Brake debooster valve

[ahmed88]

on a HP system, it reduces the pressure and slowly releases the brakes or does it apply the brakes slowly and release the brakes quickly ? ??

im thinking the 2nd choice, since on release there is more fluid volume on the bigger piston side so it goes back quickly, but i need to be sure.

thanx.

[BAe146s make me cry]

Brake Debooster Cylinder (http://www.tpub.com/content/aviation/14018/css/14018_474.htm)

After reading the second paragraph - go get some rest (Get the banana's enroute to exam in the morning) :ok:

BAe146??? :{:{:{

[ahmed88]

thanks, yeah ill go to bed now, exam at 10 am, its 9:05 here, good night.

[SNS3Guppy]

Ahmed,

A debooster doesn't allow greater or smaller amounts of fluid in or out of the brake. It's not a restrictor.

A debooster simply changes pressure for volume on the brake. By applying a high pressure to a small piston, the piston is used to move a larger piston. Think of it as a piston that's small at one end and big on the other. Fluid doesn't pass through the piston...it's pushed at high pressure on the small end, and as the piston is pushed, it in turn moves fluid on the large end.

The large end of the piston has a much larger area; it moves more volume, but at a lower pressure value because the pressure placed upon it at the small end is averaged over the surface area of the big end. Think of it this way. If I poke you with a large stick, 3 inches across with a force of twenty pounds, it may hurt. If I poke you with a stick that's the diameter of a pencil, using the same force, it will hurt a lot more...because the force I'm exerting on the stick is concentrated on a much smaller area. Somewhat the same for the brake debooster...but exactly the opposite. Big force concentrated on small end of the piston is felt as a weaker force at the big end of the piston. The result...more fluid moved with less pressure per unit of surface area. Ten pounds per square inch on the small end equals one pound per square inch if it's ten times the area, on the big end.

Clear as mud?

The total pressure remains the same on either side of the piston, but it's spread over a larger area, with less pressure per unit of area. The brake will apply the same total pressure value, but it releases easier, and applies a little slower, with less pressure over the entire surface if measured per unit of surface area (pounds per square inch, etc). It's not really the speed at which the brake applies and releases, however...as the fluid isn't transferring from one side of the debooster to the other, there's no fluid exchange and no return flow from the brake. What's happening is high pressure is being exchanged via the mechanical disadvantage of the piston, for lower pressure and higher volume. This allows a larger surface area piston to apply pressure to the brake, which increases bearing or friction area, as well as increasing the area over which heat is developed and dissipated. More volume means the brake fluid doesn't heat as fast, and brakes don't fade as quickly or experience heat degredation as fast.

[ahmed88]

i see, that cleared up a few things !, thanks for the well put explanation, its worthy of a print out :ok:.

[mitzy69]

the de-booster also acted as a fuse, if there was a leak on the brake pistons or the hose leaks then only a limited amount of fluid is lost, when the piston reaches the end of the bore no more fluid is pushed down to the brake. shud stop a fire or loss of lots of hyd fluid.

[ahmed88]

hmm that makes sense, thanx.