Applies to: N2-BLAST FPS-1750, FPS-3000 and FPS-6000 — the Type II Series. These are legacy models and still supported; parts availability and upgrade paths vary by unit.
These units put nitrogen into dry and pre-action sprinkler piping in place of compressed air, so the oxygen that drives internal corrosion is not there to drive it. They are wall mounted and fed by an external air compressor.
▲ Attention — this is not the same kind of machine as the FPS-650 or FPS-1250 The Type II Series separates nitrogen with a membrane element. The FPS-650 and FPS-1250 use pressure swing adsorption beds. That is a different technology, and almost everything that follows from it differs too — the compressor, the number of filters, the filter kit, the setpoints and the electrical supply.
Do not carry a maintenance procedure, a filter kit number, an electrical figure or a setpoint from one family to the other. The table below is the short version of why.
Do not carry a maintenance procedure, a filter kit number, an electrical figure or a setpoint from one family to the other. The table below is the short version of why.
| FPS-1750 / 3000 / 6000 | FPS-650 / FPS-1250 | |
|---|---|---|
| Separation | Membrane element | PSA adsorption beds |
| Air compressor | External | Integral, inside the cabinet |
| Filters | Three — particulate, coalescing, adsorber | Two — particulate, coalescing |
| Filter kit | FRP-002 | FRP-007 |
| Nitrogen cut-out | About 80 PSIG | 70 PSIG nominal |
| Nitrogen cut-in | About 72 PSIG | About 62 PSIG |
| Electrical | 110 V / 60 Hz | 110–240 V / 50–60 Hz |
| Mounting | Wall mounted | Wall or floor (650), floor only (1250) |
The bypass handle
A manual bypass ball valve switches the sprinkler system between nitrogen from the generator and bypass air. On this family the layout sheet records it as nitrogen = handle out (normal operation) and air bypass = handle up — the same way round as the FPS-1250, and the opposite of the FPS-650 and the current FPS-500 and FPS-900.
⚠ Warning — the placard on the unit governs The operating manual for these models states no handle polarity at all. The drawing above is the only source we have for this family, and handle legends have not been printed the same way across every South-Tek model generation. Read the placard on the machine in front of you and follow it if it disagrees with this article.
The mistake worth avoiding is specific: a technician who reads the wrong polarity leaves the generator bypassed on air while believing the system is on nitrogen. The system keeps its pressure and quietly loses its corrosion protection.
If there is no placard, or you cannot read it, do not work it out by trial. Get the position from the installation layout drawing supplied with the system, or call us with the model and serial number. Then mark the handle.
The mistake worth avoiding is specific: a technician who reads the wrong polarity leaves the generator bypassed on air while believing the system is on nitrogen. The system keeps its pressure and quietly loses its corrosion protection.
If there is no placard, or you cannot read it, do not work it out by trial. Get the position from the installation layout drawing supplied with the system, or call us with the model and serial number. Then mark the handle.
ℹ Note — the "Air Bypass Option" is an alarm, not the bypass These models offer a BlastOff Air Bypass Option, and the name misleads. It is not a way to bypass — it is a monitor that alarms when the generator is being bypassed by the air compressor, and it exists to catch a bypass valve left open or the generator left switched off.
The operating manual says only that it gives a visual alarm. The typical installation drawing is more specific: a handle left in the bypass position illuminates a red light on the generator and signals a local supervisory alarm if it has been connected to the building monitoring panel, until the handle is returned to the normal position.
Without the option, nothing tells you the system is on air other than the handle itself.
The operating manual says only that it gives a visual alarm. The typical installation drawing is more specific: a handle left in the bypass position illuminates a red light on the generator and signals a local supervisory alarm if it has been connected to the building monitoring panel, until the handle is returned to the normal position.
Without the option, nothing tells you the system is on air other than the handle itself.
