When a bag filter is better than a cartridge
Short answer: A bag filter is the better choice when the water is very dirty and cartridges are choking weekly. A bag holds several times more dirt than a cartridge, so it lasts much longer and reduces the work of changing.
But bag filters are usually available in coarser ratings (25 to 100 micron), so ahead of an RO plant a bag is not sufficient on its own — a cartridge must follow it.
The basic difference
| Feature | Cartridge | Bag filter |
|---|---|---|
| Dirt capacity | Lower | Much higher |
| Micron range | 0.22 – 100 | 1 – 200 (usually 25–100) |
| Flow | Moderate | Higher |
| Changing | Open the housing | Lift out the bag (easier) |
| Unit price | ₹100 – 400 | Somewhat higher |
| Service life | Shorter | Several times longer |
| Sufficient alone before RO | Yes (5 micron) | No — a cartridge is also needed |
When to fit a bag filter
- Cartridges choking weekly — the clearest indicator
- River, pond or monsoon water
- Filter feed in an ETP or STP
- Cooling tower side stream
- Pre-filtration at higher flows
When a cartridge is still better
- The final stage ahead of RO, where 5 micron is needed and bags are rarely that fine
- Small plants on clean water
- Where flow is low
The best arrangement — both together
On larger plants or dirty water we normally fit:
- Screen filter — coarse particles, cleaned and reused (Y-type screen)
- Bag filter — 25 to 50 micron, holding the bulk of the dirt
- Cartridge 5 micron — final protection, and now it lasts much longer
Housing options
| Model | Feature | Price |
|---|---|---|
| PP with bag filter | Economical, general use | ₹1,890 |
| PP with bag filter (smaller) | Smaller size | ₹1,470 |
| PP without gauge or bag | Housing only | ₹945 |
| SS304 swing bolt with bag | Industrial, quick opening | ₹35,175 |
Bags are listed separately under Filters Bag.
The advantage of a swing bolt
The SS304 swing bolt housing is expensive at ₹35,175, but changing a bag is very quick — turn the bolts and the lid opens, with no spanner required.
When that is worth paying for: where the bag has to be changed daily or every other day on very dirty water. Opening with a spanner each time takes time and wears the threads.
Choosing the bag micron
| Water | Bag micron | Cartridge after it |
|---|---|---|
| Lightly dirty | 50 | 5 micron |
| Moderately dirty | 25 | 5 micron |
| Very dirty | 100 then 25 | 5 micron |
| ETP filter feed | 25 – 50 | As required |
How to change a bag
- Stop the pump and release pressure
- Open the lid (swing bolt or nuts)
- Lift the bag out by the top in one movement, or the dirt falls back in
- Clean the basket
- Fit the new bag, ensuring its ring seats correctly on the housing seat
- Close the lid, vent air and check for leaks
The cost comparison
Take dirty water on a 3,000 LPH plant:
| Setup | Service life | Approximate annual cost |
|---|---|---|
| Cartridge only (5 micron) | 7 days | ~₹20,000 plus considerable labour |
| Bag 25µ plus cartridge 5µ | Bag 30 days, cartridge 75 days | ~₹8,000 plus much less labour |
The one-off cost of a bag filter housing (₹1,890) is recovered within the first year — and the labour saving is on top of that.
Set up bag filtration
Send your flow, water type and how long cartridges currently last, and we will suggest the complete arrangement.
💬 WhatsApp par poochhein 📞 9910646957Frequently asked questions
What is the difference between a bag filter and a cartridge?
A bag filter holds several times more dirt than a cartridge so it lasts much longer. However its micron rating is usually coarser, so ahead of an RO plant a cartridge still has to follow it.
Is a bag filter alone enough for RO?
No. Bag filters are typically twenty five to one hundred micron whereas RO needs five micron. So a cartridge must be fitted after the bag, otherwise fine particles will reach the membrane.
When should a bag filter be fitted?
When cartridges are choking weekly, or where the water comes from a river, pond or is monsoon affected. Fitting a bag filter typically extends cartridge life to two or three months and reduces overall cost considerably.
Why is a swing bolt housing expensive, and when is it justified?
Its bolts turn to open the lid without a spanner. That is worth paying for where the bag has to be changed daily or every other day, since repeated spanner work takes time and wears the threads.
What should I watch when fitting a bag?
The ring of the bag must seat correctly on the housing seat. If it does not, water bypasses the bag unfiltered while everything looks normal from outside, so this fault goes unnoticed. Always check the ring.