A shuttle valve allows flow from one of two inlet ports to a single outlet port, while simultaneously blocking flow from the other inlet port to the outlet.
Here's a breakdown of how it works:
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Basic Function: The shuttle valve selects the higher pressure input and directs it to the output. The lower pressure input is blocked.
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Key Component: The "Shuttle" or "Ball": The heart of the valve is a free-floating shuttle (often a ball or piston) that moves within a chamber.
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Operation:
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Equal Pressure: If both inlet ports have equal pressure, the shuttle remains in a central position. However, most applications involve unequal pressures.
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Pressure Differential: When one inlet port has a higher pressure than the other, the higher pressure forces the shuttle to move towards the lower pressure inlet.
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Blocking the Lower Pressure: As the shuttle moves, it seals off the lower pressure inlet port, preventing that flow from reaching the outlet.
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Flow from the Higher Pressure: The higher pressure inlet remains open to the outlet port, allowing flow to pass through.
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Reversal of Pressure: If the pressures reverse, the shuttle will move in the opposite direction, blocking the previously higher pressure inlet and allowing flow from the now higher pressure inlet to the outlet.
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Analogy: Imagine a Y-shaped pipe fitting with a ball inside. If you blow into one end of the Y, the ball will be pushed to the other side, blocking that opening and allowing air to flow out the stem of the Y. If you blow into the other end, the ball will switch position.
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Common Applications:
- Pneumatic Circuits: Used in pneumatic circuits where a signal needs to be received from either of two sources (e.g., safety circuits).
- Hydraulic Systems: Used in hydraulic systems for similar purposes, although other valve types might be preferred in high-pressure or precision applications.
- Logic Functions: Used to implement OR logic in fluid power circuits.
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Difference from Check Valves: Although a shuttle valve might superficially resemble two check valves back-to-back, it is not the same. Check valves allow flow in one direction only and block flow in the opposite direction. A shuttle valve actively directs flow based on pressure differences, and it blocks one inlet port to allow flow from the other.
| Feature | Shuttle Valve | Check Valve |
|---|---|---|
| Primary Function | Selects flow from one of two inlets based on pressure | Allows flow in one direction only, blocks the other |
| Flow Direction | Flow can originate from either of two inputs | Flow is only allowed in one pre-determined direction |
| Blocking | Actively blocks one inlet based on pressure | Blocks flow from outlet to inlet |
In summary, a shuttle valve is a simple yet effective valve that automatically selects the higher pressure source from two inlets and directs that flow to a single outlet, ensuring that the lower pressure source is blocked.
