A gas turbine engine comprising: a fan; a compressor (14,16) downstream of the fan; a combustor downstream of the fan; a turbine (20,22) downstream of the fan; a bypass duct downstream of the fan and radially outward of the compressor (14,16); and a bearing compartment assembly comprising: a fluid pump; a compartment; a fluid line extending between the fluid pump and the compartment; and a damper check valve located in the fluid line, the damper check valve being a unitary, monolithic component that is configured to restrict a reverse flow from the compartment to the fluid pump more than the damper check valve restricts a standard flow from the fluid pump to the compartment; wherein the damper check valve comprises: a converging portion; a diverging portion downstream of the converging portion; and a constriction between the converging portion and the diverging portion; wherein the converging portion comprises: an inlet portion with a straight inner shape comprising an inlet length and an inlet diameter, wherein the inlet length is between one and five times the value of the inlet diameter; and a primary convergence downstream of the inlet portion with a frusto-conical inner shape; and wherein the diverging portion comprises: a full-width portion having an exterior in contact with an interior of the fluid line around its entire circumference; and a reentrant protrusion downstream of the full-width portion having an exterior with a reduced size such that the reentrant protrusion is spaced apart from the interior of the fluid line around its circumference. a fan; a compressor (14,16) downstream of the fan; a combustor downstream of the fan; a turbine (20,22) downstream of the fan; a bypass duct downstream of the fan and radially outward of the compressor (14,16); and a bearing compartment assembly comprising: a fluid pump; a compartment; a fluid line extending between the fluid pump and the compartment; and a damper check valve located in the fluid line, the damper check valve being a unitary, monolithic component that is configured to restrict a reverse flow from the compartment to the fluid pump more than the damper check valve restricts a standard flow from the fluid pump to the compartment; a fluid pump; a compartment; a fluid line extending between the fluid pump and the compartment; and a damper check valve located in the fluid line, the damper check valve being a unitary, monolithic component that is configured to restrict a reverse flow from the compartment to the fluid pump more than the damper check valve restricts a standard flow from the fluid pump to the compartment; wherein the damper check valve comprises: a converging portion; a diverging portion downstream of the converging portion; and a constriction between the converging portion and the diverging portion; a converging portion; a diverging portion downstream of the converging portion; and a constriction between the converging portion and the diverging portion; wherein the converging portion comprises: an inlet portion with a straight inner shape comprising an inlet length and an inlet diameter, wherein the inlet length is between one and five times the value of the inlet diameter; and a primary convergence downstream of the inlet portion with a frusto-conical inner shape; and an inlet portion with a straight inner shape comprising an inlet length and an inlet diameter, wherein the inlet length is between one and five times the value of the inlet diameter; and a primary convergence downstream of the inlet portion with a frusto-conical inner shape; and wherein the diverging portion comprises: a full-width portion having an exterior in contact with an interior of the fluid line around its entire circumference; and a reentrant protrusion downstream of the full-width portion having an exterior with a reduced size such that the reentrant protrusion is spaced apart from the interior of the fluid line around its circumference. a full-width portion having an exterior in contact with an interior of the fluid line around its entire circumference; and a reentrant protrusion downstream of the full-width portion having an exterior with a reduced size such that the reentrant protrusion is spaced apart from the interior of the fluid line around its circumference.