Keeping the inlet filters clean is one of the most cost-effective ways to protect your nitrogen generator and hold purity steady. Clean elements stop oil, water, and particulate from reaching the carbon molecular sieve (CMS) beds, where contamination causes permanent, non-warranty damage. This guide covers the filter set and its order, the full element replacement procedure, maintenance best practices and intervals, and troubleshooting, including a high differential-pressure reading right after a change.
In this guide
Filter element replacement procedure
Tools and supplies needed
- New filter elements (genuine South-Tek)
- New O-rings (if applicable to your unit)
- Strap wrench (for tight or threaded filter bowls)
- Rubber mallet (for stuck bowls)
- Screwdriver or driver (for bolted-cover bowls on some CS and S units)
- Clean rags and mild soapy cleaning solution
- Silicone grease (optional, for O-ring seating)
Phase 1: Safety and depressurization
- Turn the generator off: Switch the generator to the OFF position.
- Isolate the air supply: Close the incoming air supply (inlet) valve completely to stop new air from reaching the generator.
- Relieve pressure: Open the wedge (relief) valve located immediately after the filter bank to vent trapped pressure. You may hear hissing; wait until it stops completely.
- Confirm 0 PSIG: Verify the air supply gauge reads 0 PSIG before going further.
- Leave the valve open: Keep the wedge/relief valve in the OPEN position for the entire job so pressure cannot build up while you work.
Phase 2: Disassembly and cleaning
With the system verified at 0 PSIG, remove the housing bowls. The filter assembly and a typical housing are shown below.
Figure 1: Filter assembly (exploded view): differential pressure indicator, body, O-ring, deflector vane, filter element, element retainer, bowl, and automatic drain
- Disconnect the drain tubes: If the bowl drains are tied into a condensate drain system, disconnect the tubes from the bottom of the bowls first.
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Remove the filter bowls. How the bowl comes off depends on your housing style. In every case, grip the body of the bowl, never the drain mechanism, which is fragile and can snap.
- Latch style (TS and most CS): Push the bowl latch down and rotate the bowl while pulling it down.
- Threaded / ACME style: Turn the bowl counter-clockwise. The external ribs or the hex on the bottom of the bowl give you a grip. If it is hand-tight and will not budge, use a strap wrench placed near the top of the bowl (closest to the threads) to avoid crushing the body.
- Bolted-cover style (some CS and S): Remove the screws holding the bowl to the cover, then pull the bowl off.
- Inspect the bowls: If the drain system is working properly, the bowls should not be full of water. Standing water points to a failed or blocked drain.
- Separate the drains: Remove the auto-drain mechanism from the bottom of each bowl. Check the float inside; if it is sticking or corroded, replace the drain. A failed drain can flood the generator.
- Clean the components: Wash the bowls and drains in mild soapy water and rinse thoroughly, or use a light air gun to remove debris. Remove all sediment, sludge, and calcification, then wipe with a clean, dry cloth.
- Pre-assembly: Reattach the cleaned or new drains to the bowls and set them aside in a clean area.
Figure 2: Filter housing detail, threaded/ACME style used on some CS and S units, showing the Delta-P gauge, bowl threads, ribs, and internal float drain
Phase 3: Element replacement
- Remove the old elements: Unscrew or pull each old element from the filter head. Note its condition; if an element is excessively dirty, shorten the change interval for that stage going forward. Discard elements per your facility's waste protocols.
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Inspect and replace O-rings:
- Check the O-ring seals inside the filter head.
- If your unit uses O-rings, replace them every time you change the element. Old, flattened O-rings are the number-one cause of leaks after service.
- Seat the new O-ring fully in its groove. A pinched O-ring will leak later.
- Install the new elements: Insert each new element and seat it firmly, making sure the correct element goes in the correct stage.
- Reinstall the bowls: Put each bowl back on opposite to how it was removed, making sure it seats correctly. Hand-tighten threaded bowls firmly; do not use a wrench to tighten, as that makes them very hard to remove next time. Reconnect the drain tubes.
Phase 4: Restart and verification
Bring the unit back online slowly so you do not shock the system.
- Close the relief valve: Return the wedge/relief valve to the CLOSED position.
- Pressurize slowly: Open the inlet air valve very slowly. Rushing pressure into an empty system subjects the elements and internals to a sudden pressure surge and heat from rapid compression, which can damage them.
- Leak check: As the bowls pressurize, look and listen for leaks. If you hear hissing, close the inlet immediately and recheck the O-ring seating.
- Power on: Once the system is holding pressure with no leaks, turn the generator back ON.
Phase 5: System acknowledgement
Tell the controller the filters were changed so it resets the service timers.
- On the controller, go to the Maintenance/Filter menu.
- Select Filter Change.
- If prompted for a security code, enter 6557.
Filter maintenance best practices
1. Follow the recommended change intervals
On current units (serial number after 63963), replace all three elements every 6 months:
- Particulate: every 6 months (sooner in harsh or high-dust environments).
