FPS-1650, FPS-3250, and FPS-5000 Operation & Alarms – South-Tek Systems

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

This article covers how the FPS-1650, FPS-3250, and FPS-5000 behave in normal operation, what each touchscreen state and alarm means, and what to do about it. Preventive maintenance is scheduled separately in Preventive Maintenance, and the startup and leak-isolation procedures are in Installation and Startup.

⚠ Warning The control program is proprietary and password-protected from the factory. Do not alter controls, instrumentation, or setpoints without South-Tek's written consent — unauthorized changes void the performance specification and the warranty. Before any mechanical work, isolate and verify zero energy per Safety Guidelines. Powering the unit down does not depressurize the nitrogen tank or the riser. On the FPS-3250 and FPS-5000 the air side does not bleed down on stop either.

Operating states

The operation screen draws the whole air and nitrogen train. A check mark on a component means it is working; a warning triangle means there is an issue with it. Animated blips show gas moving — blue for air, green for nitrogen — and grey piping with no animation means no gas is moving. The current state is shown in the status bar at the top right. After an alarm screen appears it times out and reverts to this operation screen, so the status bar is where you look.

Status bar	What is happening	What to do
Off	The generator is stopped. No gas is moving, the piping is grey, and the start/stop button is red. The sprinkler piping is still at supervisory pressure.	If this was not intentional, check power and the alarm history before restarting.
Standby	The storage tank is up to its cut-out pressure, so production has stopped and air delivery to the beds is shut off. The unit idles here until tank pressure falls to the cut-in setpoint.	Nothing — this is normal, and it is where a healthy system spends most of its time.
Running	The generator is separating oxygen out of the compressed air and filling the storage tank. Blue and green animation on the piping.	Nothing — normal. What matters is the trend: compare run hours against the previous visit. Continuous running is the warning sign.
Bypass	The system has switched the riser onto compressed air and paused nitrogen production. See the alarm table below.	Expected during a fill test. At any other time, investigate.

Cut-in and cut-out pressures

The generator starts and stops on storage tank pressure, read by a transducer feeding the controller.

Setpoint	FPS-1650	FPS-3250 & FPS-5000
Nitrogen cut-in — falls to here, starts producing	60 PSIG	60 PSIG
Nitrogen cut-out — rises to here, enters Standby	70 PSIG	100 PSIG
Automatic bypass cut-in — falls to here, riser goes on air	50 PSIG	50 PSIG
Automatic bypass cut-off — rises to here, riser returns to nitrogen	70 PSIG	70 PSIG

ℹ Note — read the unit before diagnosing Those are the standard factory settings. The nitrogen cut-out is the one figure that differs between the models — 70 PSIG on the FPS-1650 and 100 PSIG on the FPS-3250 and FPS-5000 — so check which machine you are standing at before you judge a reading. Confirm the actual values on the unit before you diagnose a pressure complaint: nitrogen cut-in and cut-out are on the controller's N2 Pressure Settings screen, and the bypass pair is on the Bypass Settings screen under System Settings. Record what you find on the service record. A unit configured away from these defaults is not necessarily faulty, but a unit you assume is at default when it is not will send you chasing the wrong thing. Adjusting the cut-in and cut-out without contacting South-Tek can alter the nitrogen purity and flow the system was sized for.

Bypass air is fed through the auto-bypass input assembly, which has its own regulator, solenoid valve and gauge, and takes air in through a cabinet bulkhead — so bypass air arrives from an external air source, not from the FPS-1650's internal compressor. Confirm the source on site. 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.

Starting and stopping

The start/stop button is on the home screen. Press and hold it until the status indicator beside it shows Hold and the state flips between Off and Running — allow up to about two seconds, and hold until the indicator confirms rather than counting. The button is red when stopped and green when running.

Stopping the generator is not the same as isolating the system — the riser stays at supervisory pressure and the sprinkler system stays charged. But a stopped generator makes no nitrogen, so the riser is no longer being topped up and supervisory pressure decays at whatever the system's leak rate is.

