In a recirculating aquaculture system (RAS) the blower does more than oxygenate fish — it drives the biofilter, the degassing column, and often the airlifts that move water. That means you size not for one demand but for the sum of them, at the pressure of the deepest submerged diffuser. For most RAS the single-stage YEBL-1 covers moving-bed biofilter and tank duty; deep sumps or high-back-pressure media push you to the double-stage YEBL-DS or the high-pressure series.
The blower has three jobs in RAS
Unlike a simple pond, a RAS loop has several air users on one machine:
- Culture-tank oxygenation — holding DO for the stock.
- Moving-bed biofilter (MBBR) fluidisation — air keeps the plastic media tumbling so nitrifying bacteria stay active and don't clog.
- Degassing / CO₂ stripping — air blown through a trickling or packed column drives off dissolved carbon dioxide that would otherwise depress pH and fish growth.
- Airlifts — low-head air-driven water movement in place of pumps (sized separately in airlift pumps in RAS and blower sizing).
Add the airflow of every user and size the blower to the total, at the pressure of the deepest drop.
Pressure: the biofilter and sump decide it
RAS often has deeper submergence than a biofloc tank — biofilter chambers and sumps of 1.8–2.5 m are common, and packed degassing media add back-pressure. Budget it the same way:
| Component | Typical value (industry guidance) |
|---|---|
| Deepest diffuser submergence | ~100 mbar per metre |
| MBBR / media back-pressure | 30–60 mbar |
| Degasser column | 20–50 mbar |
| Pipe + fittings + margin | 40–70 mbar |
A 2.2 m biofilter with tumbling media can demand 350–450 mbar — beyond a single stage. That is exactly the double-stage YEBL-DS band: YEBL-DS-230 (4 HP, 230 m³/hr, 410 mbar) or YEBL-DS-320V (7.5 HP, 320 m³/hr, 500 mbar).
Airflow: sum the users
Set a target for each user, then add them:
- Culture tanks: ~1.0–1.3 m³/hr per m³ of water (typical guidance)
- MBBR fluidisation: air sized to the media volume so it tumbles fully
- Degasser: air-to-water ratio set by the column design
Worked example
A 40 m³ RAS with a 6 m³ MBBR chamber and a degassing column:
- Tanks: 40 × 1.2 ≈ 48 m³/hr
- MBBR: ~60 m³/hr to fluidise the media bed
- Degasser: ~40 m³/hr
- Total ≈ 150 m³/hr at a 2.2 m biofilter → ~400 mbar
That points to a YEBL-DS-230 (4 HP, 230 m³/hr, 410 mbar) with headroom, plus a standby.
| RAS size | Air users total | Pressure | Model | Family |
|---|---|---|---|---|
| 15 m³ | ~60 m³/hr | 1.5 m / 260 mbar | YEBL-1-145 1 HP | single stage |
| 40 m³ | ~150 m³/hr | 2.2 m / 400 mbar | YEBL-DS-230 4 HP | double stage |
| 80 m³ | ~300 m³/hr | 2.4 m / 460 mbar | YEBL-DS-320V 7.5 HP | double stage |
| High-density | media back-pressure | greater than 600 mbar | YEBL-HP-DS-120 5 HP | high pressure |
Reliability is critical in RAS
A RAS carries very high biomass in a small water volume, so oxygen reserve is short — a stalled blower can crash DO within minutes, faster than an open pond. Two rules follow:
- Duty-standby with auto-changeover is mandatory, not optional.
- Back-up power — a genset or hybrid supply — because a RAS cannot ride out a long outage. The power question is weighed in solar vs grid power for aquaculture blowers.
The DO monitoring and staging that keep a RAS stable are covered in dissolved oxygen management with blowers, and the broader selection logic in the biofloc aeration pillar guide. Hatchery RAS loops with gentle-flow larval tanks are a special case detailed in blower for hatchery aeration.
Degassing: the job people forget
In a high-density RAS, carbon dioxide is as dangerous as low oxygen. Fish respiration produces CO₂ continuously, and in a closed loop it accumulates fast, depressing pH and stunting growth even when DO reads fine. The cure is a degassing (CO₂-stripping) stage — a trickling or packed column where blower air is blown counter to falling water, driving CO₂ out. This air is part of the blower's total demand, and it needs enough pressure to push through the column's media. Size the degasser air into the sum, and remember it runs continuously — CO₂ never takes a night off. Under-provide it and you get the frustrating case of good oxygen but poor growth.
Biofilter fluidisation matters
A moving-bed biofilter only works while the plastic media tumbles freely — that tumbling scours old biofilm, exposes fresh surface, and stops the bed clogging. Too little air and the media stagnates and channels; the nitrifying bacteria that convert toxic ammonia lose contact with the water. So the biofilter air is not a "nice to have" — it is what keeps the biological filter alive, and it must be delivered at the pressure of the media chamber's depth. This is the same suspension principle that biofloc relies on, explained in the pillar guide.
Commissioning a RAS blower
- Confirm outlet pressure matches the deepest-user calculation.
- Check the biofilter media tumbles fully across the whole chamber, with no stagnant corners.
- Verify the degasser actually drops dissolved CO₂ under load.
- Test the standby and auto-changeover — a RAS has minutes of oxygen reserve, so this is critical.
Water temperature and RAS oxygen demand
A RAS runs at high biomass in a small water volume, so temperature has an outsized effect on the oxygen balance. Warmer water holds less oxygen at saturation and pushes fish metabolism higher, so demand climbs while the reserve shrinks — a double squeeze that a pond, with its larger buffer, feels less. Cold-water species held below their comfort band also change the picture. The design response is the same discipline used everywhere in this cluster: size the blower to the warmest operating case at full biomass, keep 15–20% airflow headroom, and never rely on the daytime average. Because a RAS has only minutes of oxygen reserve, that margin plus a tested standby is what separates a stable loop from a fish kill. The DO monitoring behind it is in dissolved oxygen management with blowers.
Frequently asked questions
What size blower does a RAS need?
Sum every air user — tanks, biofilter, degasser, airlifts — for airflow, and size pressure to the deepest submerged diffuser. A 40 m³ loop with a 2.2 m biofilter often needs ~150 m³/hr at ~400 mbar, a YEBL-DS-230.
Why single-stage vs double-stage in RAS?
Deep biofilters and sumps (2–2.5 m) plus media back-pressure push the pressure demand past a single stage's ceiling, so RAS often uses double-stage YEBL-DS machines.
Can the same blower run the airlifts?
Yes — airlift air is simply another user in the total. Sizing airlifts specifically is covered in airlift pumps in RAS and blower sizing.
See the aquaculture and biofloc application page for the full range.
Let us size your loop
Send your tank volume, biofilter type and sump depth and we will total the air users and specify the blower plus standby. WhatsApp +91 9311693322 or email sales@yashblowers.org — engineered in Faridabad, quoted within 24 hours.