A double block and vent valve (2) comprises a housing having an inlet (4) and an outlet (6) for introducing and discharging fluid to and from the valve and is defined at its ends by a first portion (18) and an opposite second portion (20̸). The valve includes a flow directing throat (52) disposed within the housing and interposed between the inlet and the outlet for communicating fluid therethrough and has a means for venting leached or trapped fluid externally of it. The flow directing throat has a flow discharging end portion (53) associated with the housing first portion and has an opposite flow receiving end portion (51) associated with the housing second portion. The flow receiving end portion and the discharging end portion of the flow directing throat are sized diametrically differently relative to one another such that fluid flow passing through the flow directing throat from the inlet to the outlet does so without substantially impeding its flow path.
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