Oil-free compressors
The instrument air machine class: Class 0 air with no oil path to the header.
Spec oil-free instrument air
Industry: Power Generation
Compressed Air Systems for Power Generation Facilities
- Since 1978
- Sullair dealer since 1984
- 14 locations
- under 2 hour response
Instrument Air Spec Plate
- Standard
- ISA-7.0.01
- Dew point
- -40 F class desiccant
- Config
- N+1 duplex minimum
- Monitoring
- Dew point + header trend
- Dealer
- Sullair since 1984
How do I configure instrument air for a power plant with the redundancy my reliability standard requires?
When one aging compressor stands between your control valves and a unit trip, the fix is a configuration, not just a machine. Cover full instrument demand N+1, so the largest single compressor can fail with no loss of header pressure, dry to ISA-7.0.01 with a desiccant dryer holding a -40 F class pressure dew point, and monitor dew point and header pressure continuously in the DCS. The calculator below lays out the package for your demand.
The instrument air lineup
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Duplex Instrument Air
- Config
- N+1 lead-lag packages
- Air class
- ISO 8573-1 Class 0 option
- Control
- Auto swap on failure
- Use
- Valve actuation, controls
-
Desiccant Dryers
- Dew point
- -40 F pressure dew point
- Standard
- ISA-7.0.01 compliant
- Style
- Heatless and blower purge
- Monitoring
- Dew point transmitter
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Cooling Water Pumps
- Duty
- Auxiliary cooling loops
- Types
- Centrifugal, end suction
- Support
- Repair and rebuild
- Parts
- OEM stocked
-
Backup and Rental
- Response
- under 2 hr average
- Fleet
- Diesel and electric
- Use
- Outages and tie-ins
- Coverage
- 14 locations
45 + Years in Business
14 Midwest Locations
4.7 Star Google Rating
Redundancy configuration calculator
Enter your instrument air demand and pick your availability target. The output is an N+1 or N+2 package layout with machine sizing and desiccant dryer capacity, sized for purge. Starting point for a spec, confirmed against your valve list.
Recommended package
Enter your instrument air demand above for a package layout.
Run the numbers yourself
- CFM calculator: total the instrument air demand of your valves, dampers, and controls before you spec the N+1 package.
- Air receiver tank calculator: size the dry receiver for stroke-through time so valves hold position during a compressor swap.
- Compressed air leak calculator: quantify header leaks that quietly raise runtime and threaten instrument air pressure.
What compressed air really costs
- 10% of US industrial electricity goes to compressed air Source: US DOE Compressed Air Sourcebook
- 20 to 30% of compressed air is typically lost to leaks Source: US DOE Compressed Air Sourcebook
- 75% of ten year compressor cost is energy, not purchase price Source: CAGI life cycle cost data
- under 2 hr average emergency response across our territory Source: Brabazon dispatch
Where power plants use compressed air
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Pneumatic valve actuation
Control valves and dampers that must stroke on demand, every time.
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Controls and instrumentation
Transmitters, positioners, and I/P converters fed from the instrument air header.
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Soot blowing support
Air support for boiler cleaning cycles on solid fuel units.
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Emissions monitoring air
CEMS probe purge and dilution air held to instrument quality.
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Switchgear purge
Dry air purge keeping condensation out of electrical enclosures.
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Turbine support
Seal air, control air, and maintenance air at the turbine deck.
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Nitrogen blanketing
Generated nitrogen for boiler layup and tank blanketing.
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General plant air
Utility air for maintenance, kept separate from the instrument header.
The instrument air requirements that matter
Four requirements separate a compliant instrument air system from a unit trip waiting to happen. None of this is gated behind a form.
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ISA-7.0.01 air quality
The instrument air standard calls for a pressure dew point at least 18 F below the lowest ambient the line sees and never above 39 F, particles filtered to 40 micron or better, and lubricant content as close to zero as practical. In this climate that means desiccant drying to a -40 F class dew point, not a refrigerated dryer.
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N+1 redundancy
Instrument air is a trip hazard for the whole unit: lose it and valves go to fail position. N+1 means full plant demand is covered with the largest single machine out of service, implemented as duplex or triplex packages with automatic lead-lag rotation and swap on failure.
