A resin injection circuit for injecting resin into a mould for manufacturing a composite part, in particular a composite turbomachine part, said mould being suitable for receiving a preform to be impregnated with resin, said circuit comprising at least one resin injection regulator (56, 58), comprising at least one enclosure which is connected to said circuit and inside which a movable wall means is movable in a sealed manner, said movable wall means delimiting a first cavity in said enclosure, forming a resin accumulation reservoir, which is connected to at least a part of said circuit feeding said mould, and a second cavity configured to be connected to a source of pressurised fluid, said movable wall means being configured to be acted upon by the pressurised fluid feeding the second cavity in order to exert pressure on the resin contained in the first cavity, isolating said resin from said fluid, said enclosure being formed of a tubular liner and the movable wall means comprising a piston slidably movable in said tubular liner, said piston delimiting in said tubular liner a first chamber forming the first cavity and a second pressurizing chamber forming the second cavity configured to be connected to the source of pressurized fluid, the resin injection regulator comprising: - a tubular axial main body, - the liner, having the same axial length as the main body, and received in said main body, - the piston, of the same diameter as the tubular liner, and comprising a means of dynamic sealing with said tubular liner, - a first cover, configured to close a first end of said main body and a first end of the liner, and comprising a first resin passage duct opening into said liner, - a second cover, configured to close a second end of said main body and a second end of the liner, and comprising a second fluid passage duct opening into said liner, - first and second static sealing means (106, 110) interposed between said liner and the first and second covers (88, 94). said enclosure being formed of a tubular liner and the movable wall means comprising a piston slidably movable in said tubular liner, said piston delimiting in said tubular liner a first chamber forming the first cavity and a second pressurizing chamber forming the second cavity configured to be connected to the source of pressurized fluid, the resin injection regulator comprising: - a tubular axial main body, - the liner, having the same axial length as the main body, and received in said main body, - the piston, of the same diameter as the tubular liner, and comprising a means of dynamic sealing with said tubular liner, - a first cover, configured to close a first end of said main body and a first end of the liner, and comprising a first resin passage duct opening into said liner, - a second cover, configured to close a second end of said main body and a second end of the liner, and comprising a second fluid passage duct opening into said liner, - first and second static sealing means (106, 110) interposed between said liner and the first and second covers (88, 94). - a tubular axial main body, - the liner, having the same axial length as the main body, and received in said main body, - the piston, of the same diameter as the tubular liner, and comprising a means of dynamic sealing with said tubular liner, - a first cover, configured to close a first end of said main body and a first end of the liner, and comprising a first resin passage duct opening into said liner, - a second cover, configured to close a second end of said main body and a second end of the liner, and comprising a second fluid passage duct opening into said liner, - first and second static sealing means (106, 110) interposed between said liner and the first and second covers (88, 94).