Can velocity is the upward gas velocity through the net housing cross-section in a jet-pulse baghouse. It must not be confused with the A/C (air-to-cloth) ratio; high can velocity can carry dislodged dust back to the bags through re-entrainment. This article explains the formula, net-area calculation, a solved example, and the design impact.
What Is Can Velocity?
Can velocity is the upward velocity of dusty gas through the free (net) housing cross-section between the bags in a jet-pulse baghouse, expressed in m/s. It does not describe the filtration velocity through the bag surface; it describes the rising/conveying velocity from bottom to top inside the housing. During pulse-jet cleaning, dust dislodged from the bag wants to fall downward, while high upward can velocity can keep it suspended and carry it back to clean bags through re-entrainment.
For this reason, can velocity is a separate design check independent of the question, "does the filter have enough cloth area?" Even if cloth area is correctly selected, a narrow housing section makes the gas rise too quickly; dislodged dust can be carried back before it reaches the hopper, reducing real filtration efficiency. In a Hantech Filter evaluation, can velocity is read together with the A/C ratio but not confused with it.
What Is the Difference Between Can Velocity and the A/C (Air-to-Cloth) Ratio?
| Criterion | A/C (Air-to-Cloth) Ratio | Can Velocity |
|---|---|---|
| What does it measure? | Filtration velocity through the bag surface | Upward conveying velocity through the net housing section |
| Area used in the denominator | Total cloth area (m²) | Net housing cross-sectional area A_net (m²) |
| Typical unit | m/min | m/s |
| Main risk | If high: rapid bag loading, high dP, and short bag life | If high: re-entrainment, lower real efficiency, and local abrasion |
| Formula | A/C = Q / A_cloth | V = Q / (3600 × A_net) |
In short, the two values are divided by different areas and manage different problems. The A/C ratio shows how hard the bags are being loaded; can velocity shows whether dislodged dust can fall into the hopper. A filter may have a suitable A/C ratio while can velocity is high, or the opposite may be true. For that reason, both must be calculated separately. For the A/C side, you can use the Air-to-Cloth Ratio & Bag Count calculator; for the can velocity side, use the Can Velocity calculator.
How Is Can Velocity Calculated? Formula and Net Area
The basic can velocity formula is simple:
Basic formula
- Formula
- V = Q / (3600 × A_net)
- V
- Can velocity (m/s)
- Q
- Gas flow rate (m³/h)
- A_net
- Net housing cross-sectional area (m²)
- 3600
- m³/h → m³/s conversion (hour → second)
The critical point is the net area in the denominator. The gross housing cross-section is not used directly; the section occupied by the bags and any internal ducts, beams, blow-pipes, supports, or similar obstructions must be deducted:
A_net = A_gross − (number of bags × bag cross-section) − internal obstruction allowance
Bag cross-section is calculated from the bag outside diameter: cross-section for one bag = π/4 × D². For example, for a Ø160 mm (0.16 m) bag, the section is approximately π/4 × 0.16² ≈ 0.0201 m². Because net area is smaller than gross area, a calculation made with gross area shows can velocity as lower than it really is and can hide re-entrainment risk. This is one of the most common field mistakes.
Solved Example: Can Velocity in a 48,000 m³/h Jet-Pulse Filter
Sample calculation
- Flow rate (Q)
- 48,000 m³/h
- Internal housing dimensions
- 4 m × 3 m → A_gross = 12.00 m²
- Bag count
- 240 bags
- Bag outside diameter
- Ø160 mm = 0.16 m
- Cross-section of one bag
- π/4 × 0.16² = 0.0201 m²
- Cross-section occupied by the bags
- 240 × 0,0201 = 4,83 m²
- Internal obstruction/duct allowance
- 0,50 m²
- Net area (A_net)
- 12,00 − 4,83 − 0,50 ≈ 6,67 m²
- Can velocity (V)
- 48,000 / (3600 × 6.67) ≈ 2.00 m/s
In this example, if the same filter were calculated with gross area (12.00 m²), can velocity would be only 48,000 / (3600 × 12.00) ≈ 1.11 m/s. With net area, the real value is approximately 2.00 m/s. In other words, when the section occupied by bags and internal obstructions is ignored, the filter appears "safe", while the real rising velocity inside the housing is almost twice as high. This difference directly determines whether dislodged dust can drop into the hopper.
This result is not, by itself, a "suitable" or "unsuitable" decision. With fine and light dust, sticky/moist cake, or a low-emission target, the same can velocity may be riskier; with coarse and heavy dust, higher values may be tolerated. For your own filter, we recommend testing the value with the Can Velocity calculator and checking the cloth-area side together with the A/C calculator.
