In brief
Safety valve and pressure gauge legalisation for a silo trailer is a TDT requirement — the inspector checks calibration certificate validity dates at every pressure vessel inspection. A safety valve with a broken seal or expired legalisation, and a pressure gauge without a current calibration certificate, are both grounds for vehicle rejection. PHS Magnum performs replacement, adjustment, and legalisation of pneumatic armature on-site in Chorula.
A safety valve is one of the most important components of a silo trailer — its function is to protect the vessel from exceeding the permissible pressure. A valve that does not open at the right moment, or opens at the wrong pressure, is worse than having no valve — it creates a false sense of security.
That is why TDT requires regular legalisation of safety valves and calibration of pressure gauges.
Components requiring legalisation / calibration
Safety valves
The safety valve on a silo trailer automatically releases pressure when it exceeds the set value. Requirements:
- Set pressure matching vessel documentation (typically 2.0–3.0 bar)
- Seal after each calibration/legalisation — unbroken
- Validity date of legalisation — visible on seal or label
- Certificate from manufacturer or accredited laboratory
Typical legalisation frequency: every 12 or 24 months.
Pressure gauges
The pressure gauge measures vessel pressure during loading and unloading. TDT requirements:
- Calibration certificate from accredited laboratory
- Validity date — typically 1 or 2 years
- Physical condition — no cracked housing, needle at zero without pressure
- Range — appropriate for vessel operating pressure
Frequent issues — and how we fix them
Safety valve seal broken during normal operation: Drivers sometimes inadvertently break seals during daily maintenance — cleaning armature with chemicals, accidental knocks. The valve must be re-calibrated and re-sealed.
Pressure gauge with stuck needle: A gauge with the needle frozen above zero without pressure shows an incorrect operating pressure. Most common cause: condensate freezing (winter operation) or foreign particles in the capillary. Mandatory replacement.
Valve leaking at operating pressure: A valve leaking before reaching set pressure wastes compressed air and indicates mushroom or seat wear. Immediate replacement required.
Armature service at PHS Magnum
- Inspection — check all valves and gauges: seals, dates, physical condition
- List — compile items for legalisation/calibration/replacement
- Remove items for calibration — send to accredited laboratory or calibrate on-site
- Replacement — components beyond calibration (cracked, corroded) replaced from stock
- Safety valve re-calibration — set pressure adjustment, re-sealing
- Documentation — calibration certificates for vehicle documentation file
Best combined with TDT preparation — one workshop visit, complete armature service.
Contact: +48 602 716 551 | Roland Sobota (TDT): +48 504 788 385
Related: Pressure vessel inspection · TDT inspections · Spitzer service · Feldbinder service