What is a Flow Restrictor in an RO Water Purifier – And Why You Should Always Replace It with the Membrane
When it comes to maintaining your RO (Reverse Osmosis) water purifier, most people know about changing filters and membranes. But there's one small part that often gets overlooked — the Flow Restrictor. Despite its size, this component plays a huge role in the performance, efficiency, and longevity of your RO system.
Let’s understand what it does and why it’s crucial to replace it whenever you change your RO membrane.
✅ What Does a Flow Restrictor Do?
A Flow Restrictor (FRT) is a tiny device fitted on the wastewater (brine) outlet of the RO membrane. Its job is to control the rate of wastewater flow, maintaining the right pressure inside the RO membrane housing.
In simpler terms:
It helps create the necessary backpressure that pushes water through the RO membrane.
It balances the output ratio of purified water to rejected water (usually around 1:3).
It prevents unnecessary water wastage.
🔧 Why Is It Important?
Without a properly working flow restrictor, your RO system can’t function effectively.
Here’s what can go wrong:
🚱 Too little pressure inside the membrane = poor filtration and high TDS in drinking water.
💦 No restrictor at all = water flows freely, but very little gets purified.
💣 Too much pressure = stress on the membrane, reducing its life.
So, while it may seem like a small part, the flow restrictor is essential for your RO purifier to run properly.
🔄 Why You Should Replace the Flow Restrictor When Changing the RO Membrane
Here’s the big takeaway: always replace your flow restrictor when you install a new RO membrane.
Here's why:
⚙️ Old restrictors clog over time with salts, scale, and impurities.
🔄 Mismatched flow rates: New membranes may need different pressure or waste ratio.
🔬 Poor filtration performance if the restrictor isn’t compatible with the new membrane.
💸 Reduces membrane life if improper pressure causes damage.
Example: A 75 GPD membrane typically needs a 450–500 ml/min flow restrictor. If you use a restrictor from a different membrane, the system won’t work correctly.
💡 Pro Tip: Use a Pre-Matched Membrane + FRT Combo
Products like the Kent Welded RO Membrane 8" with FRT 550 ml/min come with the perfectly paired flow restrictor built-in, saving you time and ensuring proper function from day one.
🛠 Final Thoughts
Replacing your RO membrane? Don’t skip the flow restrictor!
🔁 New membrane + New FRT = Smooth performance, clean water, and long-lasting system.
If you’re unsure which flow restrictor is right for your RO system, feel free to contact our support or browse our pre-matched membrane sets at The R.O. World.