When you want to take off the vacuum hose adapter at the booster unit you need to ensure that the engine is off and that you step on the break for about four to five time to help to relieve any vacuum that may be remaining in the booster unit. Remove the vacuum hose adapter from the connector by pulling it through the rubber grommet, with a screwdriver that might be needed to slide the grommet as far as out of the way as possible. Disconnect the vacuum hose from the intake manifold connection by pulling the collar which has tabs until it clicks to remove it, gently pulling on the hose. Any problems with the hose or fittings will require replacement of the part in question. For checking, check the condition of the non-return valve and if it is damaged or if it has degenerated, replace it. The valve can be checked by blowing through the attached hoses in the respective directions; the air must go only towards the intake manifold, when it comes from the booster side of the valve. For installation, it is done in the reverse manner of removal with a right installation of a new non-return valve.