Anti-Backbend Chains for Pushing Window

Anti-backbend-chains-for-pushing-window-1

EP-06BF, EP-08BF, EP-415BF, EP-P12.7F, EP-08BF208, and EP-16AF push chain series. Rigid in the push direction, flexible in the pull direction. Pitch 9.525 mm to 25.400 mm. For automatic window actuators, skylight drives, louvre systems, and architectural ventilation controls.

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9 Models

06BF / 08BF / 415BF / 16AF

9.525 to 25.4mm

Pitch Range

Push and Retract

Rigid Push / Flexible Pull

ISO 9001

Certified Quality

Anti-Backbend Push Chain - Product Overview

Ever-Power anti-backbend chains for pushing window are a specialised family of roller chains designed to transmit both push and pull forces along the chain axis without buckling. A conventional roller chain is fully flexible in both directions - it can be pulled under tension but will buckle immediately if a compressive (push) force is applied. An anti-backbend chain is engineered with extended outer link plates and an interlocking plate geometry that prevents the chain from bending backward beyond the straight position, effectively turning the chain into a rigid push rod when loaded in compression while retaining normal articulation in the pulling direction.

The anti-backbend function is achieved through the plate geometry. The outer link plates in the EP push chain range are formed with a stepped or extended profile that bears against the adjacent inner link plates when the chain is in the straight (tensioned or compressed) configuration. This contact between plates prevents back-articulation - the chain cannot bend in the direction that would be compressive buckling. As the chain is fed out from the sprocket in the push direction, the interlocked plates form a rigid column capable of transmitting the compressive load through the chain length to the driven component. When the chain is retracted, the plates separate and the chain becomes fully flexible again, allowing it to coil or store in a compact magazine behind the sprocket.

The primary application of EP anti-backbend push chains is in window actuator systems - automatic openers for roof lights, skylights, clerestory windows, industrial ventilation louvres, smoke control ventilators, and architectural glazing systems. In these applications, the window actuator motor drives a sprocket that feeds the chain out through a guide tube to push the window open, then retracts the chain to pull the window closed. The chain must be rigid enough in the push direction to push the window open against its own weight, wind pressure, and any sealing resistance, while flexible enough in the pull direction to store compactly in the actuator housing.

The EP range covers nine models from EP-06BF34 at 9.525 mm pitch through EP-16AF101 at 25.400 mm pitch. Models marked with an asterisk (*) are bush chains - the d1 dimension in the specification table is the external diameter of the bush rather than an outer roller. The H and h dimensions in the specification table describe the outer link plate profile: H is the overall plate height (including the anti-backbend extension plate) and h is the standard plate depth within the chain height, both of which affect the guide tube or channel dimensions required to support the chain in service.

 

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Dimension key: P = Pitch (mm)  |  d1 max = Roller dia. max (bush chain: external bush dia.)  |  b1 min = Inner width between plates min  |  d2 max = Pin dia. max  |  L max = Pin length max  |  H max = Overall plate height max (outer anti-backbend plate profile)  |  h max = Standard plate depth max  |  t/T max = Inner/outer plate thickness max  |  Q min = Min. tensile strength kN/lbf  |  q = Weight kg/m  |  * = Bush chain (d1 is external bush diameter)

Ever-Power anti-backbend push chain for window actuator EP-06BF EP-08BF series

Anti-Backbend Push Chain Specifications

All dimensions in mm. Models marked * are bush chains. Q min = minimum tensile strength; q = weight per metre. H and h are plate dimension columns from the specification drawing (H = overall plate height, h = inner plate depth).

