FPS-1650, FPS-3250, and FPS-5000 Overview – South-Tek Systems

Applies to: South-Tek Systems N2-BLAST® FPS-1650, FPS-3250, and FPS-5000 fire protection nitrogen generators.

Does NOT apply to: FPS-500 and FPS-900 (see their overview) or FPS-10000, FPS-16500, and FPS-22500 (see their overview).

The FPS-1650, FPS-3250, and FPS-5000 are floor-standing nitrogen generators built for fire protection. They supply 98.5%+ nitrogen into dry-pipe and pre-action sprinkler systems to displace the oxygen and moisture that drive pipe corrosion. This is the mid-range of the N2-BLAST® line and the most commonly installed group — a step up from the compact FPS-500/900, and built around a touchscreen controller with full data logging, automatic air bypass, and BlastOff® leak detection where ordered.

Where these three sit in the N2-BLAST line

If you are not certain which article you need, find your model here first. All eight current models do the same job; they differ in how much piping they can supervise and where the compressed air comes from.

Model	Largest single zone	Layout	Compressor
FPS-500	500 gal	Modular, wall or rack mounted	Internal
FPS-900	900 gal	Modular, wall or rack mounted	Internal
FPS-1650	1,650 gal	Integrated, floor standing	Internal, oil-free
FPS-3250	3,250 gal	Integrated, floor standing	External
FPS-5000	5,000 gal	Integrated, floor standing	External
FPS-10000	10,000 gal	Integrated twin-tower skid	External
FPS-16500	16,500 gal	Integrated twin-tower skid	External
FPS-22500	22,500 gal	Integrated twin-tower skid	External, often duplex

▲ Attention — the sizing rule Size by the gallonage of the largest single zone, never by the sum of all zones and never by compressor horsepower. The requirement behind the rule is the NFPA 13 provision that the air or nitrogen supply must restore normal system pressure within 30 minutes — on a typical dry system that is about 40 PSI, while pre-action systems are commonly supervised nearer 10 PSI, so use the pressure that system is actually designed for. Verify the section number and the value against the NFPA edition your AHJ has adopted before citing it in writing. The same 30-minute duty is what drives feed-compressor selection on the FPS-3250 and FPS-5000 — size the compressor to meet it, not by matching horsepower to another job. One generator can supervise several risers when they can be tied to a single nitrogen supply line. Confirm the model selection with South-Tek before ordering.

What these systems do

Oxygen and moisture trapped in sprinkler piping drive electrochemical, galvanic, and microbiologically influenced corrosion (MIC) — the leading cause of premature pipe failure in dry and pre-action systems. Replacing that air with 98.5%+ nitrogen interrupts the corrosion reaction at its source. The generator holds a nitrogen supervisory atmosphere in the piping at low flow, running in the background and topping the system up as gas is consumed through small leaks and trip events. Background and the supporting corrosion data are in Why Nitrogen Is Used in Fire Protection Systems.

How the system works

Compressed air is filtered and fed to pressure swing adsorption (PSA) beds packed with carbon molecular sieve. The sieve adsorbs oxygen under pressure and lets nitrogen pass through to an internal storage tank; the controller alternates the beds so one side is producing while the other regenerates, giving continuous output. The bed count is not the same across the three models — the FPS-1650 and FPS-3250 each carry two beds, while the FPS-5000 carries four in a tetrad arrangement. All three use the same 48" bed fabrication; the FPS-1650's is drawn as 4" OD × 48", and the FPS-3250 and FPS-5000 use the same bed at a nominal 4" diameter. The FPS-3250 gets its extra capacity over the FPS-1650 from a larger-bore flow path and a larger external air supply rather than from more beds; the FPS-5000 adds two more beds on top of that. Production starts and stops automatically on storage tank pressure. The sieve is not consumed in the reaction, so with clean dry feed air it is a long-life component — which is exactly why the filtration and dew point requirements matter so much, and why water carryover into the beds is the one failure that is not recoverable. Air consumption depends on the purity and flow you are asking for, so there is no single air-to-nitrogen ratio; peak feed-air demand can reach up to three times the average, and South-Tek sizes the feed compressor for the job.

