Description
A simple capillary tube insert that controls waste-water flow on your RO system’s drain line — choose 420, 550, or 650 ml/min to match your membrane’s GPD rating.
Flow Rates
420 / 550 / 650
What it does
This capillary flow restrictor insert pushes directly into the end of 1/4″ OD RO tubing on your system’s waste (drain) line. A precision-bore capillary inside the insert limits how fast water can exit to drain, which controls the back-pressure on the RO membrane. Getting that pressure right is what makes the membrane filter effectively and last.
Available in three flow rates (420, 550, and 650 ml/min), each sized for a different membrane capacity. Pick the one that matches your membrane’s GPD rating — see the table below. No tools needed: cut the tubing square, push the insert in, and reconnect.
Which flow rate do I need?
Match the restrictor to your membrane’s GPD rating. Using the wrong size reduces filtration performance and can shorten membrane life.
| Restrictor |
Best for membrane |
Typical use |
| 420 ml/min |
50–75 GPD |
Standard under-sink RO |
| 550 ml/min |
100 GPD |
Countertop & under-sink RO |
| 650 ml/min |
150+ GPD |
High-output countertop & under-sink RO |
Not sure which GPD membrane you have? Check the label printed on your membrane, or see our RO Membranes page.
Key benefits
- ✓Controls the waste-to-purified ratio — keeps your membrane filtering at its rated efficiency
- ✓Extends membrane life — correct back-pressure means less stress on the membrane
- ✓Tool-free install — push the insert into the tubing end, reconnect, done
- ✓Three sizes covering 50–150+ GPD membranes
- ✓Compact capillary design — sits inside the tubing, no bulky inline housing needed
- ✓Replace when you replace the membrane — inexpensive insurance for a fresh start
Installation
How to install
- Disconnect the waste (drain) tubing from your RO system.
- Cut the tubing end square with a sharp blade for a clean seat.
- Push the restrictor insert firmly into the tubing end until it seats flush.
- Reconnect the tubing to the system’s drain port or check-valve elbow.
- Check for leaks at startup — the insert should sit snug with no drips.
Tip: Replace the restrictor whenever you replace the membrane — capillary bores can accumulate mineral scale over time, which shifts the flow rate. At this price, it’s worth swapping fresh.
Specifications
| Type |
Capillary flow restrictor insert |
| Flow rate options |
420 / 550 / 650 ml/min |
| GPD coverage |
50–150+ GPD |
| Fits |
1/4″ OD tubing (standard RO) |
| Installation |
Push into tubing end · waste (drain) line only |
| Use |
Cold water only |
| Sold as |
1 insert (select flow rate) |
| Brand |
MyWaterClub |
| SKU |
FR-INSERT (select flow rate) |
Compatibility
✓ Works with
- Countertop RO systems (Legacy & Quick Connect)
- Under-sink RO systems
- Any RO setup with a 1/4″ OD waste/drain line
- Membranes from 50 to 150+ GPD (match restrictor to membrane)
✗ Not for
- 3/8″ tubing (requires a 3/8″ restrictor)
- The purified-water output line
- Hot-water or non-RO applications
Good to know before you buy
- Match the restrictor to your membrane. Using the wrong flow rate reduces filtration performance and can shorten membrane life. Check the GPD table above.
- Installs on the waste (drain) line only — not the purified-water output. The restrictor controls how much water goes to drain.
- Replace when you replace the membrane — capillary bores can scale over time, shifting the flow rate. Swapping both together keeps performance consistent.
- A restrictor that’s too small (under-restricts) lets too much water drain and the membrane can’t build pressure. One that’s too large (over-restricts) stresses the membrane.
- If you’re not sure which GPD membrane you have, check the label on your current membrane or look up your system model.
Often used with
Check-Valve Drain Elbow
Pairs with this on the waste line
View elbow →
RO Parts & Accessories
All connection parts in one place
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Please note: Flow rates are nominal values measured under standard conditions. Actual drain flow varies with feed-water pressure, temperature, and tubing length. Always match the restrictor to your membrane’s GPD rating for best performance. When in doubt, ask us and we’ll help you pick the right one.
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