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Anti-Siphoning Mechanisms in Self Bunded Diesel Tanks
1. Physical Separation and Ventilation Design
- The tank's inner primary vessel (holding diesel) and outer bund (secondary containment) are physically isolated, with no direct fluid connection between them.
- Unlike single-walled tanks where a siphon could form through a continuous fluid path, the dual walls create a disrupted flow channel.
- The bund is equipped with independent ventilation systems (e.g., pressure-vacuum valves) that maintain atmospheric pressure in the outer layer.
Example: If the primary tank develops a leak, fuel collects in the bund but cannot form a siphon loop due to the lack of a connected outlet or shared venting system.
2. Sloped Geometry and Drainage Mechanisms
- The bund's floor is intentionally sloped (≥2% gradient) toward a drain or sump, which is closed during normal operation.
- This slope ensures that any leaked fuel pools at the lowest point rather than forming a continuous column.
- The drain valve is designed with a non-return mechanism (e.g., a flapper valve) to prevent backflow.
Example: If a pump mistakenly tries to draw from the bund, the valve blocks reverse flow, maintaining separation between the primary and secondary layers.
3. Pressure Equalization and Leak Detection
- Modern self-bunded tanks include pressure monitoring systems between the walls.
- If a siphon-like pressure gradient begins to form, sensors alert operators before a dangerous flow is established.
- Leak detection systems (e.g., liquid-level sensors in the bund) further disrupt siphon potential by triggering alarms.
4. Engineering Standards and Operational Controls
- Regulations like EN 13160 (Europe) or UL 142 (USA) mandate specific design requirements.
- Operational protocols prohibit connecting the bund's drainage system to the primary fuel supply line.
- The primary tank's outlet is always plumbed separately from the bund's drain.
Example: In refueling setups, strict hydraulic isolation is maintained between primary and secondary containment systems.