A cartridge valve for fluid flow control comprising: a cartridge defining a first internal chamber and a working fluid chamber, the working fluid chamber separated and partitioned from fluid communication with the first chamber via a piston; a valve plunger extending through the first chamber and having a first end and second end; the piston attached to the plunger at or towards the first end, the working fluid chamber capable of accommodating a working fluid and positioned to allow the working fluid to act on the piston and to provide an axial movement of the piston and the plunger within the cartridge; a bias member housed within the first chamber to bias the piston against the axial movement; an inlet and an outlet for a supply fluid to flow through a portion of the valve and be controlled by the valve via the axial movement of the plunger relative to the inlet and/or the outlet, the inlet and outlet partitioned from the first chamber by at least one seal; the second end of the valve plunger is configured to mate with the inlet or the outlet or a region therebetween so as to close the inlet or the outlet or to block a fluid flow between the inlet and the outlet via the return force of the bias member, a seat releasably attached at or towards the second end of the plunger to sit against the inlet or the outlet or a region therebetween and control the flow of fluid through the valve, characterised by a bushing interchangeably mounted at the plunger in the vicinity of the seat to allow adjustment of the position of the seat relative to the inlet or outlet to control a stroke length of the plunger wherein the relative axial position of the seat at plunger is adjustable by exchange of the position of the bushing relative to seat. a cartridge defining a first internal chamber and a working fluid chamber, the working fluid chamber separated and partitioned from fluid communication with the first chamber via a piston; a valve plunger extending through the first chamber and having a first end and second end; the piston attached to the plunger at or towards the first end, the working fluid chamber capable of accommodating a working fluid and positioned to allow the working fluid to act on the piston and to provide an axial movement of the piston and the plunger within the cartridge; a bias member housed within the first chamber to bias the piston against the axial movement; an inlet and an outlet for a supply fluid to flow through a portion of the valve and be controlled by the valve via the axial movement of the plunger relative to the inlet and/or the outlet, the inlet and outlet partitioned from the first chamber by at least one seal; the second end of the valve plunger is configured to mate with the inlet or the outlet or a region therebetween so as to close the inlet or the outlet or to block a fluid flow between the inlet and the outlet via the return force of the bias member, a seat releasably attached at or towards the second end of the plunger to sit against the inlet or the outlet or a region therebetween and control the flow of fluid through the valve, characterised by a bushing interchangeably mounted at the plunger in the vicinity of the seat to allow adjustment of the position of the seat relative to the inlet or outlet to control a stroke length of the plunger wherein the relative axial position of the seat at plunger is adjustable by exchange of the position of the bushing relative to seat.