✅ SS 316L — Required
| Grade | AISI 316L / EN 1.4404 |
| Carbon (C) | ≤ 0.03% |
| Chromium (Cr) | 16 – 18% |
| Molybdenum (Mo) | 2 – 3% ← key element |
| Nickel (Ni) | 10 – 14% |
| Why | Mo prevents pitting corrosion in RO permeate |
✗ SS 304 — Do Not Use
| Grade | AISI 304 / EN 1.4301 |
| Carbon (C) | ≤ 0.08% |
| Chromium (Cr) | 18 – 20% |
| Molybdenum (Mo) | None — corrosion risk |
| Nickel (Ni) | 8 – 10% |
| Why avoid | Fails in aggressive low-TDS RO water |
ℹ RO permeate is ion-hungry (very low TDS) and aggressively leaches ions from pipe walls. The 2–3% Mo in 316L is the primary protection against pitting corrosion and crevice corrosion at weld points.
2
Internal Surface Finish
Ra > 0.8 µm
Rough — Reject
Deep surface valleys trap bacteria and promote biofilm colonization that cannot be removed by chemical sanitization
Ra 0.4 – 0.8 µm
Acceptable
Suitable for pretreatment sections. Marginal for post-RO loop components in direct dialysis water contact
Ra ≤ 0.4 µm
Required ✓
Mandatory for dialysis-grade components. Electropolished surface preferred for maximum sanitation efficiency
ℹ Best specification: Electropolished + Passivated (ASTM A967) — removes surface iron layer, rebuilds protective chromium oxide passive film. Specify this in your RFQ.
3
Mechanical Handle Quality
Handle Material
| Required | SS316 or SS304 |
| Acceptable | PA66-GF (glass-filled nylon) |
| Avoid | Zinc alloy (Zamak) ✗ |
| Avoid | ABS plastic ✗ |
| Avoid | Chrome-plated ✗ |
| Reason | H₂O₂ and chlorine sanitization cycles degrade zinc and ABS within 12–18 months |
Actuation Mechanism
| Rotation | 90° quarter-turn only |
| Position indicator | Visual — mandatory |
| Operating torque | ≤ 10 N·m |
| Hard stop | Required at 0° and 90° |
| Ball type | Full Bore (Full Port) |
| Ball material | SS316 Electropolished |
Seals & Seats
| Seat / Seal | PTFE (Teflon) ✓ |
| Stem packing | PTFE or PEEK |
| Avoid | EPDM in RO lines ✗ |
| Avoid | NBR (Buna-N) ✗ |
| Avoid | Natural rubber ✗ |
| Reason | PTFE is chemically inert — no TOC leach into water. EPDM/NBR cause TOC spikes failing AAMI test |
4
Pressure Rating & Pipe Size
| Parameter |
Pretreatment Section |
Post-RO Distribution Loop |
Minimum Valve Rating |
Standard Reference |
| Working pressure |
3 – 6 bar |
2 – 4 bar |
≥ 10 bar WP |
ASME B16.34 |
| Test pressure |
1.5 × WP |
1.5 × WP |
≥ 15 bar TP |
ASME B16.34 |
| Pipe size (DN) |
DN25 (1") or DN32 |
DN20 – DN25 |
Per system design |
ISO 6708 |
| End connection |
NPT or BSP thread |
Compression or Tri-Clamp |
Tri-Clamp preferred |
ISO 2852 (Tri-Clamp) |
| Temperature rating |
0 – 80°C |
0 – 80°C |
≥ 100°C rated |
For hot sanitization |
| Flow characteristic |
Full bore (no restriction) |
Full bore (no restriction) |
Cv per system calc |
ANSI/FCI 70-2 |
ℹ Tri-Clamp (sanitary clamp) end connections are strongly preferred for post-RO distribution loop — allows disassembly for inspection and sanitization without special tools.
5
Required Certifications
NSF/ANSI 61
Drinking water contact materials — mandatory for any wetted component
ISO 9001
Quality management system — manufacturer certification
CE Mark
EU medical device compliance (if EU-manufactured equipment)
MTC 3.1B
EN 10204 Material Test Certificate — mandatory, request per heat number
⚠ Always request EN 10204 Type 3.1B Material Test Certificate (MTC) per heat number. This is the only way to verify the actual chemical composition of the steel used — not the manufacturer's catalog claim.
6
Recommended Brands — Medical Grade
Gemü
🇩🇪 Germany
Best-in-class for dialysis and pharmaceutical water systems. Full documentation package.
Watts
🇺🇸 USA
NSF/ANSI 61 certified. Pre-assembled bypass manifolds available.
Bürkert
🇩🇪 Germany
High precision actuation. Excellent for automated systems with position feedback.
Swagelok
🇺🇸 USA
Premium for high-pressure lines and laboratory-grade purity applications.
🧲
Quick On-Site Quality Check — Magnet Test
Hold a strong magnet to the valve body before installation. SS316L is weakly magnetic or non-magnetic due to its austenitic structure.
If the magnet sticks firmly, the valve is likely SS201, SS202, or carbon steel — reject it immediately.
This test takes 5 seconds and can save your entire system from premature corrosion failure.
Note: All SS valves become slightly more magnetic after cold working (machining). A weak attraction is normal. Strong attraction = wrong material.
⚠ Critical Engineering Warning — Cheap Chinese Valves
The market is flooded with valves labeled "SS316" that are actually manufactured from SS201 or SS202 (low-grade, high-manganese alloys with minimal or zero Molybdenum).
These corrode in RO water within months, contaminate the water with iron and heavy metal ions, and will cause your system to fail the AAMI microbiological and chemical purity test.
Rule: No Material Test Certificate (EN 10204 Type 3.1B) → No purchase. Non-negotiable for a dialysis water system.