Silencing for AODD Pumps
Air-operated double-diaphragm (AODD) pumps are a trusted workhorse across industries—from chemical processing to wastewater management—thanks to their ability to handle challenging fluids, solids-laden slurries, and corrosive materials. Their straightforward design, self-priming capability, and ability to run dry make them ideal in countless applications. Yet, despite their reliability and versatility, AODD pumps come with two persistent challenges: excessive noise and inefficient air usage, often stemming from poor silencer selection.
This article explores why proper silencing isn’t just a matter of comfort or compliance—it’s a performance enhancer. We'll explore how minimizing pressure drop and selecting the right combination of reactive and absorptive silencing can improve both the operational efficiency and acoustic footprint of your AODD pump systems. We’ll also address a common challenge: ice formation during exhaust cycles, a real hazard that can silently sabotage performance if left unaddressed.
How AODD Pumps Work
Understanding the silencing needs of AODD pumps starts with their operation. These pumps function through the oscillating motion of two diaphragms, driven by compressed air alternating between two opposing fluid chambers. The compressed air acting on the diaphragm causes one chamber to fill with process fluid, while the opposing chamber discharges process fluid—This continuous cycle of filling one chamber and while discharging the other chamber creates flow.
This video shows how AODD pumps operate. Courtesy of Northridge Pumps
A key to this operation is the exhaust of compressed air, which exits the pump during each diaphragm movement. This compressed air exhaust pulse is typically forceful and abrupt. The sudden release of high-pressure air into the atmosphere is loud and, if not correctly managed, wasteful. It can also cause downstream complications like icing and increased pressure drop that decreases performance and puts excessive strain on the diaphragms.
The Problem with Pulsed Air: Flow and Acoustic Challenges
Unlike rotary air tools or continuous-flow compressors, AODD pumps exhaust in sharp bursts. This pulsed exhaust flow creates:
- High sound pressure levels (SPL): Often exceeding safe workplace thresholds
- Tonality: Characteristic “hammering” sounds that are particularly harsh to the human ear
- Backpressure risks: If the exhaust path is restricted, it can reduce pump efficiency and increase cycle times
Poor silencer choices can exacerbate these problems. A muffler that creates too much restriction might reduce noise, but it can restrict the airflow, leading to reduced diaphragm stroke force, and eventually, decreased throughput.
Why Low Pressure Drop Matters
Pressure drop across a silencer isn’t just a spec on a datasheet—it directly impacts pump performance. Every ounce of backpressure at the exhaust side means your pump must work harder to complete each cycle. Here’s why that matters:
- Increased air consumption: More air is required to overcome backpressure, raising energy costs
- Reduced flow rate: Backpressure reduces the stroke efficiency, cutting into the pump’s output
- Premature wear: Extra effort during each cycle increases mechanical stress, shortening the pump’s service life
To maximize efficiency, a well-designed silencer must offer broad-frequency noise attenuation while maintaining ultra-low backpressure—a difficult balance to strike.
Cold Exhaust and Ice Formation: The Hidden Threat
Compressed air doesn't just make noise when it exhausts- it gets cold- really cold. This phenomenon is due to the Joule-Thomson effect, where rapidly expanding compressed air experiences a sharp temperature drop. In AODD pumps, this cooling can be so extreme that it leads to frost and ice crystal formation at the exhaust port.
This is more than a visual curiosity—it’s a reliability issue:
- Ice can clog exhaust pathways, especially in environments with high humidity or rapid cycling
- Blocked silencers increase backpressure dramatically and can cause the pump to stall
- Ice buildup inside mufflers can lead to permanent damage of the pump components and the silencer
AODD pump silencers must therefore be acoustically tuned, resist icing, and allow moisture to escape. High flow materials and housings that encourage draining play a critical role here.
This video is a water saturation test of the Solberg Compressed Air Muffler.
Silencing Approaches: Reactive and Absorptive
Effective noise control relies on a combination of two core silencing strategies:
1. Reactive Silencing
This method uses internal geometry, such as chambers and baffles, to reflect and cancel sound waves. Reactive designs are particularly effective for tonal noise, which is common in AODD pump exhaust.
- Pros: Excellent attenuation for specific frequencies
- Cons: Can introduce pressure drop if not properly sized
2. Absorptive Silencing
These silencers use sound-absorbing materials, typically synthetic or glass media packs, to absorb sound energy across a broad frequency range.
- Pros: Effective across wide frequency ranges
- Cons: Materials can become saturated or clogged without proper drainage
The Ideal Solution: Hybrid Designs
The most effective AODD pump silencers combine both reactive and absorptive principles. The Solberg CAM series, for example, is engineered specifically to offer ultra-low pressure drop while delivering broad-frequency attenuation. Its open-element design supports moisture release and resists clogging, helping maintain performance even under freezing exhaust conditions.
Choosing the Right Silencer for Your AODD Pump
Several manufacturers offer viable solutions for AODD pumps. The Alwitco Atomuffler® has long been a go-to in industrial applications due to its proven track record and durable construction, however its designs tend to introduce higher pressure drop and element changeout is difficult. Solberg’s CAM series mufflers offer a compelling balance—delivering broad-frequency noise attenuation with significantly lower resistance than traditional designs. Each option brings trade-offs in terms of acoustic performance, backpressure, and long-term reliability, making proper specification critical.
Selecting the right silencer isn’t one-size-fits-all. Consider the following criteria:
- Air Flow Restriction: Select a silencer that offers minimal restriction at max exhaust flow
- Noise characteristics: Tonal, broadband, or both?
- Environmental factors: Humidity, temperature, exposure to chemicals
- Maintenance: Some silencers offer replacement elements so ease of maintenance is key
A common mistake is under-sizing the silencer or using a generic muffler that doesn’t match the pump’s dynamic profile. Choosing the incorrect silencer often leads to increased equipment noise and reduced efficiency—exactly the opposite of what a silencer is supposed to achieve.
Installation and Maintenance Best Practices
A great silencer can only do its job if it is installed and maintained correctly. Here are a few tips:
- Avoid tight elbows or reducers immediately before silencer
- Inspect regularly for signs of clogging, ice formation, or backpressure buildup
- Replace elements per manufacturer recommendations, especially in high-humidity or high-cycle applications
Keep in mind that as elements saturate or clog, pressure drop increases—even if noise levels stay low—so monitoring both acoustic and flow performance is key.
Silence Isn’t Just Golden—It’s Efficient
AODD pumps are built for reliability—but they can only perform at their best when their exhaust systems are optimized. Selecting the right silencer isn’t about muffling sound at all costs. It’s about achieving the right balance between acoustic attenuation and equipment performance.
With a well-engineered silencer—like the Solberg CAM series—you can:
- Lower workplace noise levels
- Improve pump efficiency
- Reduce air consumption and operational costs
- Prevent performance degradation due to ice formation or silencer blockage
If your facility runs AODD pumps and you haven’t recently evaluated your silencing solutions, now is the time. A simple upgrade in exhaust silencing could unlock surprising gains in uptime, efficiency, and acoustic comfort.