First off, this is quite a technical article, and assumes you have knowledge of valves for the oil & gas, petrochemical, refining,chemical, industries. We make no apology for getting into the details here! So, there are two kinds of isolate valves such as ball valves and needle valves. The basic purpose of the Monoflange system is to combines these ball or needle valves in a single module. A Block and bleed monoflange is a fluid monoflange which syndicates single or more block/isolate valves i. e.