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Continuous monitoring
A dew point transmitter on the dryer outlet, header pressure trending in the DCS, and alarm points set above the valve minimums turn instrument air from a silent assumption into a monitored utility. Every package we quote includes the monitoring points to wire in.
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Dry air receivers and layup
Wet receivers ahead of the dryer and dry receivers after it buy stroke time during a compressor swap. For seasonal units, dry air layup through the instrument air system protects boilers and lines from off-season corrosion.
Featured configuration for instrument air
The configuration we quote most for instrument air is a duplex package of Sullair oil-free rotary screws with automatic lead-lag control, feeding a wet receiver, duplex heatless desiccant dryers with a dew point transmitter, and a dry receiver at the header. Everything is N+1 end to end, so a failed compressor or a dryer tower in service never touches header pressure. Machine options are on the oil-free compressor page, and outage rental backup comes through rentals.
Not every air user in the plant needs instrument-grade air: drying all
plant air to a -40 F dew point wastes purge air and energy on tools and blow-off that do
not care. Splitting the system, a right-sized instrument air package plus ordinary
utility air with a check-valved emergency crossover, usually costs less to run than one
oversized instrument-quality system. Ask us to price both before you spec the
bigger package.
Typical project: instrument air redundancy
Taking a single point of failure off the trip list
A common scenario at a generating station is instrument air running from one aging oil-injected compressor with a refrigerated dryer, a configuration that puts winter dew point excursions and a single point of failure on the same header that feeds every control valve on the unit. A typical project replaces it with a duplex oil-free package on lead-lag control and duplex heatless desiccant dryers holding a -40 F class pressure dew point, with a dew point transmitter and header trend wired to the DCS. That takes instrument air off the top of the trip-risk list, and the old machine can be kept as a maintenance-air spare behind a check valve. Brabazon configures and installs the oil-free machines, drying, and monitoring points for this kind of retrofit.
Power plant air support across the upper Midwest
Factory-trained technicians dispatch from 14 branches with an under 2 hour average emergency response and rental backup for outages. Find your nearest branch:
Questions engineers actually ask us
What dew point does instrument air need?
ISA-7.0.01 requires a pressure dew point at least 18 F below the lowest ambient temperature the air lines see, and never above 39 F. For outdoor lines in the upper Midwest that effectively means a -40 F class pressure dew point from a desiccant dryer, since winter ambients go far below what refrigerated drying can protect.
Do I need N+1 or N+2 for instrument air?
N+1 is the working minimum for any plant where loss of instrument air trips the unit: full demand covered with the largest machine down. N+2 makes sense where a trip is intolerable or maintenance windows are long, such as base load units far from spare parts. The calculator above shows both configurations for your demand.
Does instrument air have to be oil-free?
ISA-7.0.01 says lubricant content should be as close to zero as practical, and oil-free compressors are the clean way to get there because no downstream filter failure can put oil in the header. Oil-injected machines with coalescing filtration are used in some plants, but the filters become a monitored, maintained critical item.
Can plant utility air and instrument air share one system?
They can, but it usually costs more than separating them. Utility air for tools and blow-off does not need a -40 F dew point, and drying all plant air to instrument quality wastes purge air and energy. The standard fix is a smaller instrument-grade system plus general plant air, with a check-valved crossover for emergencies.
How big should instrument air receivers be?
Size dry storage for stroke-through time: enough air for controlled operation during a compressor swap, commonly several minutes at full instrument demand. A wet receiver ahead of the dryer smooths compressor cycling, and a dry receiver after it is the reserve the control room actually relies on.
Who services instrument air compressors at power plants in the Midwest?
Brabazon dispatches factory-trained technicians from 14 locations across Wisconsin, Illinois, Minnesota, and Missouri with an under 2 hour average emergency response, and stages rental backup for planned outages. We have serviced industrial compressed air since 1978.
Where to go next
Get an instrument air spec you can put in the reliability plan
Send us your instrument air demand and lowest site ambient. An engineer will lay out the N+1 package, desiccant drying, and the monitoring points to wire into the DCS.