🏊 Calplas HFS-35 960mm Side Mount Sand Filter – Up to 168,000 Litre Pool Capacity

Advanced filtration for the ultimate swimming experience in large pools

🌊 Product Overview

The Calplas HFS-35 is the flagship model in the HFS range, delivering industrial-strength filtration for the largest residential pools and demanding commercial applications. Featuring an impressive 960mm diameter tank constructed from hand-laid glass reinforced polyester (GRP) with internal steel reinforcement, this Spanish-manufactured filter represents the pinnacle of Calplas engineering excellence.

The HFS series is distinguished by its significantly taller design, providing almost 50% more filter medium than comparable standard filters. This extended filter bed maximises water contact time, resulting in exceptional filtration efficiency and superior flocculation for consistently crystal-clear pool water even under the most demanding conditions.

As the largest model in the HFS-15 and above range, the HFS-35 features an extra-large 355mm transparent filter cover, upgraded 2½” connections for maximum flow capacity, and contains approximately 20% more filter medium than smaller models. The integrated special AFM diffusor ensures optimal water distribution across the entire filter bed, eliminating channelling and crater formation. Capable of handling pools up to 168,000 litres with an 8-hour turnover, the HFS-35 is the definitive choice for large estate pools, commercial leisure facilities, and installations where uncompromising water quality is essential.

⭐ Key Features

✅ Premium GRP Construction – Hand-laid glass reinforced polyester tank with internal steel reinforcement, manufactured to EN 13121-3 standards for maximum strength

✅ 50% Greater Media Capacity – Tallest filter bed in the range provides almost 50% more filter medium for unrivalled filtration performance

✅ Extra-Large 355mm Transparent Lid – Oversized inspection port allows comprehensive visual monitoring of media condition

✅ Upgraded 2½” Connections – Larger inlet/outlet ports handle higher flow rates with reduced pressure loss

✅ Integrated AFM Diffusor – Specialised water distribution system ensures uniform flow across the entire 0.70 m² filter area

✅ 2.5 Bar Industrial Pressure Rating – Heavy-duty pressure handling with 3.75 bar test pressure (7 bar versions available on request)

✅ 6-Way Valve Compatible – Accepts exclusive Calplas 6-way multiport valve with automatic or manual operation; Besgo backwash valve fits as standard

✅ Three-Grade Media Configuration – Optimised for traditional sand/gravel or advanced AFM activated filter media achieving filtration down to 1 micron

✅ 40°C Temperature Tolerance – Suitable for heated pools, warm climates, and high-intensity commercial use

✅ Complete Filter Package – Supplied with pressure gauge, air vent, drain plug, and extra-large transparent lid as standard

✅ 5-Year Tank Warranty – Comprehensive manufacturer warranty on the flagship model

✅ White Option Available – Alternative colour to suit premium installation aesthetics

📊 Technical Specifications

Specification	Value
Filter Type	Sand / AFM Media Filter
Tank Diameter	960 mm
Overall Height	1,240 mm
Filter Area	0.70 m²
Flow Rate (Normal Filtration)	21 m³/h (at 30 m³/h/m²)
Flow Rate (Backwash Capacity)	35 m³/h (at 50 m³/h/m²)
Pool Capacity (6-hr Turnover)	Up to 126,000 litres
Pool Capacity (8-hr Turnover)	Up to 168,000 litres
Sand Capacity	28 kg sand + 6 kg gravel
AFM Media Capacity	15 × 21 kg Grade 1 + 8 × 21 kg Grade 2 + 7 × 21 kg Grade 3
Maximum Operating Pressure	2.5 bar
Test Pressure	3.75 bar
Temperature Rating	Up to 40°C
Inlet/Outlet Connections	2½” (63 mm) threaded
Filter Opening Diameter	355 mm
Distance from Ground	360 mm
Distance Between Connections	250 mm
Tank Material	Hand-laid GRP (Glass Reinforced Polyester)
Reinforcement	Internal steel reinforced
Weight (Empty)	75 kg
Valve Type	Side mount (6-way valve optional)
Warranty	5 years (tank)
Product Code	1519250135
Manufacturer	Calplas (Spain)
Manufacturing Standard	EN 13121-3

📏 Pool Sizing Guide

Sizing Principle: The filter flow rate should achieve complete pool water turnover within 6-8 hours for optimal clarity, hygiene, and chemical efficiency.

