Applicable direction of globe valve

         Globe valves, so-called because of their outside shape, are widely used in plant piping. They are suitable for manual and automatic operation. Unlike the gate valve, the globe valve can be used for regulating flow or pressures as well as complete shutoff of flow. It may also be used sometimes as a pressure relief valve or as a check valve. Compared with a gate valve or ball valve, the globe valve has considerably higher pressure loss in the fully open position. This is because the flow of fluid changes direction as it goes through the valve. The L/D ratio for this type of valve is approximately 340. Globe valves are manufactured in sizes up to NPS 16. They are generally hand wheel–operated.

　　Globe valves are used primarily in situations where the throttling of the commodity is required. By simply rotating the handwheel, the rate at which the commodity flows through the valve can be adjusted to any desired level. Having the valve seat parallel to the line of flow is an important feature of the globe valve. This feature makes the globe valve efficient when throttling commodities as well as yielding minimal disc and seat erosion. This s-shaped configuration, however, creates a large amount of resistance within the valve. The design of the globe valve body forces the flow of the commodity to change direction within the valve itself. This change in direction creates substantial pressure drop and turbulence. The globe valve is therefore not recommended when flow resistance and pressure drop are to be avoided. In most installations, the commodity is routed into the valve’s body from below the valve seat and disc. This flow direction uses the pressure of the commodity to aid in the opening operation of the valve. It also reduces wear on the valve seats and disc. One exception however is when high-temperature steam is routed through the valve. The extreme temperature of the steam contacting the valve seat from below creates a significant temperature difference between the top of the seat and the disc. This temperature difference across the valve’s seats and disc cause the metal of the disc to contract which results in leakage. Therefore when high-temperature steam is routed through a globe valve, it is routed into the valve from the top of the disc, opposite of normal commodity flow direction.

　　Globe valves are very good for low leakage shut-off and regulation. As the valve size and the operating pressure increase, the hydraulic load on the stem becomes greater making the valve difficult to operate manually. This problem was first experienced with steam engines as sizes and steam pressures increased to produce more power. The double-beat globe valve reduces the hydraulic load by balancing the forces on the discs.

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