A valve device for mounting in an environment having a first ambient pressure level (P A60:1), the valve device comprising: a valve housing (100, 200) having an input for connection to a fluid supply piping system (35, 72) having a second pressure level (P F60:1); an output for connection to a fluid outfeed conduit (74, 40, 40:1); and a housing body (100, 200, 130) positioned between the input and the output, said housing body having an inner surface forming a first channel for connecting the input with the output; and a valve unit which, in operation, is capable of switching between a first state and a second state dependent on a pressure difference (ΔP) between said first ambient pressure level (P A60:1) and said second pressure level (PF60:1), the valve unit having a movable valve member and a transit channel, wherein the valve member is adapted to rest against a first valve seat, provided at a bottom of the inner surface of the housing body, such that fluid is prevented from leaving the first channel when the valve unit is in the first state, and wherein the valve device is such that, when the second pressure level (PF60:1) is beneath said first ambient pressure level (PA60:1) and said pressure difference (ΔP) exceeds a threshold value, said pressure difference (ΔP) causes the valve unit to assume said second state such that ambient fluid, such as air, can flow into the first channel from the housing environment; characterized in that the housing body comprises an upper ridge member (360, 460) provided at an upper part of the inner surface of the housing body, which upper ridge member co-operates with the movable valve member to separate an upper space of the input side from an upper space of the output side when the second pressure level (PF60:1) is beneath said first ambient pressure level (PA60:1) and said pressure difference (ΔP) exceeds the threshold value. a valve housing (100, 200) having an input for connection to a fluid supply piping system (35, 72) having a second pressure level (P F60:1); an output for connection to a fluid outfeed conduit (74, 40, 40:1); and a housing body (100, 200, 130) positioned between the input and the output, said housing body having an inner surface forming a first channel for connecting the input with the output; and a valve unit which, in operation, is capable of switching between a first state and a second state dependent on a pressure difference (ΔP) between said first ambient pressure level (P A60:1) and said second pressure level (PF60:1), the valve unit having a movable valve member and a transit channel, wherein the valve member is adapted to rest against a first valve seat, provided at a bottom of the inner surface of the housing body, such that fluid is prevented from leaving the first channel when the valve unit is in the first state, and wherein an input for connection to a fluid supply piping system (35, 72) having a second pressure level (P F60:1); an output for connection to a fluid outfeed conduit (74, 40, 40:1); and a housing body (100, 200, 130) positioned between the input and the output, said housing body having an inner surface forming a first channel for connecting the input with the output; and a valve unit which, in operation, is capable of switching between a first state and a second state dependent on a pressure difference (ΔP) between said first ambient pressure level (P A60:1) and said second pressure level (PF60:1), the valve unit having a movable valve member and a transit channel, wherein the valve member is adapted to rest against a first valve seat, provided at a bottom of the inner surface of the housing body, such that fluid is prevented from leaving the first channel when the valve unit is in the first state, and wherein an inner surface forming a first channel for connecting the input with the output; and a valve unit which, in operation, is capable of switching between a first state and a second state dependent on a pressure difference (ΔP) between said first ambient pressure level (P A60:1) and said second pressure level (PF60:1), the valve unit having a movable valve member and a transit channel, wherein the valve member is adapted to rest against a first valve seat, provided at a bottom of the inner surface of the housing body, such that fluid is prevented from leaving the first channel when the valve unit is in the first state, and wherein the valve device is such that, when the second pressure level (PF60:1) is beneath said first ambient pressure level (PA60:1) and said pressure difference (ΔP) exceeds a threshold value, said pressure difference (ΔP) causes the valve unit to assume said second state such that ambient fluid, such as air, can flow into the first channel from the housing environment; characterized in that the housing body comprises an upper ridge member (360, 460) provided at an upper part of the inner surface of the housing body, which upper ridge member co-operates with the movable valve member to separate an upper space of the input side from an upper space of the output side when the second pressure level (PF60:1) is beneath said first ambient pressure level (PA60:1) and said pressure difference (ΔP) exceeds the threshold value.