Mechanical Engineering - Automobile Engineering - Discussion

Most of the braking fluid contains glycol fluid. It is hygroscopic fluid. The conversion of water in the brake fluid to steam when the brakes are heated significantly which causes compressibility in the brake system. This vapour lock leads to increased pedal travel and can result in a significant loss of brake effect.

Please clarify the concept of vapour lock.

Whether it occurs due to temp rise by frequent operation of the system or by hygroscopic nature of brake fluid? Or both?

Is this vapour changes to the liquid state when is cooled so that the brake gets restored to the normal state?

Due to their hygroscopic nature, they absorb moisture from atmosphere resulting in a decrease in boiling temperature and hence changing the fluid in vapour state. As vapour is highly compressible the brake stops working.

These problems are taking place in the hilly area the car does not drive smoothly more time brakes can be held down.

Although brake fluids are designed to work at extreme temperatures above 250C but still as the age of brake fluids goes on increasing, it starts loosing its properties and hence under high pressure and temperatures developed by applying brakes causes vapour lock.

The Hygroscopic nature of the glycol which is often used in now days modern vehicles can easily absorb water from any available surrounding.

This water so absorbed boils at 100'c (even far away from the fluids temperature). Vapour formed is compressible at high pressure hence making the brake to loss it's effect.

During the life of a vehicle or even a drum of brake fluid sitting on the floor of a workshop things happen to Glycol fluids because they are what we call "Hygroscopic". They absorb water even through the walls of the (would you believe) slightly previous rubber brake hoses and open top on cans or vehicle master cylinders.

This water vapour drawn into the fluid will of course boil at somewhere around 100 degrees (or a little more under Pressure) so any water content in a brake fluid is bad news. It also causes system internal parts to corrode.

This is a term used when the brake fluid in a vehicle brake system is overheat and loses efficiency.

First we will explain what brake fluids usually consist of there are three main types of brake fluids, Mineral brake fluids, Glycol brake fluids and silicone brake fluids. The GLYCOL brake fluid is most common and used in 99.5% of modern vehicle brake systems.

There can be up to 2 pints of brake fluid used in a vehicle brake system and this is piped around the vehicle using copper or rubber hoses to feed the fluid from the operator to the brake system.

Operating the brake forces the fluid into the master cylinder and then brake calipers or wheel cylinders to actuate the brake.

Basically Brake Fluid are of mainly three types:

1) Mineral.
2) Glycol.
3) Silicone.

Mainly in all of the automobile Glycol is used as Brake Fluid.

Glycol is Hygroscopic in nature, So it absorb Water from the environment during its life from the Master Cylinder, Rubber Hose etc.

Due to Severe Braking or Continuous Braking the temp of the Fluid Rises and Water will convert into Vapour at 100'C.

Being Compressible in nature it lead to loss in Braking Effect or termed as Vapour lock in Brake System.