⚠ Attention — a planned stop is an impairment of the supervisory gas supply Notify the building owner or their impairment coordinator and the alarm monitoring company before you stop the unit, tag the system under the site's impairment program, keep the stop no longer than the work needs, and watch riser pressure while it is down. When the work is finished: restart the generator, confirm the status bar reads Running and then reaches Standby, confirm the riser is back at supervisory pressure, and clear the tag with whoever you notified.

Alarms

When an alarm trips, the controller jumps to the operation screen, flags the affected component with a warning triangle, and flashes the alarm in the status bar. Press the red bell icon to temporarily silence the buzzer — that silences the sound only, it does not clear the condition. Alarm screens time out back to the operation screen, so use the status bar and the Alarms menu to see what is active.

Alarm	What triggers it	What to do
Bypass	The 30-minute fire protection piping fill test, or the generator not functioning correctly. Entry and exit are a pressure comparison: the system goes to bypass when the bypass pressure falls to the bypass cut-in setting (50 PSIG as standard), and returns to normal run when it rises to the bypass cut-off setting (70 PSIG as standard). Confirm both on the Bypass Settings screen for that unit. While in bypass it switches the riser onto compressed air and pauses nitrogen production.	During a fill test this is normal and the unit returns to nitrogen on its own. At any other time, investigate — the riser is being supervised with air, not nitrogen, and is not protected from corrosion. This is the alarm most often missed.
BlastOff®	A potential leak, or nitrogen being overdrawn — the generator has run continuously past the BlastOff® timer setting without reaching Standby. The timer value is set per job — read the setting and the live countdown off the BlastOff® settings screen, and that countdown is the most useful pre-alarm warning the controller gives you.	Inspect and test for leaks and component failures. Inspect and test for leaks and component failures first — find the cause before you clear the alarm. The alarm is reset by power-cycling the unit. That is a fire protection impairment: the generator stops making nitrogen, and the cycle drops the common alarm contact — and the power loss contact where it is fitted — so the fire panel or BMS sees it. Notify the building owner or their impairment coordinator and the alarm monitoring company first, tag the system under the site's impairment program, and put the points on test. Before you leave: confirm the unit returns to Running and then Standby, confirm the alarm has cleared at the panel, confirm the riser is at supervisory pressure, take the points off test and clear the tag with everyone you notified. Do not keep resetting it without finding the cause — continuous running shortens compressor life, and on a fire protection system it means the piping is not holding the nitrogen it should. Isolation procedure: Installation and Startup.
Compressor issue	The generator has detected a problem with the air compressor. A warning triangle appears on the compressor in the diagram.	Check the compressor for power, line leaks, and other equipment failures. On the FPS-3250 and FPS-5000 that is the external compressor, with its own manual and its own service requirements.
Dryer issue	The generator has detected a problem with the air dryer. Applies where drying is fitted — an ordered option on the FPS-3250 and FPS-5000.	Check the dryer for power, line leaks, and equipment failure. Do not run the generator for long on undried air — moisture into the PSA beds is damage the warranty does not cover.
Filter / change filters	1 year (calendar days) or 1,000 run hours, whichever comes first. A warning triangle appears on the generator and the status bar flashes Change Filters.	The system keeps running — this is a maintenance reminder, not a fault. Change the filters as soon as practical, then reset the alarm (see below).
N2 tank pressure	The screen labels this the Low Tank Pressure Alarm. It has both an alarm point and an alarm cut-out point, and the alarm itself can be switched on or off in the alarm settings.	Verify the alarm point and alarm cut-out point on the N2 Pressure Alarm Settings screen — those are what drive this alarm, not the production cut-in and cut-out. Then check the storage tank and the feed side for a leak or a supply problem.
O₂ purity	Purity has fallen below the configured alarm point. Available where the optional oxygen sensor is fitted.	Check for air ingress, APS tuning, and feed-air quality. On a new install, purity climbs over the initial purge period before it settles, so record the day-one reading and judge the trend at the next visit rather than treating an early low reading as a fault.