Feature	What it does	Models
Filtration	Three stages on every model, replaced together once a year. On the FPS-1650: an intake pre-filter on the internal compressor, then a particulate and coalescing pair in a single combination body. On the FPS-3250 and FPS-5000: a 5-micron filter/regulator combo at the air inlet ahead of the dryer, then a 0.01-micron coalescing filter and an adsorbing filter in a separate assembly after the dryer. Every filter in the air train downstream of the compressor has an auto-drain and needs a drain line. The FPS-1650's compressor intake pre-filter and the FPS-3250/FPS-5000 adsorbing filter do not.	All three
Nitrogen storage	A nitrogen tank inside the cabinet with ball valves, ASME safety relief and a gauge, feeding an external manual ball valve for the site connection. Nominal capacity is 14.8 gal.	All three
Automatic cut-in / cut-out	A pressure transducer signals the controller to start and stop production. Setpoints are factory set — read them off the controller's N2 Pressure Settings screen and record them, and do not adjust them without consulting South-Tek.	All three
Touchscreen controller	A UL 508A panel with a graphical interface, live system status, sensor and performance logging, trend graphs, and remote monitoring over Ethernet or Modbus TCP/IP. Programs are proprietary and password-protected.	All three
Automatic air bypass	If the generator cannot keep up with demand, the system switches the riser to compressed air, alarms, and logs the time spent in bypass. It also triggers during the 30-minute fire protection piping fill test, which is a normal cause and not a fault. The bypass cut-in and cut-off values are on the controller's Bypass Settings screen — read and record them from the unit. Automatic bypass starts at the FPS-1650 — the FPS-500/900 use a manual bypass valve.	All three — see the note below on optionality
Safety relief	ASME safety relief valves protecting against component failure. Read the set pressure off the tag on the valve itself — never disable, plug, or adjust one.	All three
AutoPurge System (APS)	A patented pneumatic device, one per riser, that continuously bleeds residual air out at the remote end of the piping so the zone actually reaches and holds 98.5% nitrogen. It needs no power and stays in service continuously — a riser-room purge alone cannot reach dead-end runs. It does need to be tuned to the system at commissioning — see AutoPurge System (APS) Field Tuning Instructions. Confirm the APS quantity and scope of supply against the order.	All three
Monitoring outputs	Voltage-free dry contacts for a fire alarm panel or BMS — common alarm, a separate bypass alarm relay where auto air bypass is fitted, a purity contact where the oxygen sensor is fitted, and an optional power loss contact — plus analog outputs for tank pressure and tank trace O₂ — 0–10 V on the FPS-1650; on the FPS-3250 and FPS-5000 confirm the range and scaling against the drawing package supplied with the unit before specifying the receiving equipment. Receiving equipment is installed by others. The power loss contact is wired the opposite way round to the common alarm; behaviour and terminals are in Operation and Alarms.	All three
Air source	The FPS-1650 carries its own oil-free compressor inside the cabinet, with a pre-compressor intake filter. The FPS-3250 and FPS-5000 are fed by an external compressor and need refrigerated drying to hold the feed-air dew point below 40°F. Drying is an ordered option: it is either a dryer fitted inside the generator cabinet or a separate dryer standing in the room. On the FPS-3250 a cabinet dryer is powered from the generator's own supply; on the FPS-5000 confirm the arrangement against the drawing package supplied with the unit. Confirm which is on the job — it changes site prep, startup and maintenance.	Differs

ℹ Note — a new install does not reach purity on day one The generator drives oxygen out of the piping over an initial purge period, so a day-one purity reading below 98.5% is expected rather than a fault. Set that expectation with the building owner at handover, and purge time depends on the volume and condition of the piping rather than on a setting in the generator, so record the day-one purity reading per zone and the controller run hours at handover and judge the trend at the next visit. Purity is measured at the zone, not at the generator.

The BlastOff® feature set

All four BlastOff® levels are available on this group. Level II, automatic air bypass, starts at the FPS-1650 — the smaller FPS-500/900 bypass manually.

ℹ Note — “available” is not the same as “fitted” BlastOff® and automatic air bypass are ordered options, fitted on most current configurations but not on all, and older units in the field were built to different specifications. Several capabilities are still specified per order, though — the equipment alarm, oxygen sensor, power loss alarm, dew point monitor, flow meter, backup air compressor, and internal dryer are each ordered individually, and older units in the field were built to different specifications. So “all three” in the tables above means available on all three. Before troubleshooting a feature a customer says is missing, confirm what that unit was built with using the serial number.

