A flow-control valve has a housing having first and second input ports and respective first and second output ports for respective first and second separate fluid streams and formed between the first and second port with first and second valve seats. Respective first and second valve bodies are axially shiftable in the valve seats, and a coupling element connected axially between the valve bodies moves the valve bodies axially jointly. A diaphragm between the first piston and the housing defines an axially inner compartment into which the first input port opens and between the diaphragm and the housing an axially outer compartment. The first valve body is formed with a passage extending through the first valve body and having an axially extending part opening into the outer compartment and a transversely extending part opening into the housing between the first seat and the first output port.