GRP Sectional Category 5 Break Tanks
Tricel manufactures hot-press moulded GRP sectional tanks with a Type AB air gap – a raised inlet valve housing with an AB air gap spill slot (weir overflow) – for mains connections serving a fluid category 5 risk. Site-assembled from modular panels, from 1,000 to over 4 million litres, for plant rooms where a one-piece Cat 5 tank cannot be delivered or is too small.
- •Type AB air gap – rated by the Regulators for fluid category 5, the highest risk level
- •Non-mechanical: a permanent physical air gap, with no check valves in the protection path
- •EFB, IFB and TIF configurations – Cat 5 suitability confirmed at enquiry stage
- •Regulation 4(1)a approved sectional tanks; WRAS-approved fittings where specified
- •Assembled on site by Tricel-trained installation teams across the UK
Cat 5 Sectional Break Tank – Key Parameters
Air gap type
Type AB (raised housing + spill slot)
Fluid category
Category 5 - highest risk
Capacity range
1,000 L – 4M+ litres
Configurations
EFB / IFB / TIF
Panel construction
Hot-press moulded GRP
Approval
Regulation 4(1)a / WRAS fittings
Regulations
WSFR 1999 / Scotland Byelaws 2014 / NI 2009
Manufacturer
Tricel Water UK - UK manufacturer
What is a Category 5 sectional break tank?
A Category 5 sectional break tank is a GRP sectional cold water storage tank, assembled on site from hot-press moulded panels, fitted with a Type AB air gap so that it can be connected to the mains where the downstream system presents a fluid category 5 risk under the Water Supply (Water Fittings) Regulations 1999. The mains inlet sits in a raised inlet valve housing, and an AB air gap spill slot (a rectangular weir overflow) sets the critical water level. The air gap between the lowest point of the inlet and that critical level must be at least 20 mm or twice the inlet bore, whichever is greater. Because there is no physical connection between the inlet and the stored water, backflow into the public supply cannot occur by back-siphonage or back pressure. Tricel manufactures GRP sectional tanks in EFB, IFB and TIF configurations from 1,000 to over 4 million litres; the sectional format suits Cat 5 installations that need larger capacity, restricted-access delivery or like-for-like replacement in an existing plant room.
01
Fluid Categories
Understanding Fluid Categories and Why Category 5 Requires an Air Gap
The Water Supply (Water Fittings) Regulations 1999 classify contamination risk into five fluid categories. The category of the downstream system determines the minimum backflow protection on the mains connection. At category 5 only a non-mechanical air gap rated for that category – such as Type AA or Type AB – is acceptable. A Type AG air gap is rated for fluid category 3 at most.
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Category
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Risk level
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Fluid description
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Examples of protection rated for this category
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|---|---|---|---|
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1
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No risk
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Wholesome water supplied by a water undertaker
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None required
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2
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Aesthetic
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Water that would be wholesome but for a change in temperature, taste, odour or appearance
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Single check valve, or any device rated for a higher category
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3
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Slight health hazard
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Fluid containing substances of low toxicity
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Type AG air gap; double check valve
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4
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Significant health hazard
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Fluid containing toxic, carcinogenic or pesticide substances
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Type BA (RPZ) valve; Type AF air gap
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5
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Serious health hazard
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Fluid containing pathogenic organisms, radioactive or very toxic substances, or faecal, human or animal waste
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Non-mechanical air gap only – e.g. Type AA or Type AB. No mechanical device is acceptable.
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The fluid category is set by the risk of the downstream system, not the water stored in the tank. The water undertaker or a competent person must assess and confirm the category for each installation. Full device ratings are set out in the Regulators’ Specification for backflow prevention arrangements and devices.
02
The AB Air Gap
How a Type AB Air Gap Works on a GRP Sectional Tank
On a Tricel sectional tank, the Type AB air gap is formed by a raised inlet valve housing and an AB air gap spill slot. The arrangement is designed for each tank configuration and confirmed at design stage.
