If you operate or build reverse osmosis systems, you already know the pressure vessel is not where you cut corners. It holds your membranes at operating pressure for years, sometimes decades. The wrong housing choice means leaks, premature membrane failure, and costly downtime. The right one runs quietly in the background while your system hits its targets every day.

Carver Water Technology (CWT) is now an authorized distributor of Protec Arisawa membrane pressure vessels and OEM replacement parts, serving water treatment operators across Florida, the Southeast United States, and the Caribbean. You can browse and purchase directly at our online store.

This guide covers what you need to know before you buy: pressure ratings, configurations, parts breakdown, and how Protec stacks up against the competition.

Who Is Protec Arisawa?

Protec Arisawa is a Japanese-American manufacturer of fiberglass-reinforced plastic (FRP) RO membrane pressure vessels. Their U.S. operation, Protec-Arisawa America, is headquartered in Vista, California. They have supplied pressure vessels to some of the largest desalination and water reuse plants in the world, including projects executed by IDE Technologies, and have vessels operating in over 200 facilities globally.

Their product line covers 4-inch and 8-inch diameter vessels rated from 300 PSI up to 1,200 PSI, in both side-port and end-port configurations. Every vessel ships complete with the shell, end closure hardware, mounting straps, and saddles.

Pressure Ratings: Choosing the Right Vessel for Your Application

This is the most common spec error operators make when sourcing replacement vessels. Protec vessels are available in the following pressure ratings, each suited to different water sources and system designs:

300 PSI — Light brackish water, commercial RO, food and beverage, pharmaceutical, car wash, and low-TDS groundwater applications. The most common rating for inland Florida groundwater systems.

450 PSI — Standard brackish water RO. Covers the majority of municipal and industrial BWRO applications in Florida and the Caribbean.

600 PSI — Higher-TDS brackish water, aggressive groundwater, and some industrial process water systems. Also used where additional design margin is required.

1,000 PSI — High-pressure brackish and transitional seawater applications. Used in coastal installations and systems treating challenging water chemistry.

1,200 PSI — Full seawater reverse osmosis (SWRO). This is the rating required for desalination systems processing open-ocean seawater. The BPV-8-1200 series is specifically engineered for high-pressure SWRO service.

If you are unsure which rating your system requires, call us before ordering. Running a 300 PSI vessel in a 600 PSI application is a safety and liability issue, not just a performance one.

Side Port vs. End Port: What's the Difference?

Side-port (SP/MSP) vessels have the feed and concentrate connections located on the side of the vessel body. This is the dominant configuration in commercial and industrial systems because it eliminates the need to disconnect high-pressure piping just to pull and replace membranes. Maintenance time drops significantly. Protec's side-port line uses localized filament overwinding around the port cutouts to restore wall strength, a proprietary engineering solution that keeps pressure integrity intact at those penetration points.

End-port (EP) vessels have the feed and concentrate connections at the ends of the vessel. These are simpler to manufacture and common in lower-pressure or space-constrained installations, but membrane changeouts require disconnecting the feed piping. Better suited for systems where membrane swaps are infrequent.

Multi-side port (MSP) configurations add additional port positions along the vessel body, used in parallel manifold systems and high-element-count arrays where flow distribution matters.

CWT can provide both configurations. Specify your port type and pressure rating when ordering.

OEM Parts: What's Available Through CWT

One of the most common issues we see in the field is operators sourcing non-OEM or mismatched parts during membrane changeouts. Brine seal failures, O-ring leaks at the permeate port, and cracked end caps after a rough swap are almost always traced back to incorrect parts selection. CWT carries the full Protec OEM parts catalog for 8-inch SP/MSP vessels. Here is what is available:

Head / End Cap Assemblies (Complete) The complete end cap assembly includes the bearing plate, sealing plate, permeate port, head seal, retaining ring, and all internal hardware. Available for PRO-8-300 through PRO-8-1200 and BPV-8-1000/1200 series. Permeate ports are standard Noryl; PVC, PET, and 316L stainless steel upgrades are available at additional cost.

