ABSTRACT The invention provides a jet expelling assembly comprising a reservoir and an impulse chamber assembly. The impulse chamber assembly comprises a chamber portion defining a cavity having a general axis, a piston received in the cavity along the general axis and comprising a fluid inlet, thereby defining a variable-volume impulse chamber with an outlet nozzle. The inlet comprises a conduit adapted to slidably engage a reservoir outlet during relative movement therebetween. The chamber portion is arranged stationary relative to the reservoir, whereby expelling an amount of drug from the reservoir to the impulse chamber via the inlet causes the piston to move towards the reservoir, the impulse chamber thereby receiving the expelled amount of drug. Fig. 2
