Medical care settings are often stressful, making it hard for patients to rest or sleep—both of which are important for healing and recovery.
 
As the portability of medical technology continues to rapidly evolve, an increasing number of medical devices and equipment can be utilized at the patient’s bedside in the hospital, or even in the patient’s home—examples include point-of-care diagnostics, dialysis, compression therapy, wound therapy, and portable oxygen concentrators.
 
For the best possible healing experience, medical equipment should be as non-intrusive as possible. However, a frequent complaint from patients and other end-users is the disruptive noise that medical equipment can generate. These devices often rely on moving components that create sounds that can interfere with a patient’s level of comfort and quality of sleep, potentially slowing recovery.
 
Diaphragm pumps, in particular, are a main contributor of unwanted noise in the patient setting. Their key role in medical equipment is to produce gas flow and pressure.Compression therapy equipment, for example, which prevents clotting in a patient’s legs and feet during hospital stays and surgery, utilizes diaphragm pumps that cycle on and off over long stretches of time. This can interfere with rest and sleep. Pump volume may also be excessive, adding to the disruptive environment. Therefore, it is essential for medical equipment manufacturers and their engineers to factor sound mitigation into their designs to minimize operational noise and enhance the end-user experience.
 
Sources of Noise in Medical Equipment
Common components in medical equipment that often generate noise are:
 

• Diaphragm pumps
• Solenoid valves
• Fans

 
Of these, diaphragm pumps are the largest contributor of noise. Their motors rotate a crank that moves a connecting rod up and down, flexing the diaphragm inside a closed chamber. Elastomeric check valves regulate an aspirating stroke and a compression stroke, which builds pressure or vacuum and generates flow at the pump ports.
 
In pump engineering, there are two main sources of sound generation:
 

• Structure-borne noise, which includes vibration and other physical structure-generated sound
• Pneumatic noise, which isemitted by flow or movement of air

 
As the pump operates, the connecting rod and diaphragm are driven by a rotating eccentric. This offset rotating mass connected to the motor and the reciprocating mass of the diaphragm assembly cause vibrations in the pump. This is the primary contributor to structure-borne noise. The elastomeric diaphragm movement, the check valves, and the turbulent, pulsatile gas flow are the primary contributors of pneumatic noise.
 
Noise Reduction Solutions
OEMs often report that noise generated by their equipment is the number-one end-user complaint. However, only a few component manufacturers are committed to making sound reduction a top priority in their product enhancement activities. Pump developers must invest in research, design, and testing to mitigate the noise generated by diaphragm pumps and develop quieter products that improve the patient experience.
 
Noise reduction is a key component of Parker’s new product development projects, especially sound mitigation techniques for diaphragm pumps. Parker engineers evaluated several methods for reducing the aforementioned sounds, including:
 

• Oversizing the pump
• Using vibration isolating mounts to secure the pump
• Adding a muffler to the pump
• Adding an additional pump enclosure, lined with soft acoustical foam

 
Structural Noise
One way to reduce vibrational impact is securing the pump to mounting plates; elastomeric feet on the mounting plates reduce vibration transmission to the final device. Noise reduction can be significant—for example, when a diaphragm pump at 3,100 rpm was secured with mounting plates to an open platform, an average noise reduction of 3 decibels (dB) was measured 12 inches from the pump. Adding a customized pump enclosureachieved up to 9 dB in sound reduction.
 
Pneumatic Noise
Reducing pneumatic noise can be achieved by oversizing the pump. This still maintains the pneumatic performance of the pump but reduces the pneumatic noise. Oversizing the pneumatic performance of the pump and running it at a slower speed reduced the number of pulsatile flow peaks, achieving up to a 3-dB sound reduction.
 
Another way to reduce pneumatic noise is adding a muffler to the diaphragm pump. Installing a muffler is a simple, effective, and low-cost method to control unwanted sound. An expansion chamber muffler reflects sound waves due to the change in cross-sectional area of the flow path. Mufflers can help reduce sound across a range of applications. For a typical diaphragm pump, installing an expansion chamber resulted in a 4-dB sound reduction when measured 12 inches from the pump.
 
Combining methods for reducing both structural noise and pneumatic noise can have even bigger impacts on sound reduction for medical equipment. For example, atotal noise reduction of 6 to 9 dB can be achieved when some or all of these techniques are combined. These relatively simple and inexpensive solutions can be easily built into medical devices and diagnostic equipment, creating a much more desirable environment for the end user.
 
Optimizing the Healthcare Experience
Although these pump modifications are effective in noise reduction, the best solution is working with pump engineers to create the ideal product or system for the application.Pneumatic system design engineers can offer a broad range of motor options that can be customized to deliver the desired performance specifications.
 
Successful sound reduction requires close collaboration between OEM engineers and pump supplier application engineers. Since each device and mounting configuration is unique, based on the allowable size, weight, and other constraints of the design, A supplier’s applications team should be able to design the optimal configuration for each device. For example, customizing diaphragm pumps can require the configuration of hundreds of component options to deliver a device designer’s requirements, which includes both pneumatic and structure-borne noise control.
 
Enhancing user comfort through medical technology advancements represents the core value proposition for OEMs. Incorporating effective noise reduction solutions into medical device design is essential for a positive patient experience and long-term use of the equipment.
 

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Jamie Campbell is a product manager at Parker Precision Fluidics. To find out more about sound reduction techniques for medical equipment and what the company has to offer for accessories and application engineering solutions, reach out via ppfinfo@parker.com or download a white paper from http://solutions.parker.com/SoundMitigation_WP.