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What are the reasons for affecting the filling accuracy of peristaltic pump

With the increasing popularity of peristaltic pumps, filling accuracy is no longer a manufacturing problem because the filling weight/volume can be calibrated by manual process control or an automatic closed-loop online weighing inspection control system. However, achieving high precision is still a concern for users of peristaltic pumps, and also a challenging problem in the manufacturing industry.
The article referred to in this article was published in 2016. The authors attempted to achieve 3% accuracy at a target filling volume of 0.3ml for a high viscosity fluid (10cP). Through experiments, we try to determine the potential mechanism of peristaltic pump affecting filling accuracy, and how to alleviate these potential causes to improve filling weight accuracy. It is expected that the results of this study will help scientists and engineers develop pre-filled syringe/vial products to better understand the principles and challenges of high-concentration formula filling.
Pure water PW and monoclonal antibody A preparation (200 mg/ml; Manufactured at Genentech, South San Francisco, California) or sucrose solution (48% W/W). For each experiment, a benchtop filling system was used, with various straight filling needles of different sizes (ID and wall thickness) made of different types and materials.
For the first time, a systematic investigation was attempted to assess the influence of various parameters associated with peristaltic pumps on filling weight accuracy. These parameters can be divided into five categories: pump setup, line size, setup configuration, filling needle characteristics, and liquid characteristics.
The results of these preliminary studies indicate that the suction function has a direct effect on the filling weight accuracy. Other parameters associated with the peristaltic pump (e.g., speed) and experimental devices (e.g., line length) also appear to affect filling weight accuracy, but in inconsistent and non-repeatable ways.
In actual production, filling needles and pipes with inner diameters less than or equal to 1.0mm are usually used for low-volume filling (less than 0.5ml). However, to better understand the influence of suction on filling weight accuracy, filling needles with an inner diameter greater than or equal to 1.5mm are used in subsequent studies. After all, small sizes of lines and filling needles can increase the difficulty of reduction control, especially for viscous liquids.
It is well known that droplet is not expected during the filling process, as it can cause problems such as splash/blistering during the filling of liquid products, and can also cause filling weight changes.
A drop of liquid (such as water or a liquid of similar viscosity) is usually about 0.05ml in volume. For a target filling volume of 0.3mL (3% equals +/-0.009mL), a droplet of this size can easily push the filling weight beyond the 3% accuracy range.
Suction is therefore an important function that reverses the peristaltic pump to pull the liquid flow back into the filling needle at the end of each filling action to prevent residual liquid from dripping into the filled container. In addition, during prolonged process interruptions, solidification of tip droplets can cause filling needle blockage, while reduction can prevent filling needle blockage (see article: Effect of equipment shutdown on high concentration mab filling).
The authors suggest that filling weight variation may come from two sources: "occipital" pulsation and inconsistent fluid flow behavior at the tip of the filling needle. Pump pulsation and mechanical control are inherent to the pump and are therefore outside the scope of this paper. Since the authors found that reduction and liquid properties consistently affected the filling weight accuracy, further studies, including photographic analysis (visual observations), were conducted to better understand whether inconsistent liquid flow behavior at the tip of the filling needle was the root cause of the filling weight variation.
So what causes the change in reduction height? Two potential causes:
(1) The liquid flowing out of the filling needle tip is broken by a variety of factors, including the liquid nature, the interaction between the liquid and the nozzle tip material, and the pump suction, which may affect the liquid flow rupture point.
For example, liquid properties, such as surface tension, density, and viscosity, may influence the way the liquid jet breaks. The effect of viscosity is studied in detail according to the physical principle. In general, a thin stream of liquid can split into many discrete droplets or large droplets. The case for forming a large droplet is a "clean" separation. Viscoelastic streams can form thin filaments before breaking. Therefore, filling high viscosity liquids with high precision can be more challenging.
Another example is liquid/filling needle interaction: By comparing hydrophobic (silicone and Teflon ®) and hydrophilic (glass and stainless steel) filling needles, the interaction between liquid and nozzle tip material and its effect on flow rupture can be intuitively evaluated.
(2) the pressure drop change at the end of filling when the pump roll stops or reverses
In addition to the position of liquid crushing, another factor that may affect the accuracy of filling weight is the pressure change caused by pumping action when the pump roller stops (no reduction) or reverses (reduction).
In addition, a custom nozzle was assembled and tested for comparison to mitigate flow rupture and pressure drop at the tip of the injection needle. The experiment shows that the liquid level change is improved effectively.

In summary, the research results show that reducing the variation of suction height is the key to improving the filling accuracy of the peristaltic pump. The liquid characteristics, the influence of the liquid/filling needle interaction, and pressure changes during the reduction process are inherent factors in the change of filling weight.

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