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Safety Valves, Hopper Safety Valves, Silo Safety Valves

The silo or hopper safety valves, also known as safety flap, are simple but extremely effective and important devices to protect the silo from being over pressurised or exposed to a vacuum. Either of these conditions can result in catastrophic damage to the silo and surrounds.
When filling a silo pneumatically, the filter unit allows air to escape from the tank, thus preventing the pressure from increasing substantially. Should the filter or the filter bags be clogged or even if the filter is undersized, the pressure within the silo will rise. Typically the peak air flow is reached at the end of a conveying cycle, when the tanker or blow vessel vents through the conveying line into the silo. Should this burst of air not escape via the filter, the rise in pressure could result in structural damage or even total destruction of the silo. Even regular pressure rises that do not exceed the silo design pressure can lead to fatigue failure of welds or weakened material.
The silo safety valves are essentially weighted flaps that will open when the pressure exceeds the design value of 9 kPa. The Bulk Technik designed safety valve ensure that there is no ingress of water into the tank and furthermore, if installed correctly, will not stick or jam. The design also ensures that each time it has opened, it will close as soon as the pressure has dropped below the design value.
Conversely to the pressure safety valve, a tank also needs to be protected against a vacuum. This mainly occurs when product either collapses within the silo or when it discharges at a rapid rate, combined with the action of a filter fan. A weighted vacuum safety valve will protect the silo from imploding under these conditions. The Bulk Technik designed vacuum safety valve is designed to open at a negative pressure of -2.0 kPa. A weather cowl prevents any water from entering the silo which may then lead to lump formation and potential blockages.
Bulk Technik has also designed a safety valve that combines the two functions described above, thereby protecting the silo both for over and under pressures. All the safety valves are fitted with standard flanges (SABS or ANSI) and are therefore easily bolted to a silo roof nozzle.
All of our silo safety valves can be supplied with a proximity switch to provide feedback to the control room of high or low internal silo pressures. This will assists with filter maintenance and avoid dust contamination.

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