A delivery device for patient-controlled infusion of a medicament, the delivery device comprising a reservoir for the medicament and a pump having a predetermined delivery
dose which is capable of displacing the medicament from the reservoir and delivering it to a patient, wherein the pump comprises a pumping means, a first conduit, capable of restricting flow rate, chosen in conjunction with the delivery
dose of the pumping means to define a predetermined maximum dosage rate, said conduit connecting the reservoir to a pumping means, a one-way valve in fluid communication with the first conduit and the pumping means which permits medicament flow into the pumping means but prevents reverse flow, a controlling means, and a second conduit extending from the pumping means and having a distal end through which the medicament may be released, wherein the controlling means: (a) is in fluid communication with the pumping means and the second conduit; (b) opens when pressured within the
dose chamber exceeds a predetermined minimum opening pressure for the controlling means; and, (c) is adapted to prevent the reverse flow of medicament and air into the pumping means.