Double-Stage Ring Blower | High Pressure, Deep Vacuum, Up to 1040 mbar

A Double-Stage Ring Blower is what you reach for when a single-stage unit doesn’t have the pressure or vacuum depth your system demands. It’s the same side channel technology — oil-free, maintenance-free, one moving part — but with two impellers mounted in series on the same motor shaft, separated by an intermediate port that feeds the output of the first stage into the inlet of the second.

The result: roughly double the pressure or vacuum capability, with some trade-off in maximum flow. If a single-stage ring blower tops out at around 290 mbar of pressure or -280 mbar of vacuum, the double-stage version pushes those numbers to over 1000 mbar and -730 mbar, respectively.

Browse the full ring blower lineup: Ring Blowers overview →

How It Works

The operating principle is identical to any side channel blower. Air enters, an impeller accelerates it through a ring-shaped channel, and it exits at higher pressure than it entered. The difference is what happens between the two impellers.

In a double-stage unit, the air doesn’t exit after the first impeller. Instead, it passes through an internal port into a second impeller chamber — same diameter, same blade geometry — where it gets accelerated and compressed again. The two impellers sit back-to-back on the same shaft, driven by a single motor. No additional motor. No coupling between stages. Just a carefully machined gas path that routes the partially-compressed air from stage one into stage two.

Because the second stage is identical in diameter to the first, the overall flow capacity is constrained by the first stage’s intake. That’s why double-stage blowers deliver less maximum flow than their single-stage equivalents — the bottleneck is always at the inlet. The payoff is the pressure. Each stage multiplies the compression ratio, so the cumulative output pressure or vacuum depth is far beyond what a single impeller can achieve.

Why Double-Stage Ring Blower

The decision tree is simple:

• If you need more flow at moderate pressure → single-stage
• If you need more pressure or deeper vacuum → double-stage

Here are the real-world situations where double-stage matters.

You’re aerating a pond that’s deeper than two meters. The water column above the diffuser creates back-pressure that a single-stage blower struggles against. Flow drops off. The diffusers don’t bubble evenly. A double-stage blower pushes against that water column without choking.

You’re running a biofloc system. The water is dense with suspended solids — effectively heavier than clean water. The back-pressure at the diffuser depth is higher than the same depth in clear water. Single-stage works at the margin. Double-stage gives you headroom.

You’re pulling vacuum on a pneumatic conveyor that moves powder over a long pipe run with multiple bends. The pressure drop along the pipeline is significant. A single-stage blower can’t pull deep enough vacuum to overcome the line losses. A double-stage can.

You’re operating at high altitude — say, above 2000 meters. Air is thinner. A blower that performs adequately at sea level delivers less flow and less pressure at altitude. The extra compression stage compensates.

In short: whenever a single-stage blower is operating at the top of its pressure curve, working hard and running hot, a double-stage unit sized for the same pressure will run cooler, quieter, and last longer — because it’s not operating at its limit.

Upgrading from a single-stage blower that isn’t keeping up? Tell us what you’re running now → and we’ll confirm whether a double-stage is the fix.

Model Specifications

Table shows double-stage configurations (D suffix). All models available in 50 Hz and 60 Hz versions. Custom voltage configurations on request. Bold rows = most popular 1 HP and 2 HP models.

→ Download complete double-stage spec sheet (PDF)

Popular Models

1 HP Double-Stage Ring Blower

The entry point for double-stage. Same motor frame as the popular 1 HP single-stage, but with the two-impeller configuration. Used where a small operation needs more pressure than a single-stage 1 HP can deliver — a deeper pond, a longer pipe run, a biofloc tank with dense solids. The price step from single-stage to double-stage at this power level is modest, and if the application is borderline, the double-stage buys you insurance against under-performance.

2 HP Double-Stage Ring Blower

This is the workhorse for medium-scale operations that have outgrown single-stage capacity. Common applications include:

• Biofloc shrimp tanks with water depth over 1.5 meters
• Vacuum conveying of cement, flour, or plastic pellets over moderate distances
• Central vacuum systems in factories serving multiple pick-up points
• Aeration in deep equalization tanks at industrial wastewater plants

The 2 HP double-stage finds its way into applications where a single-stage 3 HP or 5 HP might be considered — but the double-stage achieves the same pressure with a smaller motor, lower current draw, and less heat generation.