What the compressor and dryer alarms actually watch

These two are not a diagnostic the controller works out for itself. They come from the equipment alarm instrumentation — physical pressure switches plumbed into the air side and wired to PLC inputs. When pressure on the monitored line falls to the switch's closing point, the switch changes state, the PLC sees it, and the controller raises the alarm — and it stays raised until pressure recovers to the reopening point. That is why a compressor or dryer that has stopped, tripped, or lost its supply shows up on the panel as an equipment alarm rather than as a generator fault.

It also means the alarm is verifiable in the field: read the pressure on the monitored line and compare it against the closing and reopening points recorded for that unit. Use an existing gauge or test point where there is one — if you have to break into the line to fit a gauge, isolate and depressurize that section first, and prove 0 PSIG on a gauge before you break any joint. On the FPS-3250 and FPS-5000 these switches sit on the feed-air side upstream of the cabinet inlet regulator, so that line can sit at the feed compressor's cut-out — 175 PSIG on a South-Tek-supplied compressor — not the 120–125 PSIG the generator itself runs on. The switch settings are set at the factory and are not a field adjustment. Record the closing and reopening points for that unit at commissioning — once they are on the service record, the alarm becomes verifiable on every later visit.

⚠ Warning — these are COMPRESSED-AIR settings, not nitrogen setpoints These are compressed-air pressure switches, not nitrogen setpoints. Whatever you read off them has nothing to do with the nitrogen tank cut-in and cut-out or the bypass setpoints earlier in this article — do not compare the two sets, and do not “correct” one to match the other. These switches are set at the factory and are not a field adjustment.

Model	Switches fitted	Air-side switch setting
FPS-1650	Two positions, both optional — PS-1 with the equipment alarm option, and PS-2 with the backup air compressor option. Each senses air pressure on the line, not the compressor's electrical state, so trace it on the unit before you test it. No dryer on this model, so no dryer switch	Set at the factory and not published per model. Read the closing and reopening points off the switch on the unit, or from the drawing package supplied with it, and record them.
FPS-3250 & FPS-5000	Two — one on the air compressor and one on the air dryer, which is why these two report separately on the panel	Set at the factory and not published per model. Read the closing and reopening points off each switch and record them.

ℹ Note — what an equipment alarm does and does not tell you The switch reports pressure on the line, not the health of the machine. A compressor alarm means the air is not there — which could be the compressor itself, its breaker, a closed valve, or a leak upstream of the switch. A dryer alarm on an FPS-3250 or FPS-5000 works the same way. Equally, a compressor can be running badly and still hold pressure, so the absence of an equipment alarm is not a clean bill of health. Use it as a first indication, then check the equipment itself.

Two things that catch people out. First, the deadband: the alarm asserts on falling pressure at the closing point and will not clear until pressure comes back up to the reopening point. Restoring pressure to just above the closing point therefore leaves the alarm up, and that is correct behaviour, not a fault — work from the closing and reopening points recorded for that unit. Second, this instrumentation is a build option — it is ordered as the equipment alarm option, and on systems supplied with BlastOff® III (Early Warning) it comes as part of that package. A unit built without it has no compressor or dryer alarm at all, and that is a configuration question rather than a fault. Confirm what the unit was supplied with against the order, using the serial number.

Which alarms you actually have depends on your BlastOff® level

BlastOff® ships in four levels, and not every unit has all four. Level III is the one usually called Early Warning — the diagnostic tier. Before chasing an alarm a customer says is missing, check what the system was supplied with.

Level	What it does	What you see on the controller
I — Leak detection	Tracks runtime and alarms if the generator runs past the BlastOff® timer without reaching Standby, giving warning before a low-air condition.	The BlastOff® alarm and its settings screen, with the timer value and countdown.
II — Auto air bypass	Switches the riser onto compressed air automatically if the generator cannot keep up, and logs the event.	The Bypass alarm, the bypass settings screen, and the bypass log.
III — Early Warning	The diagnostic tier — a trouble alarm that confirms the supporting components are working and helps pinpoint where a leak is in the nitrogen system.	The equipment status alarms — compressor issue and dryer issue — their contacts and audible alarms, and the diagnostic detail behind the alarm screens.
IV — Onboard purity	Monitors the nitrogen purity going into the fire protection system, trends it, and alarms below the configured O₂ purity alarm point. 98.5% is the system's purity specification, not a fixed alarm point — the alarm point and its cut-out are set on the O₂ Purity Alarm Settings screen.	The O₂ purity alarm and its alarm point, the O2 % graph, and purity in the sensor logs. These appear only where the oxygen sensor is fitted.

