Filter Backwash: Step by Step

Introduction

Backwashing is one of the most important maintenance operations for sand and glass filters. This process reverses the water flow through the filter, cleaning accumulated debris and restoring filtration capacity.

In Margem Sul, where many pools are surrounded by pine trees and abundant vegetation, filters accumulate debris more quickly, requiring more frequent backwashing. Knowing when and how to perform this operation correctly is essential for keeping water crystal clear.

This step-by-step guide teaches you how to backwash safely and effectively, maximising your filter's lifespan and ensuring optimised filtration.

What is Backwashing

How It Works

Why It's Necessary

When to Backwash

Main Indicators

Frequency Table

Reading the Pressure Gauge

Equipment Needed

Check Before Starting

Types of Valves

Step by Step: Complete Backwash

Preparation

1. Turn off the pump

• ALWAYS turn off the pump before changing valve position
• Wait for the pump to stop completely
• Never change the valve with the pump running

2. Check the waste hose

3. Check pool water level

• Should be above the skimmer
• Backwashing uses pool water
• Prepare to top up water afterwards

Backwash Procedure

4. Set valve to BACKWASH

5. Turn on the pump

• Watch the sight glass (if present)
• Water will come out cloudy initially
• Wait...

6. Watch the discharge water

7. Backwash time

• Minimum: 2 minutes
• Typical: 2-3 minutes
• Maximum: 5 minutes (don't exceed)
• Stop when water is clear

8. Turn off the pump

• ALWAYS turn off before changing position
• Wait for complete stop

Rinse Procedure

9. Set valve to RINSE

• This step is important!
• Settles sand and cleans piping

10. Turn on pump in RINSE

• Duration: 30-60 seconds
• Water still goes to waste
• Settles the filter media

11. Turn off the pump

• Wait for complete stop

Return to Normal Operation

12. Set valve to FILTER

• This is the normal operating position

13. Turn on the pump

• Check the pressure gauge
• Should show normal (low) pressure
• Check flow at return jets

14. Check water level

• Top up water if needed
• Backwashing typically uses 200-500 litres

Multiport Valve Positions

6-Way Valve

Flow Diagram

FILTER:      Pool → Pump → Filter (cleans) → Pool
BACKWASH:    Pool → Pump → Filter (reverse) → Waste
RINSE:       Pool → Pump → Filter (normal) → Waste
WASTE:       Pool → Pump → Direct to Waste
RECIRCULATE: Pool → Pump → Direct to Pool

Common Problems and Solutions

Pressure Doesn't Drop After Backwash

Water Still Cloudy

Sand Coming Out During Backwash

Valve Difficult to Move

Valve Maintenance

Lubrication

Annual Check

• [ ] O-ring in good condition
• [ ] Valve moves smoothly
• [ ] No leaks in any position
• [ ] Indicators readable
• [ ] Handle secure

Backwashing Different Filter Types

Sand Filter

Glass Filter

Cartridge Filter

Diatomaceous Earth (DE) Filter

Backwash Checklist

Before

• [ ] Pump off
• [ ] Waste hose positioned
• [ ] Water level adequate
• [ ] Note current pressure

During

• [ ] Valve on BACKWASH
• [ ] Pump on
• [ ] Watch discharge water
• [ ] Time it (2-3 min)
• [ ] Pump off
• [ ] Valve on RINSE
• [ ] Pump on (30-60 sec)
• [ ] Pump off

After

• [ ] Valve on FILTER
• [ ] Pump on
• [ ] Check pressure (should have dropped)
• [ ] Check flow
• [ ] Top up water level
• [ ] Note backwash date

Water Consumption

Estimates

Reducing Consumption

Special Situations

After Algae Treatment

1. Brush entire pool
2. Let debris settle (2-4 hours)
3. Vacuum to WASTE if very dirty
4. Do extended backwash
5. Repeat if necessary

Season Opening

1. Check filter condition
2. Do initial backwash
3. Check reference pressure
4. Adjust filtration time

Season Closing

1. Do final backwash
2. Let water drain from filter
3. Set valve to WINTERIZE (if available) or between positions
4. Protect from frost

Well Water

In Margem Sul, especially in Palmela, Azeitão and Moita, many use well water with high mineral content.

Frequently Asked Questions

How often should I backwash?

Base it on pressure gauge reading, not the calendar. When it rises 8-10 psi above normal, it's time. Typically this happens every 1-2 weeks, but can vary according to use and debris amount.

Can I backwash too often?

Yes. Excessive backwashing wastes water, chemicals (new water needs treatment), and can remove sand from the filter. Only do it when needed, as indicated by the gauge.

What happens if I never backwash?

The filter progressively clogs, pressure rises dangerously, flow reduces drastically, water becomes cloudy, and eventually can damage the pump or burst hoses.

How long should backwashing last?

Typically 2-3 minutes. Watch the discharge water - when it goes from cloudy to clear, you can stop. Don't exceed 5 minutes to avoid losing sand.

Why should I RINSE after BACKWASH?

The rinse settles the sand that was agitated and cleans the piping before returning to normal mode. Without this step, dirty water and loose sand can return to the pool in the first few minutes.

Conclusion

Backwashing is a simple but essential operation for keeping the filter functioning efficiently. The key points are:

• Watch the pressure gauge - it's your best indicator
• ALWAYS turn off the pump before moving the valve
• Don't exceed 3 minutes of backwashing
• Do RINSE after each backwash
• Top up water and check chemicals afterwards
• Note the dates to track patterns

A well-maintained filter with regular backwashing keeps water crystal clear and protects the entire filtration system.

If you need professional help with your pool filter maintenance in Margem Sul, ManutençãoPiscinas is here to help. Contact us for a no-obligation quote.