Non-return valve

A non-return valve, comprising:

• a valve housing defining an interior fluid passage extending along a longitudinal axis of said housing, and having a wall with a first guide slot opening extending in an axial direction of said valve housing;
• a seat element in said fluid passage defining a valve seat;
• a closing spring in said valve housing;
• a detent element biased by said closing spring and mounted for axial movement in said passage between a detent position adjoining said seat element and opening positions spaced from said valve seat against biasing of said closing spring, said closing spring biasing said detent element against said valve seat;
• a first control pin extending through and guidedly movable in said slot opening and having an interior end seated in a radial hole of said seat element and an exterior section projecting from an exterior of said valve housing;
• and
• a displacement member actuatable on said exterior of said valve housing and engaged with said control pin to fix said control pin and said seat element in axial adjustment positions to adjust magnitudes of closing forces of said closing spring.