ℹ Note — before troubleshooting a “missing” alarm If a screen or alarm described here is not on the unit in front of you, the feature is most likely not fitted rather than faulty. Current FPS-1650, FPS-3250, and FPS-5000 builds ship with BlastOff® leak detection and the automatic air bypass, but an older or custom-built unit may not have them — check the build before treating either as missing. Beyond the BlastOff® tiers, the following are separately ordered options, each of which adds or removes something you would see on the controller: equipment alarm (the compressor and dryer pressure switches above), max O₂ sensor, dew point monitor, flow meter, power loss alarm, remote stop switch (wired by others), a backup air compressor on the FPS-1650, and an internal dryer on the FPS-3250 and FPS-5000. Check the order or ask South-Tek with the serial number before opening a service ticket.

Clearing the filter alarm

Open Alarms from the home screen. With a filter alarm active, pressing the Active button opens the filter detail screen, which lists the replacement kit number, the individual filter part numbers, the last change date, the status of each element, and South-Tek's contact details for ordering. After the filters are changed, press Change Filters and then hold the Reset button to acknowledge the change.

The three elements listed on that screen are not the same across the family. The FPS-1650 has an air inlet pre-filter, a particulate filter, and a coalescing filter. The FPS-3250 and FPS-5000 have a 5-micron filter/regulator combo at the air inlet ahead of the dryer, plus a 0.01-micron coalescing filter and an adsorbing filter (spelled “absorber” on some screens) in a separate assembly after the dryer — which is why the kits differ: FRP-007 for the FPS-1650 and FRP-022 for the FPS-3250 and FPS-5000. Older FPS-3250 and FPS-5000 units with three black filter bowls on one bracket take the legacy FRP-013 kit instead. Reset the timer every time filters are replaced, even if the alarm had not yet appeared — otherwise the next reminder arrives at the wrong interval. Schedule and procedure: Preventive Maintenance.

Dry contacts and analog outputs

Alarms do not only appear on the screen. The generator provides voltage-free dry contacts for the building fire alarm panel or BMS, and, where the sensors are fitted, analog outputs for trending. These are the connections a monitoring company sees, so when a customer says “we never got notified,” this is where to look. Wiring, terminal detail, and end-of-line supervision are covered in Fire Alarm and BMS Wiring for FPS Dry Contacts; the authority for any given unit is its own electrical schematic, not this table.

Output	What it reports	Fitted
Common alarm dry contact	An alarm condition on the generator. This is the one most sites actually monitor, and it is a pooled contact — the generator's alarms drive it in common, so anything that raises an alarm, or drops power to the unit, reaches the panel through it. Function-test it end to end at commissioning and confirm what the panel actually receives	On the base schematic — confirm against your order
Bypass alarm dry contact	A separate bypass alarm relay is provided (labelled BYPASS DRY CONTACT ALARM on the schematic) — the system is on air, not nitrogen. Worth monitoring in its own right. Identify this relay on the unit and function-test it before relying on it — its terminal assignment is not marked alongside the common alarm and power loss contacts	Where auto air bypass is fitted
Purity alarm dry contact	Nitrogen purity below the configured alarm point. The controller's Alarm Contacts test screen (Maintenance menu) exercises Purity Alarm and Common Alarm as two separate contacts — so purity is not necessarily covered by monitoring the common contact alone	Where the oxygen sensor is fitted
Power loss alarm dry contact	Loss of supply to the generator. A dead unit cannot raise a common alarm, so this is the contact that covers that gap	Option
Tank pressure analog out	Nitrogen storage tank pressure, for trending on a BMS. 0–10 V. Confirm the scaling on the receiving equipment against the range the controller is configured for before you trend it	On the base schematic — receiving equipment installed by others
Tank trace O₂ analog out	Trace oxygen in PPM at the tank — the purity trend, exported. The FPS-1650 schematic gives this output as 0–10 V, the same as tank pressure; on the FPS-3250 and FPS-5000, read the range and scaling off the schematic supplied with the unit	Reads only where the oxygen sensor is fitted

⚠ Warning — the power loss contact works the opposite way round The common alarm contact and the power loss contact do not behave the same way. In terminal numbers:

Common alarm — alarm active: 11-12 CLOSED, 11-14 OPEN.
Power loss alarm — alarm active: 11-12 OPEN, 11-14 CLOSED.

