A plate valve, especially for diaphragm pumps, having a valve plate (8), a valve seat (15), and a valve chamber bounded by a valve housing is provided, with the valve plate being held at the edges thereof. The valve plate (8) is preset under tension elastically in the installation position between outer edge holding devices, with the elastic pretensioning being at least large enough that deformations due to edge clamping can be compensated. Preferably, the valve plate (8) is held at the edge in a positive fit and is preset under tension elastically between its outer edge holding devices in the installation position.