What does the vacuum system do in packaging?
Vacuum packaging removes air from around the product before the pack is sealed. In a chamber machine, the product in an open bag sits inside a chamber which is evacuated; the bag is heat-sealed under vacuum and the chamber is then vented to atmosphere. In modified-atmosphere packaging (MAP), air is removed and replaced with a gas mix, often nitrogen and carbon dioxide, before sealing. On thermoform-fill-seal machines and tray sealers, vacuum is used both for forming the bottom web and for evacuating packs in the sealing station.
Each cycle therefore contains several states: loading, closing, evacuation, optional gas flush, sealing, cooling and venting. Only part of the cycle time is available for evacuation, and that window is what the vacuum system must meet.
How are packaging vacuum demands different by machine type?
| Machine type | Typical vacuum duty | Main design concern |
|---|---|---|
| Single or double chamber machine | Repeated evacuation of a fixed chamber to low pressure | Evacuation time per cycle, product moisture |
| Belt or rotary chamber machine | High cycle rate, larger chambers | Pump capacity and recovery between cycles |
| Thermoform-fill-seal line | Forming vacuum plus sealing-station evacuation | Two different duties from one or several pumps |
| Tray sealer with MAP | Evacuation then gas flush | Final pressure and gas consumption balance |
| Bag sealer with nozzle | Small, local evacuation | Product carry-over into the pump |
Plants with many machines often move from one pump per machine to a central vacuum system, which can reduce noise and heat in the packing hall and allow standby capacity, provided pipework and controls are designed for the combined, fluctuating demand.
How do you work out evacuation time and pump size?
For a first estimate, the time to evacuate a volume V from pressure p1 to p2 with a pump of effective speed S is t = (V ÷ S) × ln(p1 ÷ p2). It assumes constant pump speed and no leakage or vapour, so it gives a best case.
Worked comparison (illustrative only): two chambers, 20 litres and 40 litres of free volume after the product is loaded, must each reach 10 mbar absolute from 1,013 mbar (dry product assumed). The pressure ratio is about 101, and ln(101) is about 4.6. With an effective speed at the chamber of 100 m³/h (about 28 l/s), the 20 litre chamber needs roughly 20 × 4.6 ÷ 28, about 3.3 seconds, and the 40 litre chamber about 6.6 seconds. Doubling the chamber volume doubles the time at the same pump speed, so keeping to the same cycle needs twice the effective speed or a reduced free volume.
In practice, pump speed falls at low pressure, valves and hoses restrict flow, and moisture boiling from the product adds load. Reducing free volume with filler plates, shortening the line between chamber and pump, and using a correctly sized valve often improves cycle time more cheaply than a bigger pump.
Why does product moisture matter so much?
Water boils when the surrounding pressure falls below its vapour pressure, which is about 23 mbar at 20 °C and about 42 mbar at 30 °C, lower for chilled product. When a moist product such as meat, cheese, fish or cooked food is taken below that pressure, water begins to evaporate from it. The pump then spends its capacity removing vapour, the chamber pressure stops falling as expected, and the product can lose weight, bubble or be damaged.
That is why packaging cycles are usually set to an end pressure suitable for the product, sometimes with a sensor that stops evacuation when boiling begins, rather than simply “as low as possible”. The vapour also reaches the pump: in oil-sealed pumps it condenses in the oil, turning it milky and reducing sealing and lubrication. Gas ballast, regular oil changes, allowing the pump to reach normal running temperature and suitable inlet filtration all help.
Which vacuum pumps suit packaging?
- Oil-sealed rotary-vane pumps are the most common choice on chamber and tray machines because they reach low pressure in a compact unit. They need oil and exhaust-separator maintenance and care with moist products.
- Dry claw pumps are oil-free, robust and efficient in the medium vacuum range, and are often used for central systems and for forming vacuum on thermoform-fill-seal lines.
- Dry screw pumps handle vapour well and suit larger central systems.
- Roots boosters ahead of a backing pump shorten evacuation time on large chambers and high-speed lines.
- Liquid-ring pumps tolerate wet duty but use seal water and are less common in modern packing halls.
The vacuum system should not be taken as proof that a packaging process is suitable for food contact or approved for a product. Hygiene design, material approvals and shelf-life validation belong to the food business and the packaging-machine maker.
