Fiber Splicing & Installation

# Fiber Blowing

TLDR

Fiber blowing, also called jetting, installs cable into duct using high volume airflow combined with a mechanical pusher, so the cable floats along the duct instead of being dragged through it. It places long continuous runs at very low tension, which protects the cable and removes intermediate splice points. Success depends on clean, proofed, correctly sized duct.

## How Blowing Actually Moves the Cable

Compressed air is forced down the duct at high volume, and the drag of that moving air acts along the entire length of cable already inside. A drive mechanism at the head end pushes the cable in at the same time. The result is distributed force rather than a single point of pull at the far end.

That distinction is the whole advantage. A pull applies its entire load at the pulling eye and builds friction with every foot and every bend behind it. A blow spreads the force along the cable, so tension at any single point stays low even on a run measured in thousands of feet.

Because tension stays low, the cable arrives with less stress in the glass. That shows up later as cleaner traces at 1550 nm, where placement stress and tight bends reveal themselves first.

## Duct Condition Decides Whether a Blow Succeeds

Blowing needs a sealed, continuous, clean duct. Air escaping through a crack, an unsealed coupling, or a duct crushed by settlement or a later excavation kills the airflow that is doing the work, and the cable stops well short of the target.

We proof duct before we blow, not after a run stalls. That means a mandrel or proofing device pulled through to confirm inner diameter and detect obstructions and deformation, plus a pressure check where the duct system supports one. Finding a collapsed section with a mandrel costs an afternoon. Finding it with a stuck cable can cost the cable.

Debris and water are the other two enemies. Duct that has sat open collects sand and grit, and duct in a high water table collects water. Both get cleared before the cable goes in, because grit under a moving jacket abrades it and standing water changes how the cable behaves in the airstream.

## Fill Ratio, Cable Design, and Distance

There is a working window between a cable too small for the duct and one too large. Too large and there is not enough clearance for airflow to develop around it. Too small and the air passes without gripping enough jacket surface to move it. Manufacturers publish the workable ratios for their cable and duct combinations, and we place inside them.

Cable design matters as much as size. Jacket friction, stiffness, and weight per foot all change how far a cable will travel. Cables designed specifically for jetting, including microduct cable, are built to be moved by air, and they routinely outrun a general purpose cable of the same diameter in the same duct.

Route geometry sets the practical limit. A straight run with gentle sweeps goes far. A run with repeated tight bends, undulation from following grade, or several direction changes at handholes consumes the available force faster. We plan the shot from the actual route, not from a catalog distance figure.

## Setting Up Long Runs Without Adding Splice Points

The reason to blow a long run is to avoid splices. Every intermediate access point you eliminate removes a closure, a set of splices, a slack coil, and a future failure location. That is a real saving in loss budget and in maintenance exposure.

Where a run is longer than a single shot supports, the answer is not automatically a splice. Cable can be blown in one direction, figure eighted at an intermediate access point to reverse it without twisting, and blown onward in the second direction as one continuous length. An intermediate assist machine can also be staged mid route to add push where the airflow has weakened.

Figure eighting is exactly what it sounds like and it exists to manage twist. Laying the cable in a figure eight pattern instead of a coil lets it pay back out without accumulating turns that would otherwise translate into torsion in the duct. It takes ground space and it takes care, and it is far cheaper than an unplanned splice.

## When Blowing Is the Wrong Method

Short runs between adjacent structures rarely justify staging a compressor and a jetting machine. A controlled pull is faster and the tension over that distance is not a concern.

Occupied duct is the other common case. Once a duct carries an existing cable, the clearance for airflow is compromised and a blow becomes unpredictable. Pulling into the remaining space with proper lubrication is usually the controllable option.

Damaged or unverifiable duct rules out blowing entirely. If the duct cannot be proofed, the honest answer is to repair it, replace the section, or place new duct by directional drill rather than gamble a reel of cable on it. We would rather have that conversation before mobilizing a jetting crew.

