Metal Pall Ring vs Metal Cascade Mini Ring: Which Random Packing Should You Select?

Metal Pall Ring and Metal Cascade Mini Ring are both open metal random packings, but they should not be treated as interchangeable products. Pall Ring uses a taller cylindrical body with punched and formed internal surfaces, while Cascade Mini Ring uses a lower-height, more open geometry designed around a different relationship between surface area, bed openness and geometric packing resistance.

The practical selection question is:

Should the project stay with the widely used Metal Pall Ring geometry, or does the hydraulic and operating duty justify moving to Metal Cascade Mini Ring?

The answer depends on:

• required mass-transfer contacting;
• gas or vapor throughput;
• allowable pressure drop;
• fouling tendency;
• tower diameter;
• existing internals;
• retrofit risk;
• supplier-specific physical data.

Neither geometry is universally superior.

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1. Direct Answer

Choose Metal Pall Ring more readily when:

• it is already the proven packing in the tower;
• replacement compatibility is important;
• standard ring geometry is preferred;
• the process does not justify a geometry change;
• procurement simplicity is important.

Choose Metal Cascade Mini Ring more readily when:

• hydraulic openness is a stronger priority;
• pressure-drop margin is limited;
• high gas or vapor throughput is important;
• the project intentionally seeks a lower-height, more open random-packing geometry;
• a retrofit review confirms that the different bed characteristics are acceptable.

The key principle is:

Do not replace Pall Ring with Cascade Mini Ring merely because both are metal random packing.

A geometry change is an engineering decision.

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2. What Is the Structural Difference?

Metal Pall Ring

Metal Pall Ring retains the basic cylindrical concept of a ring but incorporates:

• wall openings;
• inward-formed metal surfaces;
• internal liquid-contacting structures.

Its geometry creates more internal surface and more open flow paths than a simple Raschig Ring.

Metal Cascade Mini Ring

Metal Cascade Mini Ring uses a substantially lower-height body relative to its characteristic width.

DAIER's catalog-confirmed series includes:

• OP;
• 1P;
• 1.5P;
• 2P;
• 2.5P;
• 3P;
• 4P;
• 5P. 

The CMR geometry is therefore not simply:

a short Pall Ring.

Its product family has its own:

• dimensions;
• surface areas;
• void fractions;
• packing counts;
• packing factors.

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3. Why the Geometry Difference Matters

When random packing is installed, individual elements create the entire packed-bed network.

Changing element geometry changes:

• local gas paths;
• liquid spreading;
• packing-to-packing contacts;
• characteristic void spaces;
• hydraulic resistance.

Therefore:

two products with similar nominal width can still create very different beds.

That is exactly what DAIER's verified catalog data show.

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4. Approximate 25 mm-Class Comparison

A useful example is:

Metal Pall Ring 25 mm

DAIER's catalog-confirmed values are approximately:

• dimensions: 25 × 25 × 0.4 mm;
• surface area: 212 m²/m³;
• void fraction: 96.2%;
• bulk density: 288 kg/m³;
• packing count: 53,500 pcs/m³;
• dry packing factor: 229.8 m⁻¹. 

Metal Cascade Mini Ring 1P

DAIER's catalog-confirmed values are approximately:

• dimensions: 25 × 22 × 8 × 0.3 mm;
• surface area: 230 m²/m³;
• void fraction: 96%;
• bulk density: 270 kg/m³;
• packing count: 150,000 pcs/m³;
• dry packing factor: 40 m⁻¹. 

These are not identical nominal products, but they occupy a similar dimensional class.

The comparison is revealing.

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5. Similar Surface Area Does Not Mean Similar Bed Behavior

At this approximate size class:

Surface Area

Pall Ring:

212 m²/m³

CMR 1P:

230 m²/m³

Void Fraction

Pall Ring:

96.2%

CMR 1P:

96%.

Those values look relatively close.

But:

Dry Packing Factor

Pall Ring:

229.8 m⁻¹

CMR 1P:

40 m⁻¹. 

That means:

surface area and void fraction alone do not describe the full hydraulic position of a random packing.

Geometry matters enormously.

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6. Approximate 50 mm-Class Comparison

A second example makes the same point.

