Turning the Actuator drives the Stem Assembly, which raises or lowers the disc. The Packing & Gland seals the stem, the Flange Set bolts the valve into the line, and the Backseat Bushing lets the packing be serviced with the line still under pressure.

How it works

Because flow approaches the seat from below and pushes the disc open, only a short lift, roughly a quarter of the port diameter, is needed to expose the full seat area. The actuator turns a threaded Valve Stem running in a bronze Stem Nut held in the Yoke, converting rotation into that short linear travel. As the Disc / Plug lowers onto the Seat Ring, the last fraction of travel does the throttling, which is why globe valves give such fine control near the closed position.

The shape of the disc sets the flow characteristic. A flat disc gives near on/off behaviour; a contoured parabolic plug, often run inside a slotted Guide Cage, opens flow area gradually so that valve position maps smoothly to flow, the equal-percentage trim that control loops prefer. On a modulating valve the Position Transmitter reports stem travel back to the controller so it can hold a setpoint. Seating the disc squarely each cycle, helped by the swivelling Disc Nut, is what lets the same valve both throttle for years and still shut drop-tight when commanded closed.