Formula:

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

Pool Size Compatibility:

Pool Type	Volume Range	Suitability
🏠 Large in-ground residential	80,000 – 120,000 L	✅ Excellent – generous capacity
🏠 Extra-large estate pools	120,000 – 168,000 L	✅ Excellent – optimal match
🏢 Commercial leisure pools	Up to 126,000 L	✅ Excellent – 6-hr turnover
🏨 Hotel/resort pools	Up to 126,000 L	✅ Excellent – handles high traffic
🏫 School/institutional pools	Up to 126,000 L	✅ Good – robust performance
🏊 Competition/training pools	Up to 140,000 L	✅ Good – professional grade

This Filter:

📍 Normal Filtration Flow Rate: 21 m³/h
📍 Maximum Backwash Flow Rate: 35 m³/h
📍 Recommended Pool Size: Up to 126,000 litres (6-hour turnover)
📍 Maximum Pool Size: Up to 168,000 litres (8-hour turnover)

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🔌 Installation Requirements

Plumbing:

Requirement	Specification
Inlet Connection	2½” (63 mm) female thread
Outlet Connection	2½” (63 mm) female thread
Connection Spacing	250 mm between ports
Valve Position	Side mount

⚠️ Note: The HFS-35 uses larger 2½” connections compared to 2″ on smaller HFS models. Ensure compatible pipework and valve selection.

Physical Installation:

Requirement	Details
Base	Reinforced concrete pad capable of supporting 600+ kg when filled
Minimum Height Clearance	950 mm above filter for lid removal
Distance from Ground	360 mm (integrated legs)
Access Clearance	800 mm all around for servicing
Weight Consideration	75 kg empty; plan for delivery and positioning

Pump Compatibility:

⚠️ Critical: Filter must be paired with an appropriately rated pump for optimal performance.

Parameter	Specification
Recommended Pump Flow Rate	14 – 22 m³/h
Maximum Pump Flow Rate	Do not exceed 35 m³/h
Pump Connection	2½” or adapt from 2″ with appropriate fittings
Pump Head	Factor in filter pressure drop when sizing

💡 Tip: For finest filtration results, operate towards the lower end of the recommended flow range. Higher flow rates reduce media contact time and filtration quality.

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🔄 Maintenance Guide

Routine Maintenance:

Task	Frequency	Procedure
Check pressure gauge	Weekly	Record baseline; monitor for pressure increases
Backwash filter	When pressure rises 0.5-1 bar	Run until sight glass clears (4-5 minutes for this size)
Rinse after backwash	After every backwash	Run 60-90 seconds to fully resettle media
Inspect transparent lid	Monthly	Check for cracks, seal condition, clarity
Check O-rings and seals	Seasonally	Replace if worn, hardened, or showing leakage
Inspect media level	Annually	Top up if significantly settled
Full media replacement	5-7 years (sand) / 10-15 years (AFM)	Complete media change

Pressure Gauge Guide:

📊 Clean filter baseline: Record pressure immediately after thorough backwash
📊 Backwash trigger: 0.5-1 bar above baseline reading
📊 Maximum operating pressure: 2.5 bar – never exceed

Winterisation (UK Climate):

❄️ Essential winter protection for the HFS-35:

1. Turn off pump and fully isolate electrical supply
2. Close all inlet and outlet valves
3. Set multiport valve to “Winterise” or position handle between settings
4. Completely drain filter tank via drain plug (allow extra time due to size)
5. Remove drain plug and store securely indoors
6. Leave air vent open to prevent vacuum or pressure build-up
7. Cover filter with weatherproof cover or relocate to frost-free storage
8. Never allow water to remain in filter during freezing conditions

⚠️ Important: Frost damage from residual water is excluded from warranty coverage. Due to the HFS-35’s large capacity, allow adequate time for complete drainage before winter.

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🪨 Filter Media Information

Compatible Media Types:

Media Type	Filtration Rating	Lifespan	Key Benefits
Silica Sand	20-40 microns	5-7 years	Economical, proven, readily available
Glass Media	10-15 microns	10+ years	Finer filtration, lighter weight, eco-friendly
AFM (Activated Filter Media)	1-5 microns	10-15 years	Exceptional clarity, self-sterilising, reduced chemicals
ZeoSand	3-5 microns	5 years	Superior clarity, ammonia removal properties

Media Capacity for HFS-35:

Media Type	Quantity Required
Sand + Gravel	28 kg sand (0.4-0.8 mm) + 6 kg gravel (2-4 mm)
AFM Media	15 × 21 kg Grade 1 + 8 × 21 kg Grade 2 + 7 × 21 kg Grade 3 (630 kg total)

AFM Three-Grade Configuration:

Grade	Bags	Weight	Layer Purpose
Grade 1 (0.4-1.0 mm)	15	315 kg	Primary filtration layer
Grade 2 (0.7-2.0 mm)	8	168 kg	Transition/support layer
Grade 3 (2.0-4.0 mm)	7	147 kg	Base support layer
Total	30	630 kg

💡 Recommendation: The HFS-35 includes a special AFM diffusor engineered for optimal AFM media performance. Upgrading to AFM provides filtration down to 1 micron, self-sterilising properties, and 10-15 year media life – ideal for commercial and high-end residential applications.

