Silo over-pressure during filling — safety valve, filter and alarms
Symptom
Cement on the roof around the safety valve, the safety valve lifts at deliveries, or the pressure alarm stops deliveries early.
Likely causes
- Top filter blocked or blinded, often because the cleaning air is off or wet.
- Pressure sensor set at the same value as the safety valve, or its port is blocked.
- Silo overfilled because the high-level indicator failed or is too short.
- Tanker pressure too high, or residual tanker pressure vented into the silo.
- Inlet valve not failsafe, or its air line kinked to bypass it.
Most likely and cheapest to check first.
Checks
- Read the alarm log and delivery records. Treat any safety-valve lift as a near miss.
- Check the filter cleaning air is on and at 5–6 bar, and look at the cartridges.
- Check the set-points: pressure sensor about 40 mbar, safety valve about 50 mbar.
- Function-test the high-level indicator and the pressure sensor from ground level. A lamp test is not a test.
- Remove air or power from the inlet valve. It must close by itself.
Fix
- Clean or replace the filter cartridges; restore dry cleaning air.
- Correct the set-points; clean the sensor port.
- Clean the safety valve; replace springs and gaskets (about every 24 months).
- Replace a non-failsafe inlet valve with a failsafe-closed one.
- Post the delivery rules at the fill point and brief the drivers.
Stop the equipment if
The safety valve is seized, the high-level indicator does not alarm, or the inlet valve does not close on alarm. No deliveries until fixed.
Parts you may need
Six parts, one system
A safe delivery depends on six parts working together. The safety valve is only the last of them and should never open in normal use.
| Part | Where | Correct setting |
|---|---|---|
| Top filter | Silo roof | Passes 1,700–2,000 m³/h; cleaning air working |
| Pressure sensor | Silo roof | Alarm at about 40 mbar; closes the inlet valve at once |
| High-level indicator | Roof, 1–1.5 m below the top | Alarm at once; closes the inlet valve after about 30 s |
| Pressure relief valve | Silo roof | Opens at about 50 mbar |
| Inlet shut-off valve | Fill point | Closes by itself when air or power fails |
| Control panel | Fill point | Alarms, beacon, true ground-level test |
A silo shell can be damaged above about 0.07 bar of internal pressure. A road tanker can deliver at up to 2 bar.
DANGERNever vent the tanker's residual pressure into the silo, and never leave a delivery unattended. A kinked or tied air line on the inlet valve defeats the protection.
COST OF NEGLECTA safety valve used as a normal vent packs with cement and finally does not open. The next mistake ends with the filter blown off the roof.
FIELD TIPPowder around the safety valve is a sign of over-pressurisation, not overfilling. Check that every fill point has an anti-whip restraint for the hose and the driver instructions posted: maximum pressure, what to do on an alarm, never vent into the silo, lock the fill point afterwards.
⚠ Every check inside a machine starts with full lockout. Safety disclaimer