Abstract: A housing of diaphragm valve has two valve chambers (11, 12). A central channel (21, 22) opens in each valve chamber and has an external connection (B, D). On each side of the central channels there are first (17, 19) and second side channels (18, 20) having an external connection (A, C). Each valve chamber has two valve seats (13, 14, 15, 16). Diaphragms (23, 24) are arranged to seal against the valve seats. Control means (25, 26) are arranged to press portions of the diaphragms (23, 24) against one valve seat each, thereby shutting passage between a central channel and a side channel, and to raise portions of the diaphragms off the valve seats, thereby to open passage between a central channel and a side channel. The first side channels (17, 19) are interconnected and both are connected to a common external connection (A), and the second side channels (18, 20) are interconnected and both are connected to a common external connection (C).