Specifications
| Item | All three models |
|---|---|
| Nitrogen purity | 98.0% or better |
| Nitrogen storage pressure | Up to 80 PSIG |
| Nitrogen cut-out (enters standby) | About 80 PSIG |
| Nitrogen cut-in (returns to run) | About 72 PSIG — 7–10 PSIG below cut-out. Factory preset, no field adjustment required. |
| Cabinet port connections | ½" NPT female |
| Compressor | External — not part of the cabinet |
| Installation | Wall mounted only |
| Electrical | 110 V / 60 Hz / 1 phase, 20 A. A 20 A breaker is built in and a standard 3-prong cord is supplied. |
| Listing | UL 508A ICP approved |
| Ambient temperature | 40 °F to 90 °F, indoors, upright and level |
| Noise | Under 80 dBA |
| Size and weight | 42.3" H × 17" W × 11.8" D, about 85 lb |
| Nitrogen storage tank | The documentation describes this two ways. The operating manual says the tank is housed inside the cabinet, plumbed out to an external manual ball valve. The typical installation drawing shows a separate 100 lb tank supplied with a wall bracket and strap. Look at the unit in front of you — it matters, because it decides which valves you are being told to close during a BlastOff reset. |
| Warranty | 12 months or 1000 hours from shipment, whichever comes first |
How it runs
The generator starts and stops on a pressure switch rather than a programmed controller. When storage tank pressure reaches the cut-out pressure of about 80 PSIG, the unit enters standby: the green Operating light goes out and the amber Standby light comes on, air flow through the generator stops, and the external compressor stops once it reaches its own cut-off. When the system draws nitrogen and tank pressure falls to about 72 PSIG, the switch puts it back into run and refills the tank automatically.
Standing by rather than purging continuously is deliberate — it saves compressor motor hours and extends membrane and filter life. A unit that never reaches standby is telling you something. The manual is direct about one cause: line leaks make the generator run excessively, shortening its life and wearing the compressor. See N2-BLAST System Leak Check Procedure.
| What to do | |
|---|---|
| Starting | Connect to the storage tank outlet with thread sealant, open all valves, plug into a 110 VAC outlet and turn on the rocker switch. The external compressor starts if the tank is not already up to pressure. |
| Normal running | Leave it powered on. It starts and stops on its own between the preset cut-in and cut-out pressures. |
| A quick sanity check | The gauge on top of the cabinet should read between 50 and 80 PSIG. If it is low, check power first, then leak-check the system. |
| The hour meter | On the outside bottom right corner of the cabinet — this is what the 1000-hour filter interval is measured against. |
BlastOff leak detection
An option on these models, factory fitted or retrofitted in the field with some rewiring. It watches for the signature of a leak downstream of the generator — pinholes, loose fittings, a poorly seated connection out in the piping. When it trips it sounds a buzzer and lights a red light on the lower left side of the cabinet.
ℹ Note — the manual gives the reset two different ways In one place it is simply a power cycle — turn the generator off, turn it back on. In another it says to turn the power off and close the nitrogen tank valves, then power back on. Both appear in the same manual.
The valve version is the more informative one, because closing the tank valves turns the reset into a diagnostic — but it only makes sense if you reopen them. Whichever you use, the system must end up exactly as it started.
The valve version is the more informative one, because closing the tank valves turns the reset into a diagnostic — but it only makes sense if you reopen them. Whichever you use, the system must end up exactly as it started.
| Step | What to do | What it tells you |
|---|---|---|
| 1 | Turn the power off. If you are using the diagnostic version, close the nitrogen tank valves as well. | Isolating the tank is what lets the restart tell you which side the leak is on. |
| 2 | Turn the power back on and watch what the unit does. | Goes to Standby with the orange light → the generator is working properly and the leak is downstream, out in the piping. |
| 3 | Reopen any tank valve you closed and confirm the system is back on nitrogen before you go any further. | This step is not optional. Tank valves left shut isolate the storage from the sprinkler piping, so the system has no make-up nitrogen at all — and nothing at the generator will tell you, because it looks like it is running normally. |
| 4 | Find and correct the leak, then return the system to service. | If no leak can be found, leave the unit turned off and call your fire protection contractor — see the warning below. |
⚠ Warning — a unit left switched off is a system with no make-up nitrogen The documented protocol is to leave the generator off until the leak is found and corrected. Understand what that means on a fire protection system: nothing is replacing the gas the system is losing, and supervisory pressure falls at whatever rate the leak dictates.
