💦 Calplas AFM-640 Semi-High Bed Sand Filter – 74,000 Litre Capacity

Professional-grade filtration engineered for medium to large residential pools with exceptional water clarity

🏊 Product Overview

The Calplas AFM-640 is a robust semi-high bed filter designed for medium to large residential swimming pools up to 74,000 litres. Featuring a generous 640mm tank diameter and 900mm filter bed depth, this filter delivers outstanding water quality through superior media contact time and flow distribution.

Manufactured by Calplas in Spain since 1970, the AFM-640 is constructed from hand-laminated glass-fibre reinforced polyester (GRP) with internal steel reinforcement at high-stress points. The filter is specifically optimised for use with AFM (Activated Filter Media), featuring a special diffuser that ensures even water distribution and prevents channelling through the filter bed.

The 305mm service manhole provides excellent access for media inspection and replacement, whilst the transparent acrylic lid and 3″ sight glass enable easy monitoring of filter operation. Compatible with Besgo automatic backwash valve systems, the AFM-640 offers both manual and fully automated operation for convenient pool maintenance.

With a standard flow rate of 9.3 m³/h and backwash capacity of 15.5 m³/h, this filter provides the ideal balance of filtration performance and efficient cleaning for pools requiring reliable, long-term water treatment.

💫 Key Features

✅ Semi-High Bed Design – 900mm filter bed height maximises water contact time for superior filtration performance

✅ Generous 640mm Diameter – Larger tank provides 0.30 m² filter area for increased flow capacity

✅ AFM-Optimised Diffuser – Specially designed diffuser prevents crater formation and ensures uniform water distribution

✅ Premium GRP Construction – Hand-laminated glass-fibre reinforced polyester with internal steel reinforcement

✅ Large Service Manhole – ø305mm access with transparent acrylic cover for easy media inspection

✅ 3″ Sight Glass – Larger sight glass for clear monitoring of backwash water clarity

✅ Besgo Valve Compatible – Designed for both automatic and manual Besgo backwash valve systems

✅ Complete Package – Includes pressure gauge, drain plug, and air vent as standard

✅ Dual Media Compatibility – Optimised for AFM activated glass media and traditional silica sand

✅ 5-Year Tank Warranty – Manufacturer-backed warranty demonstrates confidence in build quality

✅ EN 13121-3 Certified – Manufactured and pressure-tested to European standards

✅ UV-Resistant Finish – External gelcoat in blue RAL 5015 (white available on request)

⚙️ Technical Specifications

Specification	Value
Filter Type	Semi-high bed sand/AFM filter
Tank Diameter	640 mm
Filter Area	0.30 m²
Filter Bed Height	900 mm
Overall Height	1440 mm
Distance from Ground (A)	420 mm
Connection Spacing (B)	190 mm
Inlet/Outlet Connections	2″ Female thread (GAS)
Filter Opening (Top)	ø190 mm
Service Manhole	ø305 mm
Sight Glass	3″
Working Pressure	2.5 bar
Test Pressure	3.75 bar
Maximum Temperature	40°C
Tank Material	Hand-laminated GRP with steel reinforcement
Tank Colour	Blue RAL 5015 (white available on request)
Weight (Empty)	75 kg
Flow Rate @ 30 m³/h/m²	9.3 m³/h
Backwash Flow Rate @ 50 m³/h/m²	15.5 m³/h
AFM Media Capacity	17 bags (9× Grade 1 + 8× Grade 2, 21kg bags)
Sand Media Capacity	16 bags (8× fine + 8× coarse, 25kg bags)
Warranty	5 years (tank)

⚠️ Note: Higher working pressure versions (up to 7 bar) available on request from manufacturer.

📏 Pool Sizing Guide

Sizing Principle: The filter flow rate should turn over the entire pool volume within 6-8 hours for optimal water quality.

