Applies to: legacy N2-BLAST fire protection nitrogen generators — FPS-650, FPS-1250, FPS-1750, FPS-3000, FPS-6000, FPS-15000 and FPS-20000. These are not current-generation N2-BLAST models, and they are not South-Tek industrial nitrogen generators.
These machines are still supported for service, maintenance and parts guidance, though parts availability and upgrade paths vary by unit. This article is here to help you work out which one you are standing in front of, and then send you to the article that covers it properly.
⚠ Warning — the legacy range does not agree with itself on the bypass handle This is the one thing to get right before you touch anything. Across the legacy models, the handle position that means "bypass" is not the same from family to family, and on most of them it is the opposite of the current FPS-500 and FPS-900.
The consequence is specific: a technician who reads the wrong polarity leaves the generator bypassed on air while believing the system is on nitrogen. The system holds its pressure and quietly loses its corrosion protection. See the table further down, and read the placard on the machine — it governs.
The consequence is specific: a technician who reads the wrong polarity leaves the generator bypassed on air while believing the system is on nitrogen. The system holds its pressure and quietly loses its corrosion protection. See the table further down, and read the placard on the machine — it governs.
Which one is this?
Start with the nameplate. If it is readable, the model number settles it and you can go straight to the right article. Legacy nameplates are often painted over, faded or gone, so the table below identifies the family from what you can see instead.
| If you see this | It is | Go to |
|---|---|---|
| A touchscreen. Floor or skid mounted, two tall sieve bed towers with a gauge on top of each, and a separate air compressor, dryer and air receiver alongside. Roughly 24" × 20" × 64" and 600–730 lb. | FPS-15000 or FPS-20000 | FPS-15000 and FPS-20000 Legacy Overview |
| Wall mounted, no compressor inside the cabinet, three filter bowls. A separate air compressor and refrigerated dryer stand nearby. Green "Operating" and amber "Standby" lights rather than a screen. Hour meter at the bottom right corner. Roughly 42" tall, 17" wide, 85 lb. | FPS-1750, FPS-3000 or FPS-6000 — the Type II Series | FPS-1750, FPS-3000, and FPS-6000 Legacy Overview |
| Compressor inside the cabinet, two filter bowls, a controller with numbered buttons. Wall mounted or on the floor, small — about 12.7" wide and 29.5" tall, 84 lb — with a separate 100 lb nitrogen tank strapped to the wall. | FPS-650 | FPS-650 and FPS-1250 Legacy Overview |
| Compressor inside the cabinet, two filter bowls, numbered-button controller — but floor standing and large: about 26" wide, 59" tall, 265 lb, with the nitrogen tank inside the cabinet. | FPS-1250 | FPS-650 and FPS-1250 Legacy Overview |
ℹ Note — the quickest three questions 1. Is there a touchscreen? Yes → FPS-15000 or FPS-20000. 2. Is the air compressor inside the cabinet? Yes → FPS-650 or FPS-1250, and the size tells you which. No → the Type II Series. 3. How many filter bowls? Two → FPS-650 or FPS-1250. Three → everything else.
If you still cannot tell, send us a photo of the cabinet inside and out with the serial number if you can find one — that is faster than guessing, and guessing on these machines has consequences.
If you still cannot tell, send us a photo of the cabinet inside and out with the serial number if you can find one — that is faster than guessing, and guessing on these machines has consequences.
The bypass handle across the whole range
Every one of these families has a manual bypass ball valve that switches the sprinkler system between nitrogen and bypass air. The handle convention changed across the range. Here is every model we have a documented position for, side by side.
| Model | Handle UP | Handle OUT | Where it comes from |
|---|---|---|---|
| FPS-500, FPS-900 (current) | Nitrogen — normal | Bypass | Current production ruling |
| FPS-650 | Nitrogen — normal | Bypass | FPS-650 layout sheet |
| FPS-1250 | Bypass | Nitrogen — normal | Operating manual Appendix B, and the FPS-1250 layout sheet |
| FPS-1750, FPS-3000, FPS-6000 | Bypass | Nitrogen — normal | Type II layout sheet |
| FPS-15000, FPS-20000 | Bypass | Nitrogen — normal | FPS-15000/20000 layout sheet |
▲ Attention — the FPS-650 is the exception Read that table again if you work across models. Among the legacy range, only the FPS-650 follows the same convention as the current FPS-500 and FPS-900. Every larger legacy family is reversed: on those, handle up means the system is running on air.
So the habit you build on one machine is wrong on the next one, and it is wrong in the direction that leaves a system unprotected rather than the direction that makes a noise. Read the placard on the unit every time.