What hygiene and contamination points apply?
The vacuum line draws air, moisture and sometimes product from the chamber towards the pump, so the main contamination risk is to the pump rather than to the pack. Even so, the installation must be designed for the hygiene of the packing area:
- Fit an inlet filter and, for wet or messy products, a separator or liquid trap to protect the pump.
- Pipe exhaust from oil-sealed pumps out of the packing hall, so oil mist and heat do not enter clean areas.
- Protect pumps and electrics from washdown water; place pumps outside the high-care zone where practical.
- Use oil-free, dry compressed air for gas flush support, pneumatic sealing jaws and blow-off where it can contact product or packaging, with filtration appropriate to the product.
- Keep check valves working so oil or contaminated air does not flow back towards the chamber when the pump stops.
Why is my vacuum packing machine slow or not sealing properly?
- Check the machine’s vacuum reading against its usual end pressure and evacuation time.
- Inspect the chamber lid seal and sealing-bar area for cuts, product residue and wear.
- Check the inlet filter and any liquid trap; a blocked filter slows every cycle.
- Check pump oil level and condition. Milky oil means water from the product.
- Check the exhaust separator element for blockage, which raises back-pressure.
- Test the pump with its inlet blanked to see whether it reaches its normal ultimate pressure.
- Look at the product: wetter or warmer product than usual increases vapour load.
| Symptom | Likely cause | Action |
|---|---|---|
| Evacuation takes longer than before | Blocked filter, worn pump, lid seal leak | Clean filter, check seal, test pump |
| Pressure stalls before end point | Product moisture boiling, wet pump oil | Review end pressure, oil change, gas ballast |
| Loose packs after sealing | Insufficient vacuum or seal fault | Check end pressure and sealing settings |
| Oil mist in packing hall | Separator saturated, exhaust not piped out | Replace element, pipe exhaust outdoors |
| Pump overheating in summer | High room temperature, poor ventilation | Improve ventilation, check cooling |
How Reddy Compressors helps
Reddy Compressors, based at Tarnaka, Secunderabad, has served industry since 2002 as an independent multi-brand compressed-air, vacuum and blower specialist. We are not an authorised dealer of any brand. We have tie-ups with all major and reputed brands. Our service teams cover all of Telangana and Andhra Pradesh, including food processing in and around Hyderabad and the food parks of Andhra Pradesh, and we supply equipment and spares across India.
- Servicing rotary-vane, claw and screw vacuum pumps and Roots boosters on packaging machines and central systems.
- Supplying oils, inlet filters, exhaust separator elements, vanes and other spares, identified from the pump nameplate and confirmed before quoting.
- Assessing whether several machines could be served by a central vacuum system.
- Supplying, renting and servicing oil-free and oil-injected compressors, dryers and filtration for gas flush support and pneumatic functions.
- Helping to diagnose slow cycles and poor vacuum by separating pump, line and machine causes.
Call +91 99590 60718 or +91 92468 88812, or email reddycompressors@gmail.com. Office: Srinilayam, 12-13-200, First Floor, Street No. 1, Tarnaka, Secunderabad 500017.
What to send us
- Packaging machine make, model and type, with chamber size and cycle rate.
- Vacuum pump make, model and nameplate photo.
- Products packed, and whether they are chilled, moist or powdery.
- Required end pressure and current evacuation time.
- The problem: slow cycles, poor seals, oil mist, overheating or capacity expansion.
Frequently asked questions
What vacuum pump is best for a vacuum packaging machine?
Oil-sealed rotary-vane pumps are the most common choice for chamber and tray machines because they reach low pressure in a compact unit. Dry claw and dry screw pumps suit central systems and oil-free requirements, and Roots boosters speed up large chambers. The right choice depends on chamber volume, cycle rate, end pressure, product moisture and whether one pump or a central system serves the machines.
Why is my vacuum packing machine taking longer to evacuate?
Common causes are a blocked inlet filter, a worn or leaking chamber lid seal, wet or degraded pump oil, a saturated exhaust separator raising back-pressure, or a worn pump. Wetter or warmer product also adds vapour load. Check the filter and lid seal first, then oil and separator, and finally test the pump with its inlet blanked to confirm whether it still reaches its normal vacuum.
Why does water get into the oil of my packaging vacuum pump?
