Why classify the duty before choosing a machine
Most compressed-air enquiries are straightforward: air in, air out at 7–10 bar, with a known quality class. Specialist duties are different. The same “compressor” request might really be a low-pressure blower for aeration, a booster for nitrogen, a sealed machine for biogas or a vacuum pump for drying. Choosing the technology first, before the duty is understood, is how plants end up with machines that overheat, leak gas, corrode or never reach the required vacuum.
A sound enquiry therefore starts with the facts of the duty. Once those are clear, the right family of machine usually follows, and the questions about materials, seals, cooling, controls and safety become specific instead of general.
The five facts that define a specialist duty
- Media. Air, nitrogen, natural gas, CNG, biogas, carbon dioxide, hydrogen, helium, oxygen, steam or process vapour. Note its composition, and how it changes during start-up, upsets and cleaning.
- Pressure regime. Suction and discharge pressure, stated as gauge or absolute. Vacuum is always best given in absolute terms, such as mbar(a).
- Flow basis. Mass flow or volume flow, and at what conditions: inlet volume, normal m³/h or free air delivery. Give the minimum, normal and peak.
- Temperature and contaminants. Suction and discharge temperature limits, moisture, condensable vapours, dust, fibres, oil and corrosive components.
- Process function. What the gas or vacuum must achieve: aerate, convey, hold, dry, degas, boost, recover or test. This defines what “good enough” means.
Which pressure regime are you in?
| Regime | Typical pressure | Typical technologies | Example duties |
|---|---|---|---|
| Vacuum | Below atmospheric, given in mbar(a) | Liquid-ring, rotary-vane, dry claw, dry screw, scroll, Roots booster, ejector | Drying, degassing, packaging, holding, distillation |
| Low-pressure blower | Up to about 1 bar(g) (about 15 psig) | Roots, screw, centrifugal, side-channel blowers | Aeration, pneumatic conveying, combustion air |
| Plant and process air | About 4–13 bar (58–188.5 psig) | Screw, piston, centrifugal compressors | Plant air, instrument air, process air |
| High-pressure air | Above about 13 bar, up to 30–40 bar and beyond | Multi-stage screw and piston, boosters | Drilling, PET blowing, testing |
| Process gas | From slight boost to very high pressure | Reciprocating, diaphragm, screw, centrifugal | CNG, nitrogen, biogas, process gas |
Pressure ratio drives design. A blower for aeration works at a small pressure rise and very large volume; a CNG compressor works at a high ratio over several stages with intercooling. A duty that sits on a boundary, for example 1.5 bar(g) conveying air, needs an honest comparison of blower and compressor options rather than a default choice.
Gas properties change the machine
Gases do not behave like air. Light gases such as hydrogen and helium are hard to compress in dynamic machines and leak easily through seals. Heavy or wet gases such as carbon dioxide and biogas change discharge temperature, condensation and power. Flammable, toxic and oxygen-rich gases bring strict rules on materials, cleanliness, sealing, venting and electrical equipment. The specific heat ratio, molecular weight and compressibility of the gas all affect discharge temperature, the number of stages and the power needed, so we ask for a gas analysis rather than assuming air figures apply.
Oxygen, hydrogen and toxic-gas duties always follow the gas-specific codes and the maker’s design rules. These are specialist designs, and we treat them as such.
Contamination, condensation and materials
- Moisture and condensable vapour. Water and solvent vapour can condense in coolers, separators and vacuum pumps, causing corrosion and loss of performance. Interstage cooling and separation, and vapour handling in vacuum duty, must be designed for it.
- Dust and fibres. Common in conveying, cement, textiles and agricultural processing. Inlet filtration and machine type must suit the load.
- Oil and product contamination. Where gas or air touches product, oil-free machines or effective separation are needed, and the direction of contamination (machine to process or process to machine) matters.
- Corrosion. Hydrogen sulphide in biogas, chlorides near the coast and acidic condensate attack standard metals and elastomers. Materials and seals must be chosen for the gas.
Gas compressors: CNG, nitrogen, process gas and boosters
We sell new and used or refurbished gas compressors, rent them, service them and supply their spares, for CNG, nitrogen, process gas and booster duties. Reciprocating machines dominate high-ratio duties such as CNG and nitrogen boosting; diaphragm compressors suit high-purity and hazardous gases where zero leakage to atmosphere matters; screw and centrifugal machines suit higher flows at moderate ratios. Pulsation, vibration, interstage cooling, seal leakage and capacity control all need attention in gas service.
- Process gas compressor selection requirements
- Gas properties and compression behaviour
- Natural gas booster systems
- Nitrogen booster compression
- Biogas compression and pretreatment
- Landfill gas compression
- Carbon dioxide compression
- Hydrogen compression equipment
- Helium recovery compression
- Cryogenic process compression
- Diaphragm process gas compressors
- Oil-free reciprocating process gas compression
- Gas compressor capacity control
- Interstage cooling and separation
- Pulsation and vibration in gas compressors
- Gas compressor seals and leakage
- High-purity gas sampling and verification
- Hazardous-area compressor packages
Blowers and low-pressure air
We sell new and used or refurbished blowers, rent them, service them and supply their spares: Roots, screw, centrifugal and side-channel types. Low-pressure duties are often energy-intensive because they run continuously, so turndown, control and the match between blower curve and process demand matter. Positive-displacement blowers need attention to pulsation and silencing; aeration duties need good control as oxygen demand changes through the day.