Metal Pall Ring 50 mm

Verified values:

• 50 × 50 × 0.5 mm;
• 106 m²/m³ surface area;
• 97.5% void fraction;
• 185 kg/m³ bulk density;
• 6,500 pcs/m³;
• 128.5 m⁻¹ dry packing factor. 

Metal Cascade Mini Ring 2.5P

Verified values:

• approximately 51 × 44 × 17 × 0.4 mm;
• 127 m²/m³ surface area;
• 97% void fraction;
• 186 kg/m³ bulk density;
• 17,900 pcs/m³;
• 17 m⁻¹ dry packing factor. 

Again:

• bulk density is almost identical;
• void fraction is close;
• geometric area is of the same order;

yet the published packing factor is dramatically different.

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7. Why This Comparison Cannot Be Reduced to “Which Has More Surface Area?”

Engineers sometimes compare random packing using only:

m²/m³

That is insufficient.

For Metal Pall Ring vs Metal Cascade Mini Ring, evaluate at least:

• specific surface area;
• void fraction;
• packing factor;
• packing population;
• element geometry;
• operating gas and liquid loads.

A higher area value may provide more potential contacting surface.

But if the process is strongly limited by:

• gas capacity;
• pressure drop;

the geometry with greater hydraulic openness may become more attractive.

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8. When Metal Pall Ring Has the Stronger Position

Metal Pall Ring remains highly relevant because it is:

• widely understood;
• available in many sizes;
• familiar in packed-tower operation;
• straightforward to specify.

It may be the stronger choice when:

Existing Tower Already Uses Pall Ring

Like-for-like replacement reduces uncertainty.

Hydraulic Performance Is Already Acceptable

There is little reason to change geometry solely for modernization.

Existing Bed Height Is Proven

Keeping the same geometry can simplify process-performance expectations.

Existing Support Grid Is Designed Around the Current Packing

This can reduce retrofit modifications.

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9. When Metal Cascade Mini Ring Has the Stronger Position

CMR deserves stronger consideration when the project specifically needs to improve the balance toward:

• hydraulic openness;
• gas or vapor throughput;
• lower geometric resistance.

DAIER's P-series illustrates this position clearly.

For example:

• 1P — 40 m⁻¹ packing factor;
• 2P — 22 m⁻¹;
• 3P — 14 m⁻¹;
• 5P — 7 m⁻¹. 

This is one reason CMR can be a strong candidate when:

the tower's hydraulic margin is more critical than maintaining a conventional Pall Ring geometry.

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10. Does Lower Packing Factor Mean Lower Actual Pressure Drop?

Not automatically.

Packing factor is useful for:

• geometry description;
• hydraulic correlations;
• preliminary comparison.

But actual tower pressure drop also depends on:

• gas velocity;
• gas density;
• liquid load;
• liquid properties;
• packed height.

Therefore:

Do not convert the catalog packing-factor difference directly into a claimed percentage reduction in pressure drop.

That requires an actual hydraulic evaluation.

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11. Which Is Better for High Gas or Vapor Flow?

Where high gas or vapor throughput is a dominant design constraint, Metal Cascade Mini Ring may deserve stronger preliminary consideration.

Why?

Its geometry can provide a very low packing-factor position in the catalog.

However, the process still needs sufficient:

• liquid contacting;
• mass transfer;
• packed height.

Therefore:

high capacity does not automatically mean CMR should replace Pall Ring.

The correct question is whether the existing Pall Ring bed is actually hydraulically limiting the project.

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12. Which Is Better When Pressure Drop Is Critical?

When allowable pressure drop is very restrictive, CMR may move higher in the candidate list.

Possible cases include:

• vacuum-related service;
• blower-limited gas systems;
• revamps with limited hydraulic margin.

But Metal Pall Ring may still be completely suitable where:

• operating velocities are moderate;
• the existing bed pressure drop is acceptable;
• a geometry change creates unnecessary retrofit risk.

Selection should therefore be:

constraint-driven

rather than:

product-fashion-driven.

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13. Which Is Better for Mass Transfer?

There is no universal answer.

Mass-transfer performance cannot be predicted from product name alone.

It depends on:

• geometric area;
• effective wetting;
• fluid properties;
• gas/liquid rates;
• bed height;
• liquid distribution.

CMR can provide competitive geometric area even at relatively open hydraulic positions.

