RO Membrane Brine Seal Dimensions
These RO membrane brine seal dimensions cover the material, lip type, sizing and orientation of the brine seal that stops feed water bypassing the element inside the pressure vessel.
- MaterialEPDM rubber
- TypeU-cup lip seal
- RoleStops feed bypass
- Used onIndustrial sizes
What the Brine Seal Does
The brine seal is a flexible lip seal that fits around the outside of the element near the feed end. When pressurised, the lip presses against the inside of the pressure vessel and forces all the feed water to pass through the element rather than slipping around it. Without it, feed bypasses the membrane and the system never reaches its rejection target.
For the why behind it, see why elements need a brine seal. It is mainly used on industrial elements (4040, 8040); small household elements seal differently.
Brine Seal Specifications
Typical specifications for RO membrane brine seals. Exact dimensions are matched to the element and vessel, and confirmed per order.
| Property | Typical specification |
|---|---|
| Material | EPDM rubber (other elastomers on request) |
| Type | U-cup / chevron lip seal |
| Function | Prevents feed water bypassing the element in the vessel |
| Sizing | Outer diameter matched to vessel bore, by element size (mainly 4040, 8040) |
| Cross-section / lip height | [Confirm per element & vessel] |
| Orientation | Lip faces upstream, toward the feed inlet |
| Temperature / chemical compatibility | Suitable for standard RO feed and cleaning conditions |
| Also known as | Brine seal, bypass seal |
Sizing and Fitting the Brine Seal
Two things decide a good seal: the right diameter for the vessel bore, and the correct lip orientation toward the feed. Fit it the wrong way round and it will not inflate against the wall under pressure. Check seating during visual inspection and confirm incoming seals against spec in incoming inspection.
Match the seal to the element size using the element size reference, and see how it fits the full build in the raw material selection guide.
Get the seal right
- Diameter to suit the vessel bore
- Lip facing the feed inlet
- EPDM in good, uncracked condition
- Seated evenly in its groove
- Matched to the element size
A Small Seal With a System-Wide Effect
The brine seal is inexpensive, but if it fails the whole element under-performs — even when everything else is perfect.
Feed Bypass
A wrong-size or worn seal lets feed slip past, so rejection falls system-wide.
Wrong Orientation
Fitted backwards, the lip cannot press against the vessel and barely seals.
Damaged Rubber
Cracked or hardened EPDM loses its spring and leaks around the element.
Need brine seals for your elements?
Tell us your element sizes and vessel bore — we’ll supply brine seals matched to your combination.
Brine Seal FAQ
What is an RO membrane brine seal made of?
Brine seals are typically EPDM rubber, formed as a U-cup or chevron lip seal. EPDM is chosen for its flexibility and compatibility with RO feed and cleaning conditions.
Which way does the brine seal face?
The lip faces upstream, toward the feed inlet. Under pressure the lip presses outward against the vessel wall, forcing feed water through the element instead of around it. Fitted backwards, it will not seal.
How do I choose the right brine seal size?
The outer diameter is matched to the pressure vessel bore for the element size — mainly 4040 and 8040. Use the element size reference to identify the size, then confirm the exact seal dimensions for your vessel.
Do household RO elements have a brine seal?
Small household elements such as 1812 generally seal differently and often do not use a separate brine seal. Brine seals are mainly used on industrial elements in pressure vessels.