Applies to: South-Tek N2-BLAST fire protection nitrogen generators. The generator-side procedure below applies to any South-Tek PSA nitrogen generator.
A nitrogen generator that runs longer than it used to is usually telling you the system is losing gas somewhere. Three to five hours a day is typical for a correctly sized, tight system — but the number that matters is this system's own run time when it was commissioned and working. Compare against that. This article is how you find where the gas is going.
⚠ Warning — nitrogen displaces the air you breathe Nitrogen has no smell, no color and no warning. It is not poisonous — it kills by displacing the oxygen you breathe, and a person who walks into a displaced space can lose consciousness before realizing anything is wrong. A leak hunt puts you next to venting gas, often in a riser closet, valve room, attic or ceiling space with no ventilation.
Ventilate the space before and while you work in it. Vent to outdoors or into a large open area, never into a small closed room. Prop the door. If a space is small, enclosed and has been holding a discharge, treat it as a confined space and use a personal oxygen monitor — do not judge it by how it feels. A PSA generator also vents oxygen-enriched waste gas: keep ignition sources away from the exhaust.
If someone collapses in a space that may be oxygen-deficient, do not go in after them. More people die attempting the rescue than in the original event, and the gas gives the rescuer no warning either. Call emergency services, ventilate the space from outside it if you can do that from a safe position, and leave entry to trained rescuers with supplied air.
Ventilate the space before and while you work in it. Vent to outdoors or into a large open area, never into a small closed room. Prop the door. If a space is small, enclosed and has been holding a discharge, treat it as a confined space and use a personal oxygen monitor — do not judge it by how it feels. A PSA generator also vents oxygen-enriched waste gas: keep ignition sources away from the exhaust.
If someone collapses in a space that may be oxygen-deficient, do not go in after them. More people die attempting the rescue than in the original event, and the gas gives the rescuer no warning either. Call emergency services, ventilate the space from outside it if you can do that from a safe position, and leave entry to trained rescuers with supplied air.
Before you touch a valve: rule out what is not a leak
Every check in this section is free, none of them takes the fire protection system out of service, and one of them is very often the answer. The isolation test that follows does take the system out of service, so do these first.
| Check | Why it produces the same symptom |
|---|---|
| Anything done to the system recently | A drain-down, a trip test, an inspector's test, a head replacement, a branch extension — each of these fills the piping with air and the generator then has to push it back out. Run time climbs for days afterwards and there is nothing wrong. Ask what was done and when, and compare run time against the days before the work. |
| The weather | Gas pressure falls as it cools. A system in an unheated warehouse, attic or parking deck loses supervisory pressure on a cold night and calls for make-up gas with no leak present. Check whether the high run time started when the temperature dropped. |
| The purity setpoint | Every additional point of purity costs disproportionately more run time to produce, so a setpoint that has been raised above the commissioned value shows up as high run time with nothing leaking. Confirm it is at the commissioned value — do not lower it below. The purity setpoint is what the corrosion protection depends on; changing it is an engineering decision, not a field adjustment. |
| What has been added since commissioning | Zones, branches or additional AutoPurge Systems added after the generator was sized mean more volume to fill and more purge flow to feed. The generator is not faulty; it is undersized for what the system has become. |
| The feed air supply | A PSA generator makes nitrogen out of compressed air. A feed compressor that is not delivering rated pressure and flow, or a fouled inlet filter, makes the generator run far longer to produce the same nitrogen. Check inlet pressure at the generator against its nameplate before you assume a leak. |
Start here: isolate the generator and see if it holds
There are two completely different searches in this article and they share almost nothing. Do not start looking until you know which side of the outlet valve you are on. One test tells you, and it is the same test either way: shut the generator and its storage tank into a closed volume and find out whether that volume holds pressure.
ℹ Note — two different pressures, two different gauges This article uses two names and never mixes them. Generator pressure is read at the generator or its nitrogen storage tank, upstream of the nitrogen outlet valve. System supervisory pressure is read at the dry pipe or pre-action valve gauge, downstream of it. The nitrogen outlet valve is the isolation valve between the storage tank and the fire protection system — the storage tank stays on the generator side of it.
Standby means the generator has reached its cut-out pressure and stopped making gas. It restarts at its cut-in pressure. Both vary by model.
