Working Principle of Globe Valves
When the globe valve disk move upward while actuating, an annular opening is forming in between the disc and seating this allow the fluid to flow from upstream to downstream. The area of opening is directly controls the flow ,when the opening area can be controlled precisely by the controlling the seating profile of disc. The profile can be manufactured to get linear, quadratic ,logarithmic varying area of opening. See below figures of opening and closing of globe valve
1. Fully Open Condition
When the disc is at maximum possible upward position gives a maximum the orifice opening area. At this point the pressure drop is minimum and flow rate maximum. This result a maximum capacity flow through the valve.
2,3. Throttling
When the stem and disc actuates down by rotating the flywheel reduces the orifice opening area in turns increases the pressure drop and reduces the flow rate.
4. Fully Closed Condition
As the disc advances down, the opening area reduce further and finally get closed. The fluid flow volume also relatively reduces with respect to the linear downward motion of stem due to the varying orifice opening. Finally the flow stops when the disc remains in tight contact with the seat without any leakage .