The two contacts are wired the opposite way round from each other by design: a de-energized relay on power loss has to present the alarm state. Do not infer one from the other. Wire the power loss contact the way you wired the common alarm and your supervision reads backwards — healthy when the unit is dead, in alarm when everything is fine.

Work from the terminal numbers, not from N.O./N.C. habit. If you want the fail-safe side on both contacts — the pair that is closed while the system is healthy and opens on alarm — that is 11-14 on the common alarm and 11-12 on the power loss contact. Land them the same way and one of the two reads backwards. Whatever you wire, function-test every contact end to end at commissioning: trip the condition and confirm the panel or BMS actually receives it. Terminal detail and landing guidance: Fire Alarm and BMS Wiring for FPS Dry Contacts.

The home screen has two pages. Page 1 gives you Dashboard, Operation, Graphs, Alarms, Product Info, and a Next Screen button; page 2 gives you System Settings, Maintenance, Alarm Settings, Communication Settings, Factory Settings, and Previous Screen. If you cannot find a menu, you are on the wrong page.

Screen	What it gives you
Dashboard (page 1)	Nitrogen tank pressure on a large gauge, total run hours, and nitrogen leakage averages in SCFH for the last measurement, the current day, and the current month.
Operation (page 1)	The live system diagram and status bar described above.
Graphs (page 1)	Historical trending. Tank pressure is trended on every unit; optional sensors add air-in flow, nitrogen out flow, nitrogen dew point, incoming air temperature, and oxygen.
Alarms (page 1)	Status of every alarm at once — nitrogen pressure, purity, BlastOff®, bypass, and equipment status. Where the detail arrow appears, press it for more.
Product info (page 1)	Serial number, build date, commission date, software version, and total run time. This is the screen to photograph before calling support.
Data logs (via Dashboard)	Reached from the Dashboard. Sensor graphing, sensor and data log, system performance log, equipment status log, nitrogen leakage log, and bypass log — the bypass log records the date, time, and duration of every bypass event. Before removing the micro SD card, press Eject and wait for the safe-to-remove status.
System settings (page 2)	N2 Pressure Settings, sensor calibration, BlastOff® settings, and bypass settings. Sensor calibration and the bypass setpoints are genuine user procedures; the cut-in and cut-out pressures are not — do not change them without consulting South-Tek.
Maintenance (page 2)	Valve controls, alarm contacts, and filter status. The valve controls screen toggles each valve individually and the Automatic Bypass. Do that only with the unit stopped and the nitrogen outlet valve closed. Closing that valve stops nitrogen makeup to the riser and is a fire protection impairment: notify the building owner or their impairment coordinator and the alarm monitoring company, tag the system, and keep the window as short as the work requires. The alarm contacts screen and the Automatic Bypass toggle drive real outputs to the fire alarm panel or BMS — put the points on test with the monitoring company before you touch either. Before you leave: set every toggle back to Off, reopen the nitrogen outlet valve, restart the generator, confirm it runs and reaches Standby, confirm the panel shows no active trouble from the generator, take the points off test, and clear the tag. Before you leave: set every toggle back to Off, reopen the nitrogen outlet valve, restart the generator, and confirm on the operation screen that it runs and reaches Standby. Leaving Automatic Bypass toggled on — or the outlet valve shut — after a service visit is exactly how a riser ends up supervised with air, or with nothing at all.
Alarm settings (page 2)	Six categories: general, O₂ purity, BlastOff®, N2 pressure, bypass, and equipment status. Purity and N2 pressure carry adjustable alarm points and alarm cut-out points; general carries the Alarm Buzzer Mute Time and the Timeout to Op Screen; BlastOff® carries the timer setting and its countdown; bypass and equipment status are on/off toggles for the alarm and its buzzer. These screens can switch alarms off — on a fire protection system a switched-off alarm is a silent loss of notification. Switching any of these off impairs the notification path: tell the alarm monitoring company before you do it and put the point on test, write down anything you turn off, turn it back on before you leave, function-test it, and confirm with the monitoring company that it reads normal again. The bypass screen can also switch off the Automatic Bypass System itself, not just its alarm; left off, the riser has no air backup.
Communication settings (page 2)	Ethernet setup for remote access, SD card access, and Modbus TCP/IP. Requires a static IP entered at the controller; an intranet-only connection needs no subnet or gateway. Press Connect or power-cycle the controller to establish the link.
Factory settings (page 2)	Password-protected for South-Tek technicians. Contact South-Tek if you need something in here.

