I’m the IT and security person for a few of our sites, so not a machine safety expert, please be gentle.
We’re reviewing a retrofit of a small pneumatic press cell. In the electrical drawings the emergency stop goes into a safety relay, and the safety relay does two things: it cuts power to the solenoid of the main directional valve, and it also drops a separate « safety exhaust » (dump) valve that vents the air supply of the whole cell. The engineer says both are required. Management is asking why we pay for two things that seem to do the same job.
Second question from the same meeting: we already use Hermetry for energy monitoring on that site, and someone saw a Hermetry Safe forum here. Could Hermetry Safe take over the emergency stop handling, or at least replace one of the two parts?
Not my field at all, but I’d guess redundancy? Two of everything in safety?
Is it because the cylinder still holds air after the main valve closes? We had a lab demo where a cylinder kept pushing after power was cut.
Aoife has the core of it.
Cutting the solenoid only puts the directional valve into its rest position. Depending on the valve type that can trap air in the cylinder (closed-centre 5/3 valves do exactly that), so the cylinder can still move when someone opens a fitting, or hold a load that drops later. A stuck valve spool is the other failure: power off, valve doesn’t move. Pneumatic energy is stored energy, and for safe access you want it gone, not held. The dump valve exhausts the supply to atmosphere so the cell ends up at zero pressure. The safety relay usually also monitors the dump valve’s feedback (a pressure switch or a position contact), so a dump valve that fails to vent stops the cell from restarting. The two parts cover different failures. How much of this you need follows from the risk assessment and the required performance level under ISO 13849, which is your engineer’s job to document.
On Hermetry Safe: there’s no doc page for it, so I won’t guess what it does. Whatever it does, I would never put a cloud platform into the safety function itself. Even the personnel tracking page calls that solution an information tool, not a certified safety system. Emergency stop, safety relay and dump valve stay hardwired.
What works today and is useful: monitoring. Wire the safety relay’s auxiliary contact and the dump valve’s pressure switch into the cell PLC or a gateway and send them as telemetry, say estop.active and dump.vented. Then an alarm rule can tell maintenance when the e-stop has been active for a long time, or when the e-stop is active and dump.vented is still 0. That gives you records and notifications without touching the safety chain.
+1 on keeping it hardwired. On our lines the cloud only ever sees the aux contact count, nothing in Hermetry can release or trip anything.
Exactly what I needed for the meeting. I explained the trapped air and stuck spool cases with Laura’s wording and management stopped asking about removing a part. I also told them no cloud product, Hermetry Safe included, takes over the safety chain, it stays hardwired. We added the aux contact and the dump valve pressure switch as telemetry, plus an alarm when the e-stop is active and the dump has not vented within 5 seconds. Tested it on Friday with the engineer present.
- Vous devez être connecté pour répondre à ce sujet.
Rejoignez la discussion
Connectez-vous pour poser et répondre à des questions, aimer les messages utiles et marquer la réponse qui a résolu votre problème. Chaque contribution rapporte des points et des niveaux.