e g by means of a pin 39 in a way that the angle area with the largest power lies below the top dead centre of the inclined plate 4 the top dead centre is the point in which the pistons 9 assume their largest deflection and the cylinder 10 assumes it smallest volume shortly before this operation position the gas volume enclosed in the cylinder 10 exerts its largest counterpressure on the pistons and thus also on the pressure spring 17 thus it would be even better if the angle area of the pressure spring 17 having the largest power was placed somewhat before the top dead centre in the top dead centre the cylinder 10 is namely already empty again so that the largest forces appear shortly before this top dead centre as operation in both directions of the compressor is often desired it is sufficient to have the largest counterforce below the top dead centre the cylindrical surface area of the piston 9 is provided with a groove this groove is engaged by a pin 22 formed e g by the end of a screw 23 screwed radially into the middle part 27 of the housing from the outside together with the groove 21 the pin 22 forms a torsion prevention for the piston 9 during its up and down movement the piston 9 is drawn somewhat into the inside of a housing 33 in this connection it is almost unavoidable that a small quantity of particularly gaseous refrigerant escapes or leaks into the inside of this.