# Analysis of the Energy Efficiency of a Pneumatic Booster Regulator with Energy Recovery
## 2 Working Principle of the Booster Regulator  
Based on [PERSON]'s law, low pressure can be transferred to high pressure for the area of difference. A typical commercial booster regulator (VBA series, SMC, Tokyo, Japan) is shown in Figure 1. It is composed of two drive chambers, two boost chambers and a movable piston. As shown in Figure 1, the piston moves from left to right. The pressurised air flows into drive chamber A and boost chamber B, and the air in drive chamber B discharges directly to the atmosphere. The force on the left side of the piston can be twice as great as that on the right side, so the pressure in boost chamber A can become twice as high as the supply pressure. When the piston moves to the end of its stroke, the switching valve changes its position, which causes the piston to change direction. Thus, the booster regulator can continuously exhaust high-pressure air.  
However, the compressed air in the drive chamber is exhausted directly to the atmosphere with each stroke, so considerable energy is wasted over a long run-time. In order to reuse this energy to enhance the energy efficiency, and with reference to the expansion energy used (EEU) booster proposed in the reference [PERSON] (1975); [PERSON] _et al._ (2015); [PERSON] _et al._ (2015), a new booster regulator was proposed, as shown in Figure 2 (it is called the VBA-R, corresponding to the old type of VBA). The drive and boost chambers are the same as a traditional booster regulator. However, two more chambers (called recovery chambers) were added to the middle to recover the exhausted energy, and a seven-way two-position (7/2) solenoid valve was introduced to control the air flow. There are also other elements, such as check valves, regulators and magnetic rings, and so on.  
When the piston is located at the left end, the magnetic signal was detected and the position of the 7/2 solenoid valve was set as shown in Figure 2. The compressed air flows into drive chamber A and boost chamber B. The piston then moves from left to right, and the air in boost chamber A is further compressed so that the pressure becomes higher than the supply pressure. The compressed air in drive chamber B, instead of exhausting to the atmosphere, flows into recovery chamber A through the 7/2 solenoid valve, and the recovered air is reused to move the piston. It also helps to increase the area of difference so that the boost ratio can be further enhanced. After the piston moves to the right end, an impulse signal is detected once again, and the 7/2 solenoid valve changes its position so that the piston can move in a reciprocating manner and continuously discharge high-pressure air. When the booster regulator works with a different load, the boost ratio can be set by adjusting regulator 14 to output a different air pressure.  
Figure 1: Schematic of booster regulator (VBA). 1-Drive chamber A, 2-piston, 3-booster chamber A, 4-switching valve, 5-check valve, 6-booster chamber B, 7-piston rod, 8-drive chamber B, 9-regulator, 10-air source. The pressure is higher in red lines than in green lines.  
Figure 2: Structure schematic diagram of booster regulator with energy recovery (VBA-R). 1: drive chamber A, 2: piston, 3: booster chamber A, 4: air source, 5: recovery chamber A, 6: recovery chamber B, 7: check valve, 8: boost chamber B, 9: piston rod, 10: drive chamber B, 11: magnetic switch, 12: magnetic ring, 13: 7/2 solenoid valve, 14: regulator, 15: power source.