Why boost nitrogen at all?
On-site nitrogen generators (PSA and membrane) typically deliver nitrogen at roughly 5–8 bar(g) (about 70–115 psig), close to their feed-air pressure. Many uses need more than that:
- Laser cutting of stainless steel and aluminium, where high-pressure nitrogen assist gas, often in the 15–30 bar range (about 220–435 psig), clears the kerf and prevents oxidation.
- Pressure and leak testing of vessels, pipelines and components under the client’s approved procedure.
- Purging and inerting of tanks, reactors and pipelines in pharma, chemical and oil and gas plants.
- Cylinder or bank filling to high pressure for storage or distribution.
- Injection moulding gas assist, tyre filling and food packaging, each with its own pressure and purity needs.
A booster lets a plant replace bought-in high-pressure cylinders or liquid nitrogen with nitrogen made on site, as long as the generator, booster and storage are matched as one system.
How a nitrogen booster works
Most nitrogen boosters are reciprocating compressors, oil-free or with a design that keeps oil out of the gas, in one to four stages depending on the ratio. Each stage compresses the gas, an intercooler removes heat, and the next stage takes it higher. Some designs are air-driven gas boosters (a large air piston drives a small gas piston), used for small flows and very high pressures. Larger continuous duties use motor-driven multi-stage piston machines.
Key design features to look for:
- Oil-free compression or a proven oil-separation design, so the nitrogen is not contaminated.
- Seals and packing designed to stop air being drawn in, because oxygen ingress lowers purity.
- Intercoolers and an aftercooler sized for high Indian ambient temperatures.
- Relief valves on every stage and a discharge non-return valve.
- Shutdowns for low suction pressure, high discharge pressure and high discharge temperature.
The nitrogen source decides the booster duty
| Nitrogen source | Typical feed behaviour | What it means for the booster |
|---|---|---|
| PSA generator | Cycling output, purity depends on flow drawn; pressure close to feed air | A buffer receiver between generator and booster is essential; drawing too fast lowers purity |
| Membrane generator | Continuous output; purity falls as flow rises; temperature affects performance | Match booster suction flow to the purity-flow curve of the membrane |
| Liquid nitrogen vaporiser | High purity and dry; pressure set by the tank and regulator | Watch suction temperature after the vaporiser; cold gas can affect seals and materials |
| Pipeline or plant nitrogen header | Pressure varies with other users | Specify minimum header pressure when other users draw at the same time |
Never assume that the generator’s nameplate capacity is available at the booster inlet at all times. Purity, temperature, compressed-air supply and other users all change what actually arrives.
Flow and mass balance: the generator, receiver and booster as one system
State flow in Nm³/h with the reference condition named. Then balance the system:
- Work out the user’s demand pattern: steady, cyclic (a laser that cuts in bursts) or batch (a test that fills a vessel).
- Check that the generator can supply the average demand at the required purity, plus the booster’s own losses.
- Size a low-pressure buffer receiver between generator and booster so the booster never pulls the generator below its purity point.
- Size a high-pressure receiver or bank after the booster to cover peaks, so the booster does not start and stop too often.
- Set the booster’s start and stop pressures, or its unloading control, so that it follows demand within its duty-cycle limits.
Worked example: a laser needs 30 Nm³/h at 25 bar(g) on average, with short peaks higher. Choose a generator able to give at least that average at the purity the laser requires, a booster rated above the average at the minimum suction pressure, and a high-pressure receiver that covers the peak volume over the cutting burst. The maker’s data for each item confirms the figures.
Purity, moisture and contamination
Boosting does not improve purity; it can only keep it or spoil it. Common causes of purity loss after a booster are air drawn in through seals during low-suction conditions, a leaking suction line, oil carry-over from a lubricated design, and moisture from an undried feed. Practical safeguards:
- An oxygen analyser at the booster discharge or at the user, with an alarm and, where needed, an automatic dump of off-spec gas.
- A low-suction-pressure shutdown so the booster cannot pull a vacuum on the suction line.
- A dry feed: generator feed air should be properly dried and filtered, typically with a refrigerated dryer (pressure dew point about +3 °C) and filters to the generator maker’s requirement.
- Final filtration after the booster where the application needs it.
High-pressure safety boundaries
High-pressure nitrogen stores a great deal of energy and is also an asphyxiant. A leak indoors can lower oxygen levels without any smell or warning. The design should cover:
- Receivers and banks designed, certified and inspected for their pressure under the applicable rules, with the receiver’s maximum allowable pressure above the booster’s relief setting.
