RO Pressure Vessels
FRP and stainless steel pressure vessels for 4" and 8" reverse osmosis and nanofiltration elements, for new RO trains and replacements across Canada and the USA.
The housing that holds your membranes under pressure
An RO pressure vessel is the long cylindrical housing that holds spiral-wound membrane elements end to end and contains the system's operating pressure. Feed water enters at one end, passes through every element in turn, and leaves as permeate through the centre tube and as concentrate at the far end.
Choosing the right vessel means matching four things to your system: the element diameter, the number of elements per vessel, the pressure rating and the port layout. We supply vessels for new RO trains and for replacing aged, damaged or under-rated housings in existing systems.
Match the rating to the duty
The vessel's rated pressure must be at or above the highest pressure your feed pump can deliver. Typical classes:
| Duty | Typical rating | Used for |
|---|---|---|
| Low pressure | 150 to 300 psi (10 to 21 bar) | Nanofiltration, low-energy RO, softening membranes |
| Brackish water | 450 to 600 psi (31 to 41 bar) | Well, surface and municipal water, most industrial RO |
| Seawater | 1,000 to 1,200 psi (69 to 83 bar) | Desalination and high-TDS brines |
Four decisions for the right vessel
- 01
Element diameter
4" or 8", matching the membrane elements the vessel will hold.
- 02
Elements per vessel
One to eight. Larger systems commonly use six or seven 8" elements per vessel.
- 03
Pressure rating
At or above your maximum operating pressure, with the code stamp your site requires.
- 04
Port layout
End-port or side-port, port size and position, to fit your existing pipework.
Signs a vessel needs replacing
- Leaks at the end caps, ports or permeate connections
- Cracks, blistering or exposed fibres on an FRP shell
- Corroded or damaged heads and retaining rings
- A rating below your new operating pressure after a system change
- Adding capacity with more vessels in an existing train
What is the difference between side-port and end-port vessels?
End-port vessels take feed and concentrate connections through the end caps. Side-port vessels have ports in the shell wall near each end, which lets several vessels share common headers and makes multi-vessel trains more compact and easier to service.
How many elements go in one pressure vessel?
Anywhere from one to eight 40" elements. Larger industrial and municipal systems commonly use six or seven 8" elements per vessel; smaller systems use fewer, shorter vessels.
FRP or stainless steel: which vessel should I choose?
FRP (fibreglass) vessels are light, corrosion-resistant and the most common choice for RO and nanofiltration. Stainless steel vessels suit some high-temperature, sanitary or specialist duties. Tell us the application and we'll recommend one.
Can my vessel's pressure rating be lower than my pump pressure?
No. The vessel's rated pressure must be at or above the highest pressure the feed pump can deliver to it, including during start-up and upset conditions.
What is an ASME-coded pressure vessel?
An ASME-coded vessel is designed, built and stamped to the ASME Boiler and Pressure Vessel Code; FRP vessels are covered by Section X. Many North American sites and jurisdictions require coded vessels, so tell us if yours does.