Warning: Do not remove the one-way vacuum valve from the vacuum hose.
2. Check the operation of the one-way vacuum valve using a vacuum pump (Rom. 15.12). The valve is in good condition if, when connecting the pump to the side of the valve that goes to the brake vacuum booster gel, a vacuum is created and maintained, and when connecting the pump to the side of the valve that goes to the intake manifold, a vacuum is not created.
Fig. 15.12. Using a vacuum pump to test a one-way vacuum valve
Warning: If the one-way vacuum valve is faulty, replace it together with the vacuum hose.
The original material is here (MitsubishiMan)