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By bitubo

The bitube or double tube amortisator are the most common currently used as first-equipment equipment originating in utility and medium-sized models.

They can be classified as presurized or non-presurized.

In Figure A we can see a bitubo amortisator and the scheme of its operation:

 Monotubo vs bitubo

The Compression Career:

When the vessel penetrates, the oil that is in the interior chamber flows without resistance through the hole A, B, C and D without resistance and the non-return vave 19 towards the generated space on the other side of the piston.Simultaneously a volume of oil is moved through the space that occupies the cottage in the interior room.

This oil forcibly passes through the standing valve to the reserve, which can be full of air at atmospheric pressure or with nitrogen gas pressed from 4 to 8 bar.

The extension career:

When the steak pulls the piston up in extension, the oil that remains above the piston is compressed and passed through the vavulas that are in it, the resistance that the oil finds at its passage through the valves is the strength of extension.The oil that had arrived in the reserve room (6) returns without finding resistance by the standing valve to the interior room to compensate the volume released by the cage.

Unprecedented bitub amortisers

They have the clue that air bags can be formed in certain circumstances:

The amortizator is stored or transported horizontally before it is installed.The oil column of the main chamber falls by gravity when the vehicle remains standing for a long time.At high temperatures (can reach up to 150 degrees) air bubbles are formed in ebulation and this causes dead points in the amortizing function.

Priced bitub amortisers

This solution is being used today in most series vehicles, the introduction of a gas under a pressure of between 4 and 8 bars is enough to eliminate all the above-mentioned disadvantages that do not suffer.

The monotube amortisator

The monotubo amortisator appeared after the bitubo version, originally as a high performance amortisator for competition.

In 1953 Christian Bourcier of Carbon invented and patented the monotube amortisator with high-pressure pressurized gas.Later a license was sold to the German company Bilstein to be able to manufacture larger units and for street cars, initially used for competition, but soon Bilstein realized the high-tech and safety could be at the reach of the street driver.

In Figure C, we can see a presurized monotune amortizator and the scheme of its operation:

Monotubo vs bitubo

Functioning Monotubo Amortisation

The Compression Career:

Unlike the monotube amortisator, the monotube has no oil reserve camera, and as its name indicates, the operation occurs within a single cylinder or tube.

The problem of placing the volume of oil displaced by the space that occupies the cottage, is solved with the incorporation of a camera with variable volume.For this, a floating piston is incorporated that separates the hydraulic camera from the variable in which a gas under pressure is introduced that can oscillate between 20 and 40 and bars.

By pushing down the steak piston, this makes the oil push the floating piston and compress the gas making the pressure increase on both sides, both in the hydraulic and gas chambers.The oil is forced to pass through the piston valves and the amortisation force comes given by the resistance that oppose the valves to the oil passage.

The extension career:

By stretching the piston upward, the oil above the piston makes it compressed and has to pass through the valves, and the resistance it finds at its passage is the amortisation force in extension, due to the decrease of pressure below the piston, makes the floating piston recover its original position

Monotubo vs bitubo

Benefits of Monotubo Amortisator

The advantages of a monotubo system against a bitubo system are several:

Better cooling since the camera is in direct contact with the air, it is to keep in mind that the oil can reach temperatures close to 150 degrees since the amortisator's mission is to transform the kinetic energy into heat.

A greater diameter of piston to the same carcass diameter, which allows to reduce the operating pressure.

The oil level does not fall by gravity after a period of inactivity, since the presurized gas keeps it under pressure, which prevents poor functioning when starting in cold.

Due to the gas chamber, the formation of bubbles and foam is avoided by avoiding cavitation problems, resulting in an effective amortization even with small high frequency vibrations.

Thanks to the gas chamber, the assembly position, transport and storage are not restricted.

As disadvantages to quote some, but that are not determining; greater production cost by the use of more quality materials and greater accuracy of tolerance for gas stainability.

Due to the pressure of the gas, the carrossery can rise a few millimeters as well as its center of gravity, making it recommendable the reajust of the height and geometry quotas.

See types of amortizers and symptoms of defective amortizers