Raised inlet valve housing – The inlet connection and float valve are mounted in a housing raised above the main tank lid, so the point of discharge sits well above the stored water.
AB air gap spill slot – A rectangular weir overflow sets the critical water level – the level reached under fault conditions, measured two seconds after the inlet is closed. If the float valve fails, water discharges through the slot before it can rise to the inlet.
Measured air gap – The vertical gap between the lowest point of the inlet and the critical water level must be no less than 20 mm or twice the inlet bore, whichever is greater. It can be confirmed by test or calculation.
Unrestricted discharge – Neither the water path to the spill slot nor the discharge from it may be restricted, so the space outside the slot must allow full, unimpeded discharge.
No mechanical parts in the protection path – Unlike RPZ or check valves, an air gap has no seals or moving parts that can fail. Protection is maintained by the physical gap itself.
Modifying the inlet housing, spill slot position or inlet arrangement after installation may compromise the air gap. If the inlet comes into contact with the tank contents – for example through splashing or foaming – the air gap is considered compromised. Confirm any changes with Tricel.
03
Why Sectional
Why Specify a Sectional Cat 5 Break Tank?
Tricel also manufactures one-piece Category 5 break tanks. A sectional tank is the alternative where access, capacity or the plant room layout rule out a complete moulded unit.
01
Restricted-access plant rooms
Panels are delivered individually and bolted together on site, so the tank can be installed via stairwells, narrow corridors and goods lifts where a one-piece Cat 5 tank cannot be positioned.
02
Capacity beyond the one-piece range
Sectional tanks run from 1,000 to over 4 million litres. Capacity is set by footprint and headroom, not a fixed product size – one-piece tanks are supplied in fixed sizes up to 16,000 litres.
03
Replacement of existing tanks
An existing tank can be dismantled panel by panel and a new Cat 5 sectional tank assembled in the same space, including where perimeter clearance is limited (TIF).
04
Configurable to the project
Inlet position, raised housing, connections, access hatch and base type are designed per project, with standard 1m panels plus half-panel increments.
05
Maintenance without losing supply
An internal maintenance division can split the tank into two compartments so one can be isolated for cleaning or inspection while the other continues to supply the building.
06
Made by the manufacturer
Panels are hot-press moulded in-house at Weston-super-Mare and Lanark and assembled by Tricel-trained crews – no distributor between design and installation.
04
Tank Types
EFB, IFB and TIF Cat 5 Sectional Tank Configurations
All three sectional configurations use hot-press moulded GRP panels. The right type depends on headroom, perimeter clearance, access route and pipework position. Cat 5 AB air gap suitability is confirmed for each configuration at enquiry stage.
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Tank type
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Best for
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Key advantage
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Cat 5 consideration
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|---|---|---|---|
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EFB – External Flanged Base
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Open-access sites with standard perimeter clearance and headroom
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Raised self-draining base; access below the tank for cleaning and maintenance
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Allow for the overall height of the base frame plus the raised inlet valve housing
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IFB – Internal Flanged Base
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Sites where headroom is limited
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Lower installation height than EFB; flat base or levelled steel beams
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Raised housing still adds height above the lid – check hatch and housing clearance
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TIF – Totally Internally Flanged
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Constrained plant rooms and retrofit
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Assembled from inside; ~50 mm clearance achievable on three sides
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~500 mm on the pipework side; spill slot discharge must remain unrestricted
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05
Applications
Where Category 5 Sectional Break Tanks Are Specified
Category 5 protection is needed wherever a mains connection serves a system with a fluid category 5 risk. Typical sources include laboratories, mortuaries, veterinary practices, clinical areas in hospitals, agricultural livestock systems and bin stores. The sectional format is commonly chosen in these sectors where storage volumes are large or plant rooms are constrained.
Healthcare & NHS
Hospitality & Leisure
Infrastructure & Utilities
Data Centres
High-Rise & Multi-Storey
Industrial & Manufacturing
Education
Agriculture
Food & Beverage
Local Authority & Public
The required fluid category for any specific installation must be confirmed by the water undertaker or a competent person registered under an Approved Contractor Scheme. Do not determine fluid category without a formal assessment.
