to the drawings there is seen in fig1 a schematic representation of the proportioner according to the invention shown is the proportioner 2 in its outer shape of a substantially t like configuration and having an inlet port 4 and an outlet port 6 branch 8 of proportioner 2 is usually although not necessarily inclined and has an additive inlet 10 proportioner 2 according to the invention requires no external energy for its mixing operation the energy used up coming from the pressure drop u03b4p between the inlet side p in of proportioner 2 and its outlet side p out hence u03b4p p in p out e g an optional pressure drop of about 0 3 atm this embodiment requires the additive to reach its inlet 10 at a pressure identical to the carrier 39 s input pressure p in there is seen a tapering valve head 12 which is connected to a valve stem 14 the valve head 12 is biased by a helical spring 16 to close a gate 18 that separates inlet space 20 from outlet space 22 spring 16 is calculated to start yielding only to a pressure of the predetermined u03b4p beyond that spring 16 gives gradually and valve head 12 slowly advances and because of its conical shape gradually increases the size of the annular gap between valve head 12 and gate 18 until the established gate opening is sufficient to drop the u03b4p upon the inflow of the carrier liquid valve head 12 withdrawal is therefore an indicator of the instantaneous inflow of the proportioner tapering valve head 12 is provided with a number of ribs 24 for better guidance further seen.