EP Model P (mm) d1 max (mm) b1 min (mm) d2 max (mm) L max (mm) H max (mm) h max (mm) t/T max (mm) Q min (kN/lbf) q (kg/m)
EP-06BF34 9.525 6.35 3.80 3.28 10.00 12.38 7.88 1.04 7.0/1574 0.47
EP-*06CF22 9.525 5.08 4.77 3.58 11.60 12.86 8.38 1.30 7.9/1776 0.51
EP-*06CF30 9.525 5.08 4.77 3.58 13.90 13.05 8.55 2.03/1.25 7.9/1776 0.71
EP-*P9.525F1 9.525 5.08 4.77 3.58 11.60 13.00 8.55 1.30 7.9/1776 0.57
EP-08BF6 12.700 7.95 7.85 3.96 16.60 17.00 11.00 1.50 13.8/3102 0.91
EP-415BF4 12.700 7.75 4.88 4.09 16.40 17.00 11.00 1.3/3.1 12.0/2698 1.07
EP-P12.7F4 12.700 7.50 5.50 4.45 15.60 14.30 8.50 2.03 15.0/3372 0.99
EP-08BF20 12.700 8.51 7.75 4.45 16.70 16.50 10.50 1.60 18.0/4046 1.04
EP-08BF208 12.700 8.51 7.75 4.45 17.00 16.50 10.50 1.60 10.0/2248 1.06
EP-16AF101 25.400 15.88 15.75 7.92 32.70 26.90 14.80 3.25 56.7/12746 3.45

Anti-Backbend Push Chain - Key Technical Features

Anti-Backbend Plate Geometry

The extended outer link plates bear against adjacent inner link plates when the chain is in the straight configuration, blocking back-articulation and preventing compressive buckling. The chain is fully rigid in the push direction and normally flexible in the pull direction. This dual behaviour - rigid rod when pushed, flexible chain when pulled - enables a single chain to both push a load open and pull it closed from the same actuator without a separate push mechanism.

Compact Storage in Retracted Position

When the window actuator retracts the chain, normal chain articulation resumes and the chain folds compactly into the actuator magazine or storage channel behind the drive sprocket. The actuator housing can be significantly shorter than the maximum window opening stroke, because the chain stores in a folded configuration rather than remaining extended. The EP-06BF34 at 9.525 mm pitch and the EP-08BF6 at 12.700 mm pitch are the most common sizes for compact residential and light commercial window actuators.

Guide Channel and Tube Compatibility

EP anti-backbend chains are designed to operate within a guide channel or tube that supports the chain along its push length, preventing lateral buckling under high compressive loads. The H and h dimensions in the specification table are the key parameters for sizing the guide channel cross-section. H gives the overall chain height including the anti-backbend plate extension, and h gives the inner plate depth. The guide channel bore must clear H on the chain height axis and b1 (plus pin protrusion) on the chain width axis to allow smooth travel without binding.

Bush Chain Variants

Models marked * - EP-*06CF22, EP-*06CF30, and EP-*P9.525F1 - are bush chain (sleeve chain) variants where no separate outer roller is fitted. The d1 dimension for these models is the external diameter of the bush, not an outer roller. Bush chain variants are lighter than roller chain equivalents at the same pitch and are used where roller wear from sprocket engagement is not a concern due to the low cycle count of typical window actuator applications. The absence of the outer roller also reduces the overall chain height slightly.

Low Maintenance - Low Cycle Application

Window actuator push chains operate at very low cycle rates - typically 1 to 10 open-close operations per day - and at very low speeds (0.01 to 0.1 m/s chain speed). These characteristics mean that lubrication requirements are minimal and chain wear is negligible under normal operating conditions. The EP push chain range is supplied pre-lubricated and requires no additional lubrication for normal building ventilation applications. For industrial applications with higher cycle rates, periodic light mineral oil application to the joint areas is recommended.

Corrosion Resistant Options

Window actuator chains are frequently installed in humid, coastal, or chemically challenging environments - pool enclosures, conservatories, marine buildings, and industrial facilities with chemical atmospheres. EP push chains in the 06BF and 08BF series are available in stainless steel (SUS304 or SUS316L) on request for these environments. Nickel-plated carbon steel variants are also available for moderate corrosion resistance at lower cost. Please specify the required surface treatment or material grade when requesting a quotation.

