The radiator cap

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Radiator cap is a device that allows to pressurize the coolant inside the engine. Here its function, history, as an opera is explained.

Radiator cap

The radiator cap or radiator cap is a device that allows to pressurize the coolant inside the engine, to raise its boiling point. This is achieved through a spring-loaded closing system that opens and closes at a specified pressure. By increasing the boiling point of the coolant, it is possible to improve the performance of the cooling system at the critical points of the engine, such as the chambers and blocks where water circulation is slow in some cases.

Without a pressurized system, water in these low-speed zones would partially change its state to gaseous, greatly limiting its cooling capacity.

Then as you can see, the radiator cap works more like a pressure valve.

History of Radiator Cap.

historia tapon radiador

The above patent drawing contains the modern type of radiator pressure cap and radiator fill opening that was given to C.H. Lines in 1946 for Stant Mfg. Co. This device equipped with a spring-loaded internal valve that opens at an established pressure directs boiling water and steam through an outlet (11) to the overflow tube during overheating.

From then on, the novel, simple and mechanical design of this lid allowed the development of higher compression ratios and greater power in postwar engine designs..

¿What function the radiator cap meets?

- It allows filling the system with the coolant when the pressure drops.

- Allows the refrigerant to exit to the reservoir when the cooling liquid expands due to heating.

- Maintains the system pressure at an adequate value to avoid boiling the liquid, but without dangerous overpressures. It is important to always evacuate the overpressure since the accumulation of it can cause bursting pipes and chamber packing.

¿How the radiator cap works?

In the illustration you can see the radiator cover, which is composed mostly of calibrated springs to act at specific pressures. This is why it is important to use the right one for our engine.

tapón de radiador animacion de funcionamiento

Assuming this is a 10.1 bar lid, as long as the system pressure is maintained in that range the force of the main spring maintains sufficient pressure so that the outlet lid does not open. If the pressure of 10.1 bar is exceeded, the spring acts and the water outlet cover opens and it will be directed to the refrigerant container by the hose on the right.

When the engine cools, the system loses pressure and the water returns to its pure liquid state, which produces negative pressure inside the system. This negative pressure activates the lower water inlet cover, which will draw water from the reservoir again.

This keeps the system in balance, free of dangerous pressures that damage the system.

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Written by

Dennis García

Chica Mecánica




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    The radiator cap

    The radiator cap

    Radiator cap is a device that allows to pressurize the coolant inside the engine. Here its function, history, as an opera is explained.

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