## What Should Be Ready Before a Jetting Crew Arrives?

A jetting crew is most productive when the duct is ready and the access points are open. Every hour spent finding a buried handhole lid, waiting on a lane closure, or chasing down which duct in a bundle is the right one is an hour the compressor sits idle. Most of that can be settled before mobilization.

Duct records matter most. We want to know the duct size and type, how the bundle is color coded, where couplings were made, and whether the duct was proofed and plugged when it was installed. If the conduit came from an HDD bore, the bore logs and any notes about tight sections help us set realistic shot lengths before the reel is on site.

Cable and reel details complete the picture. The cable data sheet gives jacket type, diameter, and the manufacturer guidance for jetting, and the reel length tells us whether a route can be placed as one continuous length or needs a planned splice point.

- Duct size, type, and color code for each pathway in the bundle.
- Locations of handholes, vaults, and couplings along the route.
- Proofing and plugging records from duct installation, if they exist.
- Cable data sheet and actual reel lengths delivered.
- Traffic control needs at any access point in or near a travel lane.
- Permit conditions and work hour limits for the route.

## How Does Florida Heat Affect a Blow?

Heat changes how both the duct and the air behave. HDPE duct lying in direct sun on a summer afternoon gets hot, and a warm duct is softer and grips the cable jacket differently than one that is buried or shaded. Exposed duct at a handhole or a riser is where that shows first.

Compressed air brings its own heat and moisture. Compressors produce hot, humid air, and on a Florida summer day that moisture can condense inside the duct. Air is cooled and condensate is managed where the setup calls for it, because hot, wet air works against the cable and leaves water in a duct that should be dry.

Scheduling helps as much as equipment. Long shots are often started in the cooler part of the day, and afternoon storms are planned around so a duct entry is not left open in a downpour. A blow interrupted by lightning has to be restarted from a stable point, which is cheaper to plan for than to recover from.

## Key takeaways

- Fiber blowing moves cable with airflow along its whole length, so tension stays low even on long runs.
- A blow is only as good as the duct, which is why duct is proofed before a reel is staged, not after a cable stalls.
- Figure eighting at an intermediate access point lets a long route be placed as one continuous cable without adding a splice.
- Blowing is the wrong method for short runs, occupied duct, and duct that cannot be verified, where a controlled pull is the safer choice.

## Key terms

**Fiber jetting**: Another name for fiber blowing. A jetting machine pushes cable into a duct while compressed air flows along it, so drag from the moving air carries the cable forward. The force is spread along the cable instead of concentrated at a pulling eye.

**Duct proofing**: Testing a duct before cable placement by passing a mandrel or proofing device through it. Proofing confirms the inner diameter and finds obstructions, crushed sections, and deformation, and it is often paired with a pressure check to find air leaks at couplings.

**Fill ratio**: The relationship between the cable diameter and the duct inner diameter. Too large a cable leaves no room for airflow, and too small a cable lets air pass without moving it. Cable and duct manufacturers publish the workable range for their products.

**Figure eight**: A way of laying cable on the ground in a figure eight pattern at an intermediate access point. It lets the cable be reversed and placed onward in the other direction without building up twist, so a long route can stay one continuous length.

**Microduct**: Small diameter duct, often supplied in bundles inside a common jacket, designed for cable placed by air. Each microduct can hold its own cable, which lets an owner add capacity later by blowing into an empty pathway rather than building new conduit.

*Fiber blowing versus fiber pulling*

| Factor | Blowing (jetting) | Pulling |
| --- | --- | --- |
| How force is applied | Spread along the cable by airflow plus a pusher | Concentrated at the pulling grip |
| Tension on the cable | Low throughout the run | Builds with length and every bend |
| Duct requirement | Sealed, clean, proofed, correct fill ratio | Clear path, pull line, lubricant |
| Occupied duct | Usually unpredictable | Workable with care and lubrication |
| Setup | Compressor, jetting machine, sealed entry | Winch, rope, sheaves, blocks |
| Splice points on long routes | Fewer, thanks to long continuous shots | More access points between pull sections |

*Microduct bundle*

## What this means for your project

Blowing is one of the few placement choices that reduces long term cost as well as installation time. Each intermediate splice point you remove takes a closure, a set of splices, a slack coil, and a future failure location out of the network. On a long route that adds up to real savings in loss budget, material, and maintenance exposure.

