Medical technology continues to evolve toward diagnosis and treatment devices that are closer to the patient, or even in the patient's home. Compression therapy, wound therapy, dialysis, point-of-care testing, and portable oxygen concentrators are just a few such instruments. Many of these instruments include active components that create noise that can impact a patient's sleep quality and level of comfort and can create stigma around using device. A diaphragm pump, which produces gas flow and pressure, is often one of the main sound contributors, and reducing the noise it makes can significantly affect the overall noise generated by the device. Engineers must balance performance needs and sound quality with increasing demands for miniaturized and application-specific equipment. These concerns have created a growing challenge to reduce the amount of noise generated by the device and its components.

Through collaboration with OEMs, Parker's noise mitigation techniques can help turn a noisy device into a more successful product and pleasant experience for end-users.

Miniature diaphragm pumps have become a popular choice for engineers due to the reliable operation, low cost of ownership, and ability to provide a clean, oil-free, isolated flow path with a wide range of flow rates, vacuum, and pressure capabilities. Although there are many positives to the technology, the diaphragm pump does generate noise that should be mitigated. In order to discuss the sources of noise in a diaphragm pump, it is important to describe the operating principle. A diaphragm often includes a motor that rotates an eccentric installed in a connecting rod that mechanically flexes a diaphragm inside a closed chamber. There are two elastomeric check valves per pump head that regulate an aspirating stroke and a compression stroke to create a pressure or vacuum at the pump ports.

Since the market has pushed medical devices to become portable and more reliable, system engineers have sought miniature diaphragm pumps that are smaller, lighter, more powerful, quieter, and more efficient, while lasting longer. However, miniature diaphragm pumps can be a leading contributor to the noise caused by medical devices.

With the shift of importance toward sound mitigation, it is essential for pump developers such as Parker to identify, categorize, and mitigate noise generation in diaphragm pumps to help customers develop quieter products which can, in turn, increase patients’ quality of life.

There are many different pump technologies available to systems engineers today, some offer very quiet operation (such as a vane pump), while others are significantly noisier (such as a piston pump). Miniature diaphragm pumps tend to operate in a more moderate range, and have become a popular choice for engineers due to the reliable operation, low cost of ownership, and provide a clean, oil-free, isolated flow path with a wide range of flow rates, vacuum, and pressure capabilities.

With the shift of importance toward sound mitigation, it is essential for pump developers such as Parker to identify, categorize, and mitigate noise generation in diaphragm pumps to help customers develop quieter products which can, in turn, increase patients’ quality of life.

Identify

Pumps are used in diagnosis and treatment devices to move fluids through the system. Diaphragm pumps use a reciprocating mechanism that moves elastomeric membrane to transport a fluid by increasing and decreasing the volume of the compression chamber. The reciprocating mechanism is achieved by use of an eccentric on a motor shaft. The offset rotating mass on the motor and the reciprocating mass cause vibrations in the pump. For each revolution of the motor shaft, the membrane will fill and evacuate the compression chamber, resulting in the generation of a pulsating flow of fluid through the pump. The operation of the pump can create noise in other ways as well. For example, noise can be created by the elastomeric membrane movement and the check valves, which prevent back flow through the pump.

Categorize

Therefore, the two main sources of sound generation in diaphragm pumps are the noise caused by vibrations, which is a structure-borne noise, and the noise caused by the pulsatile flow, referred to as pneumatic noise. Different strategies are used to mitigate these occurrences.

Mechanical noise reduction techniques focus on vibration reduction in the pump's design and on mounting and enclosing the pump in a system, while pneumatic noise control is centered around attenuating the sound due to the pulsatile flow.

The combination of reducing vibration and pneumatic noise has a drastic effect on the sound level in an instrument.

Mitigate

A possible source of noise occurs when the vibration from the pump is transmitted to the end device and is allowed to radiate the noise outside of the device. Since each device and mounting configuration is unique based on the allowable size, weight, and other constraints, Parker's applications team, for example, can recommend the optimal configuration for each unique device. Engineers recommend using a vibration-isolating mount designed to dampen the transmission of vibrations when attaching the pump to device. For example, Parker offers the EZ-Mount series of mounting plates for diaphragm pumps, which were designed to do just that. These plates not only make the pump easier to mount but also feature elastomeric feet that reduce vibration transmission to the final device. These mounting solutions have shown a significant reduction in noise. Testing on an example Parker Diaphragm pump at 3100 rpm showed an average noise reduction of 3 dB when measured at 12 in. from the pump, when mounted on an open solid platform. When a pump is installed into a system enclosure that resonates the vibration, isolating that vibration can lead to even greater reduction.

A very effective way to reduce pneumatic noise is to use a muffler on the diaphragm pump. An expansion chamber muffler causes the reflection of sound waves due to the change in cross sectional area of the flow path. Mufflers can aid in noise reduction across a range of applications. Engineers often recommend using a muffler as a first line of defense in the battle against sound because it is regarded as the single largest impact on sound reduction, with the least cost. The muffler often also acts as a system filter, reducing the chance for life-reducing debris entering the pump and pneumatic circuit. Using a muffler can result in an average sound reduction of 4 dB for a typical Parker diaphragm pump when measured at 12 in. from the pump.

Simply adding a filter/muffler to a diaphragm pump inlet or outlet can reduce noise level by several dB while also improving sound quality.

Of course, the best solution would involve choosing the right pump for the application. Flexibility in performance is one of the key advantages to diaphragm pump technologies. Parker Precision Fluidics Division (PPF), for example, specializes in customizing diaphragm pumps by configuring hundreds of component options to meet a device designer's requirements as closely as possible. Engineers offer applications expertise to recommend the quietest pump solution to aid with both pneumatic and structure-borne noise control.

A pump designed with low vibrations, such as the new BTX-Connect, will by its nature mitigate the vibrations transmitted to the end device. Another option is to oversize the pneumatic performance of a diaphragm pump and then running it at a slower speed. This quieter solution still maintains the pneumatic performance. This can decrease the pneumatic sound from the pump. In certain applications, this technique can result in a 3 dB sound reduction when measured at 12 in. from the pump. Pneumatic system design engineers should check that diaphragm pump suppliers fully understand their requirements and can offer a broad range of motor options and request that the supplier's applications engineering team provides recommendations and can offer customized solutions if required. In the example discussed, by combining an oversized pump, a muffler, and vibration isolation, the noise level generated by the diaphragm pump was reduced by 6 dB, which can significantly affect an end-user's perception of the device.

Summary

Effective noise reduction of diaphragm pumps requires a thorough understanding of the application and the mounting and enclosure of the final device. Even the quietest pump solution can result in loud final products with incorrect mounting and pneumatic control.

Sound reduction requires close attention and collaboration between OEM engineers and pump supplier application engineers. The user, through its own analysis and testing, is solely responsible for making the final selection of the system and components and assuring that all performance, endurance, maintenance, safety, and warning requirements of the application are met. The user must analyze all aspects of the application, follow the information concerning the product in the current product catalog and in any other materials provided from suppliers. Once the supplier properly configures the pump and motor, it is the responsibility of the OEM engineering team to control the pump properly.

Reducing noise levels and improving sound quality can greatly improve the success of a medical device. Acceptable noise provides a greater sense of quality by practitioners or lab technicians and greater patient comfort can increase compliance, ultimately improving patient care and patient outcome.

This article was written by Aylin Tumer, Design Engineer, and Indy Reilley, Marketing Specialist, Precision Fluidics Division, Parker Hannifin Corp, Hollis, NH. For more information, visit here.