Why Energy Recovery Matters in SWRO
The single largest line item in the operating cost of a seawater reverse osmosis plant is electricity, and the lion's share of that electricity is consumed by the high-pressure feed pump that overcomes the osmotic pressure of seawater. For typical Pacific or Atlantic feed at 35,000–40,000 mg/L TDS, that osmotic pressure sits around 25 bar, and the membrane operating pressure required to drive flux through an 8-inch SWRO element lands between 55 and 70 bar. Without energy recovery, more than half of the hydraulic energy delivered by the high-pressure pump simply exits the system as a pressurized brine stream that is throttled to atmosphere through a control valve — pure waste.
Energy recovery devices (ERDs) capture this brine-side hydraulic energy and return it to the feed side. For systems in the 25–70 m³/h feed range, the FEDCO HPB-60 has become one of the most specified turbocharger ERDs on the market, and for good reason: it bolts onto the high-pressure circuit without an auxiliary lube system, electrical service, or external control valve, and it does so with corrosion-resistant Super Duplex stainless. This review walks through the spec sheet, the technology underneath, and the trade-offs that decide when an HPB-60 is the right call versus a positive-displacement pressure exchanger.
The HPB-60 at a Glance
The HPB-60 is a single-shaft centrifugal energy recovery turbocharger. The high-pressure brine enters the turbine side, expands through the rotor, and the recovered shaft power immediately compresses the feed stream on the pump side of the same rotor. Because the turbine and pump impellers are integrated on a single rotating element with no external shaft penetration, there are no mechanical seals, no bearings outside the wetted path, and no need for an oil system or a VFD to drive it.
| Parameter | Metric | Imperial |
|---|---|---|
| Feed flow | 57.3 m³/h | 252 GPM |
| Brine flow | 34.4 m³/h | 151 GPM |
| Membrane pressure | 58.0 bar | 841 psi |
| Feed boost pressure | 24.0 bar | 348 psi |
| Max operating pressure | 83 bar | 1,204 psi |
| Max operating temperature | 70 °C | 158 °F |
| Dimensions (L × W × H) | 288 × 229 × 203 mm | |
| Weight | 28.1 kg | 62 lbs |
| Pipe connections | 2″ feed / 1.5″ brine, Victaulic Style 77 cut-groove | |
| Wetted materials | Super Duplex SS 2507 std / Duplex 2205 option | |
| Brine energy recovery | >80% | |
At 28.1 kg and a footprint smaller than a desktop tower PC, the HPB-60 is genuinely small, which matters more than it sounds: skid layout in containerized SWRO plants is a real constraint, and an ERD that hangs directly off the membrane housing manifold instead of demanding its own concrete pad changes the design entirely.
Inside RotorFlo Technology
The defining feature of the HPB family is the patented RotorFlo single-piece rotor. Where a conventional turbocharger uses a turbine wheel on one end of a shaft and a pump wheel on the other — with bearings, seals, and balancing complications between them — the RotorFlo rotor is a single investment-cast or machined component that carries both the turbine and the pump vanes. There is no shaft penetration to the atmosphere, so there are no shaft seals to fail and no oil reservoirs to maintain.
The rotor is hydraulically supported. As soon as the unit is pressurized, the rotor floats on a thin film of process fluid acting as both bearing surface and thrust balance. This is why the HPB requires no external lubrication and why startup is uneventful: the rotor lifts off as the feed and brine streams equalize and stays centered as long as differential pressure remains within the operating envelope. There is one moving part. That is the entire mechanical bill of materials, and it explains the unusually long mean time between failures FEDCO reports across its installed base of more than 5,000 units worldwide since the company was founded in 1997.
The wetted parts are Super Duplex Stainless Steel UNS S32750 (alloy 2507) as standard, with PREN values above 40 making them genuinely seawater-rated for chloride concentrations that would put 316L into crevice corrosion within months. For lower-salinity service — high-TDS brackish water around 10,000–15,000 mg/L — Duplex 2205 (UNS S32205) is offered at a meaningful cost reduction and a shorter lead time.
Integral Variable-Area Brine Control
One of the genuinely useful design choices in the HPB-60 is the integral variable-area brine control. In a conventional SWRO P&ID, the brine stream exits the pressure vessels at high pressure and passes through a separate motorized or manual brine control valve before any energy recovery device. That valve sets the recovery rate of the membrane array. With the HPB-60, the brine throttling function is built into the turbine nozzle ring itself, characterized by a published Kvo (fully open) and Kvc (fully closed) flow coefficient pair specific to the model. The result: one fewer valve, one fewer instrument, and one fewer thing to fail in seawater service.
This is also why HPB selection is so tightly coupled to the membrane array's design recovery. Because the turbine's flow area sets brine flow at any given pressure drop, the HPB model number (HPB-60, HPB-130, HPB-300, etc.) effectively encodes a feed/brine flow band that must match the array. Over- or under-sizing the turbocharger is not a soft compromise the way it would be with a downstream throttle valve — it changes the system's recovery curve directly.
Materials of Construction
| Component | Standard Material | Optional |
|---|---|---|
| Casing | Super Duplex SS 2507 | Duplex 2205 |
| End cap (feed and brine) | Super Duplex SS 2507 | Duplex 2205 |
| Rotor (single piece) | Super Duplex SS 2507 | Duplex 2205 |
| Bolting | Duplex SS / Super Duplex SS | — |
| Bearing surfaces | Tungsten-carbide / process-lubricated | — |
| O-rings | EPDM (std) | FKM / Viton |
EPDM O-rings are the standard and are appropriate for the chemical environment of SWRO feed and concentrate — salt, antiscalant, residual SBS for dechlorination, and occasional citric or sulfuric acid CIP. Specify FKM only where the CIP regimen is unusual or where elevated temperature service is anticipated.