How Does Can Velocity Affect Design? Geometry, dP and Pulse Cleaning
Can velocity directly affects three design decisions. The first is housing geometry: as the housing cross-section narrows, net area decreases and can velocity rises. Carrying the same airflow in a wider or deeper housing, reducing bag diameter while increasing bag count, or adding compartments increases net area and lowers velocity.
The second is the relationship between differential pressure (dP) and efficiency: at high can velocity, dust dislodged by the pulse is carried back to the bags before it can reach the hopper. This re-entrainment can make dP higher and less stable than expected, leave a persistent load on the bag surface, and reduce real filtration efficiency. In some cases, low dP and high stack dust appear together, which may indicate dust carryback rather than effective cleaning.
The third is pulse-jet cleaning behavior: when can velocity is high, increasing pulse frequency often does not improve the situation; instead, it can suspend more dust and worsen carryover. If the root cause is housing section/net area, the solution is geometry, not the pulse program. For pulse-side symptoms, the pulse-jet cleaning system and pulse-jet valve failure symptoms articles should be read together.
Diagnosis and Decision Table
| General reference band (indicative) | Field symptom / interpretation | Decision and action |
|---|---|---|
| Low band | Dislodged dust drops regularly into the hopper, dP is stable, and the stack is clean | Geometry appears suitable; continue monitoring A/C, pulse behavior, and moisture |
| Medium / monitoring band | dP rises slowly, stack dust appears intermittently, and pressure does not fully drop after cleaning | Dust characteristics, bag arrangement, and net area are rechecked; enlargement is evaluated for critical processes |
| High band | Low/unstable dP + stack dust, with early wear in the upper bag area | Increase net area (housing cross-section, bag diameter/count, or compartmenting); do not only increase pulse frequency |
| Value calculated with gross area | The report says "safe", but re-entrainment is present in the field | Repeat the calculation with net area (A_net); subtract the bag and internal obstruction sections |
These bands are general references, not fixed universal limits. The real threshold changes with dust density, stickiness, particle-size distribution, pulse design, and OEM/process conditions. The table is meant to interpret the measured value together with field symptoms; it is not a standalone pass/fail test.
What I Would Not Do in This Situation
Calculators, Related Products and Quote
To test values for your own filter: the Can Velocity calculator gives net area and can velocity from housing dimensions, bag diameter, and bag count; the Air-to-Cloth Ratio & Bag Count calculator calculates the A/C ratio and required bag count. Reading the two values together balances housing geometry and cloth-area decisions at the same time.
Related product families: baghouse filter systems, filter bags, pulse-jet valves, and fan and air systems. Housing cross-section, bag diameter/count, and fan operating point determine can velocity together, so these components should be evaluated as a system rather than separately.
If you share flow rate, housing dimensions, bag diameter/count, and current dP trend through the quote form, we can evaluate can velocity, A/C ratio, and pulse design together and prepare a recommendation suited to your site conditions.
Technical Review Note
Technical review: Doğuhan Kırmacı — industrial filtration and dust collection.
The can velocity bands and example values in this article are for preliminary evaluation. There is no universal fixed safe can velocity limit; the real threshold changes with dust characteristics, particle-size distribution, moisture/stickiness, pulse design, bag arrangement, and housing geometry. Final design and limit values must be verified together with the filter OEM design and process data: airflow, temperature, dust load, and emission target. The formula and example here do not replace that verification; they help structure it.
Frequently Asked Questions
What is can velocity?
Can velocity is the upward velocity of dusty gas through the free (net) housing cross-section between the bags in a jet-pulse baghouse, calculated in m/s as V = Q / (3600 × A_net). It describes the rising velocity inside the housing, not the filtration velocity through the bag surface.
Is can velocity the same as the A/C (air-to-cloth) ratio?
No. The A/C ratio is found by dividing gas flow by total cloth area and indicates filtration velocity through the bag surface, usually in m/min. Can velocity is the upward conveying velocity through the net housing section, in m/s. The two values are divided by different areas and manage different risks: one affects bag loading, the other affects re-entrainment and dust carryover.
How is can velocity calculated?
First calculate the net area: A_net = housing cross-sectional area − section occupied by the bags − internal obstruction/duct allowance. Then apply V = Q / (3600 × A_net). When flow rate is entered in m³/h and area in m², the result is in m/s. Bag cross-section is calculated from the bag outside diameter (π/4 × D²).
Is there an acceptable can velocity limit?
There is no universal fixed limit. As a general reference, lower bands are safer and the risk of re-entrainment increases as the value rises; however, the real threshold depends on dust density, stickiness, pulse design, and OEM/process validation. A fixed upper limit should not be memorized and used to lock the design.
What should be done if can velocity is high?
Increasing housing cross-sectional area (a wider/deeper housing), reducing bag diameter while increasing bag count, reviewing airflow/number of compartments, or improving bag arrangement increases net area and lowers can velocity. Increasing only the pulse frequency without confirming the root cause does not solve the problem and often worsens dust carryover.