Moist products such as meat, cheese and cooked food release water vapour when the chamber pressure falls below the vapour pressure of water. That vapour is drawn into the pump and condenses in the oil, turning it milky. Use gas ballast where fitted, let the pump reach normal running temperature, set a suitable end pressure for the product and change the oil more often on wet duties.
How long should a vacuum packaging cycle take?
It depends on chamber free volume, end pressure, pump speed, line restriction and product moisture. A simple estimate is volume divided by effective pump speed, multiplied by the natural logarithm of the pressure ratio. Doubling the free volume roughly doubles evacuation time at the same pump speed, so filler plates and short, large-bore connections are effective ways to shorten cycles.
Is a central vacuum system good for a packaging plant?
It can be, especially with many machines. A central system can remove pump heat and noise from the packing hall, provide standby capacity and use speed-controlled pumps that follow demand. It must be sized for the realistic combination of cycles and have pipework and valves that let each machine reach its end pressure without being affected by the others.
Does vacuum packaging need oil-free compressed air?
Where compressed air supports gas flushing, sealing jaws, blow-off or anything that can contact product or packaging, it should be clean, dry and free of oil to a level suited to the product. Many food plants use oil-free compressors or oil-injected units with suitable filtration, plus a dryer. The food business and packaging-machine maker define the required air-quality class.
Related pages
Calculators and worked examples
These tools give indicative figures for screening, comparison and for preparing an enquiry. They run in your browser and send nothing. No prices or tariffs are assumed: enter your own to see costs. Efficiencies and other figures shown are example values: replace them with your own. Results are not a performance guarantee or a design certificate; final selection is confirmed by a service engineer against the machine data sheet and the site.
Vacuum pump-down time and required pumping speed
Evacuation time of a packaging chamber, best case, and the speed needed for a cycle window. Default: the page example, 20 litres of free volume from 1,013 to 10 mbar a at 100 m³/h; set the water option for moist product.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Evacuated volume incl. piping and connected equipment (unit below): 20
- Volume unit: litres
- Start pressure (mbar a): 1013
- Target pressure (mbar a): 10
- Pump speed at its inlet, average over the range from the curve (unit below): 100
- Line conductance, same unit as the speed (0 = no line loss): 0
- Speed and conductance unit: m³/h
- Continuing gas load: leaks + outgassing + vapour (0 = none): 0
- Gas load unit: mbar·m³/h
- Required pump-down time, for the speed check (min; 0 = skip): 0
- Liquid water in the vessel or product?: No (dry)
- Temperature of that water or wet product (°C): 20
Result
- Evacuated volume: 0.02 m³ = 20 litres
- Effective speed at the vessel: 100 m³/h = 27.78 L/s (no line loss entered)
- Pressure ratio p₀ ÷ p₁: 101.3 ln = 4.618
- Ideal pump-down time (no gas load): 3.33 s (0.055 min, 0.00092 h)
Method. Ideal pump-down: t = (V ÷ S_eff) × ln(p₀ ÷ p₁), with V the whole evacuated volume (vessel, piping, filters, condensers), absolute pressures and S_eff the average effective speed over the range. Effective speed through a line: 1/S_eff = 1/S_pump + 1/C. A continuing gas load Q (leaks, outgassing, vapour, as pressure × volume flow) sets a floor p_floor = Q ÷ S_eff; with that load the time becomes t = (V ÷ S_eff) × ln((p₀ − p_floor) ÷ (p₁ − p_floor)), and a target at or below the floor is never reached. Holding duty: the effective speed needed to hold a pressure p against Q is Q ÷ p. Required speed for a target time: S_eff = V × ln(p₀ ÷ p₁) ÷ t (solved numerically when there is a gas load), then the pump speed that gives it through the line. Units: 1 L/s = 3.6 m³/h; 1 mbar·L/s = 3.6 mbar·m³/h. Water boils when the pressure falls below its vapour pressure (Magnus formula: about 23 mbar at 20 °C, 42 mbar at 30 °C). Constant speed is assumed: real pumps lose speed towards their ultimate pressure, so treat the result as a lower bound and check the maker’s curve, or use the banded tool.
What to take from it. If the target is near the floor Q ÷ S_eff, find and cut the gas load (leaks, wet product, a condenser) before buying a bigger pump; if the line conductance is close to the pump speed, fix the line first.
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.