Why Cars Does Not Have Vacuum Pressure Release Lever?

kenlitting · 17th April 2011, 07:54 AM

i have seen a pressure release lever in buses for vaccum release i suppose which the driver presses to remove vaccum pressure accumulated on vehicle stoppage, why this system is not present in cars which have vaccum assisted brakes

raj_5004 · 17th April 2011, 09:06 AM

It is for the air brakes. cars done have air brakes, they use hydraulic brakes.

kenlitting · 17th April 2011, 11:00 AM

but dont newr cars use vaccum assist along with hydraulics for braking thats why once u switch off the engine braking efficiency decreases so u have to pump the brakes my question is how vaccum pressure is controlled in cars unlike release valves in buses

Mr.Boss · 17th April 2011, 11:08 AM

Quote:

Originally Posted by kenlitting

but dont newr cars use vaccum assist along with hydraulics for braking thats why once u switch off the engine braking efficiency decreases so u have to pump the brakes my question is how vaccum pressure is controlled in cars unlike release valves in buses

Dude, what you find in trucks and bus is not vacuum release.
That is releasing the compressed air from the spring loaded brake chamber, which in turn engages the parking brake by spring load.

ilango[speed thirst] · 17th April 2011, 11:24 AM

cars use hydraulic brake system (vaccum assisted but that is different , read only system)

Trucks/bus use air brake system.

what you find as brake oil is air in truck and bus.

you have brake oil reservoir.
truck have air tank.

air is filled by a compressor run on engine power.

only during running high pressure is needed and it self release the excessive air .

during stopping/parking that is done by the driver. its not advisable for the air tank to be in high pressure during parking

Mr.Boss · 17th April 2011, 11:49 AM

Quote:

Originally Posted by ilango[speed thirst]

...........during stopping/parking that is done by the driver. its not advisable for the air tank to be in high pressure during parking

Small correction ilango. It is not that driver is releasing the compressed air from reservoir during parking. Air in the reservoir / tank remains on it in the same pressure (no harm in maintaining high pressure, the system is designed to withstand the pressure) but the air from brake chambers are released so that the spring loaded parking brake will be engaged (Parking brakes cannot be disengaged without air pressure). Will try to post some pics to explain the same.

kenlitting · 17th April 2011, 12:48 PM

so is airbrake more powerful than hydraulic brakes and which is safer
what are power brakes as mentioned in stickers on some cars

Mr.Boss · 17th April 2011, 01:12 PM

Quote:

Originally Posted by kenlitting

so is airbrake more powerful than hydraulic brakes and which is safer
what are power brakes as mentioned in stickers on some cars

Both holds their own advantages and disadvantages.
For example, Response time in Air Brake is very less compared to Hydraulic brakes, but the system requires a compressor for pressurised air, reservoirs to store them, which indeed increases the no. of components and weight.
IMO air brakes are highly responsive, efficient & safer than hydraulic brakes.

No clear idea bout Power Brakes. I have seen such stickers in Ambassador Cars, AFAIK they are with some after market bigger brake boosters (vacuum assisted)