N2-BLAST Fire Protection Systems Overview – South-Tek Systems

Applies to: All N2-BLAST nitrogen generators for dry and pre-action fire sprinkler systems, current and legacy. N2-BLAST is a separate product line from South-Tek industrial nitrogen generators and from the beverage systems — do not use an industrial or beverage article on a fire protection unit.

An N2-BLAST replaces the compressed air in a dry or pre-action sprinkler system with high-purity nitrogen. Oxygen is what drives corrosion inside sprinkler piping; take the oxygen out and oxygen-driven corrosion largely stops. The generator makes its own nitrogen on site from compressed air, holds it in storage, and feeds the system through the air maintenance device the same way a compressor would. Filling the system is only half the job — the air already trapped in the piping has to be purged out, which is what the AutoPurge Systems below are for.

This article is the starting point. Find your model family below, then work from that family's articles — the models differ enough that guidance written for one will mislead you on another.

Start by identifying the unit

Read the model number off the nameplate on the unit before you open any article or manual. Do not go by the size of the cabinet, by what is on the purchase order, or by what the last technician wrote on the service tag. Cabinets were reused across models and across the legacy and current lines.

▲ Attention — legacy and current models share almost nothing The model numbers are close enough to catch you out. FPS-1650 is current; FPS-1750 is legacy. FPS-3250 is current; FPS-3000 is legacy. FPS-16500 is current; FPS-15000 is legacy. These are different machines with different controls, different filters and different service intervals. The specifications in this article are for the current line. If your nameplate reads FPS-650, FPS-1250, FPS-1750, FPS-3000, FPS-6000, FPS-15000 or FPS-20000, go to the legacy articles below and do not apply anything from the current-line sections to it.

Current model families

Family	Form	Where to start
FPS-500, FPS-900 and FPS-900-RS	Compact, wall mounted. Optional air compressor.	FPS-500 and FPS-900 Overview
FPS-1650, FPS-3250, FPS-5000	Mid-range cabinet with an internal nitrogen storage tank. Compressor options from 2 to 10 HP.	FPS-1650, FPS-3250, and FPS-5000 Overview
FPS-10000, FPS-16500, FPS-22500	Large cabinet. Air dryer is internal, plumbed and piped inside the generator.	FPS-10000, FPS-16500, and FPS-22500 Overview

An FPS-900 nitrogen generator: a single-door red cabinet lettered N2-BLAST, Nitrogen Generator, Corrosion Inhibiting System, with a side-mounted controller, an outlet ball valve and a pressure gauge at the base — **FPS-900 — the compact end of the current line.** The FPS-500 and the FPS-900-RS share this cabinet, so read the nameplate rather than going by shape.

An FPS-22500 nitrogen generator: a tall two-door red floor-standing cabinet lettered N2-BLAST with the SMART-Trak display panel mounted on the upper right door — **FPS-22500 — the large end.** Two doors, floor standing, with the SMART-Trak display on the upper right door.

Legacy model families

These units are no longer built. They are still in service and still supported, but they are documented separately and the current-line specifications do not apply to them.

Family	Where to start
FPS-650, FPS-1250	FPS-650 and FPS-1250 Legacy Overview
FPS-1750, FPS-3000, FPS-6000	FPS-1750, FPS-3000, and FPS-6000 Legacy Overview
FPS-15000, FPS-20000	FPS-15000 and FPS-20000 Legacy Overview
All legacy models	Legacy N2-BLAST Fire Protection Systems Overview

Three legacy N2-BLAST generators side by side: a skid-mounted unit with a vertical storage tank and twin sieve towers, a tall narrow FPS-3000 floor cabinet, and a narrow FPS-650 cabinet — **The legacy line.** Useful for recognizing a unit on site, but **confirm against the nameplate** — several of these cabinets were used for more than one model.

What every current N2-BLAST delivers

Specification	Value	What it means for you
Nitrogen purity	98.5% or better	A minimum, measured at the generator outlet. It is not a statement about what any one sprinkler zone is reading — a zone reaches its own purity over time as the trapped air is purged out, and is judged against the setpoint programmed for that zone.
Product gas dew point	-35 °F	Far drier than compressed air, and the reason nitrogen carries almost no moisture into the piping. It depends on the feed air meeting specification, which matters most where the compressor and dryer are supplied by others.
Nitrogen source	Generated on site	Pressure swing adsorption, from ordinary compressed air. No cylinder deliveries, no dewar, no bulk contract.

