Abstract: The invention relates to a starting valve for progressive build-up of pressure in an installation through which pressure medium flows, comprising a housing with a first opening for coupling to a first component of the installation and a second opening for coupling to a second component of the installation, a channel connecting the two openings, a piston which is movable to and fro in the housing between a closed and an open position and has at least one first and one second pressure surface, wherein on the first pressure surface the pressure prevailing in the region of the first opening applies and on the second pressure surface the pressure prevailing in the region of the second opening applies, means for maintaining a low flow of pressure medium--while the piston is in the closed position--from one opening to the other, and a spring element which pushes the piston into the closed position. According to the invention all pressure surfaces have an action which pushes the piston into the open position.