What Does the “On-Time” Setting on a Control Board Mean

What Does the “On-Time” Setting on a Control Board Mean?

Understanding pulse duration, cleaning energy, and why longer is not always better

On a dust collector control board, few settings are adjusted as casually—or misunderstood as often—as “On-Time.” Operators increase it to fight rising differential pressure, reduce it to save compressed air, and rarely stop to ask what it actually controls inside the baghouse.

In reality, the On-Time setting defines how much cleaning energy is delivered to each filter bag per pulse. Used correctly, it stabilizes filtration. Used incorrectly, it accelerates bag wear and masks deeper system problems.

What “On-Time” Actually Controls

On-Time is the duration (usually in milliseconds) that a pulse valve remains open during a cleaning cycle.

When the valve opens:

• Compressed air is released into the blowpipe
• A pressure wave travels down the filter bag
• The bag flexes outward
• Dust cake detaches from the surface

On-Time does not control how often cleaning happens. It controls how hard each individual pulse hits the bag. Frequency and intensity are separate parameters.

Why On-Time Exists as an Adjustable Setting

Dust collectors operate under widely varying conditions:

• Different bag lengths and diameters
• Different dust types and cake strength
• Different compressed air pressures
• Different manifold and nozzle designs

A fixed pulse duration would over-clean some systems and under-clean others. On-Time allows the cleaning energy to be matched to the physical system, not guessed.

What Happens When On-Time Is Too Short

If On-Time is set too low:

• The pressure wave is weak
• The bag flexes insufficiently
• Dust cake only partially releases
• Residual dust accumulates cycle after cycle

Operational symptoms include:

• Gradual DP increase
• Increasing cleaning frequency
• Bags appearing “dirty” even after pulsing

In this case, raising On-Time can restore effective cake release—but only up to a point.

What Happens When On-Time Is Too Long

This is the more common mistake.

When On-Time is excessive:

• The pressure wave does not get “stronger” after a certain point
• Extra air simply vents without additional cleaning benefit
• Bag movement becomes violent rather than controlled

Consequences include:

• Accelerated fabric fatigue
• Snap band and seam stress
• Increased cage contact wear
• Higher compressed air consumption
• Dust re-entrainment instead of controlled release

Longer On-Time does not equal better cleaning. After the initial pressure wave, returns diminish rapidly.

Why On-Time Cannot Fix an Undersized or Unstable System

A key misunderstanding is treating On-Time as a cure-all.

Operators often increase On-Time when:

• Air-to-cloth ratio is too high
• Dust is penetrating deep into the felt
• Conveying velocity is unstable
• Temperature or moisture is causing blinding

In these cases:

• Stronger pulses do not solve the root cause
• They simply delay failure while increasing mechanical damage

If a system requires continuously increasing On-Time to stay operational, it is signaling a capacity or design mismatch, not a cleaning problem.

On-Time vs Cleaning Frequency: A Critical Distinction

Two systems can show the same cleaning activity but behave very differently:

• Short On-Time + frequent pulses
  Many gentle cleaning events
• Long On-Time + infrequent pulses
  Fewer, more aggressive cleaning events

From a bag life perspective, gentler pulses are almost always preferable, provided cake release is complete.

On-Time should be tuned to achieve just enough energy per pulse, not maximum energy.

How Bag Length and Design Affect On-Time

Longer filter bags require:

• Sufficient pulse duration to propagate the pressure wave
• Proper nozzle alignment to avoid uneven expansion

However, this does not mean “as long as possible.”

Excess On-Time in long bags often:

• Over-flexes the upper section
• Adds little energy to the lower section
• Increases top-end wear without improving bottom-end cleaning

Good cleaning depends on pulse shape and distribution, not duration alone.

Practical Signs That On-Time Is Misadjusted

On-Time may be too high if:

• Bags show early fatigue or seam damage
• Compressed air consumption rises without DP improvement
• Dust clouds appear in the clean air plenum during pulsing

On-Time may be too low if:

• DP rises steadily despite frequent cleaning
• Visible dust remains on bags after pulsing
• Increasing frequency helps more than increasing duration

These signs are more reliable than numbers on a control panel.

A Practical Engineering Takeaway

The “On-Time” setting controls pulse duration, not cleaning frequency—and more is not better.

It works best when:

• Set just high enough to release the dust cake
• Combined with DP-based cleaning control
• Adjusted conservatively and infrequently
• Used as a tuning parameter, not a compensation tool

A stable dust collection system does not rely on extreme On-Time values. It relies on:

• Proper airflow and conveying velocity
• Appropriate filter media selection
• Controlled dust cake formation
• Balanced cleaning energy

When On-Time is correctly understood and applied, it quietly supports filtration stability. When misunderstood, it becomes a lever that hides system problems while shortening filter bag life.

Omela Filtrations supports dust collection optimization by aligning filter media behavior, cleaning mechanics, and control strategy, helping operators tune On-Time settings as part of a stable system—not as a last-resort fix.

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