The main risk is duct that was never verified. A stalled blow halfway down a route costs crew time, may cost cable, and often ends with an excavation to find the problem. Proofing the duct first, and sharing installation records with the blowing crew, turns that risk into a known repair list before the reel is staged.

For your documentation, ask for placed footage at each access point, the shots and assist locations used, and any duct condition findings. Those records tell your engineers what is in each pathway and how much spare capacity remains, which matters when the next cable goes into the same bundle.

## Related reading

- [Blowing versus pulling explainedA plain comparison of the two main cable placement methods.](https://strillacommunications.com/blog/how-fiber-blowing-differs-from-pulling)
- [Fiber pulling servicesWinch placement for short sections, vault transitions, and occupied duct.](https://strillacommunications.com/services/fiber-splicing-installation/fiber-pulling)
- [Conduit verificationProofing and testing duct before cable goes in.](https://strillacommunications.com/services/conduit-installation/conduit-verification)
- [Multi-duct and microduct installationPlacing the bundled pathways that fiber is later blown into.](https://strillacommunications.com/services/conduit-installation/multi-duct-installation)
- [HDPE conduit placementInstalling the HDPE duct most blowing work depends on.](https://strillacommunications.com/services/conduit-installation/hdpe-conduit-placement)
- [How directional drilling worksHow bored duct is installed under roads and waterways before placement.](https://strillacommunications.com/resources/guides/how-directional-drilling-works)

## What's Included

- Duct proofing with a mandrel or proofing device before any cable is placed.
- Duct cleaning and water removal where the duct has been open or holds water.
- Jetting into conventional HDPE duct and into microduct systems.
- Figure eight staging at intermediate access points to place long runs continuously.
- Intermediate assist staging where a single shot will not reach.
- Cable and duct pairing checked against manufacturer fill and distance guidance.
- Duct sealing and plugging at every entry after placement.
- Placement footage, access points used, and duct condition findings reported daily.

## Our Process

- 01 ### Duct Verification The duct is proofed end to end for inner diameter, obstructions, and deformation, and cleared of debris and water. Findings that affect the plan, including collapsed or damaged sections, are reported before a reel is staged rather than after a cable stalls in the duct.
- 02 ### Shot Planning Route length, bend count, grade changes, and access point spacing determine where each shot starts and ends and whether an intermediate assist or a figure eight reversal is required. The goal is the fewest splice points the route will support, not the shortest setup.
- 03 ### Staging and Sealing The jetting machine, compressor, and reel are set at the head end, the duct entry is sealed to the machine, and the cable head is prepared so it enters cleanly. Downstream access points are opened and protected, and traffic control is set where an access point sits in a travel way.
- 04 ### Placement and Monitoring Cable is jetted with air pressure and push force monitored throughout, and speed is watched as the tell that something has changed in the duct. A slowing run gets diagnosed rather than forced. Footage is logged as it goes so the record matches what is actually in the ground.
- 05 ### Termination of the Shot At the far end the cable is measured out for slack, coiled or figure eighted for the next shot, and protected. Duct entries are sealed and plugged, unused ducts are re-plugged, and the placed length is reconciled against the reel footage before the crew leaves the location.