Standby means the generator has reached its cut-out pressure and stopped making gas. It restarts at its cut-in pressure. Both vary by model.
⚠ Warning — read this before you close the outlet valve With the nitrogen outlet valve shut the sprinkler system is not receiving make-up gas, on a system you already know is losing it. If system supervisory pressure falls to the trip point, a dry pipe valve operates and the piping fills with water. On a pre-action system, falling pressure normally produces a supervisory or trouble signal rather than water — but on a single-interlock system it can still admit water, and either way it is a signal at the panel and a call to the monitoring company.
Before you close it: tell the building owner or their impairment coordinator and the alarm monitoring company, and let them decide whether this is handled as an impairment — that is their call, not yours.
While it is shut: stay with it, tag the valve, and watch system supervisory pressure, not the generator. Write down the low-air supervisory setpoint and the trip point before you start, agree a reopen pressure with the owner that sits clearly above the higher of the two, and reopen the moment you reach it — the test is never worth a tripped system. If nobody will give you a figure, reopen on the first sustained fall from the pressure you started at.
The whole isolation should be about an hour and a half at most — the fill, then a settle and a hold. It is not a valve you leave shut while you look for something. Reopen it when you are done either way, whichever result you get.
Before you close it: tell the building owner or their impairment coordinator and the alarm monitoring company, and let them decide whether this is handled as an impairment — that is their call, not yours.
While it is shut: stay with it, tag the valve, and watch system supervisory pressure, not the generator. Write down the low-air supervisory setpoint and the trip point before you start, agree a reopen pressure with the owner that sits clearly above the higher of the two, and reopen the moment you reach it — the test is never worth a tripped system. If nobody will give you a figure, reopen on the first sustained fall from the pressure you started at.
The whole isolation should be about an hour and a half at most — the fill, then a settle and a hold. It is not a valve you leave shut while you look for something. Reopen it when you are done either way, whichever result you get.
| Step | What to do | What you should see |
|---|---|---|
| 1 | Before closing anything, write down: system supervisory pressure, the low-air supervisory setpoint, the trip point, generator pressure, and the current run time. | You now have the numbers to judge the result against, and the pressure at which you reopen the valve. |
| 2 | Close the nitrogen outlet valve, and close any sample return line running back to a cabinet analyzer. Leave the storage tank connected to the generator. | The generator and its storage are now one closed volume. If you isolate the tank from the generator by mistake, the test proves nothing about the tank, the tank trim or the outlet piping — which is where a good share of generator-side leaks are. |
| 3 | Let the generator build to standby, and note how long it takes. | It reaches standby and stops. Cut-in and cut-out pressures vary by model — see What Are My Cut In/Out Pressures?. Fill time depends on model and storage volume; if you do not know what is normal for this unit, give it an hour before you call it a failure. |
| 4 | Let it settle 10 to 15 minutes after standby, then record generator pressure and the time. Leave it isolated for at least 30 minutes, longer if the site allows and system supervisory pressure is safe. Record pressure and time again. | The settling time matters: gas cools after the compressor stops and pressure drops a little with no leak present. What you are looking for is a reading that keeps falling after it has settled, or a generator that cuts back in during the hold. |
Now read the result.
| Result | What it means | Go to |
|---|---|---|
| It reached standby and generator pressure held steady. | The isolated volume did not lose measurable pressure over the hold. A very small leak can still hide inside it, but the gas the system is losing is going out into the building. | Leaks in the fire protection piping, below. |
| It reached standby but the pressure kept falling, or it cut back in. | There is a leak inside the isolated volume — the cabinet, the tank, or the piping between them. | Leaks at the generator, below. |
| It never reached standby. | Either a large generator-side leak, or the generator is not making nitrogen properly. Rule out the second one first — that is the first paragraph of the next section. | Leaks at the generator, below. |
| You had to reopen the valve before the hold finished. | The test is inconclusive and proves nothing either way. Do not read a result into it. | Restore supervision first. Then either retest with backup air or nitrogen supporting the system while the generator is isolated, or work the free checks above and the fire protection piping without isolating again. |
▲ Attention — a clean hold test does not clear the generator of everything Holding pressure proves the isolated volume is not leaking. It does not prove the generator is producing what it should — purity, capacity, sieve condition and cycle valve operation are separate questions, and any of them will drive run time up on their own. Nor does a large downstream leak rule out a small one at the generator at the same time. If you fix what you find downstream and run time does not come back down, return and run this hold test again.
