Abstract — Liquid ring vacuum pumps and compressors are mechanical positive displacement turbomachines that can operate in the mode of both vacuum compressor and vacuum pump. They are widely used in the fields of filtration, cryogenic, reaction, gas injection, condensation, evaporation, and drying. Despite their low performance, they have many advantages such as low costs, simplicity, reliability, improve suction characteristics, and in many cases, can provide a more efficient option. Improving efficiency is the key to decrease energy consumption and costs. The article analyzed and evaluated the previous investigations regarding these machines with a focus on challenges of improving efficiency, advances in numerical simulation, and experiments to afford beneficial insight on future research and next steps. The study revealed that the thermal interaction and the cavitation phenomenon are among the most important problems that require further research. Index Terms — liquid ring vacuum pumps and compressors, global efficiency, numerical simulation, experimental research, energy saving. I. INTRODUCTION iquid ring vacuum pumps and compressors (LRVPs) are special and different types of positive displacement pumps and compressors, the reason for this is the difference in their working principle. They provide several functions such as compression, creation of a vacuum, and pumping of fluids [1]. An ejector can be used in systems working with LRVPs. The key advantages of these machines are high dependability, longevity, isothermal compression, sustainability, design simplicity, high productivity, low cost, and compliance with environmental standards [2]. LRVPs can easily handle * 1 Mohammed Ali Sami Mahmood is a Postgraduate Student at the Mechanics and Engineering Graphics Department of Tambov State Technical University, Tambov, Russia, (Email: Mr.mohammedali1993@gmail.com). 2 Rodionov Yuriy Viktorovich is a Doctor of Technical Sciences, Professor at the Mechanics and Engineering Graphics Department of Tambov State Technical University, Tambov, Russia, (E-mail: rodionow.u.w@rambler.ru). 3 Nikitin Dmitry Vyacheslavovich is a Candidate of Technical Sciences, Associate Professor at the Mechanics and Engineering Graphics Department of Tambov State Technical University, Tambov, Russia, (E-mail: dmitryndv@gmail.com). 4 Voronin Nikolai Vladimirovich is a Postgraduate Student at the Technology and Methods of Nanoproducts Manufacturing Department of Tambov State Technical University, Tambov, Russia, (Email: voronin.nikolay.1994@yandex.ru). 5 Dmitriy Nikolayevich Protasov is a Candidate of Economic Sciences, Associate Professor at the Higher mathematics Department of Tambov State Technical University, Tambov, Russia, (E-mail: dnprotasov.75@mail.ru). condensable vapor using a range of fluids without sacrificing pump efficiency. They have only one rotating component, making them cost-effective and easy to repair and maintain. Thanks to its advantages, it is used in many applications and industries such as automobile, concrete, food, petroleum, water treatment, metallurgical, radio engineering, electrical, thermal power, grinding, distillation, production of fuel, extraction, filtration, de-airing of liquids and solids, and convective drying of materials [3–10]. Figure 1 presents the main components of the basic design of LRVPs. The accessory devices of the LRVPs system are a heat exchanger for cooling the recirculating seal liquid and a separator to separate the exhaust mixture of gas-liquid, pipelines, and liquid circulating pump as illustrated in Figure 2. The motivation of the current article is to offer a comprehensive review and beneficial insight about LRVPs to be the cleared review article published in the field of these types of machines. In the current article, a comprehensive review and analysis of previous investigations are presented to identify challenges related to LRVPs and to provide a database on which researchers can rely on the next steps to enhance global performance. Fig. 1. Basic LRVPs. A Comprehensive Review of Liquid Ring Vacuum Pumps and Compressors for Improving Global Efficiency and Energy Saving Mohammed Ali Sami Mahmood 1 *, Rodionov Yuriy Viktorovich 2 , Nikitin Dmitriy Vyacheslavovich 3 , Voronin Nikolai Vladimirovich 4 and Dmitriy Nikolayevich Protasov 5 L AJSE Volume 21, Issue 1, Page 26 - 36 Page 26 AIUB JOURNAL OF SCIENCE AND ENGINEERING ISSN: 1608 – 3679 (print) 2520 – 4890 (Online) Published in AJSE, Vol:21, Issue: 1 Received on 17 th November 2021 Revised on 10 th January 2022 Accepted on 31 th January 2022