Applications

Roof Lights, Skylights and Clerestory Windows

EP-06BF34, EP-*06CF22, and EP-08BF6 push chains are the standard specification for motorised roof light and skylight actuators in residential, commercial, and institutional buildings. The actuator is typically mounted at the hinge end of the roof light, and the chain pushes along the frame profile to open the glazed panel against gravity and wind pressure. The compact folded storage of the retracted chain allows slim actuator housings that suit the narrow frame profiles of modern roof light systems.

Smoke Ventilation and Fire Safety Systems

Automatic smoke ventilators and fire-triggered vent opening systems use EP push chains in the 08BF and P12.7F series for their higher tensile strength and push force rating. In smoke ventilation applications, the actuator must hold the vent reliably closed against wind uplift during normal conditions, then open it rapidly and hold it fully open against wind load during a fire event. The anti-backbend locking geometry provides the structural rigidity needed to maintain the open position under lateral wind loading without requiring a separate mechanical hold-open device.

Industrial Ventilation and Louvre Actuators

EP-08BF20, EP-P12.7F4, and EP-16AF101 chains for industrial building ventilation louvre drives, agricultural building vent panels, greenhouse ridge vent openers, and large-format motorised windows in factories and warehouses. The EP-16AF101 at 25.4 mm pitch with 56.7 kN minimum tensile strength is the choice for high-force industrial actuator applications where the window or louvre area is large, wind loading is significant, or multiple vents must be driven from a single chain circuit.

Ever-Power anti-backbend push chain production and assembly

Matching Sprockets and Other Chain Types

Ever-Power sprockets and chain wheels for anti-backbend push chains

Matched drive sprockets for EP anti-backbend push chains, including actuator-grade pinion gears and sprocket-shaft assemblies, are available through our partner site sprocket-chain.net.

