1. Process for calibration of the mobile core spring of a solenoid valve comprising an electromagnet subassembly associated with a pneumatic switching subassembly with a valve plug, the valve plug being moved in the body of the pneumatic switching subassembly firstly by a spring located in the mobile core of the electromagnet subassembly through a pusher, and secondly by a spring located under the valve plug and bearing around the lower seating of the pneumatic switching subassembly, this process comprising the following steps: a force sensor is put into position, either at a predetermined distance from the upper face of the mobile core, this distance being equivalent to the actual travel distance of the mobile core, or directly in contact with the face of the core when it is required to adjust the spring based on its force after the travel distance (core in contact on the yoke); the spring is installed in a reaming providing for this purpose in the axis of the mobile core: an elastic split pin is put into position behind the said spring, that is forced more or less into the reaming of the mobile core while measuring the force generated by the spring on the sensor, and the split pin is no longer forced into the core as soon as the required force is measured by the sensor.