Hydraulic cylinder, in particular main cylinder for hydraulic brake system

The cylinder has pistons each exhibiting a pressure chamber and a central valve (22), which is opened in a resting position of the piston to connect a pressure chamber with an equalization and castor connection over a piston channel. A valve body (34) is provided with a passage between a seal hub (30) at the piston channel and a guide section, over which the pressure chamber communicates with the channel by the opened valve.