Fixed Displacement Pump Pressure Compensation
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Solution Overview
Problem
High-speed centrifugal pumps used in fuel systems for aircraft engines do not provide sufficient elevated fuel pressures for engine start-up at low engine speeds, necessitating the integration of a supplemental fixed displacement pump to address pressure and flow requirements.
Innovation Solution
A fuel system incorporating a high-speed centrifugal pump and a supplemental fixed displacement pump with a bypass valve control system, which is pressure-compensated to ensure consistent pressure and flow, allowing the fixed displacement pump to operate only when necessary to maintain minimum pressure levels and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a high-speed centrifugal pump is used in the fuel system, then power consumption is reduced and the pump is lightweight with extended life, but the pump does not provide sufficient elevated fuel pressures for engine start-up at low engine speeds
Solution Approach 1:
The fuel pumping system is divided into two distinct stages: a high-speed centrifugal pump for normal operation and a supplemental fixed displacement pump for start-up conditions. This segmentation allows each pump to be optimized for its specific function, with the centrifugal pump providing efficient continuous operation and the fixed displacement pump delivering high pressure at low speeds when needed for engine start-up
Solution Approach 2:
The fuel pumping system is designed to perform multiple functions through a single integrated arrangement: the centrifugal pump handles normal fuel delivery with low power consumption, while the fixed displacement pump provides supplemental pressure for engine start-up. The system universally addresses both low-speed start-up requirements and high-speed operational efficiency through the combination of these two pumping mechanisms working in parallel
2Stress or pressure
If a fixed displacement pump is added to provide additional pressure and flow at engine start, then start-up requirements are satisfied, but the system complexity increases and power consumption increases when the fixed displacement pump operates
Solution Approach 1:
The fixed displacement pump is equipped with a bypass valve that dynamically adjusts its operation based on system pressure requirements. During engine start-up when high pressure is needed, the bypass valve closes to force all flow through the main delivery line. Once start-up is complete and the centrifugal pump is running, the bypass valve opens to allow the fixed displacement pump to operate in a lower-power mode or bypass mode, dynamically adapting its function to current system needs
Solution Approach 2:
The bypass valve on the fixed displacement pump is designed to automatically regulate the pump's operation based on system conditions. The valve self-adjusts the pump's output by diverting excess flow back to the suction side when full pressure is not required, allowing the pump to serve itself in regulating its own operation and minimizing power consumption when operating alongside the centrifugal pump
3Measurement precision
If the fixed displacement pump is pressure compensated to work in the throttling style metering system, then accurate metered flow is achieved, but the device complexity increases
Solution Approach 1:
The pressure compensation mechanism is merged with the bypass valve already present on the fixed displacement pump. The same valve that controls the pump's bypass flow also serves as the pressure compensation element by responding to downstream pressure conditions. This merging eliminates the need for a separate pressure compensation device, achieving accurate metered flow in the throttling style metering system while minimizing additional complexity
Solution Approach 2:
The bypass valve on the fixed displacement pump is designed to perform multiple functions: it controls the pump's bypass flow for power management, provides pressure compensation for accurate metering in the throttling style system, and enables the pump to adapt to varying system pressure requirements. This multi-functionality allows the single valve to achieve pressure compensation and accurate flow metering without adding separate dedicated components
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration ensures reliable engine start-up and additional pressure beyond the centrifugal pump's maximum output, while minimizing power consumption and maintaining system stability through hydromechanical pressure compensation.
Implementation Method 1
a passage 370 having a cross-sectional area less than a cross-sectional area of the discharge passage 332 at an outlet of the positive displacement pump 306, thereby increasing a pressure of the fuel flow 114
Implementation Method 2
a high speed centrifugal pump 302
Data Source
Figure 1~2
Figure 3A
Figure 3B
AI summary
A fuel system includes a pump unit having at least a fixed displacement pump supplying pressurized flow. A fuel control assembly receives flow from the pump unit and includes at least one metering valve and at least one throttling valve. A control (bypass valve control) for the fixed displacement pump receives first and second pressure signals indicative of a pressure differential across the throttling valve, or across the metering valve/throttling valve combination, for altering output from the fixed displacement pump in response to the pressure differential. In other embodiments, the pump unit includes a centrifugal pump and a fixed displacement pump that can be fully or partially redundant depending on sizing of the pumps, and the system requirements.