Every vacuum pump datasheet prints two big numbers: pumping speed (m³/h) and ultimate vacuum (Pa). Most people buying vacuum cooling equipment ask about the second one. In fact you should ask about the first.
A vacuum chiller only has to reach about 600 Pa. At that pressure water boils near 0°C, evaporation absorbs heat, and that is the principle of vacuum cooling. 600 Pa is not demanding and an ordinary vane pump reaches it easily. What really decides your production rhythm is how long it takes to get to 600 Pa — that single number determines your batch cycle.
What Each of the Two Parameters Governs
Pumping speed: the volume of gas the pump moves per hour at a given inlet pressure. It determines how long the vacuum chamber takes to go from atmospheric pressure to 600 Pa.
Ultimate vacuum: the lowest pressure the pump can reach with the inlet blanked off. Vane pumps used in food machinery generally reach 0.5 Pa or lower, which is 1200 times deeper than the 600 Pa the equipment needs.
That is exactly where the trap lies. A pump labelled at 0.5 Pa ultimate vacuum sounds impressive, but if its pumping speed between 100 and 10000 Pa is poor, the cooling cycle gets stretched. The datasheet ultimate vacuum is measured at zero flow; real operation happens at several hundred pascals, and that is where pumping speed is the number that matters.
The Selection Formula We Use
CVF series pump selection uses this formula:
S = V chamber × k / t evacuation
- V chamber: vacuum chamber volume (m³)
- k: empirical factor 5–8, covering leakage and outgassing from the product
- t evacuation: target evacuation time (min)
Take CVF-1000-2P as an example:
V chamber = 8 m³
k = 6
t evacuation = 5 min
S = 8 × 6 / 5 = 9.6 m³/min = 576 m³/h
In practice this machine carries one Leybold SV300 (about 300 m³/h) and needs 8–10 minutes to reach 600 Pa. The design accepts that time because the refrigeration system keeps removing heat during pumping. What settles this configuration is pumping speed, not ultimate vacuum.
Real Pump Configurations on Delivered Machines
| Model | Brand | Pumping speed | Power | Used on |
|---|---|---|---|---|
| SV200 | Leybold | about 200 m³/h | 5.5 kW | CVF-500-1P |
| SV300 | Leybold | about 300 m³/h | 7.5 kW | CVF-1000–3000 |
| RD0360A | Busch | about 360 m³/h | 7.5 kW | CVF-2000-4P |
| V0630B | Domestic | about 630 m³/h | 18.5 kW | CVF-8500-12P |
| SV300B | Leybold | about 300 m³/h | 7.5 kW | CVF-4500 (multiple in parallel) |
Verification from a Recent Batch of Project Analyses
A batch of food vacuum chiller projects was re-checked in August 2026, and the evacuation calculation quickly separated sound designs from optimistic ones:
- A 4.05 m³ chamber with an SV200 (200 m³/h) gives about 8.1 minutes of evacuation:
4.05 ÷ (200/3600) × ln(101325/600) × 1.3. That is 40% of the claimed 20 minute cycle before cooling even starts, so the real full cycle is over 50 minutes. - A 2.3 m³ chamber with an SV300B (300 m³/h) gives about 3.1 minutes of evacuation. At the same target pressure that is one third of the time above, because pump and chamber are matched.
- A 1.44 m³ chamber with a 4 kW pump (about 120 m³/h) gives 4.8 minutes of evacuation, 32% of a claimed 15 minute cycle. The claimed cycle does not survive the evacuation formula.
The pattern is obvious: when a quoted cycle looks optimistic, calculate the evacuation first. The bottleneck is usually the pump, not the refrigeration.
The Roots Pump Question
There is another common configuration mistake in food vacuum chilling: adding a Roots pump to look sophisticated. The working pressure range of a food vacuum chiller runs from about 70 kPa (the vapour pressure of 90°C food) down to 3 kPa (25°C). A Roots pump needs a backing pump to pull the system down to its start-up pressure of 1–10 kPa before it can add speed in the low-pressure region. A food vacuum chiller reaches its end pressure before the Roots pump can even cut in. Adding one only increases cost and failure points, with no benefit to the cycle. We never fit Roots pumps to food vacuum chillers and will point it out directly if a supplier proposes one.
Roots pumps are used only on large produce pre-coolers (10 pallets and above) and on freeze dryers, where the working pressure range is deep enough to need them.
Pump Selection Conclusions (For Retrofits or Direct Purchase)
- Target 600 Pa, not 0.5 Pa. Buying ultimate vacuum you never use costs money and changes the cycle by nothing.
- Set the pumping speed by formula: S = V chamber × k / t evacuation, with k between 5 and 8.
- Work out the share of the total cycle taken by evacuation; over 30% means the pump is undersized.
- Match the pump type to the machine: vane pumps for produce pre-coolers and food vacuum chillers; water ring plus vane pumps for high-humidity duty; Roots plus vane pumps only on freeze dryers and pre-coolers of 10 pallets and above.
The vacuum pump is the component most easily mis-sold on the wrong parameter. Pumping speed decides your cycle; ultimate vacuum is decoration on the datasheet.
Frequently Asked Questions
Q: A pump with 0.5 Pa ultimate vacuum must be better than one at 2 Pa, right?
A: For vacuum cooling, no. Both are far below the 600 Pa working target. What affects the cycle is the pumping speed between 100 and 10000 Pa.
Q: How do I estimate the pump size my chamber needs?
A: Use S = V chamber × k / t evacuation. An 8 m³ chamber with a 5 minute target needs about 576 m³/h, which is why a CVF-1000-2P carries one SV300.
Q: Why can the 15 minute cycle a supplier quoted not be achieved?
A: Calculate the evacuation first. If evacuation alone takes a third of the claimed cycle there is nowhere left for the cooling time, so the real cycle must be longer.
Q: Should a food vacuum chiller have a Roots pump?
A: No. Its pressure range (70 kPa down to 3 kPa) ends before a Roots pump can start. Adding one only increases cost and failure points.
Q: Can a produce pre-cooler and a food vacuum chiller use the same pump?
A: In most cases both use vane pumps. Large pre-coolers of 10 pallets and above add a Roots stage, food vacuum chillers do not. Where the vapour load is high, a water ring pump is used.
Author: Dongguan Yuanxian Food Machinery Co., Ltd. engineering team — vacuum-fresh.com. Data from delivered CVF equipment and the August 2026 batch of project reviews.