Blog archive
RSS

Blog

Diffuser Design and Performance

A diffuser’s design has a significant effect on how much PSI is generated for the pump, affecting the amount of air it can pump because the diffuser is the point of release. Every square inch of the diffuser’s surface area will experience PSI. The greater the surface area, the more resistance the pump with experience. Additionally, the deeper the diffuser is placed, the greater the resistance. Based on what was just said, it would appear a smaller diffuser is the better option because it can be placed deeper and will work the pump less. If you looked at that specifically, it would be true. However, what is the goal?

A diffuser with minimal surface area or with large holes for air discharge, will move less water. Less water movement means the potential for poor DO readings in certain areas of the pond, including near the diffuser. This is where the claims of a pump’s operating depth will come into play. Much like the house fan example, it’s easy and true to state a ¼ HP piston pump can operate at depths well over 50’ – as long as nothing is attached to the end of the hose. Also rarely mentioned, a system stating an operating depth of 50 feet means a total of 50 feet. If you add another diffuser, the combination of depth cannot exceed 50 feet. This includes systems that add multiple discs to a specific location (see images below). The same principle applies. The combination of the diffusers’ surface area effects the resulting PSI, whether next to each other or scattered throughout the pond.

Moving Water with Bubbles

When it comes to bubbles, every bubble released by a diffuser creates what is called drag force. As the buoyancy of a bubble forces its way to the surface, it first displaces water and then creates ‘drag’, pulling water in the direction of the bubble, which is to the surface. Creating the most drag per volume of air is dependent on the size of bubble.

Below are two images of bubbles – one single bubble on the left and numerous bubbles on the right. The typical expectation would be for a single large bubble to drag more water than smaller bubbles, but that is far from the case. What is lost with that thought is the cavity of the bubble; the volume of air within the bubble that does not have surface to create drag.

                        

 

Now, take a close look at the image on the right. The small bubbles image was laid over the single large bubble image from the left. Looking even closer at the outer edge of the small bubbles, the single row of outer edge of bubbles has created approximately the same surface area of the single bubble. Add all the remaining bubbles and we just dramatically increased the amount of surface area for drag, using approximately the same amount of air! This results in more water movement and at a greater force. Of course, what affects the size of bubbles? The holes made in the diffuser to allow for the release of pressure created by the pump.

Below are two images of diffusers in operation. Figure 1 is of a diffuser producing mostly microbubbles and has a large surface area. Figure 2 is producing mostly larger bubbles and has minimal surface area.  

 

Figure 1

 

Figure 2

Uniformity of the holes is critical too as air will travel to the point of least resistance. If a diffuser has a mix of hole sizes, holes that could produce the smaller bubbles will not be productive. Air will release through the larger holes.

Turning our focus to surface area and its relation to operating depth, Figure 2 is likely to operate in twice the depth as Figure 1, when all else is equal. The surface area of Figure 1 is substantially larger and will experience greater water pressure due to the larger surface area. Additionally, more force is required to produce smaller bubbles. This is where operating depth comes into play. Figure 1 is likely to have a maximum operating depth of 25’ with a ¼ HP piston pump whereas Figure 2 will likely have an operating depth of 50’. The thought of an aeration system performing at great depths gives the perception of a powerful system and thus must do an excellent job of aeration in comparison to other systems. As you have read, there is so much more to it.

In Conclusion

Operating depth is useless if it only creates surface turbulence, not circulation. Most pond owners judge the performance of an aeration system by the surface action produced by a diffuser. This is deceiving though. It will not matter the type of diffuser used or if there’s just a hose laying at the bottom. Air coming from the bottom and raising to the surface is going to create turbulence at the surface. What matters is what happens before and after the turbulence.  

Speaking from years of field experience, I have come across a wide variety of aeration systems. Some of them did an excellent job. Some, not so good. My appreciation for a quality and properly sized aeration system comes from understanding what happens throughout a pond. When I created my line of aeration systems, I did so knowing how the design must work. There are going to be times where things will seem as though it could not get any worse, but if you choose wisely with an aeration system and take additional steps such as adding beneficial bacteria, turning a tough situation around will happen much, much faster when the right pieces are in place.