This list is indicative only. Whether a Cat 5 risk exists depends on the activities and water uses at each installation, and must be assessed by the water undertaker or a competent person.
06
Specification
Tricel GRP Sectional Cat 5 Break Tank – Specification
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Parameter
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Specification
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|---|---|
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Tank construction
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Site-assembled GRP sectional tank – hot-press moulded panels (isophthalic polyester resin, glass fibre reinforcement)
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Panel sizes
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1m × 1m standard; 1m × 0.5m and 0.5m × 0.5m panels for half-panel increments
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Capacity
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1,000 L to over 4 million litres – confirmed per project footprint and headroom
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Configurations
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EFB, IFB, TIF – Cat 5 suitability confirmed at enquiry stage
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Air gap type
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Type AB – raised inlet valve housing with AB air gap spill slot (weir overflow)
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Fluid category protection
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Category 5 (back-siphonage and back pressure)
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Air gap dimension
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≥ 20 mm or 2 × inlet bore (whichever is greater), to the critical water level
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Approval
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Regulation 4(1)a approved sectional tanks; WRAS-approved fittings available where specified – confirm requirements at quotation
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GRP reference standard
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BS EN 13280:2001 – GRP cold water storage tanks
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Backflow reference
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BS EN 1717; Regulators’ Specification for backflow prevention
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Insulation
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Insulated and uninsulated panel options – specify to suit location and use
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Float valve sizing
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Confirmed to incoming mains supply at order
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Options
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Internal maintenance division, internal/external ladders, access manway, level switches, temperature sensor, drain connection
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Manufacturer
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Tricel Water UK – Weston-super-Mare and Lanark
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07
AG vs AB Air Gap
AG Air Gap vs AB Air Gap: What Is the Difference?
Both are non-mechanical air gaps with the same minimum gap dimension. The difference is the overflow: AG uses a minimum-size circular overflow and is rated up to fluid category 3; AB uses an unrestricted rectangular weir and is rated for category 5.
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Feature
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Type AG Air Gap
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Type AB Air Gap (Cat 5)
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|---|---|---|
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Fluid category rating
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Up to category 3
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Up to category 5 (highest)
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Overflow type
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Circular, minimum 19 mm bore throughout
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Rectangular weir / spill slot, unrestricted
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Minimum air gap
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20 mm or 2 × bore, whichever is greater
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20 mm or 2 × bore, whichever is greater
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|
Protects against
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Back-siphonage and back pressure
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Back-siphonage and back pressure
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Inspection interval (BS EN 806-5)
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Every 12 months
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Every 6 months, including screened mesh
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Tricel sectional range
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Standard sectional tank inlet arrangements
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Raised inlet valve housing + AB air gap spill slot
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08
Sectional vs One-Piece
Sectional vs One-Piece Category 5 Break Tanks
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Requirement
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Sectional Cat 5 break tank
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One-piece Cat 5 break tank
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|---|---|---|
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Construction
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Hot-press moulded panels assembled on site
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Single moulded GRP unit, delivered complete
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Capacity
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1,000 L to over 4 million litres
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Fixed sizes within the one-piece range (up to 16,000 L)
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Restricted access
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Strong option – panels moved through stairwells, corridors and lifts
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Needs a clear route for the complete tank
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AB air gap
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Raised inlet valve housing and spill slot designed per project
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Factory-fitted raised housing and weir; WRAS-approved assembly
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Programme
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On-site assembly time depends on tank size
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Shortest on-site programme
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Best for
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Large volumes, plant room replacements, constrained sites
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Smaller volumes with clear delivery access
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09
Regulations
Regulations Governing Category 5 Break Tanks
Compliance is determined by the complete system specification – tank, fittings, pipework, overflow arrangement, insulation, access and maintenance – not by the tank alone.