Level	Name	What it gives you
I	Leak detection	Tracks generator runtime and alarms if it runs past the BlastOff® timer setting without reaching Standby, giving warning before a potential low-air alarm. The timer setting and its countdown are on the BlastOff® settings screen — it is configurable. Audible, visual, and dry-contact output to a building management system.
II	Automatic air bypass	Automatically switches between compressed air and nitrogen if the generator cannot keep up, alarms, and tracks and logs time spent in bypass. Available on the FPS-1650 and larger.
III	Early warning	Trouble alarm with diagnostics — confirms all components are working and helps pinpoint a leak location within the nitrogen system.
IV	Onboard purity	Monitors the nitrogen purity going into the fire protection system, trends it graphically, and alarms below the configured O₂ purity alarm point — that point is on the O₂ Purity Alarm Settings screen, and 98.5% is the system's purity specification rather than a fixed alarm point.

Operating pressures

Pressure	FPS-1650	FPS-3250 & FPS-5000
Cut-in and cut-out (production start and standby)	Read them off the unit. The cut-in and cut-out pressures are on the controller's N2 Pressure Settings screen. Record them on the service record before you diagnose a pressure complaint, and do not adjust them without consulting South-Tek.
Automatic bypass cut-in / cut-off	Read them off the unit. The bypass cut-in and cut-off are on the controller's Bypass Settings screen. Where the bypass air supply shuts off below the cut-off, the cut-off is set 5 PSIG below that shut-off pressure and the cut-in 10 PSIG below the cut-off. Record both values before diagnosing a bypass complaint.
Feed air at the generator inlet	Self-supplied — none required	The cabinet inlet regulator is factory set at 120–125 PSIG and is what the generator runs on — it is not a field adjustment. South-Tek-supplied feed compressors are preset to cut out at 175 PSIG; a compressor bought elsewhere must be confirmed with South-Tek before it is selected. Dew point below 40°F. The line pressure arriving at the cabinet is the compressor's, not the generator's, so rate the feed piping and fittings for 175 PSIG. Running the generator itself above 125 PSIG, by altering the cabinet inlet regulator, can cause damage that is not covered under warranty.

ℹ Note — check the controller, not just this table The controller's N2 Pressure Settings screen shows what this unit is set to. Read it there before diagnosing a pressure complaint and record what you find — no published pair substitutes for the screen. The programs are password-protected and must not be altered without South-Tek's written consent.

Specifications

Specification	FPS-1650	FPS-3250	FPS-5000
Nitrogen purity	98.5%+
Coverage (largest single zone)	1,650 gal	3,250 gal	5,000 gal
PSA sieve beds	Two, 4" OD × 48"	Two, 48" (nominal 4" diameter)	Four, 48" (tetrad; nominal 4" diameter)
Internal storage tank	14.8 gal nominal, with ASME safety relief. The vessel rating is not published per model — read it off the tank data plate on the unit
Cabinet (W x D x H)	26" x 18" x 59" — about 63.6" overall to the top gas fitting
Approximate weight	223 lb	243 lb	303 lb
Electrical	120–240 VAC, 50/60 Hz, 1-ph, < 8 A. Supply voltage is factory configured and cannot be changed after build — read the product information label on the unit to confirm what it was built for.	120–240 VAC, 50/60 Hz, 1-ph, < 5 A for the generator alone. On the FPS-3250 a dryer fitted inside the cabinet runs off the generator's supply and is not in that figure; on the FPS-5000 confirm the arrangement against the drawing package supplied with the unit. Size the branch circuit to the unit nameplate and local code, not to the draw figure. The external compressor needs its own service
Over-current protection	15 A at the cabinet power entry module. It protects the generator — it is not the branch-circuit protection and not a disconnecting means. Size and protect the branch circuit to the unit nameplate and local code, and provide a lockable disconnecting means ahead of the cabinet
Compressor	Integral, oil-free, with an intake pre-filter. Units ordered with the backup air compressor option carry two	External, supplied and piped separately
Gas connections	1/2" NPT female unless otherwise stated
Drain connections	Two 1/4" OD, low on the left side	Two 1/4" NPT female bulkheads fitted with push-to-connect connectors, low on the left side, with the run made in 1/4" OD tubing — current builds; on units built before 2024 confirm the connector type at the port before ordering drain material
Ambient temperature	40–100°F (4–38°C)
Noise level	< 90 dBA
Installation	Floor standing, indoors, on a hard flat surface rated for the installed weight with margin — up to about 303 lb for the FPS-5000, plus the feed compressor and any receiver on the FPS-3250 and FPS-5000
Filter kit — replace at 12 months or 1,000 run hours, whichever comes first	FRP-007	FRP-022 (current, white ASCO filters) — legacy black-bowl units take FRP-013

