Energy Efficiency Analysis and Experimental Test of a Closed-Circuit Pneumatic System

Abstract

In a closed-circuit pneumatic system the air from the pneumatic cylinder is not exhausted directly in the atmosphere, as done in traditional open-circuit systems, but is captured and fed to the compressor inlet. This provides an opportunity to increase the compressor inlet pressure above the atmospheric and consequently enables both higher compression efficiency and volumetric flow rate. Until the present, the advantages of the closed-circuit pneumatics were assessed only within theoretical studies without being verified experimentally due to uncertainties in performance of a real compressor under oscillating pressure and flow rate, as well as due to a risk of mutual cylinder interference caused by differences in load and required pressure profiles. Hence, this study focuses on experimental investigation of energy efficiency and practicability issues of the closed-circuit pneumatics. It is shown that simultaneous operation of two pneumatic cylinders of different size (Ø32×200 and Ø50×200) performing different tasks (high-dynamic mass handling and extension against the constant force) does not have any negative effect neither on the cylinder dynamics nor on the compressor performance. Inlet pressure increase up to 1.5 barrel leads to by factor 2.5 higher volumetric flow rate and total efficiency gain of 72 % (increase from 10.7 % to 18.4 %). The experimentally obtained results show a great potential of the closed-loop pneumatics and indicate the need in further research into design and control methods of such systems to enable technology deployment to the industry. Industrial applications can profit from the reduced energy consumption especially in case of pneumatic systems with decentralized air supply.