The Jet Suction Pump, also known as a suction jet, suction jet pump, suction pump, brake booster vacuum pump, or vacuum pump, is a critical component in the vacuum system of many 1.8T engines, including those found in the Audi TT and Volkswagen models. This article will delve into its functionality and purpose, explaining how it contributes to consistent brake booster performance.
How a Jet Suction Pump Works
A jet pump operates on the principle of venturi pressure differentials, similar to a carburetor. One fluid stream is accelerated through a constricted section called a venturi. This high-velocity stream, when positioned across or in front of a secondary fluid stream, creates a low-pressure area, effectively drawing fluid from the secondary stream.
The “suction” in a jet suction pump arises from applying a vacuum source to the outlet of the venturi. This vacuum intensifies the velocity of the primary fluid stream, further reducing pressure in the secondary line and creating a stronger vacuum than would be achieved without the pump. The effectiveness of this suction depends on the pressure of the pre-venturi fluid and the strength of the post-venturi vacuum.
Diagram of a Jet Suction Pump
The Role of the Jet Suction Pump in 1.8T Engines
In 1.8T engines equipped with a Positive Crankcase Ventilation (PCV) system and a turbocharger, the jet suction pump utilizes crankcase pressure and vacuum from the turbocharger’s intake tract to enhance brake booster vacuum.
Specifically:
- Positive Pressure Source: Blow-by gases in the crankcase create positive pressure.
- Vacuum Source: The turbocharger intake tract provides a vacuum source.
The jet suction pump combines these two forces. The crankcase pressure drives the primary fluid stream, while the turbo intake vacuum pulls the combined stream through the venturi, generating a strong and consistent vacuum for the brake booster.
Benefits of the Jet Suction Pump
While maximum vacuum is generally available from the intake manifold during braking (closed throttle), the jet suction pump offers benefits in specific scenarios:
- Improved Responsiveness: The constant vacuum assist provided by the pump enhances brake pedal responsiveness, particularly during non-typical braking situations or rapid transitions.
- Consistent Assist: By scavenging crankcase pressure and utilizing the turbo intake vacuum, the pump helps maintain consistent brake booster assist across various throttle and boost conditions. This can be particularly beneficial during partial throttle or high boost scenarios when intake manifold vacuum might fluctuate.
Conclusion
The jet suction pump plays a vital role in optimizing brake booster performance in 1.8T engines. By leveraging venturi principles and utilizing both crankcase pressure and turbo intake vacuum, it provides a reliable and responsive braking experience. Understanding its function is crucial for diagnosing and maintaining the vacuum system in these vehicles.
