When should a cartridge filter be changed
Short answer: Rather than counting days, watch the pressure drop. When the difference between inlet and outlet pressure exceeds 1 kg/cm², or reaches double what it was on a new filter, change it. As a rough guide by time: 1 to 3 months on reasonable water, 2 to 4 weeks on dirty water.
Two pressure gauges costing about ₹630 remove the guesswork entirely — and save money.
Pressure drop — the reliable method
Fit a pressure gauge before and after the filter (₹315 each).
| Difference (Δ P) | Meaning |
|---|---|
| 0.2 – 0.3 kg/cm² | New filter, all normal |
| 0.5 kg/cm² | About halfway through its life |
| 0.8 kg/cm² | Prepare to change it |
| Above 1.0 kg/cm² | Change it now |
| 1.5+ kg/cm² | Pump under strain, damage occurring |
Typical intervals by water
| Feed water | Interval |
|---|---|
| Municipal, clean | 2 – 3 months |
| Good borewell | 1 – 2 months |
| Silty borewell | 3 – 5 weeks |
| River or dirty water | 1 – 3 weeks |
| During monsoon | Roughly half the usual (more silt) |
But these are estimates only. Even on the same plant there is a big difference between summer and monsoon, which is why gauges are more reliable.
Visual signs
With a transparent housing such as the 500MM transparent housing (₹1,470) the filter stays visible:
- White turning light brown: still working
- Dark brown or black: time to change
- Red or orange: iron in the water — an iron removal filter should be considered
- Slimy or green: organic growth or algae — consider chlorination or UV
The value of a transparent housing: at ₹1,470 it is more expensive, but you can see the filter condition daily without opening anything.
What delay costs
- Strain on the pump — higher current, higher electricity bill, overload trips
- Flow drops — plant output falls
- Strain on the membrane — reduced feed pressure lowers recovery
- The filter can rupture — and then all the accumulated dirt goes straight to the membrane. This is the biggest risk
- Bacteria — an old wet filter becomes a breeding ground
The correct changing procedure
- Switch off the pump and release line pressure using the air release valve
- Open the housing nut with a spanner
- Remove the old cartridge — look at its colour, it tells you about the water
- Wash out the housing, clearing debris from the bottom
- Check the O-ring — replace it if worn, and apply a little silicone grease
- Fit the new cartridge, making sure it seats squarely
- Close the housing — hand tight only, do not over-tighten with a spanner
- Open the water slowly and vent air through the air release valve
- Check for leaks and note the new pressure gauge readings
The O-ring is often forgotten
The most common cause of housing leaks is a worn O-ring. It is inexpensive, but a leak is a real nuisance.
- Replace the O-ring every second or third cartridge change
- Apply silicone grease — it seats better and lasts longer
- Never use oil or ordinary grease — they attack the rubber
Always keep spares
Keep one or two cartridges in stock. When a filter chokes you otherwise have to either:
- Shut the plant down, or
- Keep running on a choked filter — which costs more
Cartridges are inexpensive (from ₹100), so there is no reason not to hold stock.
A simple record
| Date | ΔP at change | Days in service | Colour |
|---|---|---|---|
| 05/07 | 1.1 | 32 days | Brown |
| 08/08 | 1.0 | 34 days | Brown |
| 02/09 | 1.2 | 25 days | Dark brown |
This record shows you when filter life is shortening, which indicates that the feed water is deteriorating or something upstream has changed. That is valuable information.
Order your cartridge stock
Send your housing size and micron rating, and we will supply the right cartridges along with spare O-rings.
💬 WhatsApp par poochhein 📞 9910646957Frequently asked questions
How often should a cartridge filter be changed?
Rather than counting days, watch the pressure drop. When the difference between inlet and outlet exceeds one kg per cm2, change it. As a rough guide it is one to three months on clean water and two to four weeks on dirty water.
What pressure drop is normal?
About zero point two to zero point three kg per cm2 on a new filter. When that rises above one kg, or reaches double the new-filter figure, it is time to change.
What happens if I delay changing the filter?
The pump is strained so the electricity bill rises, plant flow falls, and the greatest risk is that a choked filter ruptures and sends all the accumulated dirt straight to the membrane.
What does the colour of the filter tell me?
Brown is normal silt. Red or orange indicates iron in the water and suggests iron removal is needed. A slimy or green appearance points to organic growth or algae, for which chlorination or UV may be appropriate.
When should the O-ring be replaced?
Every second or third cartridge change, with a little silicone grease applied so it seats properly. Never use ordinary oil or grease, as they attack the rubber.