Tell the building owner and the alarm monitoring company before you leave a unit switched off, let them decide how it is handled, and treat finding the leak as urgent rather than scheduled.
Never reset it repeatedly. A BlastOff that trips daily is reporting a real fault, and clearing it each morning is how a leak runs for months.
Tell the building owner and the alarm monitoring company before you leave a unit switched off, let them decide how it is handled, and treat finding the leak as urgent rather than scheduled.
Never reset it repeatedly. A BlastOff that trips daily is reporting a real fault, and clearing it each morning is how a leak runs for months.
For wiring into a building system, the dry contact is 11–14 normally open and 11–12 normally closed. The BlastOff assembly and the customer dry contact relay are in the upper left hand portion of the cabinet interior.
Safety
- Nitrogen is not poisonous, but it displaces the oxygen you breathe and gives no warning. Install and work on these units in a well-ventilated room, one that is not sealed off from normal air changes.
- Power switch off and the external power cord disconnected from the building supply before servicing anything.
- Only service engineers qualified on both electrical and pneumatic equipment may install, maintain or repair these units.
- Do not tamper with the equipment or exceed the technical specifications.
- Use a spray bottle on non-electrical equipment only when hunting leaks. Push-to-connect fittings are allowed a small leak rate — up to about 5 cc/min is normal and is not the fault you are looking for.
- When you find a leak, isolate that area and relieve the pressure on it before you work on it. Shut the valve, depressurize the line, then open the fitting — never the other way round.
- Use factory parts only, supplied by your distributor or by us. If there is a leak inside the unit, remove the top cover to locate it and call us before replacing anything.
Maintenance — three filters, kit FRP-002
All three elements are changed annually or every 1000 hours, whichever comes first, measured on the hour meter at the bottom right corner of the cabinet. The kit is FRP-002.
| Filter | Rating | What it does |
|---|---|---|
| Particulate | 5 micron | Catches the larger particles |
| Coalescing | 0.1 micron | Catches the remaining smaller particles |
| Adsorber | 0.003 ppm/wt oil | Captures oil carryover — this filter has no equivalent on the FPS-650 or FPS-1250 |
⚠ Warning — prove the pressure is gone before you open a bowl Power off and the external power cord disconnected from the building supply. The air supply to the unit bypassed or disconnected.
The pressure gauge on the regulator that houses the particulate filter must read 0 psi. If it still shows pressure, relieve it by pulling the ring on the safety relief valve located after the adsorber filter — do not open a bowl to find out.
The top cover comes off with four screws, but you do not need to remove it to change filters.
The pressure gauge on the regulator that houses the particulate filter must read 0 psi. If it still shows pressure, relieve it by pulling the ring on the safety relief valve located after the adsorber filter — do not open a bowl to find out.
The top cover comes off with four screws, but you do not need to remove it to change filters.
All three bowls come off the same way: press up slightly, turn the bowl ⅛ turn to the left, then pull down. The elements differ.
| Element | Removing it | Fitting the new one |
|---|---|---|
| Particulate | A threaded ring sits just under the element — unscrew it counter-clockwise, then pull the element down. | Fit the new element and secure it with the threaded ring. |
| Coalescing | Twist counter-clockwise until the element comes completely off. | Twist clockwise. Hand tight only. |
| Adsorber | Unscrew counter-clockwise. | Fit the new element with its new O-ring and screw clockwise. Hand tight only. |
- Rinse each bowl with hot water and shake it dry before it goes back on.
- Change the O-ring on the top of each bowl with the one supplied in the kit. A little light oil or grease helps if it looks dry.
- Wipe surfaces with a clean dry towel. Do not use cleaning agents — they can damage the finish on the filters.
- Reconnect power, then open the incoming air supply ball valve slowly, listen at the bowls for leaks, and let the tank fill before you leave.
