Abstract: A low pressure low volume plastic metering valve comprised of a cylinder having an external tapered port and a piston having a tapered through port for communicating with the port in said cylinder. Both the tapered port in the cylinder and the through port in the piston are offset from the axis of the cylinder and communicate with each other along an arcuate tapered passageway that varies from a maximum where the ports abut to a minimum. The piston is held by a lip on the cylinder walls which prevents axial movement of the piston but allows rotation of the piston to vary the fluid flow. Sealing is improved by constructing the cylinder of a yieldable plastic and the piston of a different plastic that is brittle and non-yielding.