ℹ Note — noise At under 90 dBA these units are considerably louder than the compact FPS-500/900, which are rated under 60 dB. Plan the location accordingly and use hearing protection when working near a running unit.

Approvals and certifications

Approval	Detail
FM Approval	FM Approval is held per assembly rather than as a blanket listing on the model line, and it varies with the configuration ordered. If the job is FM-insured, obtain South-Tek's written confirmation of FM Approval status for the specific model and configuration ordered, including the standard it is listed under, and give it to the AHJ and the insurer before the equipment is set.
UL	The control panel is built to UL 508A as an open-type industrial control panel. That covers the control panel, not the generator as a whole, and it is an open assembly protected only by the cabinet — there is no dead front behind the left-side cover. Electrical schematics are available from South-Tek on request.
CE	CE marked on CE-configured units. CE is a distinct build, not a property of the model line — it has its own cabinet fabrication, its own labelling (CE serial, ground symbol, arc-flash caution) and an alternate supply voltage. Specify CE at order; it is not a retrofit.
Pressure relief	ASME safety relief valves are fitted throughout. Vessel and valve ratings are not published per model — read them off the tank data plate and the valve tag on the unit.

Typical installation profile

Full requirements are in FPS-1650, FPS-3250, and FPS-5000 Site and Utility Requirements. In outline:

Indoor, nonhazardous, well-ventilated location at 40–100°F, floor standing on a flat surface rated for the unit's weight with margin.
The cabinet's left side is the electrical face — power entry module, UL 508A panel, touchscreen, certification and torque labels, and both drain connections. NEC 110.26 working space applies there, not at the front: 36" deep, 30" wide or the equipment width whichever is greater, and 6.5 ft high, kept clear. Allow 36" at the front for the filter change and routine maintenance, 6" minimum on the remaining sides for ventilation, and clearance above the cabinet for gas-line connections.
Two drain lines exit low on the cabinet's left side — 1/4" OD on the FPS-1650, 1/4" NPT bulkheads with push-to-connect connectors on the FPS-3250 and FPS-5000. Plumb them individually to the nearest site drain and leave them open to atmosphere.
The FPS-3250 and FPS-5000 need an external air compressor sized to the system, plus refrigerated drying to hold the feed-air dew point below 40°F. Drying may be fitted inside the generator cabinet or stand separately in the room — confirm which from the order documents before mobilizing, because it changes the power, the drain and the floor space you have to provide.
Power is 120–240 VAC single phase landed at the cabinet's power entry module, which carries the generator's built-in 15 A over-current protection. That device is not the branch-circuit protection and not a disconnecting means, so provide a lockable disconnect ahead of the cabinet and an equipment grounding conductor. Hard-wired and receptacle connections are both used. An external compressor has its own service, often three-phase, and its rotation must be verified at startup.
One air maintenance device (AMD) per riser in the downstream piping, plus bypass piping around the generator.

Identifying your unit before you follow a procedure

Confirm the exact model number on the nameplate before following a procedure or ordering parts. These three share a platform but are not interchangeable in service. The difference that matters most is the air source: the FPS-1650 supplies its own air, while the FPS-3250 and FPS-5000 depend on an external compressor and drying, which changes site preparation, the startup sequence, the alarm set, the annual filter kit, and the preventive maintenance schedule.

Manual download

FPS-1650, FPS-3250, and FPS-5000 O&M Manual

Need help? South-Tek Systems Service — Phone: (910) 415-1880 · Open a support ticket at support@southteksystems911.zendesk.com or through the Help Center.