💧 Calplas AFM-840 Semi-High Bed Sand Filter – 125,000 Litre Capacity

Commercial-grade filtration power for large residential pools and demanding commercial installations

🌊 Product Overview

The Calplas AFM-840 delivers serious filtration capability for large residential pools and commercial applications up to 125,000 litres. With an impressive 840mm tank diameter providing 0.52 m² of filter area, this semi-high bed filter handles substantial water volumes whilst maintaining the exceptional clarity that defines the AFM series.

Manufactured by Calplas in Spain—experts in filter production since 1970—the AFM-840 combines hand-laminated glass-fibre reinforced polyester construction with internal steel reinforcement to create a filter built for demanding, continuous operation. The 900mm filter bed depth and specially engineered AFM diffuser ensure thorough particle removal even at higher flow rates.

This filter excels in applications where reliability and performance are paramount: large family pools with frequent use, holiday rental properties, hotel pools, swim schools, and hydrotherapy facilities. The robust 15.6 m³/h flow rate and 26 m³/h backwash capacity provide the throughput needed for commercial-grade water treatment.

With its generous 305mm service manhole, 3″ sight glass, and full Besgo automatic valve compatibility, the AFM-840 combines powerful performance with practical serviceability.

✨ Key Features

✅ 840mm Tank Diameter – Substantial 0.52 m² filter area for high-volume applications

✅ Commercial-Grade Flow – 15.6 m³/h standard rate handles pools up to 125,000 litres

✅ Powerful Backwash Capacity – 26 m³/h ensures thorough media cleaning

✅ Semi-High Bed Design – 900mm filter bed height for maximum water contact time

✅ AFM-Optimised Diffuser – Engineered for even water distribution and consistent filtration

✅ Heavy-Duty Construction – Hand-laminated GRP with internal steel reinforcement

✅ Large Service Manhole – ø305mm access simplifies media inspection and replacement

✅ 3″ Sight Glass – Clear monitoring of backwash water clarity

✅ Besgo Valve Compatible – Full support for automatic and manual backwash systems

✅ Complete Package – Pressure gauge, drain plug, and air vent included

✅ Multi-Grade Media Capacity – Designed for three-layer AFM or sand configurations

✅ 5-Year Tank Warranty – Manufacturer-backed quality assurance

🔧 Technical Specifications

Specification	Value
Filter Type	Semi-high bed sand/AFM filter
Tank Diameter	840 mm
Filter Area	0.52 m²
Filter Bed Height	900 mm
Overall Height	1460 mm
Distance from Ground (A)	440 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)	99 kg
Flow Rate @ 30 m³/h/m²	15.6 m³/h
Backwash Flow Rate @ 50 m³/h/m²	26 m³/h
AFM Media Capacity	31 bags (15× Grade 1 + 8× Grade 2 + 8× Grade 3, 21kg bags)
Sand Media Capacity	30 bags (16× fine + 7× medium + 7× 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: 15.6 m³/h (at 30 m³/h/m²)
📍 Backwash Flow Rate: 26 m³/h (at 50 m³/h/m²)

Pool Size Compatibility:

Pool Type	Volume Range	Suitability
🏠 Extra-large residential	80,000-125,000 L	✅ Ideal match
🏊 Large in-ground pools	70,000-94,000 L	✅ Excellent with fast turnover
🏊 Very large in-ground	94,000-125,000 L	✅ Well suited
🏨 Hotel pools	Up to 100,000 L	✅ Good for moderate use
🏢 Small-medium commercial	Up to 94,000 L	✅ Robust capacity
🏢 Commercial pools	Up to 125,000 L	✅ Suitable with appropriate pump
🏊 Pools over 125,000 L	125,000+ L	⚠️ Consider AFM-960

Turnover Calculations:

Pool Volume	Turnover Time	Suitability
94,000 L (94 m³)	6 hours	✅ Optimal
109,000 L (109 m³)	7 hours	✅ Good
125,000 L (125 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	Reinforced concrete pad capable of supporting 750+ kg when filled
Filter Height	1460 mm total
Ground Clearance	440 mm from floor to connections
Clearance Above	Minimum 600 mm for lid removal and media access
Clearance Around	Minimum 500 mm for valve operation and maintenance

Pump Compatibility:

⚠️ Filter must be matched with appropriate pump.
✅ Recommended pump flow rate: 12-15.6 m³/h for filtration
✅ Backwash pump capacity: 20-26 m³/h for effective backwashing
❌ Pump must not exceed filter's maximum flow rate of 26 m³/h

Valve Options: The Calplas AFM-840 is designed for use with Besgo backwash valves (wall-mounted, coupling set required separately). Choose from:

• Manual Besgo valve for operator-controlled backwashing
• Automatic Besgo valve with solenoid control for scheduled operation
• Control panel available for fully automated backwash management

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🛠️ 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 3-5 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 4-6 minutes for larger filters)
4. Turn off pump
5. Set valve to rinse position
6. Run pump for 45-60 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 relocate to 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-840 is designed for three-layer media configurations, providing optimal filtration depth and performance with AFM (Activated Filter Media) or 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-840:

