Dosage device

A liquid metering device for a pneumatic power tool having an air inlet passage and a throttle valve, comprising a closed liquid reservoir with a lower space containing liquid and an upper space containing an air volume, an opening located in said lower space and communicating with said air inlet passage downstream of said throttle valve, a pipe extending between said opening and said upper space for communicating pressurized air in alternative flow directions between said inlet passage and said upper space, and a porous filter element located in said pipe and arranged to be penetrated by said air flow, said filter element having at least one surface continuously exposed to the liquid in said lower space and an air exposed part penetrated by said air flow, said filter element forming a flow restriction to the air flow through said pipe such that liquid absorbed from the reservoir by the at least one surface of the filter is emptied back into said reservoir by means of in-flowing air upon tool start-up when there is a positive relative pressure in the air inlet passage, and liquid absorbed from the reservoir by the at least one surface of the filter is pressed out into said air inlet passage by means of out-flowing air from the upper space when there is a positive relative pressure in the upper space upon tool shut-down, changes in pressure and resulting change in airflow direction being induced in said pipe at shifting of said throttle valve upon tool start-up and shut-down, said liquid pressed out into said air inlet passage responsive to tool shut-down providing lubrication to the tool upon a next tool start-up sequence.