## Capability Overview

| Duct types | HDPE conduit, microduct and multi microduct assemblies, existing occupied duct on verification |
| --- | --- |
| Method | High volume airflow combined with mechanical push at the head end |
| Duct verification | Mandrel or proofing device, obstruction check, water and debris removal |
| Long run technique | Figure eight reversal at intermediate access, intermediate assist machine staging |
| Fill ratio | Within the cable and duct manufacturer published working range |
| Sealing | Duct entries sealed and plugged at every access point after placement |

## Frequently Asked Questions

**How far can you blow fiber in one shot?**: Distance depends on duct condition, fill ratio, cable design, and route geometry rather than a single published figure. A straight, clean, correctly sized duct with gentle sweeps supports a much longer shot than a route with repeated bends and grade changes. We plan shots from the actual route and the manufacturer guidance for that cable and duct pairing, and we stage intermediate assist or a figure eight reversal where a single shot will not reach.

**What happens if the cable stalls partway down the duct?**: A stalling run is a symptom, so we stop and diagnose rather than raise pressure and push harder. Common causes are an air leak at a coupling, a crushed or deformed section, water or debris, or a fill ratio that is too tight for the route. Duct proofing before placement is what prevents most of this, which is why we treat proofing as part of the job rather than an optional step.

**Is blowing better than pulling?**: For long, clean, correctly sized duct, yes, because tension stays low and you can eliminate intermediate splice points. For short runs between adjacent structures, duct that already carries cable, or duct that cannot be verified, pulling with proper rigging and lubrication is the controllable choice. The method should follow the duct and the route, and we are set up to do either.

**Do you place microduct as well as blow into it?**: Yes. Microduct and multi duct assemblies can be placed by directional drill or trench as part of the same project, then proofed and jetted once they are in the ground and coupled. Handling both sides means the duct is installed by the crew that has to blow through it, which tends to produce fewer surprises at proofing time.

**Can you blow fiber into duct that has been in the ground for years?**: Often, yes, as long as it proofs clean. Older duct can collect sand, water, and debris, and it may have been damaged by later excavation or settlement. We proof it end to end, clear what can be cleared, and report any section that will not pass. If a section is collapsed or leaking air, it has to be repaired or replaced before a blow, and we would rather tell you that before the reel arrives.

**Do you need access at every handhole along the route?**: We need access at the head end, at the far end of each shot, and at any intermediate point where we stage an assist machine or a figure eight reversal. Handholes the cable simply passes through still need to be located and checked, because a damaged duct entry or an open coupling inside one can stall the blow. Lids that are buried or paved over should be found and exposed before the crew mobilizes.

**What information do you need to plan a fiber blowing job?**: Send the route drawing with handhole and vault locations, the duct size and type, and the cable data sheet with actual reel lengths. Duct installation records help a great deal, especially proofing results and bore logs if the duct was drilled. Add any traffic control and permit work hour limits. With that, we can plan shot lengths, assist points, and figure eight locations before mobilizing instead of discovering them on site.

## Related Services

- [Conduit InstallationHDPE duct, innerduct, and microduct placed by bore, trench, or plow, proofed with a mandrel, and made locatable with tracer wire and marker tape.](https://strillacommunications.com/services/conduit-installation)
- [HDPE Conduit PlacementHDPE conduit placement by directional bore, trench, or plow in Central Florida: wall rating, fused joints, controlled pull tension, and sealed, proofed runs.](https://strillacommunications.com/services/conduit-installation/hdpe-conduit-placement)
- [Conduit VerificationConduit verification in Central Florida: mandrel proofing, rodding, camera inspection, obstruction location, and a pass record before fiber goes in.](https://strillacommunications.com/services/conduit-installation/conduit-verification)
- [Multi-Duct InstallationMulti-duct and microduct installation in Central Florida: several ducts placed in one bore or trench, color coded, racked, plugged, and recorded by occupancy.](https://strillacommunications.com/services/conduit-installation/multi-duct-installation)
- [Fiber PullingFiber optic cable pulling through Florida conduit and duct. Monitored pulling tension, correct swivel and grip rigging, lubrication, and bend radius control.](https://strillacommunications.com/services/fiber-splicing-installation/fiber-pulling)

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Source: https://strillacommunications.com/services/fiber-splicing-installation/fiber-blowing