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CFM vs Suction: Choosing the Right Vacuum Specifications for Handling Dirt, Sand, and Gravel

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Expert Insights by Titus Nelson on choosing the right CFM and Suction strength of a small vacuum.

To efficiently tackle the challenges of digging holes and and conveying dirt, sand and gravel, the CFM vs Suction tradeoff is critical when choosing the right vacuum specification. This tradeoff is  a combination of powerful airflow (measured in CFM) and high suction measured in inches of water. These systems are engineered to move bulky debris without clogging. Therefore velocities often exceeding 5000 feet per minute are required.  In addition, robust suction power (measured in inches of H2O) ensures steady material flow through varying conditions. With this balance of capabilities, small vacuum systems can effectively perform heavy-duty cleaning and material conveying tasks.  They can also work in a wide range of environments, including potholing, valve box cleaning, and post hole digging.

Now, Cat 6 Tools, a Nevada company, has developed small 10 to 16 gallon high-performance vacuums specifically for this purpose. These systems are designed to provide a compact solution without compromising on the power necessary for thorough and efficient industrial cleaning tasks. Their smaller size makes them highly portable and ideal for use in confined spaces and areas where larger equipment cannot be easily maneuvered. Despite their reduced gallon capacity, these vacuums ensure a level of performance that rivals their larger counterparts, delivering the airflow and suction needed for a variety of challenging environments.


Cubic Feet Per Minute (CFM) part of the CFM vs Suction metric

When discussing the efficiency of vacuum systems, CFM is a critical metric part of the CFM vs Suction attribute. It measures the volumetric flow of air that the vacuum can move. A highly efficient vacuum system boasts the capability of swiftly processing broad volumes of waste. This equates to the removal of a substantial amount of material such as dirt, sand and gravel every second. Where CFM is key to moving material it is the velocity of the airstream that keeps the material in suspension.  As well, it is the suction that maintains the CFM of air going through the transport tube.  This keeps material moving.

It is the balance of these parameters to optimize picking up and transporting dirt, sand and gravel.  In small industrial vacuums optimizing these parameters is much easier. As the diameter of a transport hose increases, the CFM required to maintain high velocities also increases. This is why many small vacuums with high suction use smaller diameter hoses to maintain velocities.

Inches of Water Suction part of CFM vs Suction metric

The raw suction power of a heavy-duty vacuum system is quantifiable by its inches of water suction—the vertical lift of water it can achieve. This metric signifies not only the system’s power but also its ability to handle heavy and dense materials with ease, a crucial feature in industrial and construction applications. It is suction power that keeps the velocity of air at high levels when the opening of a hose is small. Because there is a tradeoff between CFM and Suction in the design of vacuum turbines, rarely will one find a high flow rate and high suction vacuum.  Typically a two stage turbine is required to achieve suction levels above 70 inches of water at the expense of CFM.   These two stage devices are also more costly to produce.

Tangential Inlets

The sophistication of these small vacuum systems extends into their design details, such as tangential inlets. These inlets are engineered to facilitate a smoother flow of debris into the vacuum, enhancing operational efficiency and reducing wear and tear on the system. When moving dirt, sand and gravel this efficiency is part of optimizing CFM vs Suction. It’s this attention to design that bolsters the vacuum’s longevity and reliability in handling rugged materials.  In addition, it is this efficiency that improves the CFM of the system.

Low Loss Hoses and Hose Length

Integral to a vacuums’ impressive material transport capabilities are the requirement for specially designed 2-inch low loss hoses. These hoses play a key role in minimizing the loss of flow rate and suction.  This improves CFM vs Suction efficiency and maintains a high removal rate, a vital attribute for productivity in demanding work environments. Key to reducing vacuum performance requirements (CFM and Suction) is to reduce hose length.  By keeping the vacuum close to the material, hose length can be reduced which greatly reduces hose velocity losses.  The rule of thumb is keep the hose as short as possible.

