Short Answer: One Job Only
In a vacuum pre-cooler or a food vacuum chiller the vacuum pump has exactly one task: hold the chamber at low pressure and remove non-condensable gas. Water vapour is not its responsibility – water vapour is condensed into ice or water by the water catcher (cold trap), which is driven by the refrigeration system. A CVF-300 food vacuum chiller uses a Leybold dry screw pump ND160 together with a Shanghai Feilu water ring pump 2BV5111 to pull the chamber to about 600 Pa, where water boils and evaporates near 0°C and the product is cooled by the latent heat of evaporation. Choose or pair the vacuum pump wrongly and the whole cooling cycle falls apart.
What Work Does the Vacuum Pump Do Inside the Machine?
The principle of vacuum cooling is not complicated: lower the pressure in the chamber and the boiling point of water falls with it. At 610 Pa water boils at 0°C and the heat of evaporation is about 2500 kJ/kg. Moisture on the surface of the product evaporates, taking the product's own heat with it, and the temperature comes down.
The problem is the water vapour. If the vacuum pump were made to pull water vapour directly, a vane pump would emulsify and fail quickly – water gets into the oil and the pump is ruined.
That is why the machine must have a refrigeration system. The water catcher (evaporator) surface is cold, water vapour hitting the cold surface condenses into ice or water, and only the remaining non-condensable gas (air, nitrogen) is left for the vacuum pump. The role of the vacuum pump is to maintain low pressure, not to pump water vapour. Once that line is clear, the selection follows naturally.
Two-Stage Pumping: Why Water Ring and Dry/Vane Pumps Are Combined
A food vacuum chiller loads at high temperature, so the water vapour concentration in the chamber is high. Pulling that with a vane pump alone carries a high risk of oil emulsification. The usual approach is two-stage:
| Stage | Pump | Function | Advantage |
|---|---|---|---|
| Rough pumping | Water ring pump (2BV5110/5111/5121) | Pull the chamber from atmospheric pressure down to about 10 kPa quickly | Tolerates water vapour and moisture, simple construction |
| Fine pumping | Vane pump / dry screw pump (e.g. Leybold SV100/SV200/ND160) | Continue down below 600 Pa | High ultimate vacuum, flat pumping speed curve |
This is exactly how real configurations are built:
| Machine | Vacuum pump configuration |
|---|---|
| CVF-100 | Leybold SV100 + Shanghai Feilu 2BV5110 |
| CVF-200 | Leybold SV200 + Shanghai Feilu 2BV5121 |
| CVF-300 | Leybold dry screw ND160 + Shanghai Feilu 2BV5111 |
Smaller models also use a single-pump solution. CVF-30 in Vietnam uses one Leybold SV40, CVF-120 in New Zealand uses an SV200, and CVF-400 in India uses two SV200B. When the volume is small and the loading temperature is not high, a single vane pump is enough; for large volumes and high-temperature loading, two-stage is mandatory.
How Are Pumps Configured on Produce Pre-Coolers?
Produce pre-coolers load field heat (25–30°C), so the water vapour load is smaller than on a food vacuum chiller and the pump configuration can be simplified. Large models still use several pumps in parallel:
| Model | Vacuum pump configuration | Pump power |
|---|---|---|
| CVF-300 pre-cooler | German Leybold SV200B × 1 | 4 kW |
| CVF-1500-4P | Busch RA0302D × 2 | 15 kW |
| CVF-2000-4P | Pumping speed 600 m³/h | 11 kW |
| CVF-3000 double door | Busch RA0203D × 3 | 22.5 kW |
| CVF-4000-8P | Busch RA302D × 4 | 30 kW |
CVF-4000-8P also has a version using 5 × 5.5 kW Busch/Leybold pumps; that is an optional configuration variant, so quotations follow the project design.
How to Calculate the Pumping Speed
The core of pump selection is pumping speed. A simplified formula is common in engineering practice:
t = 2.3 × (V/S) × lg(P1/P2)
Where t is the pumping time (seconds), V is the chamber volume (litres), S is the effective pumping speed of the pump (litres per second), P1 is the starting pressure and P2 is the target pressure. The pumping speed of a roughing pump can also be calculated as S = 2.3V·lg(Pa/P target)/t, where Pa is atmospheric pressure.
Another rule of thumb is that pump capacity needs margin: select S > (20%–30%) × Se', where Se' is the pumping rate converted to the actual system working conditions. The working point of the pump must stay away from the ultimate vacuum region, where efficiency is low and cavitation is likely.
Domestic versus Imported Pumps
We supply imported pumps by default (Leybold, Busch, Rietschle, Busch) and only consider domestic pumps when the customer's budget is tight. The differences are real:
| Item | Domestic pump | Imported pump |
|---|---|---|
| Machining precision | Coarser | Precise |
| Noise | Higher | Reasonable |
| Oil mist | Obvious | Low |
| Maintenance interval | About 3 months | About 6 months |
| Service life | 5–6 years | About 10 years |
Vane pumps are sensitive to water, so whichever origin you buy, the oil (100# vacuum pump oil) must be changed on schedule. Pump position and pipe length also affect performance: the further the pump is from the water catcher, the greater the pipe pressure loss and the lower the effective pumping speed.
FAQ
Q: If the vacuum pump fails, can the vacuum cooler still cool?
A: No. Without the pump holding low pressure the chamber pressure cannot come down, the water does not boil and evaporative cooling does not happen. The vacuum pump is a core component.
Q: Will the vacuum pump pull out the water vapour?
A: It should not be allowed to. Water vapour is condensed by the water catcher and the pump only handles non-condensable gas. Let the pump swallow water vapour and the vane pump oil emulsifies, scrapping the pump quickly.
Q: Does a food vacuum chiller have to have a refrigeration system?
A: It must. The water catcher needs a cold surface to condense water vapour. Without a refrigeration system the vacuum pump faces the water vapour directly and will not last long.
Q: How do I judge that a vacuum pump needs service or replacement?
A: Look at ultimate vacuum and pumping speed. If the time to reach 600 Pa grows, the ultimate pressure will not come down, noise increases or the oil turns milky white, either the pump or a seal is failing.
Q: How do I choose between domestic and imported pumps?
A: Choose domestic for a tight budget and diligent maintenance; choose imported for stability and low maintenance. The gap in maintenance interval and life is 3 months versus 6 months and 5–6 years versus 10 years – run your own numbers.
Summary
The role of the vacuum pump in pre-cooling and vacuum chilling equipment in one sentence: maintain low pressure and remove non-condensable gas. Three things matter when specifying a pump: is the pumping speed sufficient, does it tolerate water vapour, and what maintenance interval can you accept. The configuration data above comes from real projects and can be used directly as a reference. The produce vacuum pre-cooler and food vacuum chiller pages carry complete pump configuration parameters for model-by-model selection.
Yuanxian Machinery engineering team — 2026-08-18