ℹ Note — 98.5% is not the same target as your zone setpoint The generator produces 98.5% or better. A zone is judged against the purity setpoint programmed into the monitoring equipment for that system, which is set in percent oxygen on current Quick-Check manifolds. The two numbers describe different things and both are correct. See AutoPurge and Quick-Check Overview for how zone purity is measured and set.

Why nitrogen instead of air

Oxygen-driven corrosion inside sprinkler piping needs three things: steel, water and oxygen. The steel is the system. The water is managed by pitch, low point drains and draining the system properly after every trip — and nitrogen does not change any of that. What nitrogen removes is the third one: the oxygen.

Compressed air is roughly 21% oxygen, and a dry or pre-action system holds that air against wetted pipe walls for years at a time. Nitrogen at 98.5% or better leaves no more than 1.5% of anything else, and only part of that is oxygen. In long-term corrosion testing of Schedule 10 coupons held half full of water, nitrogen supervision extended projected service life substantially over compressed air:

Schedule 10 pipe	Projected on compressed air	Projected on nitrogen
Black steel	20 years	63 years
Galvanized steel	10 years	176 years

ℹ Note — what those numbers are, and what they are not These are projections from measured corrosion rates on test coupons, run at 98% nitrogen against compressed air. They are not observed service life, not a prediction for any particular building, and not a warranty. Use them for what they show — the size of the difference — not as a number to put in a bid. Galvanized pipe does worse than black steel on air because once the zinc layer is breached, corrosion concentrates at the break; take the oxygen away and that mechanism has nothing to work with, which is why its figure moves the furthest.

Nitrogen is also far drier than compressed air. At a -35 °F dew point there is very little water vapor in the supervisory gas to condense inside the pipe, which takes away one corrosion driver and one contributor to ice plugs in unheated spaces.

▲ Attention — nitrogen does not replace draining the system Most of the water in a dry system is liquid water left behind after a trip or an incomplete drain, and that is also where most ice plugs come from. Nitrogen removes the water vapor carried in with the supervisory gas. It does not remove standing water, it does not drain a system, and it does not change your pitch, low point drain or post-trip drainage practice. Keep draining the system exactly as you did before.

Nitrogen supervision of dry and pre-action systems is well established, but acceptance is the authority having jurisdiction's call on any given job — confirm it with them before you specify.

Why Nitrogen Is Used in Fire Protection Systems covers the mechanism in full, and Nitrogen Supervision vs. Vapor Corrosion Inhibitors (VCI) compares the two approaches.

How the generator makes nitrogen

Every N2-BLAST uses pressure swing adsorption. Compressed air is fed through a vessel packed with carbon molecular sieve. The sieve pore size is tuned so that oxygen molecules, which are slightly smaller, are held in the pores while the larger nitrogen molecules pass through. Nitrogen leaves the vessel as product gas; the oxygen is released to atmosphere when the vessel depressurizes.

Current-line units run two beds, marked A and B. One produces while the other regenerates, then they swap — which is why a running generator cycles audibly rather than holding steady, and why that cycling is normal rather than a fault.

Diagram of pressure swing adsorption: compressed air containing nitrogen and oxygen enters a vessel packed with carbon molecular sieve, and nitrogen leaves as product gas, with an inset showing the sieve pore at 3.0 angstrom against an oxygen molecule at 2.9 angstrom and a nitrogen molecule at 3.1 angstrom — **The whole principle in one picture.** The sieve pore is 3.0 angstrom. Oxygen, at 2.9, fits into it. Nitrogen, at 3.1, does not. A tenth of an angstrom either side of the pore is the entire separation.

What goes with the generator

A generator on its own fills the piping. The accessories are what get the trapped air out and tell you whether it worked. These are the current-line accessories; a legacy system may have been supplied with different equipment.