With these innovative features, coupled with an efficient flow system, each vacuum system presents a comprehensive solution that capably meets the challenges of debris management across various sectors.  These attributes described above become vital to systems that are designed for moving dirt, sand and gravel.

Optimizing CFM and Suction

Striking an optimal balance between CFM vs Suction is pivotal for a high-performance vacuum system. It is also important in choosing the right vacuum. Ideal operation occurs within the ‘sweet spot’ where maximal airflow (CFM) harmonizes with powerful suction capabilities. At full flow, the vacuum reaches its maximum CFM, but here, the suction may drop to zero, unable to lift materials at all. Conversely, at peak suction, the CFM could fall to zero, indicating no air movement despite high lift strength. A well-engineered vacuum system is adept at avoiding these extremes, calibrated to maintain a synergy between CFM and suction, ensuring efficiency without sacrificing either attribute. This equilibrium is essential for sustained performance in industrial debris management, allowing the system to tackle a full spectrum of materials with ease.

Material Conveyance Requirements

Understanding the specific needs of material conveyance is paramount in the design of an industrial vacuum system. For instance, heavy materials such as dirt, sand and gravel require a robust airflow, typically around 40 to 50 CFM per pound.  This is required to effectively manage the materials. This intense airflow is essential for both lifting and moving these dense particles.

In addition, they can flow through the system without clogging or bottlenecking. Meanwhile, to successfully transport these materials, especially in a pipeline or long hose, conveying velocities must be exceedingly high.  Velocities upwards of 5000 feet per minute (fpm) are needed. This combination of strong CFM values and high conveying velocities ensures the vacuum system can handle the rigors material transport applications with high density and abrasive characteristics.

Material Conveyance Chart

When choosing the right vacuum a chart can be useful. The chart below provides some material conveying requirements typical for large industrial systems. Note this information is relative as it pertains to ducting that is 4 inches and larger. However the weight of material, velocities and suction pickup is helpful.  Most notable is the low suction requirements.  Not mentioned is that high suctions above 45 inches of W.C. help to keep material going as it starts to fill a hose.   As the effective hose diameter narrows, the velocity will increase as long as there is good suction.  So the more suction the better.

Material Conveying Requirements
Material Approx Weight Lbs. per Cuft CFM per lb. of Material Min Conveying Velocity (fpm) Suction Pickup (inches of W.C.)
Ashes, Coal 40 42 4,500 3.0
Cement, Portland 100 35 7,000 5.0
Coal, Powdered 30 42 4,000 3.0
Corn Meal 40 38 5,400 3.5
Dust, Grinding 160 to 175 42 5,000 3.0
Lime, Hydrated 53 to 64 42 5,000 3.0
Plastic, Granulated 35 42 5,400 3.0
Sand, Dry 99 35 7,000 5.0
Sawdust, Dry 7 to 15 63 3,700 2.5
Wood Chips, Heavy 15 to 24 45 4,500 3.0
Wood Shavings, Light 7 to 15 73 3,400 2.0

Hose is critical when conveying materials

Using a seamless 2″ hose, an industrial vacuum system achieving 140 CFM can generate conveying velocities surpassing 6,400 feet per minute, an impressive figure that is more than sufficient to transport dirt, sand and gravel. This capability is critical in ensuring that the heavier and larger debris one encounters in industrial settings can move efficiently and reliably through the system without the risk of blockages or reduction in performance. As one might expect, CFM plays a critical roll in the CFM vs Suction balance.

Suction becomes vital when conveying velocities slow

Therefore, when conveying velocities start to decline, it is the suction power of the vacuum that contributes the necessary “boost” to keep particles in motion. Suction force, measured in inches of water (inH2O) or (Inches of W.C.), provides the additional lift required to maintain material flow, especially when handling the intricacies of variable loads or elevation changes within the system. For effective debris transport, an industrial vacuum must balance high airflow with robust suction capabilities to prevent system inefficiencies or failure. This is where innovative engineering design comes into play to produce an effective vacuum at a low cost.   Many vacuum systems opt for 2 or 3 low cost turbines to increase system CFM.   However, with multiple turbines, the power requirement increases and typically pushes the amperage requirement above 15 amp circuits. This is also important when choosing the right vacuum.

