COMMON MAIN CONNECTION

When two or more boilers are connected to a common steam main, the steam connection from each boiler having a manhole opening must be fitted with two stop valves having an ample free-blow drain between them. The stop valves installed on high pressure steam boilers must consist of either one automatic nonreturn valve, set next to the boiler and a second valve of the outside-screw-and-yoke type; or two valves of the outside-screw-and-yoke type. The free blow drain must ensure complete removal of all condensate and steam from between the two stop valves.