A valve assembly (2; 102; 202; 302) comprising: a valve body (4; 104; 204) comprising a first port (6; 106; 206; 306), a second port (8; 108; 208; 308) and a fluid passageway (10; 110; 210) extending between the first (6; 106; 206; 306) and second ports (8; 108; 208; 308); a valve member (12; 112; 212; 312), comprising a through port (14; 114; 214), arranged in the fluid passageway (10; 110; 210) and moveable between an open position in which fluid can flow between the first (6; 106; 206; 306) and second ports (8; 108; 208; 308) through the through port (14; 114; 214), and a closed position in which fluid cannot flow between the first (6; 106; 206; 306) and second ports (8; 108; 208; 308); and a sealing arrangement (15A; 115A; 215A; 315A), arranged between the first port (6; 106; 206; 306) and the valve member (12; 112; 212; 312), comprising: a sealing member (16; 316) arranged to seal against the valve member (12; 112; 212; 312) such that fluid cannot flow around an outer surface of the valve member (12; 112; 212; 312); a sleeve (18; 318) arranged in the fluid passageway (10; 110; 210) between the first port (6; 106; 206; 306) and the valve member (12; 112; 212; 312); characterized in that the sealing arrangement further comprises: a deformable, incompressible, medium (20; 320) contained around the sleeve (18; 318) and arranged such that, in use, a fluid within the sleeve (18; 318) exerts an outward pressure on the sleeve (18; 318) causing the sleeve (18; 318) to deform and act on the medium (20, 320) which applies a force to push the sealing member (16; 316) against the valve member (12; 112; 212; 312). a valve body (4; 104; 204) comprising a first port (6; 106; 206; 306), a second port (8; 108; 208; 308) and a fluid passageway (10; 110; 210) extending between the first (6; 106; 206; 306) and second ports (8; 108; 208; 308); a valve member (12; 112; 212; 312), comprising a through port (14; 114; 214), arranged in the fluid passageway (10; 110; 210) and moveable between an open position in which fluid can flow between the first (6; 106; 206; 306) and second ports (8; 108; 208; 308) through the through port (14; 114; 214), and a closed position in which fluid cannot flow between the first (6; 106; 206; 306) and second ports (8; 108; 208; 308); and a sealing arrangement (15A; 115A; 215A; 315A), arranged between the first port (6; 106; 206; 306) and the valve member (12; 112; 212; 312), comprising: a sealing member (16; 316) arranged to seal against the valve member (12; 112; 212; 312) such that fluid cannot flow around an outer surface of the valve member (12; 112; 212; 312); a sleeve (18; 318) arranged in the fluid passageway (10; 110; 210) between the first port (6; 106; 206; 306) and the valve member (12; 112; 212; 312); characterized in that the sealing arrangement further comprises: a deformable, incompressible, medium (20; 320) contained around the sleeve (18; 318) and arranged such that, in use, a fluid within the sleeve (18; 318) exerts an outward pressure on the sleeve (18; 318) causing the sleeve (18; 318) to deform and act on the medium (20, 320) which applies a force to push the sealing member (16; 316) against the valve member (12; 112; 212; 312). a sealing member (16; 316) arranged to seal against the valve member (12; 112; 212; 312) such that fluid cannot flow around an outer surface of the valve member (12; 112; 212; 312); a sleeve (18; 318) arranged in the fluid passageway (10; 110; 210) between the first port (6; 106; 206; 306) and the valve member (12; 112; 212; 312); characterized in that the sealing arrangement further comprises: a deformable, incompressible, medium (20; 320) contained around the sleeve (18; 318) and arranged such that, in use, a fluid within the sleeve (18; 318) exerts an outward pressure on the sleeve (18; 318) causing the sleeve (18; 318) to deform and act on the medium (20, 320) which applies a force to push the sealing member (16; 316) against the valve member (12; 112; 212; 312).