- Low-pressure aeration blower systems
- Wastewater aeration blower turndown
- Aquaculture aeration air supply
- Fermentation aeration air supply
- Pneumatic conveying blower packages
- Combustion and burner blowers
- Blower pulsation and silencing
- Vacuum blowers for holding and handling
Vacuum systems
Vacuum duties are defined by the absolute pressure needed, the gas and vapour load, the pump-down time and what the exhaust carries. Liquid-ring pumps tolerate wet and condensable loads; oil-sealed rotary-vane and rotary-piston pumps reach deeper vacuum on clean duties; dry claw, dry screw and scroll pumps avoid oil in the process; Roots boosters extend the range and speed of a backing pump; ejectors use steam or air with no moving parts. Line size, leaks and outgassing often limit performance more than the pump itself. We sell, rent and service vacuum pumps of all main types and supply their spares.
- Dry claw vacuum pumps
- Dry scroll vacuum pumps
- Oil-sealed rotary piston vacuum pumps
- Liquid-ring seal liquid systems
- Vacuum Roots booster systems
- Vacuum ejectors and steam jets
- Pump-down and vessel sizing
- Vacuum conductance and line design
- Condensable vapour handling
- Vacuum leaks and outgassing
- Vacuum exhaust and contamination control
- Vacuum drying
- Vacuum degassing
- Vacuum distillation utilities
- Vacuum packaging
- Vacuum forming and thermoforming
- Laboratory vacuum networks
- Central vacuum energy and load management
- Vacuum and blower performance acceptance
Life-safety air duties
Breathing air, diving air and hyperbaric air are life-safety systems. They are designed, tested and maintained to their own standards, with purity limits, monitoring and certification that go well beyond plant air. A plant compressor with filters is not breathing air. We explain the boundaries of these systems and what a specialist supplier must provide, and we can support the general compressed-air side where that is appropriate.
- Breathing air system procurement
- Diving air compression
- Hyperbaric facility air supply
- Design responsibility and handover
Operating pattern, site and safety
A machine that suits steady duty may fail on frequent starts or wide turndown. Tell us the hours per day, the number of starts, and the range of flow from minimum to peak. Site conditions matter too: in Telangana and Andhra Pradesh, high summer ambient temperatures, dust and variable power quality affect cooling, filtration and motor protection. For gas duties, the vent and relief routes, emissions, hazardous-area classification and interlocks must be agreed with the plant’s process-safety team before equipment is chosen.
How Reddy Compressors helps
Reddy Compressors, based at Tarnaka, Secunderabad, has served industry since 2002. We sell new and used or refurbished, rent and service gas compressors (CNG, nitrogen, process gas and booster), centrifugal compressors and blowers (Roots, screw, centrifugal and side-channel), and supply their spares. For axial compressors we provide service and spare parts. We also handle oil-free and high-pressure air compressors, and we sell new and used/refurbished vacuum pumps (rotary vane, liquid ring, dry screw, dry claw, scroll, rotary piston, Roots boosters and vacuum blowers), rent them, service them and supply their spares. For life-safety duties such as breathing air, we explain the boundaries and say plainly when a specialist supplier is the better route.
We work across brands as an independent multi-brand specialist, not an authorised distributor. We have tie-ups with all major and reputed brands. Our 20-plus engineers and technicians serve sites throughout Telangana and Andhra Pradesh, and we supply equipment, rentals and spares across India.
What to send us
- The gas or vapour, with a composition or analysis
- Suction and discharge pressure, gauge or absolute
- Flow at minimum, normal and peak, with its basis
- Temperatures, moisture and contaminants
- The process function and operating hours
- Site location, power supply and hazardous-area classification
- Existing machine nameplates, if replacing or servicing
Frequently asked questions
What is the difference between a blower and a compressor?
A blower moves large volumes of air or gas at a small pressure rise, typically up to about 1 bar(g) (15 psig), for duties such as aeration, conveying and combustion air. A compressor raises pressure much further, commonly 7–13 bar for plant air and far higher for gas and drilling duties. Blowers usually have simpler construction and lower pressure ratios, but they run continuously, so efficiency and control matter.
Can a normal air compressor be used for nitrogen or natural gas?
No. Gas compressors are designed for the specific gas, with suitable seals to prevent leakage, materials that resist the gas and its contaminants, and electrical and safety equipment for flammable or inert atmospheres. Using an air compressor on gas risks leaks, fire, contamination and damage. Nitrogen and natural gas boosting typically use purpose-built reciprocating or other gas compressors.
Which vacuum pump is best for wet or solvent-laden duty?
Liquid-ring pumps tolerate water and condensable vapours well, because the seal liquid absorbs them, but deep vacuum is limited by the seal-liquid temperature. Dry screw and claw pumps avoid oil contamination and can handle vapours when designed with suitable temperature control. Condensers upstream of the pump often help. The right choice depends on the vacuum level, vapour load and what the exhaust carries.
Does Reddy Compressors service CNG and nitrogen compressors?
Yes. We sell new and used or refurbished gas compressors, rent them, service them and supply spares for CNG, nitrogen, process gas and booster duties. Send the make, model, serial number, gas, pressures and running hours. Our team serves sites across Telangana and Andhra Pradesh, and we supply equipment and spares across India.
How do I size a blower for wastewater aeration?
Start from the oxygen demand of the process, which sets the airflow, and the depth of the diffusers plus system losses, which sets the pressure. Demand varies through the day and the seasons, so define minimum, average and peak airflow. Then choose blower types and numbers that cover the range efficiently, with turndown by speed or by staging, rather than sizing one machine for the peak.
Can I use a plant compressor for breathing air?
Not by simply adding filters. Breathing air is a life-safety system with its own purity limits, including carbon monoxide and oil, monitoring and testing requirements. It needs a purpose-designed system from a specialist supplier, with the intake location, treatment, alarms and maintenance under a defined responsibility. We can explain the boundaries and support the compressed-air side where appropriate.
Related pages
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.