Formula:

Required Flow Rate (m³/h) = Pool Volume (m³) ÷ Turnover Time (hours)

This Filter:

📍 Standard Flow Rate: 9.3 m³/h (at 30 m³/h/m²)
📍 Backwash Flow Rate: 15.5 m³/h (at 50 m³/h/m²)

Pool Size Compatibility:

Pool Type	Volume Range	Suitability
🏠 Medium above-ground	30,000-50,000 L	✅ Excellent – generous capacity
🏠 Large above-ground	50,000-74,000 L	✅ Ideal match
🏊 Small in-ground	Up to 40,000 L	✅ Excellent with fast turnover
🏊 Medium in-ground	40,000-56,000 L	✅ Optimal 6-hour turnover
🏊 Large in-ground	56,000-74,000 L	✅ Suitable with 8-hour turnover
🏊 Very large in-ground	74,000+ L	⚠️ Consider AFM-720 or larger

Turnover Calculations:

Pool Volume	Turnover Time	Suitability
56,000 L (56 m³)	6 hours	✅ Optimal
65,000 L (65 m³)	7 hours	✅ Good
74,000 L (74 m³)	8 hours	✅ Acceptable maximum

🛠️ Installation Requirements

Plumbing:

Requirement	Specification
Inlet Connection	2″ Female thread (GAS)
Outlet Connection	2″ Female thread (GAS)
Valve Position	Side-mounted (Besgo compatible)
Connection Spacing	190 mm between inlet/outlet

Physical Installation:

Requirement	Details
Base	Solid, level concrete pad or paving required
Filter Height	1440 mm total
Ground Clearance	420 mm from floor to connections
Clearance Above	Minimum 500 mm for lid removal and media access
Clearance Around	Minimum 400 mm for valve operation and maintenance

Pump Compatibility:

⚠️ Filter must be matched with appropriate pump.
✅ Recommended pump flow rate: 7-9.3 m³/h for filtration
✅ Backwash pump capacity: 12-15.5 m³/h for effective backwashing
❌ Pump must not exceed filter's maximum flow rate of 15.5 m³/h

Valve Options: The Calplas AFM-640 is designed for use with Besgo backwash valves (wall-mounted, coupling set required separately). Choose from:

• Manual Besgo valve for cost-effective installation
• Automatic Besgo valve with solenoid control for hands-free operation
• Control panel available for scheduled automatic backwashing

🔄 Maintenance Guide

Routine Maintenance:

Task	When	How
Check pressure gauge	Weekly	Normal operating: 0.5-1.0 bar
Backwash filter	When pressure rises 0.5 bar above baseline	Run until sight glass shows clear water
Rinse after backwash	After each backwash	30-60 seconds to settle media
Inspect transparent lid	Monthly	Check for debris, cracks, seal condition
Check sight glass clarity	During backwash	Water should run clear within 2-3 minutes
Inspect media level	Annually	Top up if level has dropped
Full media replacement	Sand: 5-7 years / AFM: 10-15 years	Replace completely

Pressure Gauge Guide:

📊 Clean filter baseline: 0.5-0.8 bar
📊 Backwash needed: When 0.5 bar above baseline
📊 Maximum safe operating: 2.5 bar
⚠️ If pressure exceeds 2.5 bar, stop pump immediately and investigate

Backwash Procedure:

1. Turn off pool pump (unless using Besgo automatic valve)
2. Set valve to backwash position
3. Turn on pump and run until sight glass shows clear water (typically 2-4 minutes)
4. Turn off pump
5. Set valve to rinse position
6. Run pump for 30-60 seconds to settle media
7. Return valve to filter position
8. Resume normal filtration

Winterisation (UK Climate):

• Drain filter tank completely via drain plug
• Remove and safely store drain plug
• Leave tank lid slightly open to prevent pressure build-up
• Cover filter or store in frost-free location if possible
• Never leave water in filter during freezing conditions – ice expansion can crack the tank
• Disconnect and drain all associated pipework

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✨ Filter Media Information

The Calplas AFM-640 is specifically designed for optimal performance with AFM (Activated Filter Media) but also performs excellently with traditional silica sand.

