# Analysis of the Energy Efficiency of a Pneumatic Booster Regulator with Energy Recovery
## 1 Introduction  
With the increasing awareness of the need for environmental protection, low-carbon and energy-saving technologies have become the current theme of development. Pneumatic systems, which account for industrial energy consumption of 10 to 20 percent [1; 2], are inevitably discussed as an energy-saving topic. Low energy efficiency is the main factor restricting the further development of pneumatic systems. A study shows that energy consumption can be reduced by about eight percent for each 0.1 MPa reduction in the supply pressure of the compressor [3]. Therefore, more and more Japanese factories are beginning to reduce their air supply pressure to save energy. For example, the supply pressure of the Toyota factory was gradually decreased from 0.6 to 0.3 MPa. However, in practical applications, local high-pressure air is in demand due to the existence of heavy load or high-pressure equipment. Pneumatic booster regulator systems are widely used in factories as a main solution for satisfying local high-pressure requirements. At present, almost all commercial pneumatic booster regulators (PBR) have a structure in which compressed air exhausts directly to the atmosphere. It is obvious that energy is wasted, but it is hard to evaluate the real energy efficiency for lack of an appropriate method. Therefore, a way to evaluate the efficiency of PBR systems and improve their performance has become one of the problems of enterprise that should be solved urgently. A PBR is also known as a pressure amplifier; it is driven by low-pressure air, and its output pressure is high. Pneumatic booster regulators can be categorised as either symmetric or asymmetric, with respect to their structure [4; 5; 6]. The maximum boost ratio of the symmetric type is two-fold,according to [PERSON]'s law, whereas the boost ratio of the asymmetric type can be up to three or four times, because the diameter ratio of the drive and boost chambers can be changed for different demands. However, it sacrifices the air flow rate, and more compressed air is exhausted to the atmosphere with each stroke. To improve the energy efficiency, [PERSON] (1975); [PERSON] (1975); [PERSON] _et al._ (2015) proposes an expansion energy booster in which the air supply is cut off before the piston moves to the end of its stroke, and then the residual stroke is driven by air expansion. Similarly, many other means are also used to improve the energy efficiency in the driven cylinder, such as a differential drive Li _et al._ (2015), dual pressure supply, utilising expansion energy Li _et al._ (2015), recovering energy with a rubber bladder and storing the strain energy Li _et al._ (2015), or reusing exhaust air for power generation Li _et al._ (2015). However, all of these make the circuit more complex, and when the recovery energy was directly input to the drive chamber of the cylinder, it led to velocity fluctuations, which are harmful to the life of the cylinder Li _et al._ (2015). On the other hand, there is an urgent need to assess the energy efficiency of a PBR in order to evaluate the performance of a booster regulator. In recent decades, the consumption of air [dm\({}^{3}\)/min(ANR)] or specific energy [kW-h/m\({}^{3}\)(ANR)] have been commonly used to assess the energy of compressible air [PERSON] _et al._ (2015). However, the consumption of air is a volume unit, so it does not reflect energy consumption. The specific energy is the ratio of the energy output of the air compressor to the flow-rate consumed by the component. This assessment method cannot reflect the energy consumption of the components independently because it considers the power consumed by the air compressor, and it is hard to analyse the losses of the intermediate links. In addition, both of these two methods do not reflect the effect of pressure. Other methods used for the energy assessment of compressed air include enthalpy and exergy [PERSON] _et al._ (2015).