Vacuum and Hydraulic Brake Booster Theory of Operation

[Mateospeed]

Hey folks,
I'm in the midst of figuring out the brake system on my '66 Mustang track car build. In deciding which type and model of brake booster to use, I have realize that I don't know nearly enough about them to make an educated decision. Of most interest to me is how the control valve (not the check valve) in the booster works, on both types.

Does anyone have any good references for digging into the nitty-gritty of how the control valves in brake boosters work? I'd be very appreciative.

Or, perhaps, someone could help me answer my specific questions in text form. One question is: In a vacuum booster, how does the control valve provide proportional brake assistance? I can see how the input rod actuates the valve upon activation, but to me, it seems like the cavity 'behind' the diaphragm would fill to atmospheric pressure, applying maximum differential pressure across the diaphragm, and applying maximum output force. Obviously, this is not the case in real life, as the brakes aren't an on/off switch. So, how does this work?



Any insight as to how the similar system within a hydraboost/ generic hydraulic booster works would be awesome as well! Also, folks who have considered the decision between vacuum and hydra, the pros and cons/ tips you've learned would be great.

Thanks in advance!

-Matt

[Apogee]

Here's a link to one of the more complete descriptions of how a vacuum booster works, specifically with respect to the air valve (hub), control valve and reaction disc.

While not the most technical description, here's a decent link for how a hydroboost works. It's essentially a relatively simple mechanical linkage to a hydraulic spool valve which controls the power piston attached to the output rod.

Both are valid solutions, however hydroboost tends to have an advantage where there isn't adequate vacuum (level) for vacuum accessories, isn't space for a conventional vacuum booster, or the application requires more boost than a conventional vacuum booster can provide given the application for whatever reason. In theory, you could build a booster to generate as much gain/boost as you want, but aside from the obvious fitment issues, the larger the booster, the more vacuum it consumes during operation which can become problematic since vacuum accessories are essentially parasitic devices on the engine.

Tobin
KORE3

[Mateospeed]

Thanks! For anyone else interested, I also found a decent youtube vid - of course, it didn't show up when searching, but after watching a few related videos, it showed up.

https://www.youtube.com/watch?v=Q26W1HCWOjk