The term "bypass valve" refers to a regulating device for maintaining the pressure level of a liquid or gaseous medium at a desired level by bypassing it through a bypass line. This pipe fittings automatically maintains a predetermined pressure difference between the inlet and outlet. When the set inlet pressure is exceeded, the valve opens, and when it drops below the set level, the valve closes. Full opening usually occurs when this number is exceeded by more than 20%.
Direct and indirect relief valves
The opening of the bypass (regulating) element of the valve can be carried out by two types of actions - direct and indirect. The bypass valve, in which the action of the measuring element on the control valve is carried out only by the energy of the medium, is called a device of direct action. They are divided into spring and membrane type of action on the shutter. In such valves, the opening of the shutter occurs under the pressure of the medium and is regulated by the compression of the spring. Direct-operated bypass valves are characterized by simplicity of the device, low cost and low sensitivity to contamination. The disadvantage is maintaining pressure with low accuracy. The bypass valve, in which the controller acts from the outside with additional energy, is called an indirect valve. These are more expensive and accurate devices.
In developing the turbocharger, engineers faced the problem of creating excessive pressure in the intake manifold. The rotation of the turbine impeller occurs under the action of exhaust gases supplied to the blades, the number and pressure of which depends on the engine speed. When driving fast, the engine makes a large number of revolutions, the rotational speed of the turbine rotor increases, creating an overpressure in the intake manifold. As a result, the excess of injected air can lead to the so-called “overburden” or “surge” of the engine and its failure. To solve this problem, a turbine relief valve is installed on the turbochargers, which, at a certain pressure, discharges excess gas past the impeller to the exhaust manifold. This ensures the normal functioning of the engine and turbine without failures and failures.
Turbine bypass valve can be of external and internal types. In most commercial vehicles, an internal type of valve is installed. Exterior are equipped with cars that need more bandwidth and the possibility of additional adjustments (racing models). The external pressure relief valve of the turbine is more reliable, but it has large dimensions.
Oil overflow valve
The bypass valve of the oil filter is activated when the pressure in the oil line between the pump and the filter element increases. This is due to an increase in oil density (for example, during a cold start), filter wear, or simply an increase in revolutions. When opening, the valve allows some of the oil to bypass the filter. It is very important to select a valve with the correct opening pressure. It depends on the speed at which the engine will be lubricated with crude oil. It is undesirable to use a bypass valve with a low opening pressure, because at high revs the engine will always receive “dirty” oil.
Overflow Valve Specifications
Overflow valves are characterized by values:
- Capacity coefficient is the flow rate of water (cubic m / h) at a temperature of 200 С⁰ and estimated pressure loss at the valve of 1 bar. This value is used to calculate the pressure loss in the system.
- Nominal pressure is the value corresponding to the maximum overpressure of the working medium. The calculation takes into account the temperature of the environment of long-term and safe operation - 200 С⁰.
- Nominal diameter - the inner width of the connecting pipes. This value is used to unify standard sizes of pipe fittings. The actual diameter of the nozzles may vary slightly.
- The setting range is the value of the pressure drop limits supported by the bypass valve.