Valves for Powders / Silo Over-Pressurisation
Silo over pressurisation has resulted in a number of potentially serious incidents. For example filter housings weighing hundreds of kilos and powder products have been ejected from the tops of silos. At least one serious injury has occurred because of this problem. As well as the more obvious dangers there is a potentially huge risk to the environment if an explosion should occur.
Guidelines have been issued by the Health and Safety Executive to help companies affected by this hazard. Potentially all companies with storage silos need to be aware of the problem and take steps to ensure the safe filling of them.
Although specifically targeted at the cement, concrete and quarry industries, by implication this guidance will also apply to all tanker filled silos.
When pumping powder, particles or granular products into a silo, increasing air pressure can sometimes cause damage to the silo and more seriously, bystanders can be injured if an explosion occurs. At the very least silos can be overfilled, causing waste and/or contamination of product, costing thousands of pounds.
Valves for Powders are part of a silo safety system
While the Pressure Relief Valve ultimately gives complete silo safety, the valve for powders by AKO helps to protect the environment by also helping to avoid over filling. Using a full bore 100mm diameter valve for powders with a pinching rubber sleeve allows unrestricted product flow. Tanker discharge time can be effectively reduced by more than 10%. FDA approved white rubber sleeves can be supplied with stainless steel contact parts on the valve for handling foodstuffs and pharmaceuticals.
Controlled filling systems using butterfly valves are also used on silo environmental protection systems, but the flow through the valve is restricted by the butterfly disk, slowing down the filling process. The butterfly valve seat can become contaminated with trapped product, resulting in spillage, waste and cross-contamination. The butterfly disk also wears very quickly increasing maintenance down time. Despite this some engineers feel this is necessary for their specific applications.
Previously, standard type valves for powders have failed open, but using an RGS solenoid valve on the pinch valve system, the AKO valves for powders will fail closed in most situations. When the valve is open and the driver is unloading his tanker into the silo, loss of air is detected by a pressure switch and again the bladder valve immediately closes.
The AKO valves for powders with a pinching sleeve are permanently mounted in the silo input line. As the tanker discharges its product load using its own integral pump, a paddle switch mounted in the top of the silo senses the increasing level of silo contents. When the movement of its rotating paddles is restricted by the level, it ceases rotation and trips a micro switch, sending a signal to the solenoid on the valve. The solenoid activates instantly and allows air pressure to close the sleeve in the valve. Simultaneously, the valve for powders triggers an audible alarm advising the tanker driver to stop his pump.
The Silo Safety System is unique in quality. For example the Pressure Relief Valve manufactured by Portasilo and used on their system is fully tested and certified. This is unique to the market, giving complete silo safety guaranteed. The system also offers management control at the offloading point, operating instructions with lockable valve or key switch on the controller, and fully documented maintenance for all parts of the system.
Valves for Powders have been used for years in all abrasive applications
Due to the sleeve technology, clear bore and simplicity of the AKO valves for powders, the life in certain applications can be up to 6 times longer than a butterfly valve.
Simple maintenance with the AKO valves for powders not only puts them streets ahead of the ‘traditional’ valves, but also other valves for powders with a pinching sleeve on the market. AKO valve re-sleeves can be completed in between 5-15 minutes depending on the size the valve. Replacing only the sleeve means a fraction of the maintenance cost compared with a butterfly valve.
Quality is the key to this system using quality manufactured components readily available with large stocks in the UK.
Read real life case studies involving AKO Pinch Valves in powder applications:
Valves for PVC powder producing floor tiles
