Quick answer: Size a packaging-line compressor from peak simultaneous CFM at the line’s required pressure, then add receiver storage and a leak allowance. A compressor that matches average demand will still lose pressure when several actuators fire together.

Direct Driven Air Compressor Sizing for a Packaging Line Losing Pressure

A packaging line that keeps losing pressure usually doesn't need a bigger compressor. It needs peak flow and stored air. Size it from the line's simultaneous actuator demand at the required pressure, add leak allowance and receiver recharge margin, then confirm the compressor can deliver that FAD during the busiest part of the shift.

Why a packaging line loses pressure even when the compressor is running

Pressure loss at the line is a system symptom, and not always a compressor capacity problem. The compressor may be cycling correctly while a downstream restriction, a leak, or several actuators firing at once pulls line pressure below the minimum for sealers, grippers, or indexing cylinders.

Average CFM hides the peak

Packaging machines are intermittent. A carton sealer uses air only during the sealing stroke. A labeling head may fire several small cylinders at once. Add nameplate consumption for every device, divide by shift time, and you get an average that no actuator ever sees. The compressor has to survive the peak event.

Pressure drop is not the same as compressor output

Pressure at the compressor outlet can look healthy while the far end of the line is starved. Undersized headers, long hose runs, clogged filters, quick couplings: all of them eat pressure. Measure at both points under flow before you touch compressor size.

Size for simultaneous demand, not connected load

Sizing follows peak demand, not the sum of every nameplate on the line. Work through this sequence:

1. List each air consumer with its consumption at the real working pressure.
2. Mark the consumers that can stroke at the same time, and add only that peak group.
3. Add a leak allowance for the actual condition of the line.
4. Add receiver recharge margin so the compressor can recover between events.

The formula:

Required compressor FAD = simultaneous actuator CFM + leak allowance + receiver recharge allowance

Select a compressor whose published FAD at the target pressure is above that figure. Don't select by motor kW alone. Motor kW is input power, not delivered air. Two units with the same motor rating can put out different FAD and hold pressure differently.

A narrow scenario: three or four pneumatic stations on one packaging line

Picture a single-shift pouch-filling or carton-sealing line with three or four stations: infeed gripper, fill/seal head, date coder, outfeed transfer. The line runs at 7 bar, but pressure dips when the sealer and the transfer cylinder stroke together. The existing direct driven compressor has run for years, so procurement assumes the pump is worn. Map the event before replacing anything.

Step 1: log pressure during a real shift

Fit a gauge or logger at the compressor outlet and at the far end of the line. Note the exact times when pressure drops and what the line was doing. A dip that repeats with the sealing cycle points to peak flow or storage. A slow decline over the shift points to leaks, or to a compressor that can't recover.

Step 2: calculate peak event flow

Add the CFM of every consumer that strokes together. Include the sealing jaw, the transfer cylinder, and any blow-off nozzles running during the same event. If the machine builder gives you only cylinder bore and stroke, calculate free air consumption from bore area, stroke, cycles per minute, and working pressure, then convert to standard CFM. Ask the builder for the figure in writing if you're unsure.

Step 3: size receiver and piping for the event

A receiver does not create air; it buys time. If the largest event lasts several seconds, stored air can carry the line while the compressor recovers. Size the receiver and header so line pressure stays above the minimum during that event. Too small a receiver and the compressor will cycle hard and still lose pressure.

Step 4: check the compressor duty

A direct driven compressor is a good fit for intermittent demand when the receiver is correctly sized. If the line demands full flow for long periods, verify the pump's continuous-duty rating and consider whether another compressor type suits the job better. Don't assume a larger direct driven unit will solve a continuous-flow shortfall.

Where a direct driven air compressor fits on a packaging line

Direct driven compressors couple the motor straight to the pump, so there are no belts to wear or adjust. In a small packaging plant, that usually means a compact footprint, simpler maintenance, and no belt alignment to check. The trade-offs are noise, heat, and pump duty. Direct driven piston units usually suit intermittent demand better than continuous full-load operation.

Use a direct driven unit when:

• the line has a defined peak event and a receiver to cover it;
• the compressor sits in a separate utility room or noise enclosure, or the measured noise at the operator position is acceptable;
• the duty cycle leaves time for cooling and recovery;
• the electrical supply and control voltage match the site.