Leaks at the generator
If it never reached standby, check production before you check for leaks. A generator isolated into a closed volume that still cannot build pressure is at least as often failing to make gas as it is leaking it. Confirm the feed air supply is at rated pressure and flow, that the inlet valve is open, that the unit is actually cycling, that no alarm is active and that the inlet filters are not fouled. Only when all of that checks out is a gross leak the answer.
▲ Attention — reopen the outlet valve before you start hunting The isolation existed to make the hold test mean something. It has done its job. Reopen the nitrogen outlet valve and confirm system supervisory pressure is back and holding before you go any further — finding and fixing a cabinet leak takes hours, and the sprinkler system must not spend them without make-up gas.
You do not need the volume isolated to hunt the leak, only pressurized, and it stays pressurized with the outlet valve open. If the repair itself will need the generator isolated or the piping vented, that is a planned impairment: agree it with the owner and the monitoring company, arrange backup air or nitrogen if the system needs support, and work it under the tag.
You do not need the volume isolated to hunt the leak, only pressurized, and it stays pressurized with the outlet valve open. If the repair itself will need the generator isolated or the piping vented, that is a planned impairment: agree it with the owner and the monitoring company, arrange backup air or nitrogen if the system needs support, and work it under the tag.
To find a leak inside the cabinet, work the pressurized volume with leak detection fluid.
⚠ Warning — soap solution and live electrical parts Isolate the generator at its external disconnect and lock it out before you spray anything. The generator's own control switch is not a disconnect. The volume stays pressurized with the power off, which is exactly what you want — you are testing the gas side, not running the machine.
Confirm generator pressure still reads its cut-out value before you start and while you work; with the power off there is no make-up gas, so a large leak will bleed the volume down and the bubbles will stop. Never spray into or near the electrical enclosure, the controller, the power supply or the terminals — inspect those, do not wet them.
Use a chloride-free leak detection fluid. Ordinary soaps and some commercial solutions leave chlorides behind that attack stainless steel over time. Rinse and wipe the cabinet down afterwards rather than leaving residue on metal and fittings.
Confirm generator pressure still reads its cut-out value before you start and while you work; with the power off there is no make-up gas, so a large leak will bleed the volume down and the bubbles will stop. Never spray into or near the electrical enclosure, the controller, the power supply or the terminals — inspect those, do not wet them.
Use a chloride-free leak detection fluid. Ordinary soaps and some commercial solutions leave chlorides behind that attack stainless steel over time. Rinse and wipe the cabinet down afterwards rather than leaving residue on metal and fittings.
| Where to work | What to do |
|---|---|
| Fittings, filter bowls, filter drains and their tubing | Wet each joint with leak detection fluid and watch it for a full 30 to 60 seconds — a slow leak bubbles late, and if you have already moved on you will miss it. Work one area at a time and dry it before moving on; a soaked cabinet hides the next leak. |
| Automatic condensate drains and relief valves | A condensate auto-drain stuck part open, or a relief valve that is weeping, vents continuously and looks exactly like a fitting leak on the gauge. Check them deliberately — they are easy to walk past because they are supposed to make noise sometimes. |
| The tank, its trim and the outlet piping | These are inside the isolated volume and are often overlooked because they sit outside the cabinet. Gauge connections, the fill and outlet fittings and the relief valve seat all belong in the search. |
Fixing what you find
⚠ Warning — relieve the pressure before you open anything Closing a valve stops make-up gas. It does not depressurize the pipe. Isolate the section, confirm any backup air or nitrogen supply is isolated too, vent it to zero and verify that at a gauge before you loosen a fitting. Vent to a ventilated space, not into the room you are standing in. A fitting opened under pressure lets go without warning.