Grade	Bag Size	Quantity	Total Weight	Layer Position
AFM Grade 3 (2.0-4.0mm)	21 kg	8 bags	168 kg	Bottom (support)
AFM Grade 2 (0.7-2.0mm)	21 kg	8 bags	168 kg	Middle
AFM Grade 1 (0.4-1.0mm)	21 kg	15 bags	315 kg	Top (filtration)
Total AFM		31 bags	651 kg

Sand Media Requirements for AFM-840:

Grade	Bag Size	Quantity	Total Weight	Layer Position
Coarse Gravel (2-4mm)	25 kg	7 bags	175 kg	Bottom (support)
Medium Sand (0.7-1.2mm)	25 kg	7 bags	175 kg	Middle
Fine Sand (0.4-0.8mm)	25 kg	16 bags	400 kg	Top (filtration)
Total Sand		30 bags	750 kg

💡 Tip: For this filter size, professional installation is recommended due to substantial media weight. Always fill in order: coarsest grade first (bottom), then medium, then finest 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	0.52 m²
Filter Bed Height	900 mm
Standard Flow Rate	15.6 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

Three-Layer Configuration Benefits:

The AFM-840’s three-grade media configuration provides:

• Optimal flow distribution through graduated particle sizes
• Enhanced backwash efficiency with proper support layers
• Extended filter runs between backwashes
• Superior particle capture across size ranges

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⚙️ Besgo Valve System

The Calplas AFM-840 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 luxury residential	Up to 125,000 L	✅ Ideal
🏨 Hotel pools	Up to 100,000 L	✅ Excellent
🏨 Holiday rental complexes	Up to 94,000 L	✅ Robust for high turnover
🏢 Swim schools	Up to 80,000 L	✅ Handles frequent use
🏢 Hydrotherapy pools	Up to 60,000 L	✅ Generous capacity
🏢 Health club pools	Up to 100,000 L	✅ Well suited
🏢 Small public pools	Up to 94,000 L	✅ Good for moderate bather loads

Best Suited For:

• Large residential pools with demanding filtration requirements
• Commercial pools requiring reliable, high-capacity filtration
• Holiday rental properties needing robust, low-maintenance equipment
• Facilities where water quality is paramount
• Applications requiring automated backwash capability

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❓ Frequently Asked Questions

Q: What size pool will this filter handle? A: The Calplas AFM-840 is suitable for pools up to 125,000 litres with a flow rate of 15.6 m³/h, providing an 8-hour turnover. For optimal 6-hour turnover, it’s ideal for pools up to 94,000 litres.

Q: How often do I need to backwash? A: Backwash when the pressure gauge reads 0.5 bar above your clean baseline reading. For commercial applications, this may be daily; for residential use, typically every 1-2 weeks.

Q: What filter media should I use? A: The filter uses a three-layer configuration. AFM capacity is 31 bags (651 kg total). Traditional sand can also be used – 30 bags (750 kg total).

Q: Why does this filter need three media grades? A: Larger filters benefit from three-layer configurations: coarse media at the bottom supports the bed and aids backwashing, medium grade provides transition, and fine grade at the top performs primary filtration.

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 12-15.6 m³/h for normal filtration. Ensure the pump can deliver 20-26 m³/h for effective backwashing. Do not exceed 26 m³/h maximum.

Q: How does the AFM-840 compare to smaller models? A: The AFM-840 offers 30% more filter area than the AFM-720 (0.52 m² vs 0.40 m²) and 160% more than the AFM-520. It handles pools up to 125,000L compared to 94,000L (AFM-720).

Q: Is this filter suitable for public pools? A: Yes, the AFM-840 is suitable for smaller public pools, swim schools, and health clubs with moderate bather loads. For busy public facilities, consider the AFM-960 or consult with Parts4Tubs for sizing advice.

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 heavy is the filter when filled? A: Empty weight is 99 kg. With AFM media (651 kg) plus water, expect a total operating weight of approximately 750-850 kg. Professional installation and a reinforced concrete base are essential.

📥 Downloads & Resources

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

🏆 Why Choose the Calplas AFM-840

✅ Commercial-Grade Capacity – 0.52 m² filter area handles pools up to 125,000 litres

✅ Powerful Performance – 15.6 m³/h flow rate with 26 m³/h backwash capability

✅ Three-Layer Media Design – Optimised for superior filtration and backwash efficiency

✅ Premium Construction – Hand-laminated GRP with steel reinforcement

✅ Proven Reliability – Calplas manufacturing excellence since 1970

✅ Easy Servicing – Large manhole and sight glass for straightforward maintenance

✅ Automation Ready – Full Besgo valve system compatibility

✅ 5-Year Warranty – Comprehensive manufacturer-backed coverage

⭐ 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-840 provides commercial-grade filtration for large residential and commercial pools up to 125,000 litres. With its 840mm diameter tank, 0.52 m² filter area, and robust 15.6 m³/h flow rate, this Spanish-manufactured filter delivers the performance demanded by hotels, swim schools, and luxury residential installations. The three-layer media configuration optimises both filtration efficiency and backwash effectiveness, whilst the 900mm bed depth ensures thorough particle removal. Backed by a 5-year tank warranty and designed for 10-15+ year AFM media lifespan, the AFM-840 represents a professional investment in long-term water quality excellence.