Valve monitoring system for a coaxial dual-safety valve

A valve monitoring system for a coaxial dual-safety valve of a gas valve unit, which controls a gas request of a gas burner occurring in the course of a heat request and which comprises at least the coaxial dual-safety valve and a control valve arranged fluidically connected downstream of the dual-safety valve for controlling the gas quantity,

• wherein the dual-safety valve comprises a first integral pilot valve and a second integral pilot valve arranged coaxially and fluidically downstream of the first pilot valve, which are each controllable only between an open position and a closed position,
• wherein, on the inlet side, a gas inlet pressure acts on the first pilot valve, wherein, in a fluid space formed between the first and the second pilot valves, a pressure sensor measuring a switching pressure or a pressure switch is arranged, and
• wherein, the system is configured such that a check of the switching pressure, successively a tightness check of the second pilot valve and of the first pilot valve occurs in each case depending on an open position or closed position of the control valve and on the open position or closed position of the first and second pilot valves;
• wherein the system is configured such that first pilot valve is brought into the closed position directly before the second pilot valve with a time lag (Δt).