A check valve assembly which allows fluid flow through a conduit in a first direction and prevents fluid flow through said conduit in a second direction which is opposite said first direction, said check valve assembly comprising: said conduit; and a valve stem within said conduit such that a flow path is created radially between said conduit and said valve stem, said valve stem moving along a check valve assembly axis between a closed position which prevents fluid flow through said flow path and an open position which permits fluid flow through said flow path; wherein said flow path includes: i) a first restriction configured to increase the velocity of fluid passing through said flow path; ii) a first expansion, downstream of said first restriction, configured to decrease the velocity of fluid passing through said flow path; iii) a second restriction, downstream of said first expansion, configured to increase velocity of fluid passing through said flow path; and a second expansion, downstream of said second restriction, configured to decrease the velocity of fluid passing through said flow path; said conduit includes an inner wall surface; said valve stem includes a valve stem seating surface which 1) seats against said inner wall surface when said valve stem is in said closed position, thereby preventing fluid flow through said flow path and 2) is spaced apart from said inner wall surface when said valve stem is in said open position, thereby permitting fluid flow through said flow path; and said first restriction is formed between said valve stem seating surface and said inner wall surface; said inner wall surface has an inner wall surface diverging section which diverges away from said check valve assembly axis when moving along said check valve assembly axis in said first direction; and said valve stem seating surface seats against said inner wall surface diverging section when said valve stem is in said closed position; characterised in that: said inner wall surface has an inner wall surface converging section, downstream of said inner wall surface diverging section, which converges toward said check valve assembly axis in said first direction; said valve stem has a valve stem converging section which converges toward said check valve assembly axis in said first direction; and said first expansion is located radially between said inner wall surface converging section and said valve stem converging section. said conduit; and a valve stem within said conduit such that a flow path is created radially between said conduit and said valve stem, said valve stem moving along a check valve assembly axis between a closed position which prevents fluid flow through said flow path and an open position which permits fluid flow through said flow path; wherein said flow path includes: i) a first restriction configured to increase the velocity of fluid passing through said flow path; ii) a first expansion, downstream of said first restriction, configured to decrease the velocity of fluid passing through said flow path; iii) a second restriction, downstream of said first expansion, configured to increase velocity of fluid passing through said flow path; and i) a first restriction configured to increase the velocity of fluid passing through said flow path; ii) a first expansion, downstream of said first restriction, configured to decrease the velocity of fluid passing through said flow path; iii) a second restriction, downstream of said first expansion, configured to increase velocity of fluid passing through said flow path; and a second expansion, downstream of said second restriction, configured to decrease the velocity of fluid passing through said flow path; said conduit includes an inner wall surface; said valve stem includes a valve stem seating surface which 1) seats against said inner wall surface when said valve stem is in said closed position, thereby preventing fluid flow through said flow path and 2) is spaced apart from said inner wall surface when said valve stem is in said open position, thereby permitting fluid flow through said flow path; and said first restriction is formed between said valve stem seating surface and said inner wall surface; said inner wall surface has an inner wall surface diverging section which diverges away from said check valve assembly axis when moving along said check valve assembly axis in said first direction; and said valve stem seating surface seats against said inner wall surface diverging section when said valve stem is in said closed position; characterised in that: said inner wall surface has an inner wall surface converging section, downstream of said inner wall surface diverging section, which converges toward said check valve assembly axis in said first direction; said valve stem has a valve stem converging section which converges toward said check valve assembly axis in said first direction; and said first expansion is located radially between said inner wall surface converging section and said valve stem converging section. said inner wall surface has an inner wall surface converging section, downstream of said inner wall surface diverging section, which converges toward said check valve assembly axis in said first direction; said valve stem has a valve stem converging section which converges toward said check valve assembly axis in said first direction; and said first expansion is located radially between said inner wall surface converging section and said valve stem converging section.