The Energy Recovery PX 70S Pressure Exchanger® is a positive-displacement energy recovery device for seawater reverse osmosis. A single ceramic rotor transfers pressure energy directly from the high-pressure reject stream to the incoming feed, at up to 96% peak efficiency, handling 70 gpm (16 m3/hr) per device. There is no gearbox, no pistons and no lubricating oil — the rotor is the only moving part.
Documentation & Drawings
A 3D STEP model is available for system layout — request it here.
Technical Specifications
| Operating Conditions | |
| Service | 3. Reference |
| Liquid | Seawater |
| Maximum high-pressure inlet flow | 70 gpm (16 m3/hr) |
| Maximum low-pressure outlet flow | 70 gpm (16 m3/hr) |
| Maximum inlet high pressure | 1200 psig (82.7 barg) |
| Minimum discharge pressure | 14.5 psig (1 bar) |
| Operating temperature | 33°F-120°F (0.6-49°C) |
| Maximum temperature | 120°F (49°C) |
| Specific gravity | 1.03 |
| Viscosity | 1.06 cP @ 70°F (21.1°C) |
| Filtration requirement (nominal) | 20µm |
| Performance | |
| Peak efficiency | 96% |
| Maximum high-pressure differential | 15 psig (1 bar) @ 70 gpm |
| Maximum low-pressure differential | 16 psig (1.1 bar) @ 70 gpm |
| Maximum lubrication flow | 2.2 gpm (0.5 m3/hr) |
| Maximum rotational speed | 1500 rpm |
| Maximum salinity increase at membranes | 3% @ 40% Recovery |
| Materials of Construction | |
| Housing | GRP |
| Rotor, sleeve & endcover assembly | Ceramic-alumina |
| Port fittings | CN3MN |
| Tension rod assembly | *AL-6XN / C-276 |
| Fasteners & hardware (non-wetted) | 316SS |
| O-rings | EPDM |
| Shipping Weight & Dimensions | |
| Cartridge shipping dimensions | 15x11x12 inch |
| Cartridge weight | 15 lbs. (7 kg) |
| Identification | |
| Manufacturer | Energy Recovery, Inc. (San Leandro, CA) |
| Model | PX-70S |
| Data sheet reference | ERI 80031-01 |
How the PX Pressure Exchanger Works
A ceramic rotor turns inside a sleeve. Each duct is alternately opened to the high-pressure brine leaving the membranes and to the low-pressure feed entering the system. The high-pressure stream pushes directly against the feed water inside the duct, transferring its pressure with almost no loss; the duct then rotates, the depressurised stream is flushed to drain, and the cycle repeats. Because the transfer is direct hydraulic displacement rather than a mechanical conversion, efficiency is very high and the only moving part is the rotor.
Watch the PX in Operation
Video courtesy of Energy Recovery, Inc.
Where the PX-70S Fits
The PX-70S is specified on brine (concentrate) flow, not permeate — the pressure exchanger sits on the reject stream. ERI rates it for 40–70 gpm of brine at up to 1,200 psi, at 96% efficiency.
At the 40–45% recovery typical of seawater systems, one unit at full flow supports roughly 67,200–82,473 GPD of permeate (254–312 m³/day). That places a single PX-70S in containerised and skid-mounted SWRO packages, marine and offshore watermakers, island and resort supply, and remote or emergency water systems.
PX units are installed in parallel arrays, so larger plants simply use more of them — four PX-70S units cover about 1,018–1,249 m³/day on the same basis. Below 40 gpm of brine, step down to a smaller model rather than run this one under its minimum.
Capacity figures are indicative, derived from the rated brine flow at typical recovery. Actual output depends on your feed salinity, temperature, membrane configuration and recovery rate — send us your design conditions and we will confirm the model and the number of units.
Frequently Asked Questions
How many PX-70S units do I need?
What pre-filtration is required?
Does it need a motor?
What maintenance is involved?
How much energy does it save?
Specifications reproduced from the Energy Recovery technical data sheet for this model. PX® and Pressure Exchanger® are registered trademarks of Energy Recovery, Inc. ERI reserves the right to make specification changes without prior notice; confirm critical values against the current data sheet before purchase.