Signs Media Requires Replacement:

• Persistent water cloudiness despite correct chemical balance
• Rapid pressure rise between backwash cycles
• Cloudy water returning during normal filtration
• Filter media particles appearing in pool
• Elevated sanitiser consumption
• Visible channelling or uneven media bed surface

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💎 Filtration Performance

Metric	Value
Filter Area	0.70 m²
Filtration Rating (Sand)	20-40 microns
Filtration Rating (AFM)	1-5 microns

Micron Rating Guide:

Rating	Particle Types Removed
40+ microns	Leaves, insects, visible debris
20-40 microns	Sand, grit, visible suspended particles
10-20 microns	Fine particles, some algae spores
5-10 microns	Very fine matter, most algae types
1-5 microns	Ultra-fine particles, bacteria, all algae

Superior Filtration Design:

The HFS-35’s extended filter bed height delivers almost 50% more media contact time compared to standard filters. Combined with the largest filter area in the range (0.70 m²), performance advantages include:

✅ Maximum flocculation efficiency for finest particle capture
✅ Superior removal of organic matter and suspended solids
✅ Exceptional water clarity and sparkle
✅ Significantly reduced chemical consumption
✅ Extended intervals between backwash cycles
✅ Consistent performance under high bather loads
✅ Commercial-grade reliability for demanding applications

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⚙️ Valve Positions & Functions

The HFS-35 accepts a 6-way multiport valve (sold separately) with these functions:

Position	Function
Filter	Normal operation – water flows through media and returns to pool
Backwash	Reversed flow flushes debris from media to waste
Rinse	Resettles media and clears lines after backwashing
Waste	Bypasses filter – water drains directly (for heavy debris removal)
Recirculate	Bypasses filter – water returns to pool (for chemical mixing)
Closed	Stops all water flow through valve

💡 Note: The HFS-35 requires a 2½” valve to match its larger connections. Besgo backwash valve fits as standard. Coupling set sold separately. Exclusive Calplas 6-way valves available in automatic or manual configurations.

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🎯 Ideal Applications

Application	Pool Size	Suitability
🏠 Large estate/luxury pools	Up to 168,000 L	✅ Excellent
🏠 Premium residential	100,000 – 150,000 L	✅ Excellent
🏨 Hotel/resort pools	Up to 126,000 L	✅ Excellent
🏢 Health club/leisure centre	Up to 126,000 L	✅ Excellent
🏫 School/university pools	Up to 126,000 L	✅ Excellent
🏡 Holiday complex pools	Up to 140,000 L	✅ Excellent
🏊 Training/competition pools	Up to 150,000 L	✅ Good

Best Suited For:

• Large residential pools requiring flagship filtration capacity
• Commercial leisure facilities with high bather loads
• Hotels, resorts, and holiday complexes
• Educational and institutional swimming facilities
• Properties where water quality is paramount
• Installations planning AFM media for superior 1-micron filtration
• Replacement of ageing commercial-grade filtration systems
• New builds requiring long-term, reliable filtration solutions

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❓ Frequently Asked Questions

Q: What size pool will this filter handle?

A: The HFS-35 is suitable for pools up to 168,000 litres with an 8-hour turnover, or up to 126,000 litres for optimal 6-hour turnover. With a 21 m³/h flow rate and 0.70 m² filter area, it’s the largest filter in the HFS range, ideal for large residential and commercial pools.

Q: How often should I backwash?

A: Backwash when the pressure gauge reads 0.5-1 bar above your clean baseline. For commercial pools with high bather loads, this may be required several times per week. Residential pools typically need backwashing every 1-2 weeks during swimming season.

Q: What filter media should I use?

A: The HFS-35 accommodates 28 kg sand plus 6 kg gravel, or AFM media totalling 630 kg across three grades (15 bags G1 + 8 bags G2 + 7 bags G3). The integrated AFM diffusor makes this filter ideal for AFM upgrades, achieving filtration down to 1 micron.