- The particulate and coalescing filters have auto-drains plumbed outside the cabinet — ¼" MNPT connections. Run ¼" tubing to a safe drain point.
Installation essentials
The installation layout drawing supplied with the system governs — there is more than one arrangement. Ask us if it is not in the job file.
- Wall mounted. The typical installation drawing states that all Type II units must be wall mounted, and the brackets come with the unit. The operating manual phrases it as a recommendation, and documents no floor-standing arrangement.
- The brackets are a keyway system. The lower bracket slides through the keyway on the lower flanges and locks with the supplied ¼" × 1¼" bolt. The upper bracket goes on the wall — 16" center to center for standard studs, ¼" hardware minimum. Hang the cabinet by sliding the key through the keyway on the top flange, then fix the lower bracket to the wall to lock it in place.
- Air input is on the left side, nitrogen outlet on the right. Check both before opening any valve.
- There is a ½" conduit knockout underneath the cabinet panel for the power supply to the electrical panel.
- Fit flexible tubing between the compressor and the hard piping. The installation drawing calls for at least 24" of ½" ID flex rated for 200 PSIG and 135 °F, to keep compressor vibration out of the pipework — optional part number 002-310.
- Use thread sealant on every fitting, and leak check every line before the system goes into service. A line leak makes the unit run excessively and wears the compressor.
- Some installations need a nitrogen bypass for pre-filling to meet NFPA code. Whether yours does is a design question, not a field decision — work from the installation layout drawing for your system and ask us if it is not clear.
- Before installation — store dry and climate controlled at 60–80 °F, upright or as boxed, nothing stacked on top, gas lines kept dry, power not connected until the connections are made.
⚠ Warning — secure the cabinet at both flanges Fix it at the top and bottom flanges. Fixing only one risks the cabinet coming away from the wall. Keep it away from extreme heat, steam and water, all of which can damage the unit or injure someone.
AutoPurge Systems on these units
The AutoPurge System distributes nitrogen to the far branches of the piping so the whole system reaches purity rather than just the riser. Its installation and flow settings are the same as on current models and are covered properly in their own articles:
- AutoPurge and Quick-Check Overview for N2-BLAST Systems
- APS Flow Settings Reference (APS2 and APS4)
- APS Typical Installation Guide
▲ Attention — the two APS habits that get missed Close the ball valve on the APS during planned maintenance, and during hydrostatic or any pressure testing — gas or liquid. Reopen it when the system goes back online. And check the wye strainer for debris every quarter — and always after a water trip or a system flooding, not just on the quarterly schedule.
Where the documentation is unclear
| Question | What to do meanwhile |
|---|---|
| One section of the operating manual gives the storage pressure as 70 (±3) PSIG, where two other sections give cut-out at about 80 and the specification table gives storage pressure as up to 80. | Work to 80 / 72. Cut-out at about 80 is stated twice and matches the specification table; cut-in at about 72 is stated once. The 70 figure appears only in the FAQ, and the FPS-650/1250 manual carries a similar 70 figure in the same place — which suggests it traveled between manuals, though we have not confirmed that. Tell us if a unit in the field says otherwise. |
| Whether the refrigerated air dryer shown on the layout drawing is part of the package or supplied by others, as the air maintenance device is. | Confirm what is actually installed at the site. Air going into the sprinkler piping needs to be dry enough for the coldest pipe on the system, whoever supplied the dryer. |
Related articles
- FPS-650 and FPS-1250 Legacy Overview
- FPS-15000 and FPS-20000 Legacy Overview
- Legacy N2-BLAST Fire Protection Systems Overview
- N2-BLAST System Leak Check Procedure
- What Are My Cut In/Out Pressures?
- AutoPurge and Quick-Check Overview for N2-BLAST Systems
- N2-BLAST Fire Protection Systems Overview
Need help? Have the model and serial number ready, and tell us whether the unit has BlastOff and the Air Bypass Option fitted — both are options and both change the answer. South-Tek Systems Service — Phone: (910) 415-1880 · Open a support ticket at support@southteksystems911.zendesk.com or through the Help Center.