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  • PHeller

    Sept. 25, 2008 8:18 p.m. PHeller Reader

    So most cars have vacuum assisted things like brakes, cruise control, fuel pressure, etc

    In cars that are not normally turbocharged from the factory, some parts of the assisted systems already contain check valves that keep them from being affected by the boost.

    My question is this,

    Why do factory cars have check valves to prevent against boost, in what situation would boost be present in a non-modified car?

    This question came about after a discussion about my buddies future turbo Probe GT (2gen).

  • daytonaer

    Sept. 25, 2008 8:46 p.m. daytonaer New Reader

    I'm not sure what you are asking.

    If you mean, why are there check valves in a naturally aspirated engines vacuum systems, its quite simple. To keep vacuum in, not to keep boost out.

    Think about a vacuum controlled system, like the HVAC. To do something like switch the out put from dash vents to floor vents can be operated by a vacuum canister operating against spring pressure. When you step on the gas, you loose some engine vacuum and if there is no check valve the spring overpowers the lower vacuum and the air goes where you don't want.

  • foxtrapper

    Sept. 26, 2008 4:47 a.m. foxtrapper SuperDork

    Floor the throttle on a naturally aspired car and the vacuum goes to near zero. If no check valve was installed in the power brake booster line one would loose all power assist to the brakes.

  • PHeller

    Sept. 27, 2008 1:32 p.m. PHeller Reader

    So the vacuum that is in the line is enough to run the brakes when vacuum is lower (near 0)?

  • daytonaer

    Sept. 27, 2008 2:48 p.m. daytonaer New Reader

    That giant disk thing of the brake booster is a vacuum reservoir.

  • PHeller

    Sept. 27, 2008 3:28 p.m. PHeller Reader

    What about other stuff? do they all have reservoirs?

    I've never complete understood how vacuum systems work, so I'm trying to edumicate mysulf.

  • Sept. 27, 2008 3:45 p.m. dan_efi New Reader

    The check valves are also pretty good at keeping the pressure of a backfire out of your vacuum operated components. Not sure if this was a design consideration, but it ends up being a + in the end.

  • noisycricket

    Sept. 27, 2008 3:58 p.m. noisycricket New Reader

    The vacuum booster for the brakes is a giant reservoir that allows atmospheric pressure in to the backside when you apply the brake.

    The HVAC typically gets its vacuum from a reservoir as well, it's usually a coffeecan looking thing on older cars, or a plastic globe, or a bunch of small plastic globes on VWs.

  • PHeller

    Sept. 28, 2008 3:59 p.m. PHeller Reader

    Ahhh that what the globes are in VW's.

    Thanks gents, now I am know and

 
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