Aeration Pumps CFM – How to Interpret

CFM details listed on a pump are what it produces without resistance. It’s a good measuring tool when making pump comparisons and is relative to aerating a pond. CFM though, needs to be tied to HP and the ability of the pump to maintain a level of CFM against a level of pressure per square inch (PSI) and ultimately distribution through a diffuser. To put CFM into perspective, a linear pump can have approximately 6 – 8 CFM. A piston pump can have 3 – 5 CFM. A typical house fan can produce over 100 CFM. Comparing by CFM only, the house fan should be your best option, but in reality, it would come to a dead stop in a 1/4 inch of water. It doesn’t have the power or design to maintain that level of CFM against minimal PSI. The fan it is designed to move air with minimal resistance. This holds true when comparing linear pumps to piston pumps. Linear pumps generally have a higher CFM than piston pumps without resistance, but piston pumps have the power and design to hold a higher CFM against greater resistance.

Three Year Warranties on Pumps

With maximum operating PSI, most pumps of equal HP are relatively close in this manner too. However, the variation here can be greater than CFM because this is where the quality of components can come into play. Once a pump starts to experience resistance, you will ultimately find out if you have spent wisely regarding your pump. We feel so strongly about our pumps that we have an industry best Three Year Warranty!

What creates Resistance for a Pump

To be clear, everything connected to a pump creates pressure before ever getting to water. The inside diameter of airlines, a manifold, valves or number of valves, type of diffuser or number of diffusers, or anything else air must pass through before discharging into water. They all can create some form of resistance that results in PSI. This doesn’t mean a system with a manifold will cause a pump to experience more resistance than one without. On the contrary, these components are meant to assist a pump to properly deliver the most CFM at the system’s most crucial point – at the diffuser. However, when components are not sized or designed properly, the pump will work harder than it should before experiencing any pressure applied to the diffuser by water, where performance is judged.

One thing to keep in mind here is what’s keeping the pump cool. Do not under estimate the value of a properly design cabinet system. The hotter a pump operates, the shorter the life span.

How Aeration Works

Choosing an aeration system is a challenging task. So many versions of a system are available with large variations in price and claims. They are all designed, in general terms, with the same big picture items: a pump, airline, and a diffuser. I realize there are other items involved such as cabinet, valves, manifolds, or gauges, but in this article, I would like to discuss how the pump and diffuser work together in relation to proper aeration.

What Criteria’s Do Pond Owners Use to Make Their Decision?

The average pond owner is likely to start with price and what all comes with that price. Will it aerate a pond my size? Does the price match perceived valve? Who am I buying from and how they can help me after the sale. This makes sense and is the same approach I would take. If the product’s details and description fits the situation, there’s no reason not to move forward. However, there are finer details of a working aeration system to understand related to proper aeration. This will significantly change how you will choose an aeration system.

How Proper Dissolved Oxygen is Achieved in You Pond

Without an aeration system, the amount of dissolved oxygen (DO) drops dramatically every foot you go down in your pond. The top 1 – 2 feet of your pond generally will have good DO levels naturally because it’s exposed to wind and air. Wind creates water movement and the movement entraps oxygen. The winder the day, the deeper good DO is recorded. Most days though, proper levels of DO don’t go much beyond two feet.

Many pond owners believe proper DO levels are achieved by the bubbles created with an aeration system. While aeration systems technically do produce some DO, the bulk of proper levels throughout the water column comes from water movement. Essentially, circulation. An aeration system’s goal is to push the poor levels of DO at the bottom of a pond to the top, which in turns forces the good DO at the top towards the bottom of the pond. This creates the circulation motion: bottom to top, top to bottom, as illustrated below.

 

A quality and properly sized aeration system, along with strategically placing of quality diffusers, will affect the entire pond and at a great enough force to maintain a proper level of DO throughout the pond, as shown with the blue arrows in the image above. Without quality movement as pointed out with the yellow arrows above, the DO doesn’t make it to the bottom or throughout the pond. Essentially, some of a pond will not being effected at all by the system’s performance. What you have in the case of the yellow arrows is turbulence at the surface, not proper circulation. It may look the same at the surface, but below is a completely different story.