dump valve fitting / boost problem

[PureButeS12]

i've just fitted a dump valve to my ca18et S12. the valve isnt dumping & my standard boost gauge is staying around zero. i have plumed the vacume hose to the blanked niple next to the clutch master cylinder as discussed on a previous threat

the forge dump valve was off a s14. is it not dumping or reading boost beacuse the spring is too hard for my puney 7psi or have i connected the vacume incorrectly?

any help would be a great help