ℹ Note — how long “temporarily” lasts The General Alarm Settings screen sets all alarm buzzers on or off, the Alarm Buzzer Mute Time (how long the red bell silences the audible for), and the Timeout to Op Screen (how often the operation screen re-appears while an alarm is active). If a buzzer seems to come back too quickly, or an alarm screen keeps interrupting, that is where those intervals are set.

ℹ Note — menu access Some screens are behind a user password. It is printed on the second page of the O&M manual supplied with the unit — take it from there rather than from memory. It is not needed for a filter reset.

What healthy looks like

Indicator	Healthy	Investigate when
Where it sits most of the time	Standby, cycling into Run to top the system up	It rarely reaches Standby, or cycles constantly
Run time	Steady visit over visit against the baseline recorded at commissioning	A steady climb visit over visit — the earliest warning of a developing leak
Nitrogen purity	At the generator, at or above the 98.5% system specification once the initial purge is complete. At the zones, judge against the project specification and the AHJ	It will not hold 98.5% once the system is past its initial purge period
Leakage average on the dashboard	Steady month to month	A rising monthly trend, even without an alarm
Bypass log	Entries only around fill tests and known events	Unexplained bypass events, or long durations

Taking a purity reading at the generator

Units built to the auto-bypass tank assembly carry a purity sample port — a short length of 1/4" OD tubing in the outlet, provided for field purity testing, with a flow control on some builds. Where a flow control is fitted it is factory-set to a low sampling trickle and ships closed — do not adjust it. This hardware has moved between assemblies across build revisions, so on an older unit it may be in a different place or absent — confirm on the unit rather than assuming.

⚠ Warning — close the sample port after the reading Nitrogen vented from this port displaces oxygen. In a small or poorly ventilated mechanical room that is an asphyxiation hazard, not just a gas loss. Ventilate the space, open the valve only for the reading, and close it immediately afterwards. Left open it also shows up later as run hours and a rising leakage average. Full requirements are in Safety Guidelines.

A reading here tells you what the generator is producing. It does not tell you what is in the riser — for that, sample at the zone. The 98.5% figure is South-Tek's system specification. For an acceptance criterion, work from the project specification and the authority having jurisdiction. On a new system, purity at the zones rises over the initial purge period before it settles, so an early low reading at a zone is not necessarily a fault — check the commissioning documentation for the expected duration on that system.

ℹ Note — the tank has its own relief valve The internal nitrogen storage tank is protected by an ASME safety relief valve. The vessel rating and the relief setting are not published per model — read the relief setting off the valve tag on the unit, and the vessel rating off the tank nameplate where one is fitted. That valve is a code-required safety device, not an adjustment — if it is lifting, the cause is upstream and needs investigating, and the valve itself must never be blocked, plugged, or adjusted. The tank holds a nominal 14.8 gallons — the leak-rate calculation on a given unit uses whatever tank volume is entered on the leak-averages screen. Normal operating pressure is set by the tank cut-out setpoint, so read the actual setpoint on the N2 Pressure Settings screen rather than assuming the margin.

When to call support

Contact your local provider or installer first — they know the site. If they cannot be reached, contact South-Tek. Have the serial number, build date, and run hours from the Product Info screen ready, along with the active alarm and what the operation screen shows. South-Tek field service and remote support are both available — contact Service to arrange either.

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.