The bypass valve rotates with the help of exhaust gases, which untwist it, passing through the impeller blades. The propeller (rotating impeller) rotates the turbine wheel, which contributes to the creation of pressure in the manifold. The level of this pressure is determined by the total amount of air passing through the turbine.
The amount and speed of exhaust gases depend on the engine speed, that is, the more rpm is performed and the more power, the greater the number of exhaust gases passes through the turbine, respectively, creating more pressure.
On the impeller of the turbine, the exhaust gas flow should be reduced. Most often, in a run-off car, an internal turbine bypass valve is used, due to which exhaust gases are removed directly from the turbine body . But many pressure valves are installed upstream, replacing parts of the exhaust manifolds or installing a cross pipe.
The internal bypass valve has a large opening through which exhaust gas flows. In the internal valve there is a special shutter that covers this hole during turbine operation (when the required pressure is set). This valve is connected to a lever located on the outside of the turbine. And it is connected to the activator lever, which is a pneumatic device that converts pressure into linear motion using a spring and diaphragm. The lever activates the damper until it is fully open.
The solenoid is a specialized device installed in front of the activator, which changes the pressure entering the activator. With a change in duty cycles, less or more air passes through the solenoid through itself. It is controlled by a computer that reads pressure readings and gives orders to reduce or increase boost by closing or opening the valve.
The lever itself moves freely, swaying on the mount. If this does not happen and it does not move freely, when it is separated from the valve rod, it means that there is some kind of problem and it needs to be fixed. Sometimes the lever can move jerky, especially when heated. The length of the activator rod varies depending on the regulation of the degree of closure / openness of the bypass valve. Tightening shortens the valve traction and relaxing lengthens it. If the bypass valve is closed more tightly and the rod is shorter, then the activator needs more pressure to open.
The external bypass valve is a separate device designed to operate independently of the turbine housing. Usually they are designed for a larger air flow compared to internal ones. Most of them have a dual activator, which facilitates the quick opening of valves and, thus, provides better control over the spinning of the turbine. External valves can have different springs, with the replacement of which a minimum boost level can be set.