Desalination & RO
Process Overview
Desalination & RO — Process Overview
Seawater reverse osmosis (SWRO) plants pump seawater through pre-treatment (dissolved air flotation, ultrafiltration and cartridge filters) to high-pressure pumps that push it through RO membranes at 55–70 bar. Isobaric energy recovery devices transfer pressure from the brine to incoming seawater, with a booster pump making up the difference. Permeate is remineralised for supply and brine is returned to sea. Thermal plants (MED and MSF) evaporate seawater under vacuum instead, and brackish water RO treats lower-salinity ground and surface water.
For industrial effluent RO and ZLD see Industrial ETP & ZLD; for municipal plants see Municipal Water & Sewage.
Key Sealing Challenges
- Seawater corrosion: chlorides pit 316L; super duplex or titanium metal parts are used throughout.
- High pressure: SWRO pumps discharge at 55–70 bar, and ERD booster pumps see that pressure at suction, so the seal carries close to full system pressure.
- Low-lubricity water: filtered seawater and permeate lubricate poorly; SiC vs SiC face pairs are used.
- Continuous duty: desalination plants run around the clock, so seal reliability sets plant availability.
What mechanical seal is used on SWRO high-pressure and ERD booster pumps?
SWRO high-pressure and energy recovery booster pumps typically use a high-pressure balanced cartridge seal (e.g. Gipfel HP760) with super duplex metal parts and silicon carbide vs. silicon carbide faces. The ERD booster is the most demanding duty: its suction is already at 55–70 bar, so the seal must be rated for close to full system pressure.
Root-Cause Failure Analysis — Field Example
Symptom: ERD booster pump seal leaks soon after commissioning; faces show heat checking.
├── Incorrect Response: "Fit a standard balanced seal from the HP pump."
├── Diagnostic Evidence Required:
│ ├── Was the seal selected for suction pressure as on the HP pump, instead of the 55–70 bar seen at the booster suction?
│ ├── Check face loading and flush flow at full pressure.
│ └── Inspect metal parts for chloride crevice corrosion.
└── Engineered Solution:
├── High-pressure balanced cartridge seal rated for full system pressure.
├── SiC vs SiC faces with adequate Plan 11 flush.
└── Super duplex metal parts.
Frequently Asked Questions
Why super duplex instead of 316L in desalination?
Seawater and brine chlorides cause pitting and crevice corrosion in 316L. Super duplex stainless steel has a much higher pitting resistance and is the usual choice for seal metal parts.
Does the RO high-pressure pump seal see 70 bar?
It depends on the pump. On many multistage and split-case designs the seal sees suction or balance-line pressure, but some designs and all ERD booster pumps expose the seal to near-membrane pressure. The pump data sheet decides.
Related: Industrial ETP & ZLD · Municipal Water & Sewage · Marine.
Request a Seal Selection
Send your pump make and model, fluid, temperature, pressure, shaft size and speed to info@gipfelengg.com or use our enquiry form. Gipfel Engineering (ISO 9001:2015, NSIC-registered MSME, Mumbai) designs and manufactures mechanical seals, seal support systems and process pumps.
Equipment solutions: Boiler Feed & Multistage Pumps · Split-Case Pumps.
Pump Duty & Mechanical Seal Selection Matrix
Typical values for selection guidance only. Final selection is made against the customer duty sheet.
| Pump duty | Fluid | Typical temp. | Typical pressure (bar) | Seal arrangement | Faces / elastomer | API piping plan |
|---|---|---|---|---|---|---|
| Seawater Intake / Feed Pump | Seawater | Ambient | 2–5 bar | Balanced multi-spring cartridge with super duplex metal parts | SiC vs SiC / EPDM | API Plan 11 (filtered water) or Plan 32 for silt-laden intake |
| SWRO High-Pressure Pump | Filtered seawater | 20–35 °C | Discharge 55–70 bar; seal sees suction or balance-line pressure, per pump design — confirm | High-pressure balanced cartridge, stationary springs (catalogue ref. HP760) with super duplex metal parts | SiC vs SiC / EPDM | API Plan 11 |
| Energy Recovery (ERD) Booster Pump | Seawater at near-membrane pressure | 20–35 °C | Suction at 55–70 bar: the seal sees close to full system pressure | High-pressure balanced cartridge, stationary springs (catalogue ref. HP760) with super duplex metal parts | SiC vs SiC / EPDM | API Plan 11 |
| Brackish Water RO Feed Pump | Brackish ground or surface water | Ambient | 10–25 bar | Balanced multi-spring cartridge with duplex metal parts | SiC vs SiC / EPDM | API Plan 11 |
| Brine / Reject Disposal Pump | Concentrated brine | Ambient–40 °C | 2–5 bar | Balanced multi-spring cartridge with super duplex metal parts | SiC vs SiC / EPDM | API Plan 11 |
| Product / Permeate Water Pump | RO permeate (low TDS, aggressive) | Ambient | 3–8 bar | Wave-spring semi-cartridge | SiC vs carbon / EPDM (drinking-water approved grade) | API Plan 11 |
| RO Membrane Cleaning (CIP) Pump | Citric acid or caustic cleaning solutions | Ambient–40 °C | 2–5 bar | Balanced multi-spring cartridge | Sintered SiC vs sintered SiC / EPDM | API Plan 11 |
| MED / MSF Brine Recirculation Pump | Hot seawater brine under vacuum | 40–110 °C | Low suction pressure — confirm per pump | Double cartridge, back-to-back (pressurised) with super duplex or titanium metal parts | SiC vs SiC / EPDM | API Plan 53A (barrier ≥ 1.4 bar above seal chamber) to stop air ingress |
Reviewed by Gipfel Engineering’s technical team.
Technical Information Disclaimer
The information on this page, including process descriptions, flow diagrams, operating ranges, seal arrangements, materials and piping plans, is general technical guidance for information only. Values shown are typical industry ranges, not guaranteed ratings or specifications of any Gipfel Engineering product. Each application differs. Seal selection, material compatibility, installation and operation must be verified by qualified personnel against the specific equipment data sheet, process conditions, applicable codes and the pump manufacturer’s instructions. A binding recommendation is given only in a written quotation or technical offer from Gipfel Engineering.
References to standards (such as API 682, ISO 21049, ISO 3069, FDA 21 CFR 177.2600 and NACE MR0175 / ISO 15156) describe common industry practice. They do not mean that any product is certified, qualified or approved to that standard unless this is confirmed in writing for a specific order. Third-party company and product names, including “equivalent to” references, are used for identification only and remain the trademarks of their owners. No affiliation, endorsement or OEM approval is implied.
Compliance with safety, hazardous-area, environmental and statutory requirements at the user’s site remains the responsibility of the plant owner or operator. To the extent permitted by law, Gipfel Engineering accepts no liability for loss or damage arising from reliance on this general information without a confirmed written recommendation. Content may change without notice.