Review the Direct Driven Air Compressor range against the calculated FAD, not against horsepower alone. Shenron supplies direct driven air compressors to industrial buyers. A quote request you can act on includes the pressure, peak CFM, receiver size, voltage, and duty cycle.

Before you upsize: pressure-loss checks

Run these checks before you buy more compressor capacity. Most problems fall into the patterns below.

Pressure-loss symptoms and sizing actions

Symptom	Likely cause	Sizing or fix action
Pressure drops when sealer and transfer cylinder stroke together	Peak flow or receiver storage shortfall	Log simultaneous CFM; add receiver or choose a higher-FAD unit
Pressure normal at compressor, low at far end of line	Pipe, hose, filter, or coupling restriction	Measure pressure drop under flow; increase diameter; clean or replace filters
Pressure slowly falls over the shift	Leaks or compressor delivery below rating	Leak survey; service valves and filters; verify FAD at pressure
Compressor runs continuously but line still starves	Demand exceeds continuous FAD or duty cycle	Compare peak and continuous demand; consider storage or a different compressor type

• Leak survey: a leak that hisses only during production still counts against peak demand. Repair leaks before calculating new capacity.
• Filter and separator maintenance: clogged inlet filters, line filters, and separator elements reduce delivery and raise pressure drop.
• Piping and hose size: long runs, elbows, and quick couplings add restriction. Use the largest practical diameter and keep runs short.
• Pressure switch and unloader: confirm cut-in and cut-out settings, and that the compressor unloads correctly between cycles.
• Compressor delivery: worn valves, a slipping coupling, or a restricted inlet can reduce output even when the motor sounds normal.

Packaging-line compressor sizing checklist

Use this list before you request quotes:

• List every air consumer on the line with its rated CFM at the actual working pressure.
• Mark which consumers can fire at the same time, and sum that peak, not the connected total.
• Measure pressure at the compressor outlet and at the farthest actuator under flow.
• Carry out a leak survey and repair leaks before calculating new capacity.
• Add receiver storage sized to cover the largest simultaneous event.
• Check pipe and hose diameters, elbows, filters, and quick couplings for pressure drop.
• Confirm the proposed compressor FAD at the target pressure, not its displacement.
• Check duty cycle, noise, voltage/phase, and control compatibility with the line.
• Ask for the compressor's continuous-duty rating and service access requirements in writing.

Turn the checklist into a one-page brief. Ask every supplier for FAD at the same target pressure, motor kW, receiver liters, noise figure, dimensions, and duty rating. Then the quotes are comparable, and the discussion stays on delivered air rather than brochure horsepower.

Related sizing guidance

The application here is packaging, but the same motor and specification discipline applies to small oil-free units. See our Oil-Free Air Compressor for a 2-Chair Dental Clinic: Seven-Step Electric Motor Checklist and Oil-Free Dental Air Compressor for a 2-Chair Clinic: Buying Guide.

Frequently Asked Questions

What size air compressor do I need for a packaging line?

Size from peak simultaneous actuator flow at the line's required pressure, then add leak and receiver recharge margin. A unit selected on average CFM will lose pressure when multiple stations cycle together.

Why does my packaging line lose pressure when the compressor is still running?

The compressor may be delivering less FAD than the peak event needs, or the restriction may be downstream: undersized piping, clogged filters, leaks, or a receiver too small to cover simultaneous actuation. Confirm pressure at the compressor and at the line before upsizing.

Is a direct driven air compressor suitable for a packaging line?

Yes, for small-to-medium packaging lines with intermittent actuation and a properly sized receiver. Check the duty cycle, noise level, and continuous full-flow demand; a direct driven piston unit is not automatically the best match for a line that runs at full demand all shift.

Should I raise the pressure instead of buying a larger compressor?

Usually no. Raising pressure increases leaks and load without fixing a flow or storage problem. Measure pressure drop and simultaneous demand first; a larger receiver, better piping, or leak repair often solves the issue before extra compressor capacity does.

Practical close

If the line loses pressure at the same point in every cycle, the evidence is already in the pressure log: peak flow, storage, or restriction. Size the direct driven air compressor from that evidence. Specify it by FAD at the target pressure, not by horsepower.