Bearing Plates The structural backbone of the end cap. Available individually for all PRO-8 and BPV-8 series pressure ratings. If your end cap assembly shows cracking or deformation at the bearing plate, replace the full assembly, not just the plate.

Side Ports Available in 1.5", 2", 2.5", 3", and 4" configurations for SP, MSP, and MMSP vessels across all pressure ratings. Port sizing drives your system piping design. Verify your connection size before ordering.

Retaining Rings Feed/concentrate port retaining rings in 1.5" through 4" sizes. Also available: the PRO-series finger-pull retaining ring (316 SST) for easy membrane removal without tools.

O-Rings EPDM O-rings for feed/concentrate ports (F/C port) and permeate ports. Sized by port diameter and pressure series. These are a maintenance consumable and should be replaced at every membrane changeout. Do not reuse O-rings.

Head Seals (Quad Seal) The 8-inch head seal creates the primary pressure boundary between the vessel interior and atmosphere. EPDM construction. Replace any time you open an end cap.

Permeate Port Seals Separate from the head seal. EPDM. Replace at every membrane changeout as a matter of course.

Membrane Adapters Noryl and PVC/PET adapters in 1.125" through-bore and 1.5" through/plug configurations. These adapt the membrane's product water tube to the vessel's permeate port. Match to your membrane's center tube OD.

Thrust Cones PVC (standard) or Noryl (high-temp) thrust cones protect the membrane element during pressurization. TEC-model thrust cones are also available. Replace if cracked or deformed.

Shimming Rings 2mm and 5mm PVC/Noryl shimming rings for element length adjustment within the vessel. Used when element stack length does not perfectly fill the vessel, which creates element movement under pressure cycling.

Saddles and Straps Vessel mounting hardware. Saddles are rated by pressure series (300, 450/600, and 1000/1200 PSI). Straps are 8-inch standard. Replacement strap screws available individually.

Perm Port Sample Probe Valve PVC sample probe valve for permeate port monitoring. Allows individual element performance sampling without system shutdown.

How Protec Compares to Codeline (Pentair)

Codeline, now branded under Pentair, is the other major FRP pressure vessel manufacturer in North America and the most common alternative you will encounter when sourcing. Here is an honest comparison:

Construction method: Both Protec and Codeline use filament-wound FRP construction. Protec uses localized filament overwinding at side-port cutouts to restore structural integrity at those penetration points. This is particularly relevant in high-pressure applications where port reinforcement is critical.

Pressure range: Both manufacturers cover 300 PSI through 1,200 PSI. Protec's BPV series is purpose-built for SWRO service at 1,000 and 1,200 PSI.

ASME compliance: Both lines are designed to ASME Boiler and Pressure Vessel Code Section X. ASME code stamps are available from both at additional cost upon request.

Parts interchangeability: Protec and Codeline parts are NOT interchangeable. End caps, O-rings, retaining rings, and membrane adapters are all proprietary to each manufacturer. If you have Protec vessels in the field, you need Protec parts. Mixing brands on hardware is one of the fastest ways to create a leak.

Support: CWT provides engineering support with every order. If you are not sure what you need, our team, including a licensed PE on staff, can walk through your system specs and identify the correct part. That level of support is not something you get ordering from an online parts catalog.

How to Buy: Parts Online, Vessels by Quote

CWT makes it straightforward depending on what you need.

Replacement parts: order directly online. End caps, O-rings, head seals, retaining rings, membrane adapters, thrust cones, shimming rings, saddles, and all other accessories are available for purchase at . Standard lead times apply; most items ship from Vista, CA. Purchase Online Here

Pressure vessels: contact us for a quote. Because vessels involve multiple configuration variables like pressure rating, port size, port count, element capacity, and permeate port material, the right spec requires a short conversation before we can issue a price and submit to Protec. Email or call us with your system details and we will turn a quote around fast.

We serve:

• Municipal water and wastewater utilities

• Industrial water treatment operators

• Food and beverage and pharmaceutical facilities

• Car wash and commercial RO system operators

• Engineering firms and EPC contractors

• Caribbean and island water system operators (Bahamas, Jamaica, Trinidad)