A pump system comprising: a pump chamber of which at least one end is open-ended, a leadscrew extending along a longitudinal axis of the pump chamber, a first plunger and a second plunger, an inlet port and an outlet port defined in a sidewall of the pump chamber, wherein the inlet port and outlet port are located in an area of the sidewall between the first and second plungers, a reservoir, in fluid communication with the pump chamber via an inlet conduit which is coupled to the inlet port, an inlet one-way valve, disposed between the reservoir and the pump chamber, the one-way valve allowing fluid to flow from the reservoir into the pump chamber and preventing fluid from flowing from the pump chamber to the reservoir, a patient interface, in fluid communication with the pump chamber via an outlet conduit which is coupled to the outlet port, an outlet one-way valve, disposed between the pump chamber and the patient interface, the one-way valve allowing fluid to flow from the pump chamber to the patient interface and preventing fluid from flowing from the patient interface to the pump chamber, wherein the leadscrew has left-hand and right-hand threads (101a, 101b) defined thereon, wherein the first plunger is coupled to the leadscrew via the left-hand threads, and wherein the second plunger is coupled to the leadscrew via the right-hand threads, wherein rotation of the leadscrew in a first direction causes the first and second plungers (106a, 106b) to move toward each other, and wherein rotation of the leadscrew in a second, opposite direction causes the first and second plungers (106a, 106b) to move away from each other, and in that a drive is coupled to the leadscrew for rotating the leadscrew in the first and second directions. a pump chamber of which at least one end is open-ended, a leadscrew extending along a longitudinal axis of the pump chamber, a first plunger and a second plunger, an inlet port and an outlet port defined in a sidewall of the pump chamber, wherein the inlet port and outlet port are located in an area of the sidewall between the first and second plungers, a reservoir, in fluid communication with the pump chamber via an inlet conduit which is coupled to the inlet port, an inlet one-way valve, disposed between the reservoir and the pump chamber, the one-way valve allowing fluid to flow from the reservoir into the pump chamber and preventing fluid from flowing from the pump chamber to the reservoir, a patient interface, in fluid communication with the pump chamber via an outlet conduit which is coupled to the outlet port, an outlet one-way valve, disposed between the pump chamber and the patient interface, the one-way valve allowing fluid to flow from the pump chamber to the patient interface and preventing fluid from flowing from the patient interface to the pump chamber, wherein the leadscrew has left-hand and right-hand threads (101a, 101b) defined thereon, wherein the first plunger is coupled to the leadscrew via the left-hand threads, and wherein the second plunger is coupled to the leadscrew via the right-hand threads, wherein rotation of the leadscrew in a first direction causes the first and second plungers (106a, 106b) to move toward each other, and wherein rotation of the leadscrew in a second, opposite direction causes the first and second plungers (106a, 106b) to move away from each other, and in that a drive is coupled to the leadscrew for rotating the leadscrew in the first and second directions.