Applications

Deep-Water Aeration and Biofloc

This is the application driving most double-stage ring blower sales in aquaculture. As shrimp farming in particular shifts toward biofloc technology — where suspended microbial flocs clean the water and supplement feed — the aeration demand changes. Biofloc tanks are typically deeper than traditional ponds, and the water is heavier with suspended solids. A single-stage blower that handled a 1.2-meter traditional pond adequately may stall at the same depth in a biofloc system.

Double-stage blowers maintain flow against the elevated back-pressure. The 1 HP and 2 HP double-stage models are the standard fit for biofloc tanks up to about 300 square meters of surface area per blower.

Vacuum Conveying

Pneumatic conveying systems that pull material rather than push it — vacuum conveying — need a vacuum source that can maintain sufficient suction as the pipeline loads up. When material enters the pipe, the pressure drop across the system increases. A single-stage blower pulling vacuum on a long conveying line may not have enough depth to keep the material moving at an adequate velocity. A double-stage blower provides the extra vacuum headroom.

Common materials conveyed this way: cement, fly ash, flour, grain, plastic pellets, sawdust, and granular chemicals. The double-stage ring blower suits short to medium distance conveying — up to about 50 meters of pipe run, depending on material density and lift height.

Industrial Processes with High Back-Pressure

Some processes create inherent resistance that single-stage blowers can’t overcome efficiently. Examples:

• Air sparging in deep tanks. Chemical reactors, plating baths, and fermentation vessels that are several meters deep need air injected at the bottom. The hydrostatic pressure requires a blower that can push against it without flow collapse.
• Vacuum holding on porous materials. CNC vacuum tables holding down MDF or particleboard leak air through the workpiece. A double-stage blower maintains deeper vacuum to compensate for the leakage.
• Filter press air blow-down. After a filter press cycle, compressed air blows residual moisture out of the filter cake. The cake itself creates high resistance. Double-stage blowers deliver the pressure to push air through.

Special Variants

LS Type — Corrosion-Resistant

The LS (electroplated) variant applies a corrosion-resistant surface treatment to the aluminum housing and impeller. Designed for environments with acidic vapors, high humidity with condensation risk, or proximity to salt water. Extends housing life by roughly 10× in corrosive service compared to untreated aluminum. Common in coastal aquaculture installations, chemical processing exhaust, and wastewater plants with hydrogen sulfide exposure.

L Type — Water-Proof Extended

The L (extended) variant provides additional water protection for outdoor installations exposed to rain, washdown, or high-humidity environments. Specify the L type if your blower will be installed outdoors without a shelter, or in a wet-well environment.

Not sure which variant fits your environment? Describe your operating conditions when you request a quote → and we’ll recommend the right protection level.

What’s Inside

• Two impellers in series on a single shaft. No coupling between stages. No second motor. The shaft is supported by bearings at both ends, with the twin impellers mounted in the center section. This balanced layout minimizes shaft deflection at speed.
• Aluminum alloy housings and impellers, both stages. Lightweight, corrosion-resistant, good heat transfer. The intermediate port between stages is machined into the center housing section.
• NSK double-sealed bearings. Same as our single-stage units. Packed with high-temperature grease. Rated for continuous duty.
• Universal voltage motor, 50/60 Hz. One model serves global markets. IP54 protection standard. Class F insulation.
• CE certified. Compliant with EU health, safety, and environmental standards. ISO 9001 quality management.
• [X]-year warranty. All double-stage ring blowers backed by our factory warranty — bearings, housings, and impellers covered against manufacturing defects.
• Quieter than you’d expect. At 57–76 dB(A), a double-stage ring blower is still quieter than almost any roots blower. The two impellers generate more aerodynamic noise than a single-stage, but the housing absorbs most of it.

→ Download double-stage ring blower catalog (PDF)

Installation Notes

Two things matter more with double-stage blowers than with single-stage:

Always use an inlet filter. The clearance between impeller and housing is fractions of a millimeter across two stages. Any debris that gets past the inlet will seize the first impeller instantly. The repair involves replacing the impeller and possibly the housing — expensive and avoidable.

