Pressure relief valves for silos

A pressure relief valve, also known as a safety valve, is a mechanical device installed on the roof of a silo and is designed to release or inject air. When the internal pressure reaches certain levels during filling or unloading, the safety valve activates by balancing the pressure.

This way the silo remains intact regarding the pressure changes that occur internally, as the safety valve is always ready to add or remove air in case the internal pressure goes past the predetermined limits.

A pressure relief valve is made of steel and is ideal for use on cement silo in the ready-mix concrete industry, but can also be used in any other application that includes bulk material storage.

Safety valves protect silos during filling or unloading from possible overpressure or underpressure. Its installation is necessary because in case the filter is either clogged or vented (when no filter is installed), it’s very likely the silo roof will come off or its walls will be compressed internally in case the pressure exceeds certain limits. Many such incidents have taken place in several countries, due to the absence of safety valves on silos.


Α Pressure Relief Valve consist of a cylindrical casing with a bottom flange to be connected with a spigot welded on the silo roof, a disc shape inner steel lid for negative pressure operation held in position by a central spring rod, an outside steel ring for excess pressure kept in position by three spring rods, gaskets, and a weather protection cover.

Helical springs keep the valve lids closed when the pressure value remains within the preset limits. The three outside spring rods keep the external ring-shaped lid firmly closed as long as the force generated by the pressure inside the silo does not overcome the spring force. Once the pressure exceeds the pre-set value the lid is pushed up and pressure can escape. The smaller lid covers the central circular opening of the external lid from below.

It is held in the middle by a single spring rod and is pressed onto the external lid by the normal air pressure inside the silo. In the event of suction pressure the spring is compressed and allows the lid to drop. The air entering the silo from outside ensures rapid pressure balance and pushes the central lid back up into "closed" position.





Base Diameter

273 mm (11’’)

Body casing

Carbon steel

Weather protection cover casing


Stainless steel

Preset pressure limits*

Negative pressure: -0.002 bar (-0.03 psi) and

Excess pressure: +0.05 bar (0.72 psi)

* The preset pressure limits refer the pressure limits for activating the safety valve, as set at the factory. These limits can be changed accordingly to suit your needs.


  • The same valve can be used regardless of the stored material.
  • The safety valve is easily installed on the silo thanks to its lightweight design and small dimensions.
  • Maintenance friendly, thanks to its small number of parts.
  • A product version suitable for high temperature products and applications is available upon request.

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Protem Group S.A.

3, 35th Str., 133 41 Industrial Park
Ano Liossia / Athens, Greece
Τ. +30 210 5716500
F. +30 210 5710008
GCR No: 7633901000