Fail Freeze Pilot Valve Arrangement for Power Loss Position Retention
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Solution Overview
Problem
Existing digital pilot stage valve arrangements cannot achieve a fail freeze mode, where the main stage valves retain their position during a power loss, as they either go fully open or fully closed, failing to maintain the previous state.
Innovation Solution
An on-off pilot stage valve arrangement with two pilot valves, each operable between on and off states, configured to remain off during power loss, ensuring the main stage valves do not influence the controlled element, thereby implementing a fail freeze mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single pilot valve is used in a digital arrangement, then the valve can be controlled between two states (on/off), but the valve cannot maintain its position during power loss (fail freeze mode is not achievable)
Solution Approach 1:
The single pilot valve is segmented into two separate pilot valves (first pilot valve and second pilot valve), each controlling different aspects of the main valve operation. This segmentation allows independent control of pressure supply and pressure exhaust, enabling the fail freeze mode where the main valve maintains its position during power loss.
Solution Approach 2:
A control element is introduced as an intermediary component that receives control pressure from the pilot valves and transmits it to the main valve. This intermediary allows the pilot valves to indirectly control the main valve position, enabling precise position maintenance during power loss without directly actuating the main valve.
2Reliability
If power is lost in a digital pilot valve arrangement, then the valve defaults to fully open or fully closed position, but the previous position cannot be retained
Solution Approach 1:
The system is configured in advance so that control pressure is continuously supplied to the main valve through the control element, maintaining the valve in its current position. The pilot valves are pre-configured to control both pressure supply and pressure exhaust, creating a preliminary state that preserves the valve position during power loss without requiring active intervention.
Solution Approach 2:
The system changes the pressure parameters by introducing separate control for pressure supply and pressure exhaust through the two pilot valves. By independently controlling these pressure parameters, the system can maintain the main valve in any intermediate position during power loss, rather than defaulting to extreme positions.
3Reliability
If a pilot valve arrangement is designed for fail safe behavior, then the main valve goes to fully open or fully closed position, but fail freeze behavior (maintaining previous position) cannot be achieved
Solution Approach 1:
The pilot valve arrangement is segmented into two independent pilot valves, each with distinct functions: one controlling pressure supply to the main valve and the other controlling pressure exhaust from the main valve. This segmentation enables fail freeze behavior by allowing the main valve to maintain its position through balanced pressure control even when power is lost.
Solution Approach 2:
The two-pilot valve arrangement serves multiple functions: normal operation control, fail safe behavior, and fail freeze behavior. The same basic configuration can operate in different modes depending on the power supply status and control signals, providing universal functionality across different failure scenarios.
Data Source
Figure 1~3
Figure 2
Figure 4~5
AI summary
There is presented an on-off pilot stage valve arrangement (20) for controlling at least one main stage valve (9a, 9b, 9c, 9d). The on-off pilot stage valve arrangement comprises a first pilot valve (18) discretely operable between two states, an on and an off state, the first pilot valve having an input at which there is a first pressure and an output connected to the main stage valve, a second pilot valve (14) discretely operable between two states, an on and an off state, the second pilot stage valve having an input at which there is a second pressure and an output connected to said main stage valve. Both the valves are configured to be set in one of the two states in case the arrangement loses power.