The reason of the peristaltic pump pulsation phenomenon

The pulsation is an inherent phenomenon of peristaltic pump, and it is impossible to eliminate in terms of the current structure However, there are some use of the occasion where the pulsation is not allowed, or need to be appropriately reduced to meet the requirements. If the use of the occasion cannot have any pulsation, the peristaltic pump is not appropriate, so we need to choose a more stable pump type, such as impeller pump or fine gear pump.

The so-called pulse refers to a stream of liquid squirts comes instantaneously with the fluid transmission of the peristaltic pump. There are two parameters to describe the pulsating phenomenon, the frequency of pulsation and the amplitude of pulsation. (See below).

The frequency of pulsation refers to the number of pulses per unit time; the unit time can be 1 second or 1 minute or other time. Peristaltic pump work in a long period, within a minute of the total amount of transmission is consistent, that is, the amount of the last minute and the next minute transmission is equal. However, if the time is shortened to a few seconds or less, the amount of liquid will be different, because the instantaneous velocity of the peristaltic pump is periodically changing. In some cases, such as when the handheld machine dispensing glue usually need to very uniform on the bag. In order to achieve a more uniform smear process, the general method is to use the peristaltic pump to transfer glue to cotton or sponge, and then through the contact with cotton bags or sponge to take the glue evenly. If you want to smear more uniform, cotton or sponges glue saturation should ensure the relative stability. If the peristaltic pump pulsation frequency is low, the interval between the two streams will be longer because the handheld machine is always high-speed operation, this interval will take away a lot of glue, making glue in the cotton or sponge saturation significantly reduced, which led to uneven coating. So in order to apply evenly, you must quickly fill the cotton or sponge glue, so that saturation is maintained at a relatively stable value, you can solve this problem by increasing the frequency of peristaltic pump pulsation to. There are two ways to improve the ripple frequency. The first is to improve the speed of the peristaltic pump. In the case of fixed pump head, improve the speed is the most direct way to increase the ripple frequency. However, if the flow rate has strict requirements, it is not possible to improve the speed simply, because the liquid flow rate will be a corresponding increase of the motor speed is increased, it should replace the thinner hose, and then increase the speed. This will ensure that the flow rate is required, and frequency improved. The second is to increase the number of pump head roller, at the same speed, the pulse frequency will be increased significantly. Nevertheless, when the number of rollers increased with the same arc and roller structure, the pump head flow rate will be reduced. So we should increase the pump speed to achieve the same flow rate, that the frequency of peristaltic pump pulse will be further increased.

The amplitude of pulsation is another important parameter of pulsation. Different pump head and hose have different amplitude of pulsation. The amplitude of the pulsation is determined by the size of the hose and the diameter of the roller. The pipe is placed horizontally and then the roller is pressed down in the direction perpendicular to the tube. After being completely pressed, the volume of the tube that is reduced by squeezing deformation is the magnitude of the pulsation. IN fact, when the peristaltic pump fluid transmission, not only the middle of the two pulsations does not transfer the liquid, but also a short distance backflow. Then between the whole process of transmission, the fluid is the transmission - back flow - transmission, so the cycle action. In a long period, peristaltic pump transmission speed is stable, instantaneous speed is changing at any time, in some cases, such a transmission is not allowed. In order to reduce or even eliminate this pulsation, there is a product, which called pulsation damper. The general principle is that the big mouth into the liquid, small mouth out of the liquid, so that when the each liquid come quickly, the liquid is too late to quickly out of the small mouth. The pressure of the excess liquid will be absorbed by the air in the damper, with the air pressure in the cavity gradually increases, the flow rate at the small mouth will be correspondingly increase, and ultimately reach a relatively stable state. Why can it reduce the pulsation?  Because in principle, in the case of all the same state of the pipeline, as long as the air pressure in the cavity can ensured absolute stability, the flow rate at the exit will be stable. If the volume of cavity is much larger than the amplitude of the pulsation, the impact of the air pressure on the damper cavity will be small when a single pulse arrived. so that the relative pressure of the cavity will be relatively stable under a very small fluctuation The flow rate at the  small mouth will only have a small fluctuation. Because the pulsation damper cannot be unrestricted, the fluctuation of the fluid will certainly exist, but the phenomenon of backflow has been eliminated. The use of pulsating dampers is conditional. Firstly, the transmitted fluid must be accessible to the air. Secondly, the volume of the damper is compatible with the flow rate, that is, the size of the cavity to ensure that the pulse with the appropriate ratio, this is based on the requirements of the stability of the flow rate to decide. The same pulsation damper cannot accommodate all flow rates, but only for a very narrow flow rate range has a better buffer effect. So if the liquid transmission involves a wide flow rate range and must significantly reduce the flow rate of the pulse, then the pulsation dampers alone cannot be achieved. You can imagine that if the flow rate is too low, the pulsation damper cavity cannot produce a steady pressure. It cannot be very good to reduce the pulsation. If the flow rate is too fast, pulsation can be significantly reduced. However, because of the mouth want to increase the flow rate, cavity pressure will need to multiply, but the peristaltic pump itself is a low-pressure pump type, its general working pressure does not exceed 0.15Mpa, and long-term under critical pressure, the life of the hose will be significantly reduced. So, in use should be overall considered. Moreover, after using the pulsating damper, when the pump is down, because there is pressure in the cavity, exports will continue to flow out of the liquid, until the chamber pressure is reduced to the same extent as the outside pressure.

Using a similar principle, it is also possible to consider the use of the elasticity of the hose to absorb pulsations. The first requirement of the hose used by the peristaltic pump is that the elasticity should be high enough, so as to ensure the stability of the flow rate. Then the hose can be extended at the exit of the pump, generally more than one meter will have a very significant effect. At the exit of the hose, transfer the appropriate inner diameter of the fine joint or needle according to the requirements of different flow rate. Also when the peristaltic pump working, every time the pulse arrives, due to fine joints or needles too late to discharge all the liquid quickly, there will be pressure in the hose at the exit, when the velocity of the fine joint or needle is the same as the speed of the peristaltic pump, the pressure inside the hose will be stable, and every time the pulse arrives, the excess pressure will be absorbed by the overall expansion of the hose, to achieve the role of reducing the pulse. It can achieve the same effect as using a pulsating damper, and can also transmit air-sensitive liquids. So the pulsation damper has been rarely used. The same small diameter of the joints or needles can only be adapted to a very narrow flow rate range, after the pump stops, the exit will continue to flow out of the liquid, until the pressure inside and outside the tube balance.

The third way to reduce the pulse is slightly different, the used principle is that liquid level difference and pipe state unchanged, the flow rate of liquid at the outlet is constant. In fact, the most fundamental principle is the same , they are all trying to build a steady pressure, to achieve the purpose of reducing the pulse. Use a peristaltic pump to control the level of a sink to change within a small height difference, then the flow rate at the exit will certainly maintain a very stable state. But this kind of use is only suitable for very few cases, it is not much used. The most common way is the second option, use the flexibility of the hose itself to work. 

This article is write by Baoding ZHUNZE Precision Pump Manufacturing Co., Ltd. original, without authorization can not be reproduced!