I would like to know if exist some rule in the selection of the wedge type (solid, flexible, parallel slide, double disc, etc) of the gate valve. In the valve specifications that I have, the solid wedge is used for all diameters in 150# and for diameters lesser than 2" for 300# to 2500#; from 300# until 900# the flexible wedge is used for diameters bigger than 2"; for 1500# and 2500#, the parallel slide or double disc is used for diameters bigger than 2".Currently, I have to select the wedge type for the gate valve of 48" in 150# and 300#. I would like to know if I can select solid wedge for 150# and flexible wedge for 300#All valve selections, in my opinion, starts with a complete description of application, full fluid description with flow, pressure, temperature , operation mode and cyclus, certifications, material requirement,etc, etc..Secondly: within theese parameters: what is available commercially, to what deliverytime, price, operational cost including maintenance and life expectancy at local conditions. Survey to include (idealistically) all valve constructions suitable. (Why wedge valves only?)Third: selection for each single (group?) of valves, idealistically again best value cost over required lifetime.Reason: the market and product construction changes. True values ten or fifteen years ago need not necessarily be true today. Apart from this a 'rule of tumbs' and experience over time has its value, but if this is refitting or valves for a new project I would try to 'open up' for market and product input before deciding or setting up 'locked' data sheets.

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