| Fitting | How to fix it |
|---|---|
| NPT threaded | Try tightening first. If it still leaks, remove the fitting, clean the threads, reapply thread sealant or tape and reinstall. Do not keep tightening a fitting that is already tight — you will split it. |
| Push-to-connect | Push the tubing firmly home first; a partly seated tube is a common cause and costs nothing to rule out. If it still leaks, cut an inch or so off the end of the tubing and reinsert it fully — the sealing surface is the tube itself, and a scored or oval end will not seal no matter how far in it goes. Cut square. |
| Filter bowl | Check the bowl is fully seated and the seal is clean and undamaged. Bowls have pressure and temperature limits and are cleaned with neutral detergent only — see Annual Filter Replacement (FRP-007). |
Leaks in the fire protection piping
If the isolated generator held pressure, the generator is not leaking and the gas is going out into the building. This is a different job, and most of it is sprinkler work rather than generator work.
⚠ Warning — this is impairment territory Running a nitrogen system down, closing sectional valves, or opening the piping to find a leak takes fire protection out of service for as long as it takes. That is a fire protection impairment and it goes through the site impairment program: notify the building owner or their impairment coordinator and the alarm monitoring company, tag it, and restore supervisory pressure and verify it before the tag comes off. Plan the work before you start rather than discovering halfway through that the building is down.
| Where to look | Why it is worth looking there |
|---|---|
| Anything opened since the system last held pressure | Recent work is a high-yield place to start. A head replaced, a branch extended, a trim fitting disturbed during a trip test. |
| The AutoPurge Systems | An APS is a deliberate leak — that is its job. One set too far open vents nitrogen continuously and reads as a system leak. Check the flow setting against APS Flow Settings Reference, and note that a zone on a Quick-Check PowerSaver manifold uses setting D; confirm any other arrangement against that article rather than assuming. |
| Sample tubing runs to a Quick-Check manifold | A disconnected or damaged 1/4 in. line vents continuously. Where the manifold is in service it will usually flag the affected zone, as a flow alarm or as a purity reading that will not come up. |
| The air maintenance device or backup air compressor | A compressor still cutting in is not a leak, but it puts air back into the piping and produces the same symptoms — high run time and purity that will not hold. Do not simply shut it off. On many systems it is the required backup supervisory air source, and removing it leaves a leaking system with nothing to hold it up. Confirm its setpoint sits below the nitrogen setpoint so it only acts as backup, and route any change to it through the owner and the impairment program. |
| The sprinkler piping itself | Fittings, couplings, and low point drains. This is conventional sprinkler leak hunting and it is the contractor's work rather than the generator's. |
ℹ Note — let the monitoring tell you where to look Where a Quick-Check manifold is fitted, the zone that is out of specification or showing no flow is the zone to search first. A whole-building leak hunt is a last resort; where the manifold is in service it has usually already narrowed the search to one zone. See AutoPurge and Quick-Check Overview.
Before you leave
- Every valve you closed is open again — the nitrogen outlet valve, any sectional valves, and the sample return line to the cabinet analyzer, which is the one that gets left shut. Check your written list rather than your memory.
- The generator is back in normal operation, powered, off lockout and cycling.
- System supervisory pressure is restored and holding, verified at the gauge rather than assumed.
- Purity has recovered. Anything you opened admitted air. Let the system purge back up and verify purity at the far end before you call it done — pressure restored is not protection restored.
- Any impairment tag is cleared, and the owner and the monitoring company have been told the system is restored.
- Run time is being watched. One reading proves nothing — the test of whether you found it is run time coming back down over the following days.
- What you found and fixed is on the service record, with the run time before and after and the hold test numbers.
▲ Attention — if run time does not come down, you have not finished A leak repair that does not change run time means there is another one, or the original diagnosis was wrong. Do not close the job on the repair — close it on the run time. A system can hold more than one leak, and the biggest one masks the rest until it is fixed.
Related articles
- BlastOff and SMART-Trak Overview for N2-BLAST Systems
- What Are My Cut In/Out Pressures?
- Annual Filter Replacement (FRP-007)
- APS Flow Settings Reference (APS2 and APS4)
- AutoPurge and Quick-Check Overview for N2-BLAST Systems
- N2-BLAST Fire Protection Systems Overview
Need help? Have the model and serial number, the run time before and after, and your hold test numbers ready. South-Tek Systems Service — Phone: (910) 415-1880 · Open a support ticket at support@southteksystems911.zendesk.com or through the Help Center.