which is sealingly displaceable inside an inner annular collar 60 which reduces the inner diameter of the shoulder ring 26 u2032 as the transverse bore 16 meets the annular collar 60 the latter is provided only in the cross sectional region outside the transverse bore 16 and can thus only be seen in the lower half of fig2 b the annular collar 60 ensures that if the switching process is too slow the control slide 41 u2032 does not remain in a central position due to pneumatic short circuiting between the transverse bores 17 18 which would result in a failure of the control of the consumer due to the pressure differential on both sides of the outer annular collar 59 and as a result due to an additional axial force acting on the control slide 41 u2032 said pneumatic short circuit is prevented even if the spring force of the helical pressure spring 31 is inadequate and or if the pressure in the pressure chamber 33 is inadequate which means that there is achieved an improvement in operational safety the seal between the outer annular collar 59 and the inner annular collar 60 does not necessarily have to be of the sliding variety a narrow gap dimension is.