A valve (18.1 or 118.1) comprising: a housing defining a cylindrical chamber having a central axis; a first port; a second port which is spaced from the first port; a sleeve (55 or 155) concentrically mounted within the housing cylinder; a flow path connecting the first port and the second port in flow communication to allow medium containing solid particles to pass therethrough; a valve seat positioned in the flow path; a closure unit which is displaceable between a closed position in which it seats against the valve seat to inhibit the flow of medium through the flow path and an open position in which it permits the flow of medium through the flow path; a cavity configured to receive at least part of the closure unit; wherein the closure unit further comprises (i) a barrier piston configured to inhibit the flow of solid particles from the second port when the closure unit is in its closed position and thereby inhibit the passage of such solid particles into the cavity; (ii) one or more bleed passages connecting the cavity with the second port in flow communication to provide a pressure balancing arrangement that reduces a pressure differential therebetween, and (iii) a downwards sloping top extending from a central portion of the barrier piston to an outer surface of the barrier piston to permit fine particles in the cavity to settle through the one or more bleed passages towards the second port; characterised in that the sleeve (55 or 155) defines a bore transverse to the central axis of the sleeve (55 or 155) so that the second port extends through the housing and sleeve (55 or 155) into the chamber through a side of the sleeve, and wherein the sleeve (55 or 155) surrounds the barrier piston with clearance between the outer surface of the barrier piston and a radially inner surface of the sleeve (55 or 155) so that the sleeve (55 or 155) and housing provide support to the barrier piston to reduce or prevent lateral movement that may arise when ore particles are trapped between part of the closure unit and the valve seat. a housing defining a cylindrical chamber having a central axis; a first port; a second port which is spaced from the first port; a sleeve (55 or 155) concentrically mounted within the housing cylinder; a flow path connecting the first port and the second port in flow communication to allow medium containing solid particles to pass therethrough; a valve seat positioned in the flow path; a closure unit which is displaceable between a closed position in which it seats against the valve seat to inhibit the flow of medium through the flow path and an open position in which it permits the flow of medium through the flow path; a cavity configured to receive at least part of the closure unit; wherein the closure unit further comprises (i) a barrier piston configured to inhibit the flow of solid particles from the second port when the closure unit is in its closed position and thereby inhibit the passage of such solid particles into the cavity; (ii) one or more bleed passages connecting the cavity with the second port in flow communication to provide a pressure balancing arrangement that reduces a pressure differential therebetween, and (iii) a downwards sloping top extending from a central portion of the barrier piston to an outer surface of the barrier piston to permit fine particles in the cavity to settle through the one or more bleed passages towards the second port; characterised in that the sleeve (55 or 155) defines a bore transverse to the central axis of the sleeve (55 or 155) so that the second port extends through the housing and sleeve (55 or 155) into the chamber through a side of the sleeve, and wherein the sleeve (55 or 155) surrounds the barrier piston with clearance between the outer surface of the barrier piston and a radially inner surface of the sleeve (55 or 155) so that the sleeve (55 or 155) and housing provide support to the barrier piston to reduce or prevent lateral movement that may arise when ore particles are trapped between part of the closure unit and the valve seat.