94 Astro Heater Hose inline Vacuum?

I have an inline vacuum on my hoses. It is leaking. Anyone know what this is called? I cannot find it in my manuals.runaround Thanks, for your help.

So let me guess- you are commenting on your water shut off valve on the heater inlet hoses on top of HVAC module- that is vacuum actuated? so what is leaking? the vacuum or the coolant? if coolant- replace the water shut-off valve-- if vacuum - fix the vacuum hose-- some more detail may be needed to help you more......................