Jurisdiction
UK water fittings legislation
England & Wales: Water Supply (Water Fittings) Regulations 1999. Scotland: Water Supply (Water Fittings) (Scotland) Byelaws 2014. Northern Ireland: Water Supply (Water Fittings) Regulations (Northern Ireland) 2009.
Regulation 4
Fittings of appropriate quality
Water fittings must be of appropriate quality and standard. Tricel sectional tanks are Regulation 4(1)a approved for potable cold water storage where specified.
Regulation 5
Prior notification
Installing a backflow prevention arrangement for a fluid category 4 or 5 risk requires notice to the water undertaker before work starts. Consent is deemed if not refused within 10 working days. Approved contractors may be exempt – check with the scheme.
Schedule 2, para 15
Backflow prevention
Every water system must contain adequate devices to prevent backflow. Device ratings by fluid category are set out in the Regulators’ Specification.
BS EN 1717
Protection against pollution
The British adoption of the European standard on protection of potable water against pollution by backflow, classifying devices by fluid category.
ACoP L8 · HSG274
Legionella control
Stored cold water should be kept below 20°C. Insulation, correct sizing and adequate turnover support Legionella risk management.
Contravening the Water Fittings Regulations or Byelaws is a criminal offence and can lead to enforcement by the water undertaker. Always confirm requirements with the water undertaker before installation.
10
Installation
Installation and Clearance for Cat 5 Sectional Tanks
The clearance guidance for standard sectional tanks applies, plus allowances for the raised inlet housing and the spill slot discharge.
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Clearance / requirement
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Indicative guidance
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Notes
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|---|---|---|
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Perimeter – tanks up to 2m high
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500 mm
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All sides, for inspection, cleaning and maintenance
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|
Perimeter – 2.5–3m high
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800 mm
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Increased clearance for working at height
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|
Perimeter – 3.5–4m high
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1,000 mm
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Confirm at design stage
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|
TIF – pipework side / other sides
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~500 mm / ~50 mm
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Subject to design confirmation
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IFB hatch clearance
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750 mm hinged / 500 mm lift-off
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Above the hatch opening
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|
Raised inlet valve housing
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Project-specific
|
Headroom must include the housing height above the tank lid
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|
AB spill slot discharge
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Unrestricted
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Leave enough space outside the slot for full discharge under fault conditions
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|
Overflow and warning pipe
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≥ 1.5 × max inlet flow
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Route to a visible, traceable discharge point
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|
Base flatness tolerance
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2 mm per 1 m / 6 mm per 6 m
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Panel alignment and joint seal integrity
|
01
Before installation
- Fluid category confirmed by the water undertaker or a competent person
- Regulation 5 notice submitted where required
- Approval and fittings documentation agreed for the project
02
On site
- Access route checked for panel delivery
- Flat, level, load-bearing base
- Assembly by Tricel-trained crews
03
Commissioning
- Air gap verified against the critical water level
- Clean, disinfect and flush to BS 8558:2015
- Retain notification, approval and commissioning records
These are indicative design guidance values, not universal regulatory requirements. Confirm against the tank type, configuration and current Tricel installation guidelines.
11
Aftercare
Cat 5 Break Tank Aftercare and Inspection
Tricel Water UK has partnered with Hydraclean Ltd, a water hygiene and Legionella compliance specialist, to deliver aftercare compliant with ACoP L8, HSG274 and BS 8558:2015.
BS EN 806-5
AB air gap inspection
Type AB air gap installations, including screened mesh, should be inspected, cleaned and maintained as necessary every 6 months.
HSG274 · ACoP L8
Tank inspection
Best practice every six months; annual minimum. Checks include stored water below 20°C, screens, sediment and stagnation risk.
BS 8558:2015
Cleaning & chlorination
Risk-assessed cleaning and disinfection, with confined-space protocols and photographic records. UKAS-accredited sampling where required.
12
Technical Downloads
Cat 5 Sectional Break Tank Technical Resources
Technical documents for M&E engineers, specifiers, building services consultants and facilities managers. Download for design, specification, procurement and regulatory submissions.
