Abstract: A shut-off valve for pressurized fluids in an air cooling/heating apparatus having a first duct receiving a first restrictor and a second restrictor. Both restrictors are coaxially formed with a capillary through which the pressurized fluid passes and which causes the rapid expansion of the fluid when the fluid exits from a distal end of the capillary. The outer surface of the restrictors is in direct contact with the interior surface of the first duct. The valve can further include a sampling instrument located between the restrictors.