I have 3 pressure vessels on my heating system. You can't check pressure charge on air side when water in system, so had good advise to fit FLAMCO 3 way valves You have it set to system (normal) or set to drain where you can depressurise the vessel without draining system.
Q ... Existing set up is as per this pic-
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I would fix Flexcontrol valve to top top of pressure vessel and then fix pressure valve & filling loop set to this.
On this pic you can see there are 2 types of 3/4 BSP valves.
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While the left hand one had correct F at base and M at top, the right hand valve has benefits of a swivel F nut to allow easier fitting of pressure vessel. If I used this valve and removed the nut at the top of the valve, would it be acceptable practice to use this as a 3/4 male BSP fitting ?