GRP Sectional Tank Product Brochure
EFB, IFB and TIF configurations, capacities, approvals and panel sizes.
TIF Tank Technical Brochure
Totally internally flanged tanks for constrained plant rooms.
Break Tank & Booster Set Design Guide
Sizing, two-compartment arrangements and booster set interface.
13
Specification Support
Specify a Tricel GRP Sectional Cat 5 Break Tank
Information for a quotation
Fluid category confirmed (water undertaker)
Required storage capacity (litres)
Internal or external location
Available footprint and headroom (incl. raised housing)
Access route constraints
Preferred tank type, if known
Incoming mains diameter (float valve size)
Potable or non-potable duty
Insulated or uninsulated
Maintenance division required?
Regulation 5 notification status
Plant room drawings / existing tank details
Send project details to Tricel
Tricel’s technical sales team will review your requirements and advise on tank type, panel layout, AB air gap arrangement, base type and access strategy.
14
Related Resources
Plan Your Cat 5 Break Tank Project
15
FAQS
Category 5 Sectional Break Tank FAQs
Common questions from consulting engineers, M&E contractors and specifiers.
What is a Category 5 sectional break tank?
A GRP sectional cold water storage tank, assembled on site from hot-press moulded panels, fitted with a Type AB air gap – a raised inlet valve housing with an AB air gap spill slot. It provides backflow protection for mains connections serving a fluid category 5 risk under the Water Supply (Water Fittings) Regulations 1999. Tricel manufactures sectional tanks from 1,000 to over 4 million litres.
When should I choose a sectional Cat 5 tank over a one-piece Cat 5 tank?
Choose sectional where the complete tank cannot be delivered to the plant room, where the required volume exceeds the one-piece range (fixed sizes up to 16,000 litres), or where an existing tank is being replaced in a constrained space. One-piece Cat 5 tanks offer the shortest on-site programme where access allows.
Can EFB, IFB and TIF tanks be supplied with an AB air gap?
Tricel’s GRP sectional tanks and TIF configurations can be specified to meet fluid category 5 requirements. Suitability of the AB air gap arrangement for each configuration is confirmed at enquiry stage, taking account of headroom, inlet position and spill slot discharge clearance.
What is the difference between an AG and an AB air gap?
Both need an air gap of at least 20 mm or twice the inlet bore. A Type AG air gap uses a minimum-size circular overflow and is rated up to fluid category 3. A Type AB air gap uses an unrestricted rectangular weir overflow and is rated up to fluid category 5.
Do I need to notify the water undertaker?
Under Regulation 5, installing a backflow prevention arrangement for a fluid category 4 or 5 risk requires notice to the water undertaker before work begins. Consent is deemed if not refused within 10 working days. Work by an approved contractor may be exempt – confirm with the relevant scheme.
How often should a Cat 5 break tank be inspected?
BS EN 806-5 recommends Type AB air gap installations, including screened mesh, are inspected and maintained every 6 months. HSG274 recommends cold water storage tank inspection every six months as best practice, and at least annually.
Can a Cat 5 sectional tank store potable water?
Tricel sectional tanks are Regulation 4(1)a approved for potable cold water storage where specified. Potable compliance depends on the full specification – fittings, insulation, access and maintenance – and stored water should stay below 20°C. State potable duty at quotation stage.
What information is needed for a quotation?
The confirmed fluid category, required capacity, location, footprint and headroom (including the raised housing), access route, mains diameter, potable or non-potable duty, insulation and any drawings. Contact +44 (0)1934 421 499 or websales@tricelwater.co.uk.
Tricel Water UK - UK GRP Tank Manufacturer
Need a Category 5 sectional break tank for your project?
Send the confirmed fluid category, required capacity and plant room constraints. Tricel will advise on configuration, AB air gap arrangement and documentation.
This product guide is provided for general guidance and information purposes only. It does not constitute engineering advice and should not be relied upon as the sole basis for design decisions. © 2026 Tricel Water. All rights reserved.