Q: How long does filter media last?

A: Sand typically requires replacement every 5-7 years. Glass media and AFM last 10-15 years with proper maintenance. For commercial applications with high usage, inspect media annually and consider more frequent replacement.

Q: What pump do I need?

A: Select a pump delivering 14-22 m³/h for optimal performance. Never exceed the filter’s maximum flow rate of 35 m³/h. Ensure the pump has 2½” connections or use appropriate adapters. Lower flow rates within the range provide finer filtration.

Q: Why does the HFS-35 have larger connections?

A: The 2½” connections (vs 2″ on smaller models) reduce pressure loss at higher flow rates, ensuring the HFS-35 can handle its full 21 m³/h filtration capacity and 35 m³/h backwash rate efficiently.

Q: What warranty is included?

A: The HFS-35 includes a 5-year tank warranty from Calplas. Contact Parts4Tubs for complete warranty terms and conditions.

Q: Is this suitable for commercial pools?

A: Yes, the HFS-35 is designed for commercial applications. It’s suitable for hotel pools, leisure centres, schools, and similar facilities up to 126,000 litres (6-hour turnover). For larger commercial installations, multiple filters may be required.

Q: Is this suitable for saltwater pools?

A: Yes, the GRP construction provides excellent saltwater corrosion resistance. Ensure all connected equipment (valves, fittings, pumps) is also saltwater compatible.

Q: What’s the difference between HFS-30 and HFS-35?

A: The HFS-35 has a larger 960mm tank diameter (vs 840mm), greater filter area of 0.70 m² (vs 0.52 m²), higher flow rate of 21 m³/h (vs 15.6 m³/h), handles pools up to 168,000L (vs 125,000L), and features upgraded 2½” connections (vs 2″).

Q: Is the multiport valve included?

A: No, the 6-way multiport valve is sold separately. The filter accepts Calplas 6-way valves (automatic or manual) and Besgo backwash valves fit as standard. Note: 2½” valve required for HFS-35. Coupling sets required separately.

📑 Downloads & Resources

📄 Calplas HFS Filter Specifications (PDF) – Complete technical specifications for the entire HFS filter range

🏆 Why Choose the Calplas HFS-35

✅ Maximum Filtration Capacity – 0.70 m² filter area with 21 m³/h flow rate handles pools up to 168,000 litres

✅ Flagship Performance – Largest model in the HFS range with 50% more media than standard filters

✅ Industrial-Grade Construction – Hand-laid GRP with steel reinforcement manufactured to EN 13121-3

✅ Upgraded 2½” Connections – Larger ports for superior flow capacity and reduced pressure loss

✅ Extra-Large 355mm Lid – Maximum access for inspection and maintenance

✅ Three-Grade AFM Compatibility – Optimised for advanced media achieving 1-micron filtration

✅ Commercial-Ready – Suitable for hotels, leisure centres, schools, and high-end residential

✅ 5-Year Tank Warranty – Comprehensive manufacturer coverage on the flagship model

✅ Proven Spanish Engineering – Manufactured by Calplas, specialists in professional pool filtration

🤝 Why Buy From Parts4Tubs

✅ UK-Based Company – Local expertise and dedicated support from pool specialists

✅ Fast UK Delivery – Prompt dispatch for commercial and residential projects

✅ Expert Technical Advice – Professional guidance on sizing, installation, and maintenance

✅ Competitive Pricing – Outstanding value on flagship pool equipment

✅ Full Warranty Support – Direct manufacturer warranty handling

✅ Easy Returns – 30-day returns policy for complete confidence

✅ Complete Product Range – Filter media, valves, spare parts, and accessories available

✅ Trusted Supplier – Established retailer of pool, hot tub, and spa equipment

✨ Summary

The Calplas HFS-35 960mm Side Mount Sand Filter is the flagship model in the HFS range, delivering professional-grade filtration for pools up to 168,000 litres. Built with premium hand-laid GRP construction and internal steel reinforcement to EN 13121-3 standards, this Spanish-engineered filter features 50% more media capacity than standard filters, an impressive 0.70 m² filter area, and upgraded 2½” connections for maximum flow efficiency. With a 21 m³/h flow rate and optimisation for three-grade AFM media (achieving filtration down to 1 micron), the HFS-35 is the definitive choice for large estate pools and commercial installations. Supplied complete with pressure gauge, air vent, 355mm transparent lid, and backed by a 5-year tank warranty.

Order today for uncompromising filtration performance in your large pool.