Safety blow-off valves

When the output pressure rises to an unacceptable level, the safety blow-off valve opens and releases the excessive pressure. It does not block the gas flow, so that, contrary to a safety shut-off valve, it does not need to be reopened manually.
A safety blow-off valve is therefore typically used in combination with a safety shut-off valve, providing protection up to a given increase in the output pressure. It is only when the pressure continues to rise that the safety shut-off valve is triggered, blocking the gas flow.