Piezoelectric actuator-driven valveless pump has been studied for a long time in theory and structure for the features of high precision, fast response, low power consumption, compact size, reliability for long-term use and high performance. The pump has a remarkable significance for drug delivery, biological application, chemical analysis, high precision gluing, solder paste, lubrication system and electronic chip cooling system, etc. However, a higher requirement on the control circuit and power supply for the pump is raised, also, the driving voltage of the pump should be further reduced. In this review, the piezoelectric pump with and without valve is analyzed in working principle. Then, the recent trends of valveless pump in different structures are discussed. The representative structural designs in different thinking are introduced in the working media, driven voltage, frequency, flow rate, pressure, and the efficiency of the pump, the performance of different pumps are also compared. Afterwards, the application of the pump for different purposes with featured structures are presented. Next are the limitations and the outlook of the pump, which provides some potential research points for subsequent studies, and ended with a summary. This review concludes the recent trends of valveless piezoelectric pump in structural and application, attempts to guide the researchers with different professional backgrounds that can solve current problems through cross-disciplinary approaches.

This paper focuses on a new structure in the valveless piezoelectric pump, which has a combination structure of the conical flow channel and two fishtail-shaped bluffbodies in the chamber of the pump. The fishtail-shaped bluffbody is inspired by the shape of the swimming fish to diminish the backflow and optimize the performance of the pump. The performance is studied by changing the shape and size of the inlet and outlet, the bluff bodies’ height and the space between two bluff bodies. The results show that the 3 mm × 3 mm square inlet, 3 mm diameter round outlet, 3 mm height of bluffbodies, 6.8 mm pitch of bluffbodies has a best performance in all 10 prototypes, which implements a maximum flow rate of 87.5 ml/min at 170 V 40 Hz with a noise of 42.6 dB. This study makes a preliminary investigation and theoretical explanation for the subsequent optimization of this structure, improved the performance of the valveless piezoelectric pump, broaden the thinking of the design for the bluffbody for better performance of the valveless piezoelectric pump.

Piezoelectric pumps are applied in cooling systems of microelectronic devices because of their small size. However, cooling efficiency is limited by the low flow rate. A straight arm wheeled check valve made of silica gel was proposed, which can improve the flow rate of piezoelectric pumps, solve the influence of glue aging on the sealing ability of a wheeled check valve, and reduce the size of piezoelectric pumps. This paper discusses the influence of the valve arm number (N = 2, 3, and 4), the valve arm width (W = 1.0, 1.2, and 1.4 mm), and the valve thickness (T = 0.6, 0.8, and 1.0 mm) on the flow rate characteristics of piezoelectric pumps. When valve opening rises, the flow rate increases. The simulation results show that valves with 2 valve arm number, 0.6 mm valve thickness, and 1.0 mm valve arm width have maximum valve opening. The experimental results show that piezoelectric pumps with different valve parameters have different optimal frequencies. In addition, the maximum flow rate is 431.6 ml/min at 220 V and 70 Hz. This paper provides a reference for the application of piezoelectric pumps in cooling systems.

In this paper, an integral valve is proposed by connecting the inlet cantilever valve and the outlet cantilever valve with a connecting post and a rubber circle plate structure. The integral valve changes the traditional inlet cantilever valve and outlet cantilever valve to work independently and realizes the joint response of the inlet cantilever valve and the outlet cantilever valve. The integral valve was designed, manufactured, and installed, and the performance of the static experimental test equipment of the valve and that of the experimental equipment of the piezoelectric pump were evaluated. The static performance of the integral valve was tested. In addition, the performance of the integral valve piezoelectric pump and the cantilever valve piezoelectric pump was tested and compared. The experimental results show that the integral valve piezoelectric pump reaches up to 270.2 ml/min at 210 Vrms, 45 Hz; the pressure can reach 86.2 cmH₂O at 40 Hz. Compared to cantilever valves, integral valves have less forward flow resistance and better reverse shutoff. In particular, the pressure of the integral valve piezoelectric pump can be significantly improved compared to the cantilever valve piezoelectric pump. In terms of efficiency, the integrated valve piezoelectric pump will have better performance in the low-frequency region.

According to the bluffbody bypass effect, the irregular bluffbody can be used to improve the valveless piezoelectric pump. This paper designs a semi-arc bluffbody based on the bluffbody bypassing principle to alleviate the phenomenon of fluid backflow. The fluid passes through the shape of the antique tower to further enhance pumping efficiency. A positive fluid flow mechanism in the pump cavity is theoretically derived. The simulation of the velocity and pressure distribution in the tower-shaped channel of the pump cavity leads to the conclusion that the forward flow has better performance than the reverse flow, and the correctness of the theory is also verified. Experiments further proved that the volume of fluid in the forward direction was reduced by 10.8% when compared to the reverse direction. The study of the height of different semi-arc bluffbody and the angle of the tower trough shows that as the height and angle increase, the flow rate grows first and then reduces. The maximum flow rate is 243.83 ml/min when the bluffbody height is 4 mm and the channel angle is 20° (220 V, 85 Hz).