- Relief valves sized by the maker, discharging to a safe outdoor point.
- Pipe, hoses and fittings rated for the full pressure with suitable margin.
- Oxygen-depletion monitoring in enclosed rooms where nitrogen is boosted or stored.
- Pressure testing with nitrogen only under an approved procedure, because a pneumatic test carries a much higher stored-energy hazard than a hydraulic test.
Common problems and their usual causes
| Symptom | Likely causes | First checks |
|---|---|---|
| Purity drops when booster runs | Booster drawing faster than generator, air ingress through seals or suction leaks | Buffer pressure trend, suction line leak test, seal condition |
| Slow filling of the high-pressure receiver | Low suction pressure, worn valves or rings, leaks downstream | Suction pressure, stage pressures, leak test |
| High discharge temperature trip | Leaking valves, hot room, fouled cooler, low suction raising ratio | Ventilation, cooler fins, valve condition |
| Frequent starts and stops | High-pressure receiver too small, narrow pressure band | Receiver volume, control settings |
| Moisture or oil at user | Wet feed, lubricated design without proper separation | Feed dryer, filters, booster type |
How Reddy Compressors helps
We sell new and used or refurbished gas compressors, including nitrogen boosters, CNG, process-gas and booster compressors, rent them, service them and supply their spare parts. We are an independent multi-brand specialist at Tarnaka, Secunderabad, serving industry since 2002, and not an authorised dealer of any brand. We have tie-ups with all major and reputed brands.
For nitrogen boosting we can:
- Review the whole chain: feed-air compressor, dryer, filters, generator, receivers and booster, and show where the bottleneck is.
- Supply the compressed-air side for the generator, with dryers and filtration to the generator maker’s requirement.
- Source a nitrogen booster sized from the maker’s data at your minimum suction pressure.
- Service and overhaul booster compressors: valves, rings, seals, coolers, relief valves and instruments.
- Identify and supply spares from the nameplate and old part, confirming fit before quoting.
Our service teams cover Telangana and Andhra Pradesh, and we supply equipment and spares across India. Receiver certification and test procedures remain with your own competent engineer.
What to send us
- Nitrogen source (PSA, membrane, liquid, pipeline), its rated flow, purity and outlet pressure.
- Required delivery pressure and flow at the user, with the demand pattern.
- Purity and dryness needed at the user.
- Existing receivers: volume and maximum allowable pressure.
- Power supply and site conditions.
- For an existing booster: nameplate photos and the fault you are seeing.
Frequently asked questions
Can I boost nitrogen from my PSA generator for laser cutting?
Yes, this is a common arrangement. The PSA generator delivers nitrogen at about feed-air pressure, a booster raises it to the laser’s assist-gas pressure, and a high-pressure receiver covers peaks during cutting. The generator must give the required purity at the average flow, and a buffer receiver must stop the booster from pulling the generator below its purity point.
Why does my nitrogen purity drop when the booster starts?
Usually the booster is drawing nitrogen faster than the generator can supply at the set purity, so the PSA or membrane flow rises and purity falls. Another cause is air leaking in through seals or suction fittings when suction pressure drops. Check the buffer receiver size, the booster’s capacity against the generator’s rating, and suction-line tightness, and fit an oxygen analyser at the outlet.
How do I calculate the pressure ratio of a nitrogen booster?
Convert both pressures to absolute by adding atmospheric pressure, about 1 bar, then divide discharge by suction. From 5 bar(g) (6 bar a) to 29 bar(g) (30 bar a) the ratio is 5. Always check the ratio at the lowest suction pressure the booster will see, because that case gives the highest temperature and the lowest delivered flow.
Is a nitrogen booster oil-free?
Most nitrogen boosters for purity-sensitive uses are oil-free piston machines, or designs that keep lubricating oil away from the gas. Oil carry-over would contaminate the nitrogen and can damage downstream equipment. Where a lubricated design is used, suitable separation and filtration must be included. Confirm with the maker how the design keeps oil out of the gas for your purity requirement.
Is high-pressure nitrogen dangerous?
Yes, in two ways. It stores a large amount of energy, so receivers, pipes, hoses and relief valves must be correctly rated, certified and inspected. It is also an asphyxiant: a leak in an enclosed room can reduce oxygen without warning. Install oxygen-depletion monitoring where nitrogen is boosted or stored indoors, and vent relief valves to a safe outdoor point.
