New Original Pressure Regulator Suction Pressure Valve 294200-9972 SCV Valve for Auto Spare Parts

Engine start-up phase
Scenario requirements
During cold start, the engine needs a richer mixture to overcome the combustion difficulties caused by low temperature, and at the same time, the common rail pressure needs to be established quickly.
SCV valve working logic
Initial opening control: The ECU sends a small current signal to reduce the SCV valve opening, limit the fuel reflux, and allow the fuel supply pump to deliver fuel to the common rail pump with maximum efficiency, and quickly increase the common rail pressure (such as from 0 bar to more than 500 bar).
Cold start compensation: According to the water temperature sensor signal, the ECU further adjusts the SCV valve opening to increase the fuel supply to ensure fuel atomization and combustion stability during cold start.
Key role
Avoid "failure to ignite" or start delay caused by insufficient fuel flow during start-up;
Prevent idle jitter after start-up caused by slow common rail pressure establishment.

Idle working conditions
Scenario requirements
The engine load is low at idle, and the minimum stable speed needs to be maintained, while avoiding fuel waste and excessive emissions.
SCV valve working logic
Precise control of small flow: ECU sends a medium current signal based on idle speed feedback (such as 800rpm), so that the SCV valve maintains a small opening, allowing only a small amount of fuel to enter the fuel supply pump, and maintaining the common rail pressure at a low stable value (such as 300-500bar).
Pressure fluctuation suppression: When the idle load increases slightly due to the start of accessories such as air conditioning and power steering, the SCV valve will dynamically fine-tune the opening to avoid idle instability caused by common rail pressure fluctuations.
Key role
Fuel consumption is as low as 0.5-1.0L/h (typical diesel vehicle idle fuel consumption), which saves 10%-15% fuel compared to traditional mechanical pumps;
With idle closed-loop control, the speed fluctuation is controlled within ±50rpm.

Acceleration/full load conditions
Scenario requirements
When accelerating sharply or climbing a hill with full load, the engine needs to instantly increase power output, requiring a rapid increase in common rail pressure and fuel injection volume.
SCV valve working logic
Maximum flow output: The ECU detects a sudden increase in the depth of the accelerator pedal or a torque demand signal, and sends a maximum current signal to make the SCV valve almost completely closed (minimum opening), maximize the flow of fuel entering the fuel supply pump, and promote the common rail pressure to rise rapidly (such as from 500bar to 1600-2000bar).
Pressure-flow coordination: Combined with the real-time data of the common rail pressure sensor, the SCV valve dynamically adjusts the opening to ensure that the pressure rise rate matches the injection demand of the injector to avoid damage to the seal caused by overpressure.
Key role
Power response time <500ms, to meet the torque demand during rapid acceleration (such as 2-3 seconds for diesel pickup trucks to accelerate from 0-100km/h);
Prevent "ineffective acceleration" or "turbo lag" caused by insufficient fuel supply.

Deceleration/coasting conditions
Scenario requirements
When the throttle is closed for deceleration or downhill coasting, the engine is in a "drag condition" and fuel supply needs to be reduced to reduce fuel consumption and emissions.
SCV valve working logic
Large opening reflux control: When the ECU detects that the throttle signal returns to zero and the speed is higher than the idle speed (such as above 1200rpm), it sends a minimum current signal to fully open the SCV valve, and a large amount of fuel flows back to the fuel tank through the bypass. The fuel supply pump only delivers the fuel required to maintain idling (close to zero flow).
Fuel cut-off function: In conjunction with the fuel cut-off command of the injector, the SCV valve further limits the rise in common rail pressure to prevent excess fuel from entering the combustion chamber, achieving "forced idle fuel cut-off" (fuel consumption rate ≈ 0L/h).
Key role
The fuel consumption during coasting is 30%-50% lower than that of traditional mechanical pumps, and the fuel consumption of typical diesel vehicles can be reduced by 0.5-1L per 100 kilometers;
Reduce carbon smoke emissions caused by unburned fuel (PM value decreases by 40%-60%).

High temperature/high load continuous operation scenario
Scenario requirements
In scenarios such as long-distance truck transportation and continuous operation of construction machinery, the engine needs to work under high load and high temperature for a long time, and the stability of the fuel system is extremely high.
SCV valve working logic
Overheat protection mechanism: When the ECU detects that the fuel temperature exceeds the threshold (such as 60℃), it will appropriately increase the fuel return through the SCV valve, use the fuel circulation to take away the heat of the fuel supply pump and the common rail system, and prevent the fuel from gasifying at high temperature and causing "gas blockage".
Pressure decay compensation: Long-term high-load operation may cause fuel pump wear and reduced efficiency. The SCV valve compensates for flow loss by reducing the opening and maintains the common rail pressure stable (such as controlling the fluctuation from 1800bar to within ±50bar).
Key role
Avoid engine power decay caused by fuel overheating (such as torque drop of less than 5% when the truck climbs a slope);
Extend the service life of the fuel pump and common rail system (reduce mechanical wear caused by pressure fluctuations).

Emission control coordination scenario
Scenario requirements
When meeting stringent emission regulations such as National VI/Euro VI, it is necessary to accurately control the fuel injection amount and pressure to match post-treatment systems such as EGR (exhaust gas recirculation), DPF (particulate filter), and SCR (selective catalytic reduction).
SCV valve working logic
Linked with the after-treatment system:
When the DPF needs to be regenerated, the ECU increases the fuel supply through the SCV valve, raises the exhaust temperature to above 600℃, and ignites the soot in the particulate filter;
When the SCR system is working, the SCV valve cooperates to adjust the common rail pressure to ensure that the fuel atomization quality matches the urea injection amount and reduce the incomplete NOx conversion.
Multiple injection strategy support:
By precisely controlling the common rail pressure, the SCV valve provides a stable pressure basis for the "pre-injection-main injection-post-injection" multiple injection mode of the injector, reducing combustion noise and nitrogen oxide emissions (NOx can be reduced by 20%-30%).
Key role
Help diesel engines meet the National VI b emission requirements (such as reducing the nitrogen oxide limit from 80mg/kWh to 35mg/kWh);
Reduce the workload of the after-treatment system and extend its maintenance cycle.