1. Open-loop control system Closed-loop control system

2. Open-loop control systemV2 x
In Flow
(qi) h V1 x
Out Flow
(qo)
(water level)
(water level expected)
Control valve (V2)
water tank
Outlet valve (V1)

3. Closed-loop control system
(Controller)
Pneumatic valve) x
In Flow
(qi) h V1 x
Out Flow
(qo)

4. Closed-looped control system
Feedforward path
(Disturbance)
(Controller)
Pneumatic valve
(Tank)
(water level expected)
(water level)
(Float system)
Feedback path

5. Closed-loop control system
(Controller)
(Pneumatic valve)
(Disturbance) x
In Flow
(qi) h V1 x
Out Flow
(qo)

6. Advantages and Disadvantages of the control system
Open system
Advantages:
1. Less complicated, less number of equipments and cheap
2. Easy maintenance
3. System is quite stable
Disadvantages:
Need to adjust more frequently once the output has changed

7. Advantages and Disadvantages of the control system
Close system
Advantages:
1. Eliminating the disturbance
Disadvantages:
1. More number of equipments, more complicated and expensive
2. Difficult maintenance
3. There is a problem on stability