Not sure how that valve works but here is the best way to check that part of the vac system. One the main vac line from the vac pump to the break booster, put your mity vac on the same barb you did before. Plug any other barbs that stick out. Also make sure the main vac lineis tightly bolted to the break booster. Then start the car and read the vac on the gauge. If it reads 20"-25" then your vac pump and booster are fine. If it is low than one of the two is leaking. Next unbolt the line from the break booster, then seal the end of the line, I usually lick my thumb and cover the hole tightly. Start the car again. If it reads low now then your vac pump is bad. If it reads 20"-25" then the booster is leaking.

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