CFM vs Suction plays a vital part in Vacuum Recover Time

The concept of “recover time” is vital when considering the efficiency and operational readiness of an industrial vacuum system. CFM, or cubic feet per minute, plays a pivotal role in this dynamic. Essentially, the smaller the volume of the vacuum container, the less time it takes to evacuate the air and achieve full optimized suction. Conversely, larger volumes demand greater CFM to expedite the recovery time and maintain peak performance. Hence, systems with smaller vacuum volumes are synonymous with quicker recover times, necessitating less CFM for efficient operation and maintaining high suction.

This enables the allocation of additional power towards increased suction while maintaining system operation at 120 volts and under 15 amps. This is critical when choosing the right vacuum.

Optimal Vacuum Selection for Dense Materials

When choosing the right vacuum for dense materials the strategic choice often involves a unit with a smaller capacity. A vacuum in 10 to 16 gallon range is usually optimal. This reduced volume allows the vacuum to operate in the 140 to 180 CFM range. This effectively maintains high conveying velocities crucial for the quick transportation of materials such as dirt, sand and gravel.

The advantage of lower volume vacuums is the speedy recovery time, which results in more consistent performance. With the majority of the unit’s power not going to airflow, more can increase suction strength. This high suction capability is necessary to lift and transport heavy materials like slurry to considerable heights.  High suction ensures the vacuum performs optimally across varied industrial demands. A good example is sucking dirt, sand, gravel and varied debri from a valve box.   As the material matrix varies the flow rate into the vacuum varies which is evident by the changing noise of the vacuum.

These small optimized systems can have suction capacity exceeding 120 inches of water. As long as flow rate of the vacuum is over 100 CFM increasing suction makes sense.  This optimizes the CFM vs Suction for material flow by keeping velocities above the threshold for most materials.   If the movement starts to slow, the suction will act as the “boot” to keep it moving.  As material starts to fill a hose, the effective diameter decreases and the velocity greatly increases as long as suction is available.

Vacuum Hose Air Velocity Calculator

Cat 6 Tools has developed a handy calculator for determining the air velocity in vacuum hose based on the hose diameter, the hose type and length and the CFM rating of the vacuum.   This calculator will compute the air velocity in a hose wich is useful for vacuum comparisons.   When moving varied materials high velocities above 5000 fpm are desirable.  Here is a link to the Hose Air Velocity Calculator.  Note:  Investigate hose length vs vacuum CFM and hose length and diameter.

Summary of Industrial Vacuum Specifications for Efficient Material Handling

In conclusion, when choosing the right vacuum, the effectiveness of industrial vacuums requires the matching the CFM vs Suction metrics. As a result, the matching of vacuum capacity to the material type and workplace requirements is vital. By utilizing a smaller vacuum volume for dense materials, operations can capitalize on fast vacuum recovery time.  This helps to keep materials moving.  This also maintains robust suction capabilities. The lower CFM can still maintain efficient transporting of heavy particles as velocities remain high.

The tradeoff is higher CFM lowers the vacuum recovery time and enhances performance. However, one must not sacrifice high suction strength that addresses the challenge of lifting and moving demanding materials. Selecting the right vacuum specifications plays a pivotal role in optimizing material handling processes. When moving dirt, sand and gravel, and slurries, maintaining high velocities, with high CFM is vital.  In addition, a smaller vacuum container volume help to balance these trade offs. This allows for higher suctions as the high CFM is then not as critical.  Lastly, shorter hose reduces velocity losses and helps to maintain high velocities.