The invention relates to a valve for closing and opening a line system, comprising a valve body (24) which is made of metal or plastic and forms a valve seat (26); a line system (18) with a supply line (20) for supplying a fluid to the valve seat (26) and with a discharge line (22) for discharging the fluid from the valve seat (26), the fluid being under a supply pressure (pV) in the supply line (20) and under a working pressure (pN) in the discharge line (22); a closing element (28) which interacts with the valve seat (26) for closing and opening the line system, said closing element (28) releasing a throttle cross-section (A) between the valve seat (26) and the closing element (28); a restoring element (32) which applies a restoring force to the closing element (28), the restoring forcepressing the closing element (28) against the valve seat (26) in order to close the line system; and a pressure chamber (46), in which the fluid is under a closing pressure (pS), with which the fluidapplies a closing force to the closing element (28) in order to close the line system (18). The valve (10) has means (52), by which the closing pressure (pS) in the pressure chamber (46) can be reduced below the supply pressure (pV) as a function of the released throttle cross-section (A). The invention further relates to a vehicle comprising such a valve and to a method for operating such a valve.