Compatible Media:

Media Type	Filtration Rating	Lifespan	Benefits
AFM (Activated Filter Media)	4-5 microns (without flocculant)	10-15+ years	Superior clarity, self-sterilising, bio-resistant
AFM with APF/ZPM	Down to 1 micron	10-15+ years	Exceptional clarity, removes bacteria
Silica Sand	20-40 microns	5-7 years	Economical, widely available
Glass Sand	10-15 microns	8-10 years	Better than sand, good value

AFM Media Requirements for AFM-640:

Grade	Bag Size	Quantity	Total Weight
AFM Grade 1 (0.4-1.0mm)	21 kg	9 bags	189 kg
AFM Grade 2 (0.7-2.0mm)	21 kg	8 bags	168 kg
Total AFM		17 bags	357 kg

Sand Media Requirements for AFM-640:

Grade	Bag Size	Quantity	Total Weight
Fine Sand (0.4-0.8mm)	25 kg	8 bags	200 kg
Coarse Sand/Gravel (0.7-1.2mm)	25 kg	8 bags	200 kg
Total Sand		16 bags	400 kg

💡 Tip: When filling, always add the coarser grade first (Grade 2 AFM or coarse sand/gravel), then add the finer grade on top.

Signs Media Needs Replacing:

• Poor water clarity despite correct chemical balance
• Very short filter cycles between backwashes
• Cloudy water returning to pool during filtration
• Media visible in pool (indicates damaged laterals)
• Excessive media loss during backwash

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💎 Filtration Performance

Metric	Value
Filter Area	0.30 m²
Filter Bed Height	900 mm
Standard Flow Rate	9.3 m³/h
Filtration Rating (AFM)	4-5 microns nominal
Filtration Rating (Sand)	20-40 microns

Why AFM Outperforms Sand:

AFM (Activated Filter Media) is manufactured from specially processed recycled glass with a unique activation process that creates a negatively-charged, self-sterilising surface. This provides:

• 40× greater surface area than sand for superior particle capture
• Bio-resistant properties preventing bacterial colonisation
• Self-sterilising surface that doesn’t support biofilm growth
• Consistent performance without the degradation seen in sand filters after 6-12 months
• Reduced chemical consumption due to cleaner water and no bacterial growth

Micron Rating Guide:

Rating	What It Catches
40+ microns	Visible debris, leaves, large particles
20-40 microns	Sand, dirt, visible particles (typical sand filter)
10-20 microns	Fine particles, some algae spores
4-5 microns	Very fine particles, most algae (AFM without flocculant)
1 micron	Bacteria, ultra-fine particles (AFM with APF/ZPM)

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🔧 Besgo Valve System

The Calplas AFM-640 is designed for use with the Swiss-engineered Besgo backwash valve system, which replaces traditional 6-way multiport valves with a more efficient, automated solution.

Besgo Valve Positions:

Position	Function
Filter	Normal filtration mode – water flows through media to pool
Backwash	Reversed flow cleans media, water to waste

Besgo System Advantages:

• ✅ Automatic switching between filter and backwash modes
• ✅ No need to turn pump off during valve changeover
• ✅ Fail-safe design – returns to filter mode on power failure
• ✅ Lower pressure loss than traditional multiport valves
• ✅ Silent operation with no pressure hammer
• ✅ Valve operates in less than 2 seconds
• ✅ Wall-mounted design saves floor space
• ✅ Control panel available for scheduled automatic backwashing

⚠️ Note: Besgo valve and coupling set sold separately. 3-5 bar mains water pressure or compressed air required for valve actuation.

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🎯 Ideal Applications

Application	Pool Size	Suitability
🏠 Large residential above-ground	Up to 74,000 L	✅ Ideal
🏠 Medium-large in-ground pools	Up to 74,000 L	✅ Excellent
🏨 Holiday let / rental pools	Up to 56,000 L	✅ Well suited with AFM
🧖 Large swim spas	Up to 30,000 L	✅ Generous capacity
🏢 Small commercial pools	Up to 50,000 L	✅ Good for light use

Best Suited For:

• Medium to large residential pools requiring reliable filtration
• Pool owners seeking superior water clarity with AFM media
• Installations requiring automated backwash capability
• Projects where long filter media lifespan is valued
• Pools with higher bather loads needing increased flow capacity

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💬 Frequently Asked Questions

Q: What size pool will this filter handle? A: The Calplas AFM-640 is suitable for pools up to 74,000 litres with a flow rate of 9.3 m³/h, providing an 8-hour turnover. For optimal 6-hour turnover, it’s ideal for pools up to 56,000 litres.