Do you service nitrogen booster compressors?
Yes. We service and overhaul nitrogen booster compressors of different makes, covering valves, piston rings, seals, coolers, relief valves and instruments, and we also sell and rent gas compressors. Spares are identified from the make, model, serial number and nameplate, and fit is confirmed before quoting. Our service teams cover Telangana and Andhra Pradesh, with supply across India.
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.
Nitrogen booster pressure ratio and stage temperature
Convert the booster’s suction and discharge to absolute pressure, find the pressure ratio and the ideal stage discharge temperature, and compare the lowest suction pressure case.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Suction pressure (in the unit below): 5
- Suction pressure unit: bar g
- Discharge pressure (in the unit below): 29
- Discharge pressure unit: bar g
- Site atmospheric pressure (bar a; for gauge entries): 1
- Gas: Nitrogen (k 1.40, MW 28)
- Other gas: k = cp/cv (used only for Other): 1.3
- Other gas: molecular weight (kg/kmol; used only for Other): 17
- Suction temperature (°C): 35
- Number of stages (screening, equal ratio): 1
- Stage ratio for the temperature check (0 = equal split): 0
- Isentropic efficiency (%; 100 = ideal): 100
- Maximum allowable discharge temperature (°C; 0 = not checked): 0
- Mass flow (kg/h; 0 = not used): 0
- Compressibility factor Z at suction (1 = ideal gas): 1
- Running hours for the transferred mass (h; 0 = not used): 0
- Lowest credible suction pressure (same unit as suction; equal to suction = no comparison): 5
Result
- Suction, absolute: 6 bar a (5 bar g, 87 psia)
- Discharge, absolute: 30 bar a (29 bar g, 421 psig)
- Overall pressure ratio: 5 absolute discharge ÷ absolute suction
- Ratio if gauge figures were divided (wrong): 5.8 gauge ÷ gauge in the same unit; shown only to show the error
- Equal stage ratio: 5 over 1 stage
- Exponent (k − 1)/k: 0.286 k = 1.4 for nitrogen; R = 296.8 J/(kg·K)
- Ideal discharge temperature per stage: 214.9 °C (488.1 K) at a stage ratio of 5, suction 35 °C
Method. P(abs) = P(gauge) + site atmospheric pressure. Overall ratio r = P₂(abs) ÷ P₁(abs); dividing gauge figures gives a wrong ratio, worst at low suction pressure. Equal split: stage ratio = r^(1/n); interstage pressure after stage i = P₁ × (stage ratio)^i. Ideal (isentropic) discharge temperature T₂ = T₁ × (stage ratio)^((k−1)/k), kelvin, assuming intercooling back to the suction temperature before every stage; with an isentropic efficiency η, T₂ = T₁ + (T₂ideal − T₁) ÷ η. Gas constant R = 8,314.46 ÷ molecular weight. Actual suction volume = ṁ × Z × R × T₁ ÷ P₁; normal volume uses 0 °C and 1.01325 bar a with Z = 1. Transferred mass = mass flow × running hours. Rounded textbook k values near ambient; real-gas Z and the maker’s calculation for the actual composition govern. These are screening values, not equipment ratings or settings.
What to take from it. Always work in absolute pressure, and check the lowest credible suction pressure: it gives the highest ratio and discharge temperature and the largest actual suction volume for the same mass flow.
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 7 November 2026. How our engineering content is reviewed.
Pressure unit and gauge/absolute conversion
Convert between bar, psi, kPa and MPa and between gauge and absolute pressure. A mix-up between gauge and absolute is a classic cause of wrong sizing.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Pressure: 7
- Unit: bar g
Result
- bar gauge: 7
- bar absolute: 8.01
- psi gauge: 101.5
- psi absolute: 116.2
- kPa gauge: 700
- MPa gauge: 0.7
Method. Absolute pressure = gauge pressure + atmospheric (1.01325 bar at sea level). 1 bar = 14.504 psi = 100 kPa = 0.1 MPa. Hyderabad is about 540 m above sea level; atmospheric pressure there is roughly 0.95 bar, so enter the local value in the flow tool if it matters.
What to take from it. A 7 bar gauge system is 8.01 bar absolute. Ratio and flow-conversion work uses absolute pressure.