Abstract: A dual master cylinder (10) for the braking system of a motor vehicle comprising a bore (18), a primary portion and a secondary portion (14), in which the secondary piston (44) of the secondary portion comprises an outer piston (65) slidable in the bore, and a central piston (78), the central piston including a main body (86) slidable in the bore and a secondary body (92) slidable in a piston bore (64) in the outer piston, the piston bore having a shoulder (72) engageable with a first abutment face (98) on the central piston to define a check valve (62), the piston bore providing a fluid passage (96,68) between the high pressure chamber (56) and the low pressure chamber (48) of the secondary portion, the check valve allowing hydraulic fluid to flow through the fluid passage during a rest mode or a release mode of the dual master cylinder, but preventing such flow during an apply mode.

Abstract: A dual master cylinder (10) for the braking system of a motor vehicle comprising a primary portion and a secondary portion (14) in which the high pressure chamber (56) of the secondary portion includes a check valve (62) mounted within a piston bore (64) in the secondary piston (44), the piston bore providing a fluid passage (70,96,66) between the high pressure chamber and the low pressure chamber (48) of the secondary portion, the check valve allowing hydraulic fluid to flow through the fluid passage during a rest mode or a release mode of the dual master cylinder, but preventing such flow during an apply mode. Prevents damage to elastomeric cup seal (52) when back-pressure is generated by ABS dus to the absence of a dilation port in the secondary portion, which is no longer required due to the presence of the check valve.

Abstract: A dual master cylinder (10) for the braking system of a motor vehicle comprising a bore (18), a primary portion (12) and a secondary portion, in which the primary piston (16) comprises an outer piston (65) slidable in the bore (18), and a central piston (78) slidable in a piston bore (64) defined by the outer piston, the piston bore having a shoulder (72) engageable with an abutment face (98) on the central piston to define a check valve (62), the piston bore providing a fluid passage (70,96,68) between the high pressure chamber (30) and the low pressure chamber (22) of the primary portion, the check valve allowing hydraulic fluid to flow through the fluid passage during a rest mode or a release mode of the dual master cylinder, but preventing such flow during an apply mode. Prevents damage to elastomeric cup seal (26) when back pressure is generated by ABS due to the absence of a dilation port in the primary portion, which is no longer required due to the presence of the check valve.