So the habit you build on one machine is wrong on the next one, and it is wrong in the direction that leaves a system unprotected rather than the direction that makes a noise. Read the placard on the unit every time.
ℹ Note — current models above the FPS-900 have no handle The FPS-1650 and larger current models use automatic bypass, driven from the display rather than a valve handle. That is a different subject with its own article: N2-BLAST Bypass Mode — Automatic, Forced, and Restoring Nitrogen.
On the legacy machines the handle is the whole mechanism. There is no alarm, no log and no dry contact behind a handle unless the Air Bypass Alarm option was fitted — and that option is a monitor that watches the valve, not a way to bypass. Where it is fitted, a handle left in the bypass position lights a red lamp on the generator and can signal a local supervisory alarm.
On the legacy machines the handle is the whole mechanism. There is no alarm, no log and no dry contact behind a handle unless the Air Bypass Alarm option was fitted — and that option is a monitor that watches the valve, not a way to bypass. Where it is fitted, a handle left in the bypass position lights a red lamp on the generator and can signal a local supervisory alarm.
What does not carry between these families
These machines share a product line and a purpose. They do not share much else, and the differences are the kind that matter when someone orders a part or follows a procedure.
| FPS-650 / 1250 | FPS-1750 / 3000 / 6000 | FPS-15000 / 20000 | |
|---|---|---|---|
| How it separates nitrogen | PSA adsorption beds | Membrane element | PSA — two CMS beds |
| Air compressor | Inside the cabinet | External | External, with dryer and receiver |
| Filters | Two | Three | Three |
| Annual filter kit | FRP-007 | FRP-002 | FRP-006 |
| Nitrogen cut-out | 70 PSIG nominal | About 80 PSIG | Factory set per unit, read on the touchscreen |
| Nitrogen cut-in | About 62 PSIG | About 72 PSIG | As above |
| Mounting | Wall or floor (650), floor (1250) | Wall only | Floor or skid |
⚠ Warning — three families, three different filter kits FRP-007, FRP-002 and FRP-006 are not interchangeable, and the FPS-650 and FPS-1250 take two elements where the other families take three. Ordering from the wrong article is an easy mistake to make when the three overviews sit next to each other.
Confirm the family first, then the kit.
Confirm the family first, then the kit.
What they do have in common
- The job. All of them 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.
- Run and standby. All of them make nitrogen into a storage tank, stop when it is full, and start again when it draws down. A unit cycling between two pressures is a unit working correctly; one that never reaches standby is telling you something — usually a leak downstream. See N2-BLAST System Leak Check Procedure.
- A manual bypass handle — with the polarity caveat above.
- Optional BlastOff leak detection on every family, and optional Air Bypass Alarm monitoring. Both are options: do not assume a unit has either until you have looked.
- Safety relief valves throughout, ASME stamped, and never to be disabled or bypassed.
- Nitrogen displaces the oxygen you breathe and gives no warning. Every one of these units belongs in a ventilated space, and venting gas goes outdoors or into a large open area — never a small sealed room.
Where to go next
| If you have | Read |
|---|---|
| FPS-650 or FPS-1250 | FPS-650 and FPS-1250 Legacy Overview |
| FPS-1750, FPS-3000 or FPS-6000 | FPS-1750, FPS-3000, and FPS-6000 Legacy Overview |
| FPS-15000 or FPS-20000 | FPS-15000 and FPS-20000 Legacy Overview |
| A leak, or run time that has climbed | N2-BLAST System Leak Check Procedure |
| An AutoPurge System on the piping | AutoPurge and Quick-Check Overview for N2-BLAST Systems |
| A current-generation unit, not a legacy one | N2-BLAST Fire Protection Systems Overview |
Each family also has its own operating manual. Ask us and we will send the one that matches your unit — the manual for a neighboring model will mislead you on filters, setpoints, electrical supply and the bypass handle alike.
Related articles
- FPS-650 and FPS-1250 Legacy Overview
- FPS-1750, FPS-3000, and FPS-6000 Legacy Overview
- FPS-15000 and FPS-20000 Legacy Overview
- N2-BLAST Bypass Mode — Automatic, Forced, and Restoring Nitrogen
- N2-BLAST System Leak Check Procedure
- What Are My Cut In/Out Pressures?
- N2-BLAST Fire Protection Systems Overview
Cannot identify the unit? Send us a photo of the cabinet inside and out and the serial number if you can find one. That is faster than working from a model number nobody can read. South-Tek Systems Service — Phone: (910) 415-1880 · Open a support ticket at support@southteksystems911.zendesk.com or through the Help Center.