Always install a relief valve. If the discharge line gets blocked — a closed valve, a plugged diffuser, a kinked hose — the blower will “dead-head” against the blockage. The trapped air heats up rapidly because there’s no flow to carry heat away. A relief valve set just above your normal operating pressure vents the excess and prevents thermal damage.

For vacuum service, the relief valve goes on the inlet side and is set to open at a vacuum level slightly deeper than your target — preventing the pump from pulling beyond its rated vacuum and overheating.

Double-Stage vs Single-Stage: Quick Comparison

If your application is a standard pond under 2 meters, air knife drying, or simple vacuum hold-down, our single-stage ring blower is likely the more cost-effective choice.

Need help deciding between stages? Contact our engineers → Describe your setup and we’ll tell you which configuration fits.

Frequently Asked Questions

When should I choose a double-stage ring blower instead of single-stage?

Choose double-stage when your system requires more pressure (above ~290 mbar) or deeper vacuum (below -280 mbar) than a single-stage unit can deliver. Real-world triggers: pond depth over 2 meters, biofloc systems with dense suspended solids, vacuum conveying over long pipe runs with multiple bends, or operation at high altitude where thin air reduces blower performance. If your current single-stage blower runs at the top of its pressure curve, overheating or losing flow — it’s time for a double-stage.

How deep can a double-stage ring blower aerate?

Double-stage ring blowers maintain full airflow at water depths of 2–4 meters with standard fine-bubble diffusers. For biofloc tanks with dense suspended solids, they handle depths of 1.5–3 meters where the heavier water creates additional back-pressure. For extreme depths beyond 4 meters or unusual diffuser configurations, contact us with your specifications for a custom assessment.

Do I need a relief valve for a double-stage ring blower?

Yes — this is critical. If the discharge line becomes blocked (closed valve, plugged diffuser, kinked hose), the blower dead-heads. Trapped air heats rapidly with no flow to carry heat away, potentially causing thermal damage within minutes. A relief valve set slightly above your normal operating pressure vents the excess safely. For vacuum service, the relief valve goes on the inlet side, set to open just beyond your target vacuum level. This is a low-cost device that prevents expensive repairs — install one on every double-stage blower.

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What is biofloc and why does it need a double-stage blower?

Biofloc is an aquaculture technology where suspended microbial flocs clean the water and supplement feed in shrimp and fish tanks. The water is dense with suspended solids — effectively heavier than clear water — creating higher back-pressure at any given depth. A single-stage blower that handles a 1.5-meter traditional pond may stall in a biofloc tank at the same depth. Double-stage blowers provide the extra pressure headroom that biofloc systems demand.

Can I run a double-stage ring blower continuously (24/7)?

Yes. Slovdson double-stage ring blowers are rated for continuous 24/7 duty with proper installation — inlet filter, relief valve, and adequate ventilation around the motor. The aluminum housing dissipates heat effectively. Class F motor insulation handles sustained operating temperatures without degrading. NSK double-sealed bearings are specifically rated for continuous operation at the speeds these blowers run.

What is the difference between single-stage and double-stage ring blowers?

A single-stage blower has one impeller — higher flow, moderate pressure (up to ~290 mbar). A double-stage blower has two impellers in series on the same shaft — roughly double the pressure (up to 1040 mbar) and deeper vacuum (to -730 mbar), with some trade-off in maximum flow. Choose single-stage for pond aeration under 2m, air knife drying, and vacuum hold-down. Choose double-stage for deep-water aeration, biofloc, long-distance vacuum conveying, and high-backpressure industrial processes. See our single-stage ring blower page for the full comparison.

What are the LS and L special variants?

LS (corrosion-resistant) applies an electroplated surface treatment to the aluminum housing and impeller, extending housing life by roughly 10× in corrosive environments — coastal aquaculture, chemical vapors, wastewater plants with H₂S exposure. L (water-proof extended) provides additional water protection for outdoor installations exposed to rain or washdown. Specify the appropriate variant when you request a quote if your installation environment is corrosive or wet.