For example, DAIER's 1P CMR is catalog-listed at approximately:

230 m²/m³, compared with approximately 212 m²/m³ for 25 mm Metal Pall Ring. 

But that does not establish a universal efficiency ranking.

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14. Which Is Better for Fouling?

This requires more caution.

Neither packing should be described as:

• non-clogging;
• fouling-proof.

Fouling depends on:

• solids;
• crystals;
• sticky deposits;
• polymerization;
• biological growth.

CMR's low-height and open geometry may make it attractive where bed openness is important.

But Pall Ring is also available in relatively large sizes.

Therefore the correct sequence is:

Define Fouling Mechanism → Compare Passage Geometry → Select Size → Review Cleaning/Replacement Strategy

rather than simply:

CMR = fouling packing.

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15. Packing Size Can Matter More Than Product Family

A major mistake is comparing:

25 mm Pall Ring

with:

large 4P or 5P CMR

and concluding that all hydraulic differences come from product type.

Some of the change comes from:

• size;
• element population;
• geometric area.

Therefore fair comparison should use:

• similar dimensional class where possible;
• actual catalog data.

Even then, CMR and Pall Ring are different geometries, so direct one-to-one equivalence should not be assumed.

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16. Tower Diameter Can Change the Answer

The selected random packing must remain reasonable relative to tower ID.

Large packing in a small tower can create:

• strong wall effects;
• too few elements across the diameter.

Very small packing in a large tower may create:

• unnecessary hydraulic resistance;
• excessive element population.

Therefore:

the correct question is not only Pall Ring vs CMR—it is Pall Ring size vs CMR model for this specific tower diameter.

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17. Existing-Tower Retrofit: Pall Ring to CMR

This is one of the most important real-world use cases.

Suppose an existing tower contains Metal Pall Ring and the operator wants:

• higher throughput;
• lower pressure drop;
• more operating margin.

CMR may become an upgrade candidate.

But before replacement, check:

• tower ID;
• current packing size;
• current packed height;
• actual pressure drop;
• actual operating gas/liquid loads;
• support grid;
• hold-down arrangement;
• liquid distributor.

Without this information, replacing Pall Ring with CMR is only a product substitution—not an engineered retrofit.

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18. Do Not Assume the Same Bed Height

Changing geometry can change mass-transfer behavior.

Therefore:

Pall Ring bed height should not automatically be copied into a CMR replacement specification.

A retrofit should verify whether the new packing can achieve the required:

• separation;
• absorption;
• stripping

duty at the proposed height.

The existing tower shell may stay unchanged, but the engineering basis must still be reviewed.

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19. Support Grid Compatibility

Pall Ring and CMR may differ in:

• characteristic width;
• height;
• smallest retention dimension.

Therefore the existing support grid should be checked for:

• opening size;
• packing retention;
• load capacity;
• gas/liquid open area.

Do not assume:

“both are metal packing, therefore the same support works.”

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20. Hold-Down Requirements

A hold-down device restrains random packing movement.

It should not be designed to:

• compress;
• mechanically compact

the bed.

When changing Pall Ring to CMR, review:

• top-bed restraint;
• packing mobility;
• operating gas velocity.

The hold-down arrangement is an internal-system question, not simply a packing-material question.

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21. Liquid Distribution Can Override the Packing Upgrade

Installing a more hydraulically advanced packing cannot fix poor liquid distribution.

If the distributor creates:

• dry zones;
• local overloading;
• channeling;

the new packing may still perform poorly.

Therefore a Pall-to-CMR retrofit should ask:

Is the packing actually the limiting component?

Sometimes the problem is the:

• distributor;
• redistributor;
• support;
• operating condition.

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22. Metal Pall Ring Advantage: Procurement Familiarity

Metal Pall Ring often has an advantage in projects where:

• existing specifications already define it;
• operators understand the product;
• replacement inventory is standardized;
• multiple suppliers can quote comparable sizes.

For routine replacement:

standardization itself has engineering and procurement value.

A theoretically more open packing is not automatically worth changing to if the existing system performs satisfactorily.

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23. Metal Cascade Mini Ring Advantage: More Specialized Hydraulic Position

CMR's major value is that its geometry can occupy a hydraulic position that is difficult to infer from simple ring diameter.