Accessory	What it does	More
AutoPurge System (APS)	A calibrated purge point on each zone. Bleeds oxygen-rich trapped air out at a set rate so nitrogen can replace it. Fully pneumatic — no power needed. Where a Quick-Check manifold is fitted, purging on a zone stops once that zone is in specification.	AutoPurge and Quick-Check Overview
Quick-Check purity manifold	Monitors nitrogen purity from one cabinet — one zone per port — and stops purging a zone once it is in specification. Available in 1, 6, 10 and 20 port, so the port count has to match the number of zones.	AutoPurge and Quick-Check Overview
Quick-Check portable purity sensor	Handheld. Reads one zone at a time at the APS.	Quick-Check Accessories Overview
BlastOff and SMART-Trak	Leak detection, air bypass alarm, early warning and onboard purity monitoring, plus run-time tracking and remote monitoring.	BlastOff and SMART-Trak Overview

⚠ Warning — a generator alone does not purge a system Filling a dry system with nitrogen does not remove the air already in it. Without an APS on every zone the trapped air stays where it is, the zone never reaches specification, and the corrosion protection you paid for does not happen. One APS per zone — not one per riser, and not one per building.

Keeping it running

Current line. Legacy models have different filters and different intervals — work from the legacy articles above for those.

Task	When	Where
Change the filters	Annually, or every 1,000 run hours — whichever comes first	Annual Filter Replacement (FRP-007)
Clean the strainer on each APS	Quarterly	APS Typical Installation Guide
Check purity in each zone	Quarterly	AutoPurge and Quick-Check Overview
Check run time	Quarterly. A generator running far longer than it used to usually means the system is leaking, but fouled filters, a stuck-open APS or aging sieve will do the same thing.	BlastOff and SMART-Trak Overview
Find and fix leaks	Whenever run time climbs or purity will not hold	System Leak Check Procedure

If the generator stops

This is the first question most people ask, so it is worth answering plainly. Nitrogen purity is a corrosion control function, not a fire protection function. A generator that has faulted, been switched off or been isolated for service does not disable the sprinkler system, and it does not put the building out of protection.

What keeps working	What to do about it
The sprinkler system stays a functioning dry or pre-action system. Supervisory pressure is held through the air maintenance device, and the building fire alarm supervises that pressure independently of anything the generator does or reports.	Nothing, immediately. Treat it as equipment down, not as a system impairment.
Where air bypass is fitted, the air compressor takes over and holds supervisory pressure while the generator is out.	Expect an air bypass alarm — that is the alarm doing its job. Restore the generator and return the system to nitrogen. See How Do I Manually Activate Bypass Mode.
Purity starts to drift. Every hour on air is oxygen going back into the piping. Corrosion protection degrades gradually, not instantly.	Get the generator running, then confirm every zone comes back within its setpoint. A long outage may need a fresh purge period.

⚠ Warning — a shut valve is a different problem from a stopped generator Everything above is about the generator. Closing a valve on the sprinkler piping itself, or draining a riser, is a fire protection impairment and goes through the site impairment program — notify the owner or impairment coordinator and the monitoring company, tag it, and restore and verify before clearing the tag.

How long until the system is protected

Not on the day it is commissioned. Filling a dry system with nitrogen leaves the air that was already in the piping exactly where it was, and driving that out takes weeks. A newly commissioned system reads out of specification, and that is correct rather than a fault.

The monitoring equipment has a setting for this period — an Initial System Purge, factory default 40 days — which lets the zones purge without raising a purity alarm the whole time. How long a given zone actually takes depends on its volume and how well it was purged.

ℹ Note — the sprinkler system is protected the whole time The purge period is about corrosion protection reaching full effect. Fire protection is not waiting on it. The system holds supervisory pressure and operates normally from the day it is commissioned, exactly as it did on air.

Articles by model family

FPS-500 and FPS-900

FPS-1650, FPS-3250, and FPS-5000

FPS-10000, FPS-16500, and FPS-22500

Across the line

Manuals

Not sure which system you have? Have the model number and serial number from the nameplate ready and call South-Tek Systems Service — (910) 415-1880 · Open a support ticket at support@southteksystems911.zendesk.com or through the Help Center.