Silos are built to be sturdy, after all, they are built with mild steel and meant to withstand the rigours of the construction industry which is no mean feat. That being said, silos, and especially fine powder silos, have their own hazards in terms of withstanding additional pressures.
There are many cases over the years of over-pressurisation in silos; causing silos to crack/burst. This happens across numerous industries and isn’t specified to any particular powder; however, each powder will have differing pressure safety parameters.
Pressure Relief Valve (PRV)
This specified valve is usually placed on the top of the silo and plays a large role in the silo protection system. The Pressure Relief Valve (PRV) is a mechanical instrument that is set to open at certain pressure readings to avoid both positive and negative pressure and let excess air to leave the silo.
There are a number of different types of Pressure Relief Valves on the market from MIX srl, Wam and Hycontrol; some coming with sensors to detail the air emissions leaving the silo. This helps with determine the cause of the issue with the silo.
Pressure Relief Valves are not limited to silos only; they are also placed on other vessels where pressure may build, such as hoppers and ancillary equipment.
Is Silo Venting normal?
The simple answer to this is No. If the plant was designed appropriately in the first place, and regular maintenance is carried out on the silos/hoppers, etc., the Pressure Relief Valve should never need to vent. However, a strict process should be designed and operated on-site; especially for the process of filling the silo from road tankers.
Discharge from road tankers must be carefully controlled by the driver. During deliveryof powder, delivery rate should be maintained by regulating the flow of air and powder in the line through the fill-pipe. A rise in airflow is a possibility if the density of powder is reduced, normally occurring at the end of the delivery. This can result in a surge of air pressure in the silo/tank which can be minimised by correct operation of the valves in use on the silo.
SSM250 Pressure Relief Valve (PRV)
At Kearney Material Handling; we stock the MIX srl SSM250 Pressure Relief Valve which is supplied in two variations. The ‘K’ variation and the ‘L’ variation.
The difference in each variation is inclusion of Limit Switches for operation (L) or pre-disposition for Limit Switches (K).
The Mix srl SSM250 operates in temperatures between -25°C and + 70°C. Each can be supplied in either ‘Galvanised mild steel with aluminium cover’ or All metallic parts in Stainless Steel AISI 304’.
If you are in the market for pressure relief valves for your plant, please view our stock.
As a reminder, this is a follow-on from our previous instalment of a Silo Protection System series; view Part 1: Silo Filtration.