Q: How often do I need to backwash? A: Backwash when the pressure gauge reads 0.5 bar above your clean baseline reading. This is typically every 1-2 weeks depending on pool usage and debris load.

Q: What filter media should I use? A: The filter is optimised for AFM (Activated Filter Media) with a capacity of 17 bags (357 kg total). Traditional silica sand can also be used – 16 bags (400 kg total).

Q: How long does filter media last? A: AFM media lasts 10-15+ years without replacement. Traditional sand should be replaced every 5-7 years.

Q: What pump do I need? A: Match with a pump delivering 7-9.3 m³/h for normal filtration. Ensure the pump can deliver 12-15.5 m³/h for effective backwashing. Do not exceed 15.5 m³/h maximum.

Q: Do I need a multiport valve? A: The AFM-640 is designed for use with Besgo backwash valves rather than traditional multiport valves. The Besgo valve and coupling set must be purchased separately.

Q: What warranty is included? A: Calplas provides a 5-year warranty on the filter tank. Contact Parts4Tubs for full warranty terms and conditions.

Q: How does the AFM-640 compare to the AFM-520? A: The AFM-640 offers 50% more filter area (0.30 m² vs 0.20 m²), higher flow rate (9.3 m³/h vs 6 m³/h), and larger manhole (305mm vs 215mm). It’s suited for pools up to 74,000L compared to 48,000L for the AFM-520.

Q: Can I upgrade from a smaller filter? A: Yes, the AFM-640 uses the same 2″ connections as smaller models, making upgrades straightforward. Ensure your pump can deliver adequate flow for backwashing.

Q: Is this filter suitable for commercial use? A: The AFM-640 is suitable for light commercial applications with moderate bather loads. For busier commercial pools, consider the AFM-720, AFM-840, or AFM-960 models.

📄 Downloads & Resources

📄 Technical Datasheet (PDF) – Complete specifications and dimensions for AFM series

✅ Why Choose the Calplas AFM-640

✅ Increased Capacity – 50% more filter area than the AFM-520 for larger pools

✅ Premium European Manufacturing – Hand-crafted in Spain by Calplas since 1970

✅ Superior Filtration Depth – 900mm filter bed height for exceptional water contact time

✅ Large Service Access – 305mm manhole makes media inspection and replacement easy

✅ AFM-Optimised Design – Special diffuser ensures even media distribution

✅ Built to Last – GRP construction with steel reinforcement and UV-resistant finish

✅ Automation Ready – Designed for Besgo automatic backwash valves

✅ 5-Year Warranty – Manufacturer-backed warranty on the filter tank

🇬🇧 Why Buy from Parts4Tubs

✅ UK-based company with knowledgeable local support

✅ Fast UK delivery on in-stock items

✅ Expert advice from pool and spa specialists

✅ Competitive pricing on premium filtration equipment

✅ Full warranty support – we handle warranty claims directly

✅ Easy returns within 30 days if not completely satisfied

✅ Compatible accessories available – AFM media, Besgo valves, spare parts

✅ Technical guidance for sizing and installation queries

🌟 Summary

The Calplas AFM-640 delivers professional-grade filtration for medium to large residential pools up to 74,000 litres. With its 640mm diameter tank, 0.30 m² filter area, and 900mm bed depth, this Spanish-manufactured filter provides 50% more capacity than the AFM-520 whilst maintaining the same premium GRP construction and AFM-optimised design. The generous 305mm service manhole, 3″ sight glass, and Besgo valve compatibility make maintenance straightforward. Backed by a 5-year tank warranty and designed for 10-15+ year AFM media lifespan, the AFM-640 represents an excellent long-term investment for pool owners seeking exceptional water clarity and reliable performance.