A pump system for dispensing insulin, comprising: a disposable, wearable, self-contained insulin dispensing device comprising: - a housing; - an insulin container arranged in said housing, the insulin container having a perforatable dispensing end; - a pump means in said housing and adapted for pumping insulin from said insulin container to a catheter for injection of said insulin in a user of the device; - an actuator for said pump means; and - a controlling means for controlling the operation of said actuator according to a programme, the controlling means having keys and a display; characterised by said actuator comprising: - a shape memory alloy wire; - a ratchet gear or pawl wheel; - a pawl adapted for cooperating with said pawl wheel and connected to one end of said shape memory alloy wire; and a spring means connected to said pawl, the connections between said pawl and said wire and said pawl and said spring means being such that contraction of said wire rotates said pawl wheel against the spring force of said spring means, wherein the spring means is a spring wheel that has U-shaped spring arms (44, 45) for exerting a spring force on respective ends (46, 47) of the spring arms (44, 45) in a direction towards the centre of the pawl wheel such that the ends (46, 47) of the spring arms (44, 45) are constantly biased to enter into engagement with teeth of the pawl wheel, wherein one of the ends engages a first of the teeth of the pawl wheel as said pawl and prevents the wheel from rotating clock-wise. a disposable, wearable, self-contained insulin dispensing device comprising: - a housing; - an insulin container arranged in said housing, the insulin container having a perforatable dispensing end; - a pump means in said housing and adapted for pumping insulin from said insulin container to a catheter for injection of said insulin in a user of the device; - an actuator for said pump means; and - a controlling means for controlling the operation of said actuator according to a programme, the controlling means having keys and a display; characterised by said actuator comprising: - a shape memory alloy wire; - a ratchet gear or pawl wheel; - a pawl adapted for cooperating with said pawl wheel and connected to one end of said shape memory alloy wire; and a spring means connected to said pawl, the connections between said pawl and said wire and said pawl and said spring means being such that contraction of said wire rotates said pawl wheel against the spring force of said spring means, wherein the spring means is a spring wheel that has U-shaped spring arms (44, 45) for exerting a spring force on respective ends (46, 47) of the spring arms (44, 45) in a direction towards the centre of the pawl wheel such that the ends (46, 47) of the spring arms (44, 45) are constantly biased to enter into engagement with teeth of the pawl wheel, wherein one of the ends engages a first of the teeth of the pawl wheel as said pawl and prevents the wheel from rotating clock-wise. - a housing; - an insulin container arranged in said housing, the insulin container having a perforatable dispensing end; - a pump means in said housing and adapted for pumping insulin from said insulin container to a catheter for injection of said insulin in a user of the device; - an actuator for said pump means; and - a controlling means for controlling the operation of said actuator according to a programme, the controlling means having keys and a display; - a shape memory alloy wire; - a ratchet gear or pawl wheel; - a pawl adapted for cooperating with said pawl wheel and connected to one end of said shape memory alloy wire; and a spring means connected to said pawl, the connections between said pawl and said wire and said pawl and said spring means being such that contraction of said wire rotates said pawl wheel against the spring force of said spring means, wherein the spring means is a spring wheel that has U-shaped spring arms (44, 45) for exerting a spring force on respective ends (46, 47) of the spring arms (44, 45) in a direction towards the centre of the pawl wheel such that the ends (46, 47) of the spring arms (44, 45) are constantly biased to enter into engagement with teeth of the pawl wheel, wherein one of the ends engages a first of the teeth of the pawl wheel as said pawl and prevents the wheel from rotating clock-wise.