For example, verified CMR models progress to:

• 3P — 14 m⁻¹;
• 4P — 10 m⁻¹;
• 5P — 7 m⁻¹ packing factor. 

This gives engineers additional options when the tower is constrained by:

• capacity;
• pressure drop.

That is a genuine product-selection difference, not merely marketing terminology.

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24. Material Grade Does Not Decide Pall Ring vs CMR

Both product families can potentially be produced in appropriate metal grades.

Therefore:

SS304 vs SS316L is a separate decision from Pall Ring vs CMR.

Material selection answers:

Will the packing resist the process chemistry?

Geometry selection answers:

How should the packed bed balance contacting and hydraulics?

Do not mix those decisions.

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25. When SS316L Does Not Automatically Mean CMR

A corrosive process may require:

SS316L Pall Ring.

Another may require:

SS316L Cascade Mini Ring.

The need for SS316L says nothing by itself about:

• packing size;
• packing geometry.

Likewise, choosing CMR does not automatically justify a more expensive alloy.

Each selection layer must solve a real process requirement.

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26. Distillation: Which One?

For suitable distillation duties:

Metal Pall Ring May Be Preferred When

• conventional random packing is adequate;
• existing performance is proven;
• replacement simplicity matters.

Metal Cascade Mini Ring May Be Preferred When

• random packing remains desired;
• hydraulic capacity or pressure drop is a stronger constraint.

However, demanding:

• deep vacuum;
• high separation efficiency;
• very low pressure-drop

duties may instead push the project toward structured packing.

So the comparison is not always limited to only Pall Ring and CMR.

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27. Absorption: Which One?

In gas absorption:

Metal Pall Ring may be entirely suitable for many conventional packed absorbers.

CMR deserves stronger review where:

• gas throughput is high;
• hydraulic margin is tight;
• open-bed geometry is important.

But absorber selection must still consider:

• liquid rate;
• wetting;
• required removal;
• process chemistry.

The packing should not be selected from pressure-drop considerations alone.

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28. Stripping: Which One?

In stripping service, gas or vapor flow can be a strong design variable.

CMR may therefore become attractive when:

• high throughput;
• low hydraulic restriction

are important.

But Pall Ring remains a valid candidate where the required operating window is comfortably achievable.

The correct choice should reflect the actual tower duty rather than a universal geometry ranking.

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29. New Tower vs Existing Tower

New Tower

A new tower allows greater freedom to evaluate:

• Pall Ring;
• CMR;
• IMTP;
• structured packing;
• other alternatives.

The designer can optimize:

• diameter;
• bed height;
• internals

together.

Existing Tower

An existing tower has fixed:

• shell diameter;
• bed height envelope;
• support elevations;
• manways;
• distributors.

Therefore a CMR upgrade may provide hydraulic opportunity but also needs more retrofit review.

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30. When Not to Change from Pall Ring

Do not change merely because:

• CMR appears more modern;
• a supplier claims lower pressure drop;
• the catalog packing factor is lower.

Keeping Pall Ring may be preferable when:

• current tower performance is satisfactory;
• the project is only replacing damaged packing;
• no hydraulic bottleneck exists;
• process risk from changing geometry is unnecessary.

A replacement project does not need to become an optimization project.

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31. When CMR Becomes Worth Investigating

CMR deserves serious review when the project has a specific problem such as:

• insufficient gas/vapor capacity;
• excessive pressure drop;
• desired throughput increase;
• limited room to enlarge tower diameter.

Then CMR can be evaluated as part of a retrofit strategy.

The engineering question becomes:

Can the geometry change improve the limiting constraint while maintaining the required process duty?

That is the correct reason to consider an upgrade.

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32. Metal Pall Ring vs Metal CMR Decision Table

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33. Quick Selection Guide

Stay with Metal Pall Ring when:

• the tower already performs well;
• replacement is like-for-like;
• hydraulic margin is adequate;
• minimizing retrofit uncertainty matters.

Evaluate Metal Cascade Mini Ring when:

• pressure drop is a real constraint;
• capacity needs to increase;
• random packing is still preferred;
• the existing tower shell cannot easily be enlarged.

Do not select either until checking:

• material compatibility;
• tower diameter;
• gas/liquid loads;
• fouling;
• required process duty;
• existing internals.

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34. What Should Be Included in an RFQ?