Dimensions, Connections, and Skid Layout
The 288 × 229 × 203 mm envelope and 28.1 kg weight make the HPB-60 mountable on lightweight bracketry. Both ports use Victaulic Style 77 cut-groove couplings — 2″ feed-side, 1.5″ brine-side — which is the dominant joining standard for SWRO high-pressure piping in this size range. Cut-groove fittings give a serviceable union with no flange torque routine to maintain. Note that the feed and brine ports are not interchangeable; correct orientation is set by the rotor's vane geometry, and reverse plumbing will at best stall the unit and at worst overspeed the rotor.
For piping designers: keep the brine inlet flow as smooth as possible. A long-radius elbow within five pipe diameters upstream of the brine port is acceptable; an abrupt T or rapid expansion is not. The HPB is forgiving of feed-side turbulence but sensitive to brine-side cavitation, so keep brine backpressure above the published minimum and avoid throttling between the membranes and the HPB inlet.
Energy Savings Math
The HPB-60 recovers more than 80% of the hydraulic energy in the brine stream and returns it as feed boost. In the operating point shown above, the brine carries 34.4 m³/h at roughly 56–58 bar (membrane pressure minus a small pressure drop across the array). That is approximately 60 kW of hydraulic power on the brine side. The HPB transfers >80% of that — about 48 kW — to the feed stream as a 24-bar boost on 57.3 m³/h.
In practice this means the upstream high-pressure pump only needs to deliver the differential between feed source pressure and (membrane pressure minus HPB boost). A pump that would otherwise be sized for 58 bar at 57.3 m³/h now only needs to deliver roughly 34 bar at the same flow — a 40–50% reduction in shaft power. Across a typical 8,000 operating hours per year at $0.12/kWh industrial power, the savings on a 50 m³/h SWRO train can clear $25,000–$40,000 annually. ERD payback is generally inside 18 months and often inside 12.
Installation Best Practices
- Maintain brine backpressure. The HPB rotor needs hydrodynamic support from the process fluid. Do not allow the brine port to discharge to atmosphere directly; route to an open atmospheric break tank or a backpressure-sustaining valve sized for at least 0.5 bar at design flow.
- Do not pipe a bypass around the HPB. Some legacy SWRO P&IDs include a manual bypass for "emergency operation." With a properly sized HPB, bypassing the unit means the feed pump cannot meet membrane pressure — the system simply will not run. Skip the bypass and save the fittings.
- Protect the drain. The small case drain port is for commissioning and rotor inspection only. Plug it with the supplied stainless plug during operation; an open drain at 80 bar will not end well.
- Keep recovery below 50% per array. The HPB-60 is sized for typical single-pass SWRO recoveries of 40–45%. Pushing the array to higher recovery shifts the brine flow downward and starves the HPB, dropping efficiency and risking rotor instability.
- Verify the rotation indicator at startup. The HPB-60 has an external rotation indicator. Confirm the rotor is spinning within 30 seconds of feed and brine flow stabilization. If not, shut down and check for reverse plumbing or trapped air.
HPB-60 vs ERI PX vs HPB-130
| Attribute | FEDCO HPB-60 | ERI PX Q140 | FEDCO HPB-130 |
|---|---|---|---|
| Feed flow | 57.3 m³/h | ~32 m³/h | ~130 m³/h |
| Energy transfer efficiency | >80% | ~97% | >80% |
| Mixing of feed/brine | None (separate streams) | ~3% mixing | None |
| Booster pump required | No | Yes (Danfoss APP / Grundfos CR) | No |
| External lube / electrical | None | None (booster needs motor) | None |
| Footprint | Very small | Larger (PX + booster) | Medium |
| Best fit | Mid-size SWRO trains | Larger / efficiency-critical | Large SWRO trains |
The fundamental trade-off is efficiency versus simplicity. An ERI pressure exchanger hits 97% transfer efficiency but introduces a small amount of feed/brine mixing (raising feed TDS by 1–3%) and requires a dedicated booster pump, motor, and VFD. The HPB-60 gives up ~15 efficiency points but eliminates the booster, the motor, the VFD, and the mixing entirely. For mid-size containerized plants where simplicity and skid footprint dominate, that is usually a winning trade.
Spare Parts
FEDCO ships two consumable kits for the HPB-60:
- KH060-TBK — HPB-60 Top-end Bearing Kit. O-rings and rotor wear rings. Recommended at first major overhaul (typically 5–7 years).
- KH060-CBK — HPB-60 Complete Bearing Kit. Full set of wetted bearing surfaces plus the TBK contents. Recommended at second overhaul or after any abrasive event (sand ingress, antiscalant failure).
ForeverPure stocks both kits in Santa Clara for next-day shipment to North American customers.
Lead Time and Warranty
- Duplex 2205 construction: 3–6 weeks from PO.
- Super Duplex 2507 construction: 6–8 weeks from PO.
- Warranty: 36 months from shipment against defects in materials and workmanship, conditional on proper installation and operation within the published envelope.
Documentation
The full HPB-60 datasheet, including performance curves and certified dimensional drawings, is available at /datasheets/FEDCO-HPB-60-Datasheet.pdf. For application engineering support, see our FEDCO product page, or compare against the isobaric pressure exchanger family on the ERI page.
Closing Thoughts
The HPB-60 is not the most efficient ERD on the market, but it is one of the most reliable, the most maintenance-tolerant, and the easiest to integrate. For mid-size SWRO trains — mobile and containerized desalination plants, resort and industrial seawater systems, naval and offshore applications — it remains the default specification at ForeverPure for good engineering reasons. If your project sits in the 30–60 m³/h feed band and you do not have a strong reason to specify a pressure exchanger, the HPB-60 is almost certainly the right ERD.