# Accurate Modeling, Operation Laws and Commutation Timing Matching for Concrete Pumping Systems
## 3 Results and Discussion  
### Operation law of the CPS  
#### 3.1.1 Operation law of the pumping mechanism  
The movement of the pumping mechanism refers to the reciprocating motion of the left and right main cylinders, which drive the concrete cylinders to suck in and discharge concrete, respectively. Figure 7 shows the pressure curves of the large chambers of the left and right main cylinders and their connecting chambers during the pumping cycle. During the propulsion process, the pressure in the large chamber of the propulsion cylinder (about 288 bar) is much higher than the pressure in the large chamber of the absorption cylinder (about 2.5 bar), and the pressure in the connecting chamber is also very low (about 9 bar). During the main cylinder reversal, the high and low pressures of the two large chambers are exchanged, while the pressure shock in the connecting chamber is larger (about 121-163 bar).  
Figure 8 shows the pressure and flow curves of the main pump and relief valve in the pumping cycle. Due to the large load, the main pump works at constant power during the main cylinder advance, the pump pressure is 290 bar and the flow rate is 226 L/min, and the pressure and flow rate of the main pump remain basically the same during the advance. When the main cylinder reverses direction, the relief valve opens and the instantaneous relief flow reaches 960 L/min, at which time the outlet pressure of the main pump drops rapidly and works at the maximum displacement, and its flow reaches 380 L/min.  
Figure 9 shows the characteristic of the signal valve in the pumping cycle. After the main cylinder passes the detection point, the control chamber ZK or ZS of the signal valve goes into high pressure, and the signal valve opens rapidly and holds for a period. When the main cylinder changes direction, the signal valve quickly closes. The opening time of the signal valve depends on whether the main cylinder can change direction quickly, but if the signal valve opens and closes quickly, it will be unfavorable for the swing cylinder to change direction.  
Figure 6: Simulation curves of the CPS: (**a**) main cylinder displacement, (**b**) large cavity pressure, (**c**) connecting cavity pressure and (**d**) main pump output pressure.  
Figure 8: Pressure and flow curves of main pump: (**a**) main cylinder displacement, (**b**) main pump pressure, (**c**) main pump flow rate and (**d**) relief valve flow rate.  
Figure 7: Large cavity pressure of main cylinder and connecting cavity pressure: (**a**) main cylinder displacement, (**b**) left large cavity pressure, (**c**) connecting cavity pressure and (**d**) right larger cavity pressure.  
Figure 10 shows a graph of the pressure in the two chambers of the main valve during the pumping cycle. The main valve starts to change direction when the piston of the main cylinder passes the detection point. The switching time of the main valve determines the commutation speed of the main cylinder. Here, the switching time of the main valve is about 172 ms and the switching time of the main cylinder is about 120 ms. While the main valve is reversing, the main cylinder is already starting to move in the opposite direction.  
Figure 10: Dynamic characteristic curves of main valve: (**a**) main cylinder displacement; (**b**) and (**c**) main valve control pressure; and (**d**) main valve displacement.  
Figure 9: Dynamic characteristic curves of signal valve: (**a,b**) main cylinder and signal valve displacement; (**c,d**) signal valve control pressure; and (**e**) signal valve output pressure.