For a new project provide:

• process type;
• tower diameter;
• packed height;
• gas/vapor composition;
• liquid composition;
• flow rates;
• temperature;
• pressure;
• required metal grade;
• pressure-drop constraint;
• fouling information.

For a Pall Ring replacement project also provide:

• existing Pall Ring size;
• existing alloy;
• current packed height;
• support-grid details;
• liquid distributor details;
• current operating problem;
• desired throughput increase.

This allows the supplier to determine whether the requirement is:

replacement

or:

performance retrofit.

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Common Selection Mistakes

Assuming CMR Is Simply a Shorter Pall Ring

It is a separate packing family with different verified geometry and physical data.

Comparing Only Surface Area

Similar surface area can coexist with dramatically different published packing factors. 

Comparing Only Void Fraction

Voidage does not fully describe hydraulic behavior.

Claiming a Specific Pressure-Drop Reduction from Packing Factor Alone

Actual process flow conditions are still required.

Replacing Pall Ring with CMR at the Same Bed Height Without Review

Mass-transfer performance may change.

Ignoring Existing Internals

Support and hold-down compatibility must be checked.

Choosing CMR Because It Is “Better”

There is no universal winner.

Changing Alloy at the Same Time Without a Chemical Reason

Material and geometry are separate engineering decisions.

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Frequently Asked Questions

Is Metal Cascade Mini Ring better than Metal Pall Ring?

Not universally. CMR can offer a more hydraulically open product position, while Pall Ring may provide simpler replacement, greater standardization and proven tower performance.

Which packing has lower packing factor?

DAIER's catalog-confirmed CMR P-series contains very low packing-factor models. For example, 1P is approximately 40 m⁻¹ and 3P approximately 14 m⁻¹. 

Does that mean CMR always has lower pressure drop?

No. Actual pressure drop depends on gas and liquid operating conditions.

Can I replace 25 mm Metal Pall Ring with 1P CMR?

Do not treat them as direct equivalents. Their characteristic dimensions are similar, but geometry, packing population and packing factor differ substantially.

Which has more surface area around the 25 mm class?

DAIER's verified values are approximately:

• 25 mm Metal Pall Ring — 212 m²/m³;
• 1P CMR — 230 m²/m³. 

Which is better for a high-throughput revamp?

CMR may deserve stronger consideration when hydraulic capacity or pressure drop is the limiting constraint, but the retrofit must still verify process performance and tower internals.

Which is better for a simple replacement?

If the existing Pall Ring performs satisfactorily, like-for-like Pall Ring replacement usually introduces less engineering uncertainty.

Can both be supplied in SS304 or SS316L?

Material grade is a separate procurement decision and should be confirmed for the actual process chemistry and supplier manufacturing capability.

Is CMR always better for fouling?

No. More open geometry may be useful, but severe fouling or crystallization can still affect CMR.

Do I need to change the support grid when switching to CMR?

Possibly. The actual CMR model dimensions and existing support-grid openings must be checked.

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Selection Takeaway

Metal Pall Ring and Metal Cascade Mini Ring occupy different engineering positions even when their nominal dimensional classes appear similar.

For example, DAIER's catalog data show:

25 mm Metal Pall Ring → 212 m²/m³ surface area / 96.2% void / 229.8 m⁻¹ packing factor

while approximately similar-width:

1P Metal Cascade Mini Ring → 230 m²/m³ / 96% void / 40 m⁻¹ packing factor. 

Likewise, around the 50 mm class:

50 mm Pall Ring → 106 m²/m³ / 97.5% void / 128.5 m⁻¹

while:

2.5P CMR → 127 m²/m³ / 97% void / 17 m⁻¹. 

These figures do not prove a universal performance winner.

They prove something more useful:

Packing geometry can materially change hydraulic position even when surface area, voidage and physical size appear broadly comparable.

The correct selection sequence is:

Process Duty → Existing Tower or New Tower → Hydraulic Constraint → Required Mass Transfer → Fouling → Tower Diameter → Compare Exact Pall Ring and CMR Models → Material Grade → Internals Review

The key principle is:

Keep Metal Pall Ring when its proven performance and replacement simplicity solve the project. Evaluate Metal Cascade Mini Ring when the project has a genuine hydraulic reason to change geometry.