Eliminating Pump Pulsation—A Medtech Makers Q&A

By Sean Fenske, Editor-in-Chief
 
Many life-saving medical devices rely on the transfer of a type of media, whether gas or liquid, to help the patient. As such, this exchange has to happen seamlessly and reliably. If a component within the system creates a problem, designers need to seek alternative solutions to achieve the ultimate goal of the device.
 
Pumps are a common component in many medical devices and diagnostic instruments. There are many different types of pumps used, each with its own set of advantages and concerns. However, a common issue presented by all liquid displacement pumps is pulsation, which is not ideal for some applications.
 
Sharing information in this Q&A about a new solution that has eliminated the “pulse” of diaphragm pumps is Michael Gnos, product development engineer at KNF FLODOS AG, and Dave Howard, business development manager at KNF Neuberger Inc. They took the time to address questions about the challenges caused by pump pulsation and the solution they are providing.
 
Sean Fenske: What are the common applications for pumps within medical devices?
 
Dave Howard: Diaphragm pumps are used in many medical applications, performing critical tasks such as washing, liquid waste handling, metering/dosing, aspiration, degassing, transfer/recirculation, vacuum generation, and pneumatics. These include medical equipment for monitoring, diagnostics, analysis, specialty medicine, ophthalmology, dialysis, dental, critical care, cleaning, and sterilization, as well as surgical and therapeutic equipment.
 
Fenske: What causes the pulsing effect within systems connected to a pump?
 
Howard: Unfortunately, many pump technologies—including peristaltic, gear, piston, and diaphragm pumps—generate some pulsation. For diaphragm pumps, half the time the pump is drawing liquid in and the other half, it is pushing liquid out. No matter how fast you run the pump, you still have this stop and start motion of the liquid, which leads to what is felt and heard in tubing when it shakes and vibrates.
 
Fenske: What are the problems created from this pulsing effect?
 
Howard: For liquid pumps, pressure fluctuations generated by pump pulsation can lead to cavitation and air bubbles in the media; vibrating tubing, which can be felt through the system, impacting accuracy of analysis devices; tubing that wears quickly over time, leading to sporadic leakages; or an inconsistent performance depending on restrictions in the lines. Vibrating tubing and other components can also contribute to increased system noise.
 
Fenske: What has KNF done to eliminate the pulse in pumps?
 
Michael Gnos: For many years, the portfolio of proven KNF diaphragm pumps has included both a single-headed and a double-headed version. The double-headed, or commonly known as a “boxer-style” pump, incorporates a connecting rod that drives two 180° phase-shifted diaphragms simultaneously. While one diaphragm draws liquid from the suction line, the other diaphragm discharges it into the pressure line. This phase-shifted mode of operation leads to pulsation-reduced transfer of the liquid. Joining the two separate inlets and outlets of a two-headed diaphragm pump together, however, is relatively expensive and time-consuming for customers, requires more space, and introduces additional potential leak points with the added connections.
 
Further studies impressively showed flow rate peaks could be further reduced if several diaphragms were interconnected out-of-phase (Figure 1). Thus, KNF took it one step further with its FP pump series and developed low-pulsation pumps with up to five phase-shifted pump diaphragms. The individual flow volumes are joined inside the pumps. This way, customers benefit from an impressive reduction in pulsation while having only one connection on each of the suction and pressure sides. This considerably simplifies handling for the customer, reduces the space required, and eliminates additional tube connections.
 

Another approach to reduce the pressure pulsation of a single-headed diaphragm pump is the use of a so-called pulsation damper, usually mounted in the fluid system on the pressure side of the pump. This approach has also been successfully used by KNF for years in various flow and pressure rates. As mentioned previously, however, additional connections introduce additional potential leakage points, space requirements, and cost.
 
As a result, KNF developed the world’s first liquid diaphragm pump featuring an integrated pulsation damper within the pump head on both the suction and pressure sides (Figure 2). This feat was accomplished in a very short time using state-of-the-art simulation and manufacturing tools. Depending on the pump type and operating point, the pulsation can be reduced by up to a factor of 20.
 
Fenske: What does this type of solution mean for medical device developers and manufacturers?
 
Gnos: The power consumption of the pump motor is reduced, which also means less motor heat is generated. In addition, preventing high pressure pulsation can reduce cavitation and the formation of micro-bubbles, especially for liquids with low surface tension. The controllability of the pump is also significantly increased as the flow rate is linear to the speed, which provides consistent, highly predicable performance. Finally, the workload inside the pump is reduced and, therefore, all components in the customer system are under less stress due to the reduced pressure pulsation. This can increase the service life of the pump and other system components. As an additional effect, tubing vibration is reduced, which reduces noise generation and the incidence of sporadic connection leaks.
 
Fenske: Does this type of solution allow the use of diaphragm pumps to grow within medical devices? Can they be used in new ways not previously possible?
 
Howard: We are already seeing increased interest in low pulsation liquid diaphragm pumps for applications that have not been a great fit for traditional diaphragm technology. Smooth flow is critical for many medical applications and device manufacturers have been forced to use other pump technologies. With the new KNF low pulsation line of products (Figure 3), design engineers can now explore use of diaphragm pumps for recirculation, sheath fluid delivery, and transfer of sensitive media, among other applications. The configuration and electronics innovations incorporated in the new line utilize flow path components and materials already well-proven in the medical space, thus reducing new technology adoption concerns.
 


















Fenske: Do you have any additional comments you’d like to share based on any of the topics we discussed or something you’d like to tell medical device manufacturers?
 
Howard: Medical equipment manufacturers can take full advantage of the consistent, predictable performance of low-pulse diaphragm pumps when they are coupled with brushless direct current (BLDC) motors. BLDC-driven pumps can be optimized to monitor and control pump performance, and further improve efficiency and accuracy. Also, with the amount of data available and the ability to monitor, predictive maintenance, just-in-time replacement, and even self-diagnosis becomes more realistic.

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