Variable Displacement Pump Thermostatic Bypass for High Turndown
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Solution Overview
Problem
Variable displacement pumps struggle with high turn down ratios required for aerospace applications due to minimum pump flows exceeding the minimum flows needed by fuel metering systems.
Innovation Solution
A system incorporating a thermostatic bypass valve with a thermally bistable actuator to control recirculation flow based on fluid temperature, combined with an electrohydraulic servo valve and position sensors for active displacement control, ensuring stable operation by adjusting flow rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a variable displacement pump is designed with large displacement capacity, then it can meet high flow demands, but the minimum pump flow exceeds the minimum flow required by fuel metering systems, limiting the turn down ratio
Solution Approach 1:
The pump system is segmented into two parallel flow paths: a main displacement path through the VDP and a bypass path through the BPV. This segmentation allows independent control of cooling flow and system flow, enabling the VDP to operate at minimum flow for cooling while the BPV diverts excess flow, achieving high turn down ratios.
Solution Approach 2:
The bypass valve acts as an intermediary component between the VDP outlet and inlet. It mediates the flow conflict by diverting excess flow away from the system while maintaining minimum flow through the VDP, resolving the contradiction between maintaining cooling flow and reducing system flow demand.
2Measurement precision
If active control systems are used to manage bypass flow, then flow control precision is improved, but device complexity and controller I/O requirements increase
Solution Approach 1:
The bypass valve incorporates a thermostatic actuator that automatically responds to temperature changes in the fluid. When the VDP operates at minimum flow and fluid temperature rises, the thermostatic actuator automatically opens the BPV to divert excess flow, eliminating the need for external active control while maintaining appropriate flow management.
Solution Approach 2:
The bypass valve uses temperature as a control parameter instead of requiring active electronic control. The thermostatic actuator converts temperature changes into mechanical valve position changes, providing passive flow control that reduces system complexity while maintaining precision based on thermal conditions.
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
Enables stable operation with high turn down ratios by eliminating the need for active control systems and reducing inputs/outputs to the pump controller, allowing for efficient flow management during transient conditions.
Implementation Method 1
The BPV includes a thermostatic actuator configured to control recirculation flow amount through the BPV based on fluid temperature in the BPV
Implementation Method 2
The thermostatic actuator can include a thermally bistable or thermally variable structure operatively connected to adjust position of a valve member in the BPV
Data Source
AI summary
A system includes a variable displacement pump (VDP) in fluid communication with an inlet line and with an outlet line. The VDP includes a variable displacement mechanism configured to vary pressure to the outlet line. A bypass valve (BPV) includes a BPV inlet in fluid communication with the outlet line, and a BPV outlet in fluid communication with a bypass line that feeds into the inlet line upstream of the VDP. The BPV includes a thermostatic actuator configured to control recirculation flow amount through the BPV based on fluid temperature in the BPV. A method includes thermostatically controlling a bypass valve (BPV) to recirculate flow from the outlet line to an input line of the VDP in the event of flow demanded by the downstream system dropping below a predetermined low threshold of flow through the VDP based on fluid temperature in the BPV.