View Matching Sprockets →

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Frequently Asked Questions

How does an anti-backbend chain transmit a push force without buckling?
A standard roller chain buckles immediately under any compressive load because the joints are free to articulate in both directions. An anti-backbend chain is prevented from bending in the reverse (back) direction by the geometry of the outer link plates, which are extended or stepped so that they physically bear against the inner link plates at the straight configuration. When a compressive load is applied - the motor pushes the chain - the chain cannot bend backward and instead transmits the compressive force along the chain length as a rigid column. The guide channel or tube surrounding the chain provides lateral support to prevent the chain from buckling sideways under load, completing the push force transmission path to the driven window or louvre.
What guide channel dimensions do I need for a specific chain?
The guide channel cross-section must clear the full chain profile. The minimum channel height clearance is the H max dimension from the specification table plus 0.5 mm running clearance on each side (H max + 1.0 mm total height). The minimum channel width clearance is the pin length L max plus 0.5 mm running clearance on each side (L max + 1.0 mm total width). For example, EP-08BF6 has H max 17.00 mm and L max 16.60 mm, requiring a channel of at least 18.0 mm height by 17.6 mm width. For applications with significant chain speed or vibration, increase the clearance to 1.0 mm on each side. The channel must be smooth-bore on the inner surfaces and straight along the push axis - any bow in the channel will cause the chain to bind under compressive load.
What is the maximum push force a given chain can transmit?
The maximum push force is limited by the column buckling strength of the chain-in-guide system, not by the chain tensile strength. The column strength depends on the unsupported length of chain between the guide exit point and the load point (the window frame), the chain cross-section stiffness, and the end conditions. For most window actuator applications the unsupported length is very short (less than 50 mm) and the guide exit is close to the window frame, so the column strength is very high relative to the required push force. If the unsupported length is longer, a chain with a larger H dimension (taller plate profile) should be used as it has greater section stiffness. Contact EP with your actuator geometry and required push force for a recommendation.
Can EP supply chains to match existing actuator OEM specifications?
Yes. The models in the specification table cover the most widely used anti-backbend chain specifications in the window actuator industry. For actuators from major OEM manufacturers such as Sommer, Geze, Tormax, Raico, and others, please supply the existing chain designation or a chain sample so EP can verify the dimensional match. Key dimensions to verify are pitch, roller or bush diameter, inner width (b1), pin diameter (d2), pin length (L), and overall plate height (H). EP can also produce custom anti-backbend chain configurations outside the standard table if the required quantity justifies a tooling investment - minimum order for custom configurations is typically 200 metres.
What is the difference between EP-08BF20 and EP-08BF208?
Both EP-08BF20 and EP-08BF208 share the same pitch (12.700 mm), roller diameter (8.51 mm), inner width (7.75 mm), pin diameter (4.45 mm), and plate height dimensions. The difference is the minimum tensile strength: EP-08BF20 is rated at 18.0 kN/4046 lbf and EP-08BF208 is rated at 10.0 kN/2248 lbf. This reflects a difference in plate thickness or plate material treatment between the two models. EP-08BF208 is specified for lower-load applications or for actuators where the original design uses a lighter plate specification. EP-08BF20 is the higher-strength option for applications requiring greater push and pull force capacity. The pin length of EP-08BF208 (17.00 mm) is also slightly longer than EP-08BF20 (16.70 mm), which affects guide channel width sizing.
What length should I order and how is the chain stored?
The required chain length is the full push stroke of the actuator plus the storage length in the magazine plus the wrap around the drive sprocket plus a short tail for the chain anchor point. In practice, the actuator manufacturer specifies the chain length for their product as part of the system design - for OEM actuator replacement chains, simply order the length specified in the actuator service documentation. For new actuator designs, add approximately 20% to the maximum opening stroke to allow for sprocket wrap and storage tail. The chain stores in the magazine by normal chain articulation - the retracted chain folds back on itself at the sprocket exit with a bend radius equal to approximately 3 to 4 times the chain pitch, so the magazine depth must be at least this distance from the sprocket centreline.

What Our Customers Say

★★★★★

"We manufacture electric window actuators for commercial and institutional buildings. EP-08BF6 chains are now our standard specification for mid-range actuators. The dimensional consistency batch to batch is excellent - our assembly line runs with zero fit adjustments. We have shipped over 3,000 actuator units using EP chains in the last 18 months with no field failures attributable to chain quality."

A.M., Production Manager
Poland - Window Actuator Manufacturer

★★★★★

"We specify EP-16AF101 for our heavy industrial ventilation louvre drives on factory buildings. The 56 kN tensile rating gives us comfortable safety margin for large louvre panels in high-wind locations. The chain has been running on a coastal cement works installation for 4 years with minimal wear. We apply light oil at the annual service visit and nothing more."

T.O., Technical Director
UK - Industrial Ventilation Specialist

★★★★★

"EP-*06CF30 chains for our compact roof light actuators. The bush chain variant allows a slimmer guide channel than a roller chain equivalent, which is important for our slim-profile product line. EP verified the chain against our sample within 2 working days and delivered 500 metres of cut-to-length chains within the week. Exactly what we needed for a product launch deadline."

S.L., Design Engineer
Denmark - Roof Light Manufacturer

★★★★★

"We supply smoke ventilator replacement chains to the UK market. EP-08BF20 covers the majority of the field installations we encounter. The chains arrive clearly labelled with batch and dimensional data on the delivery documentation, which our service engineers need for job records. A reliable supplier for a critical life safety application."

R.P., Operations Director
UK - Smoke Ventilation Service Company

Request a Quotation for EP Anti-Backbend Push Chains

Provide the EP chain model from the specification table, the quantity in metres, and whether pre-cut lengths with connecting links are required. For OEM actuator replacement, supply the actuator brand and model or a sample of the existing chain. Stainless steel and nickel-plated variants available on request. Our team responds within one business day.

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