Pressure relief valves are among the most safety-critical components on a cement silo. They protect the vessel from over-pressurisation during pneumatic filling, and from vacuum during discharge, either of which can cause serious structural damage or worse. Because a PRV only acts in an emergency and otherwise sits idle, it is easy to assume it is working when it is not. A regular audit is how you prove it is.
This checklist is written for plant operators and owners preparing a cement silo PRV for audit, or running their own internal check. Work through each section, record the result, and act on anything that fails. Where a task calls for pressure testing or calibration, use a competent person, and remember that your local regulations, insurer requirements and DSEAR (or equivalent) risk assessment always take precedence over general guidance.
Before you start: what a PRV audit is checking
An audit is confirming three things: that the valve is correctly specified for the silo and the material, that it is physically sound and operable, and that you can evidence both with documentation. Keep those three goals in mind and the checklist below falls into place.
1. Documentation review
Gather and check the paperwork first. If the records are not in order, the physical inspection means little.
- Valve specification sheet. Confirm you hold the manufacturer's data for each PRV: set pressure (and vacuum set point if fitted), flow/venting capacity, size, connection and materials of construction. Pass: current spec on file for every valve. Fail: any valve with no spec, or a spec that does not match the silo duty.
- Maintenance and inspection history. Assemble inspection reports, repair logs and any test or calibration certificates, in date order. Pass: a continuous record showing regular checks. Fail: gaps, or no history at all.
- Explosion protection basis. For silos handling combustible dusts (cement is one), confirm your explosion protection basis of safety is documented. Dust explosion venting protective systems are covered by EN 14491:2012, and dedicated explosion venting devices (vent or rupture panels, distinct from a spring-loaded PRV) by EN 14797:2006. Pass: you can show what protects the silo against a dust explosion and on what basis. Fail: no documented basis of safety.
- Prior audit findings. Have the last audit report and evidence that its actions were closed out. Pass: previous actions completed and recorded. Fail: open actions carried over.
2. Visual inspection
Carry this out with the silo safely accessible and isolated from filling. Inspect every PRV, not a sample.
- External condition. Check the valve body, connections and seals for corrosion, cracking, distortion or impact damage. Fail triggers: visible corrosion on springs or seat, perished or cracked seals, any distortion.
- Seat and sealing surface. Where accessible, check for caked cement build-up on the seat and moving parts, the most common reason a silo PRV fails to open or reseal. Fail triggers: material caking, a seat that is not clean and free.
- Free movement. Confirm the mechanism is not seized. A valve that will not move will not vent. Fail triggers: stiff, sticking or seized movement.
- Weather protection and drainage. Check that any cover or hood is intact and that the valve is not sitting in standing water or debris. Fail triggers: missing cover, water ingress.
- Labelling and identification. Each PRV should be clearly and legibly marked with its identity and set pressure, and tagged with the last inspection date. Fail triggers: missing, illegible or insecure identification.
- Installation and access. Confirm the valve is mounted per the manufacturer's orientation and that it can be safely reached for inspection and maintenance. Fail triggers: incorrect mounting, or access that is unsafe or impractical.
3. Functional testing
Testing confirms the valve does what its label claims. Where in-situ testing is not practical or safe, plan a bench test or scheduled replacement instead. Use a competent person for any pressure work.
- Set pressure verification. Confirm the valve opens at, or acceptably close to, its stated set pressure, and record the actual figure. Fail triggers: opens outside tolerance, or does not open.
- Reseal check. Confirm the valve recloses and reseals cleanly once pressure returns to normal. Fail triggers: fails to reseal, weeps or stays open.
- Vacuum relief (if fitted). Where the valve provides vacuum relief, confirm that function operates too. Fail triggers: vacuum side inoperative.
- Associated components. Check anything that works with the PRV, filter condition, any pressure gauge or switch, so the whole pressure-safety system is sound, not just the valve. Fail triggers: blocked or blinded filter, faulty gauge or switch.
4. Calibration and internal condition
- Calibration currency. Confirm each valve requiring calibration has been calibrated within your defined interval (commonly annual, but follow the manufacturer and your risk assessment), with a certificate on file. Fail triggers: overdue calibration, or no certificate.
- Internal wear. Where the valve is opened for service, inspect springs, diaphragms and seals for wear or fatigue and replace as needed. Fail triggers: fatigued springs, degraded seals or diaphragms.
5. Compliance check
- Explosion protection. For combustible-dust silos, confirm the silo's protection against dust explosion is in place and documented, referencing EN 14491:2012 for venting protective systems and, where dedicated vent/rupture panels are used, EN 14797:2006 for those devices. Pass: documented, in date, matched to the silo.
- Local and site-specific requirements. Check any national regulations, insurer conditions and your own DSEAR or equivalent risk assessment. These can be stricter than the general standards and take precedence. Pass: all site-specific requirements identified and met.
6. Running the pre-audit and closing out
- Do a pre-audit walk-through. Run this checklist yourself before any external audit, so you find and fix issues on your own terms rather than as findings. Action: rectify anything that fails before the formal audit.
- Brief the team. Make sure maintenance and safety staff know which valves are in scope, where the documentation is, and who is presenting it. Action: confirm roles and locations in advance.
- Close out findings. After the audit, work through the report promptly, repairing, replacing or upgrading valves as required and updating every record, maintenance log, certificate and specification, to reflect the changes. Action: no finding left open, all documentation current.
Quick-reference PRV audit checklist
| Stage | Check | Pass criteria |
|---|---|---|
| Documentation | Spec sheets, maintenance history, protection basis, prior findings | Current, complete, matched to silo, actions closed |
| Visual | Corrosion, caking, free movement, cover, labelling, mounting | Sound, clean, free, protected, clearly identified, correctly fitted |
| Functional | Set pressure, reseal, vacuum relief, associated components | Opens in tolerance, reseals cleanly, all functions operable |
| Calibration | Calibration currency, internal wear | In date with certificate, internals sound |
| Compliance | Explosion protection, local and site requirements | Documented, in date, site requirements met |
| Close-out | Pre-audit, team brief, findings closed, records updated | No open findings, documentation current |
What to do when a PRV fails the audit
If a valve fails on corrosion, seized movement, degraded seals, an out-of-tolerance set pressure or an inability to reseal, take it out of service and replace it rather than nursing it along. A PRV that cannot be relied on to open and reseal at its rated pressure offers no protection, whatever its condition looks like from the ground. Specify the replacement to the correct set points, size, connection and materials for your silo and material, and keep the certificate and spec on file for the next audit.
For how PRVs work and the failure modes to watch for between audits, see our guide on why pressure relief valves are a must for silos. To specify a replacement, browse pressure relief valves, or see the wider monitoring and safety range.
Why the audit matters
A PRV audit is not paperwork for its own sake. It is how you prove, to an auditor, an insurer and yourself, that the silo is protected against the two failure modes that do the most damage. Done regularly, it keeps you compliant, keeps the plant safe, and turns an unexpected valve failure into a planned replacement rather than an incident. For operators it means fewer surprises. For those responsible for the site, it means a documented, defensible safety position.