- Coalescing: every 6 months (sooner with high oil content in the air).
- Adsorbing (absorber): every 6 months (sooner if oil vapor is present in the supply).
Replace at the interval above or when the differential pressure gauge reaches its replace zone, whichever comes first. Keep spare elements on site, since parts and field service typically take about two weeks to arrange. For the full preventive-maintenance schedule (analyzer, CMS top-up, valves), see the Preventive Maintenance article.
▲ Attention — Older / legacy units Units with serial number 63963 or earlier use a staggered schedule instead of the uniform 6-month interval:
- Particulate element: every 3 months
- Coalescing element: every 6 months
- Adsorbing element: every 12 months
This is why a legacy annual filter kit contains four particulate, two coalescing, and one adsorbing element. Your serial number is on the unit's data plate. If you are unsure, contact support with your serial number and we will confirm the correct intervals and kit.
2. Inspect filter housings regularly
- Watch the differential pressure (ΔP) across the filters. A gradual rise over the element's life is normal loading. (For a high reading right after a change, see Troubleshooting below.)
- Check the coalescing-filter drains and confirm liquid is draining properly.
- Look for oil, moisture, or particulate downstream, an early warning of filter bypass or failure.
3. Always replace elements, do not clean them
- Filter elements are not designed to be cleaned or reused.
- Cleaning can damage the media and let contaminants bypass into the PSA beds.
4. Maintain proper filter order
Filters must always be installed in sequence: Particulate → Coalescing → Adsorbing → PSA generator. Skipping or rearranging stages increases the risk of contamination.
Figure 3: Standard filter set in order, particulate, coalescing, and absorber filters, followed by the pressure regulator
| Stage | Type | Role |
|---|---|---|
| First | Particulate | Removes solid particles such as pipe scale, rust, and dust. |
| Second | Coalescing | Removes oil aerosols and bulk liquid water. |
| Third (final) | Adsorbing (activated carbon) | Removes oil vapor and hydrocarbons. This is the last line of defense before the PSA molecular sieve beds. |
5. Use genuine South-Tek filter elements
- Always use genuine South-Tek replacement elements.
- Off-brand elements may not meet the required efficiency ratings and can void the system warranty.
6. Monitor system purity
- Regularly verify nitrogen purity with a calibrated analyzer.
- If purity drops unexpectedly, inspect the filtration stages first; contaminated beds are often the result of upstream filter problems.
- After a filter change, let the system run and stabilize before judging purity. Readings can dip briefly during recovery and are not a concern on their own.
Troubleshooting: high differential pressure after a change
A gradually rising differential pressure (ΔP) over a filter's service life is normal and means the element is loading. A high ΔP reading right after a change is different. A new, clean element offers very little resistance to flow, so a high reading immediately after service almost never means a saturated element. It usually points to an installation or instrument issue, and most causes are quick to resolve on site.
Start here: confirm it is a real, steady-state reading
- Let the system fully repressurize and return to normal PSA cycling and demand before judging the reading. ΔP can spike briefly during repressurization or a cycle event.
- Mechanical ΔP gauges and piston or pop-up indicators can stick, especially after the housing was depressurized and handled. Gently tap the gauge and watch whether it settles; a piston indicator may be stuck in the tripped position and reset once flow is restored.
- If the package has a second gauge or upstream and downstream pressure references, compare them to confirm which gauge is in question.
If it is still high: step through these checks
- Verify the correct element is in the correct stage. Filtration runs Particulate → Coalescing → Adsorbing. A finer element in the wrong stage, or two stages swapped, drops more pressure than expected.
- Check element orientation and seating. Confirm the element is fully seated and the correct way up, all O-rings and seals are in place and undamaged, and any protective wrapping or shipping caps were removed before installation.
- Confirm valves are back to normal. A partially closed outlet valve, or a relief/bypass valve left mis-set after the change, shows up as high ΔP across the assembly.
- Re-check drains and bowls. A blocked drain or a flooded coalescer bowl loads the element with liquid and raises ΔP. Verify the drain works and the bowl is not holding liquid (see Phase 2).
- Re-check after a few minutes at normal demand. Confirm the reading settles into the expected low range once the system is running steady.
When to contact service
If the ΔP gauge still reads high after the checks above, the gauge itself may have failed, or site demand may be exceeding the filter's rated flow. Open a support ticket so a technician can verify the gauge against a reference and review the filtration sizing. Field service is scheduled in advance, so please allow about two weeks of lead time for an on-site visit.
Other troubleshooting
Leak at the bowl threads? This is usually a pinched O-ring or debris in the threads. Depressurize the system again, remove the bowl, wipe the threads clean, and reseat the O-ring.
Related Articles
- N2-GEN TS, CS, and S Series — Preventive Maintenance
- N2-GEN TS, CS, and S Series — Alarms & Troubleshooting
- How Frequently Should I Measure My CMS Levels and What's the Process?