A check valve unit (400, 401, 402) comprising: a housing (104, 106a;104, 106a'; 430, 106a) defining a first inlet port, a first outlet port, and a first chamber in fluid communication with the first inlet port and the first outlet port thereby defining a flow path from the first inlet port through the first chamber to the first outlet port, wherein the first chamber includes a first valve seat and a second valve seat; a first sealing disc disposed in the first chamber that is moveable from a position seated on the first valve seat to a position seated on the second valve seat; a suction Venturi in fluid communication with the first chamber; wherein a first sound attenuating member is disposed in the flow path downstream of the first chamber and downstream of the suction Venturi; wherein the housing (104, 106b; 104, 106b'; 440, 106c) further defines: a second chamber having a second inlet port and a second outlet port in fluid communication therewith thereby defining a flow path from the second inlet port through the second chamber to the second outlet port, wherein the second chamber includes a first valve seat and a second valve seat; a second sealing disc disposed in the second chamber that is moveable from a position seated on the first valve seat to a position seated on the second valve seat; and wherein the second outlet port of the second chamber has a fluid junction with the first chamber downstream of the first sound attenuating member. a housing (104, 106a;104, 106a'; 430, 106a) defining a first inlet port, a first outlet port, and a first chamber in fluid communication with the first inlet port and the first outlet port thereby defining a flow path from the first inlet port through the first chamber to the first outlet port, wherein the first chamber includes a first valve seat and a second valve seat; a first sealing disc disposed in the first chamber that is moveable from a position seated on the first valve seat to a position seated on the second valve seat; a suction Venturi in fluid communication with the first chamber; wherein a first sound attenuating member is disposed in the flow path downstream of the first chamber and downstream of the suction Venturi; wherein the housing (104, 106b; 104, 106b'; 440, 106c) further defines: a second chamber having a second inlet port and a second outlet port in fluid communication therewith thereby defining a flow path from the second inlet port through the second chamber to the second outlet port, wherein the second chamber includes a first valve seat and a second valve seat; a second sealing disc disposed in the second chamber that is moveable from a position seated on the first valve seat to a position seated on the second valve seat; and wherein the second outlet port of the second chamber has a fluid junction with the first chamber downstream of the first sound attenuating member. a second chamber having a second inlet port and a second outlet port in fluid communication therewith thereby defining a flow path from the second inlet port through the second chamber to the second outlet port, wherein the second chamber includes a first valve seat and a second valve seat; a second sealing disc disposed in the second chamber that is moveable from a position seated on the first valve seat to a position seated on the second valve seat; and wherein the second outlet port of the second chamber has a fluid junction with the first chamber downstream of the first sound attenuating member.