GLOBE VALVES

GLOBE VALVE

A globe valve has a spherical body enclosing the valve seat and valve disc. The other parts of the valve assembly include The bonnet, Gland Housing, Gland packing, valve spindle and the Handwheel used for operating the valve spindle. Flanges are provided at either side of the valve body which is used for connecting it to the adjacent pipeline and internal passages guide the liquid flow through the valve seat. Liquid flow is always arranged to come from below the valve seat so that the upper chamber is not pressurised when the valve is closed. A gland with suitable gland packing mostly of graphite material is used around the spindle for preventing the fluid from flowing out from the valve body through the valve bonnet. The upper portion of the valve spindle is threaded and passes through a similarly threaded bridge piece. A circular handwheel is used to turn the spindle and raise or lower the valve disc. The valve disc and seat have accurately machined surface such that they have a perfect match. The material used for  the valve disc  and the valve seat are a hard alloy of cobalt and chromium with cobalt as the principal component.

 

The two types of Globe valves mostly used are SDSL (Screw down Screw lift) and SDNR (Screw Down Non Return).

SDSL Valve - In a SDSL valve the valve disc is connected with the valve spindle and moves up or down as the spindle is rotated. This valve is operated with the help of a handwheel which is attached with the valve spindle. Anti-clockwise rotation of the handwheel moves the valve spindle over the threads, lifting the valve disc from its seat and thus opening the valve. Clockwise rotation of the handwheel results in the lowering of the spindle which in turn moves the valve disc over the valve seat, thus closing the valve.

 

SDNR Valve - In case of a SDNR valve, the valve disc is not attached to the spindle. The Screw Down non return valves are generally used in bilge systems to prevent back flooding. A guiding vane or guides are provided in order to keep the valve concentric with the seat when it is in the open position. The valve disc opens and closes according to the pressure of the fluid . When the pressure of the fluid becomes greater than the weight of the valve disc, the valve lifts off its seat. The lift of the valve disc is controlled by operating the valve spindle in the clockwise or anticlockwise direction. There is no reverse flow allowed in this type of valve.

 

Application : Used in the Bilge and ballast systems, Fresh water transfer systems & Cooling water systems.

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