7.2 Balling, Flushing, Poly Pigs & Cleaning-Method Selection
Key Takeaways
- Balling uses an inflatable ribbed rubber ball that spins as water passes around it, producing an annular jet at 10 to 15 ft/s that scours grease and light debris.
- Hydraulic cleaning methods create upstream head, so laterals and basements above the work must be checked before the head is raised.
- Poly pigs are foam swabs pushed by pressure through force mains, not gravity sewers, and require a launch and a recovery point.
- Cleaning-method selection depends on debris type, pipe diameter, grade, pipe condition, and available water volume — not operator preference.
7.2 Balling, Flushing, Poly Pigs & Cleaning-Method Selection
Exam Focus: The Need-to-Know Criteria lists hydraulic cleaning explicitly as balling, flushing, poly pigs, separately from jet rodding and rodding. It then lists the selection variables in the Collection System Operation area: nozzle selection, pipe size, grade, type of pipe, level of flow. Both the methods and the selection logic are testable.
Why Several Hydraulic Methods Exist
A high-velocity jetter is the default tool, but it is not always the correct one. Jetting consumes 60 to 80 gallons per minute of water, needs a truck with manhole access, and can damage a badly deteriorated pipe. Balling, flushing, and pigging solve problems that jetting solves poorly or cannot reach.
Balling
A sewer ball is an inflatable rubber sphere with helical ribs moulded into its surface, sized slightly smaller than the pipe. The ball is tethered on a cable from the downstream manhole and floated up into the line. Water is then impounded behind it in the upstream manhole.
As water forces past the ball, the helical ribs make it spin. The narrow annular gap between the ball and the pipe wall accelerates the flow to roughly 10 to 15 ft/s, and the spinning ribs direct that high-velocity sheet against the pipe wall in a scrubbing action. The operator controls the ball's downstream progress with the cable winch.
Balling excels at removing grease, sand, and light settled deposits in pipes up to about 24 inches. Its critical limitation is the head it creates upstream. Impounding water behind the ball raises the hydraulic grade line in every upstream manhole and lateral. Before raising head, the crew must:
- Identify basements, low fixtures, and service connections upstream of the work.
- Set a manhole watcher upstream to signal if the level approaches the rim or a lateral invert.
- Keep the ball cable under control so the ball can be released instantly to drop the head.
An uncontrolled ball that jams and then releases can also send a surge downstream. Balling a structurally failed pipe can push the sidewall out entirely.
Flushing
Flushing is the simplest hydraulic method: dumping a large volume of water into an upstream manhole to create a temporary high-velocity wave that carries light debris downstream to a collection point. Water comes from a flushing unit — a tank truck, a fire hydrant through a backflow-protected connection, or a stored volume released from an upstream structure.
Flushing moves only light, recently deposited solids. It will not remove compacted grease, roots, or heavy grit, and it merely relocates the debris unless a downstream manhole is bucketed or vacuumed. Its legitimate uses are dead-end mains with insufficient natural flow, post-construction cleanup, and odor suppression in low-flow lines.
Poly Pigs
A poly pig is a bullet-shaped polyurethane foam swab, sometimes with a spiral abrasive or brush wrap, that is launched into a pressurized line and pushed along by water or air. Pigging is a force main technique, not a gravity-sewer technique.
Pigging requires:
- A launch point (a launcher barrel or a removable spool) and a recovery point where the pig can be captured. A pig with nowhere to go becomes an obstruction.
- Enough differential pressure to keep the pig moving. A pig that stalls in the middle of a force main is a serious recovery problem.
- Progressive sizing. Heavily fouled mains are pigged with a soft, undersized swab first, then progressively firmer and larger pigs, to avoid packing debris into an immovable plug.
Pigging removes struvite and grease rings that reduce a force main's effective diameter, restoring capacity and lowering total dynamic head.
Scooters and Kites
- A scooter is a hinged, spring-loaded circular shield on a wheeled frame. Impounded water behind the shield drives it forward while high-velocity flow underneath scours the invert. It handles heavier debris than a ball but requires the same upstream head control.
- A kite (or bag) is a cone-shaped device that reduces the flow area and accelerates the water, used to flush lighter deposits in larger-diameter lines.
Selecting the Method
| Condition | Preferred method | Rationale |
|---|---|---|
| Grease and light grit, ≤24 in, sound pipe | Balling or high-velocity jetting | Annular scour lifts grease from the wall |
| Heavy grit, sand, gravel, large diameter | Bucket machine, then jetting | Water alone cannot transport heavy sediment |
| Roots | Mechanical cutter, then chemical foam | Hydraulic methods do not sever roots |
| Force main scale, struvite, grease ring | Poly pig | The line is pressurized and has no manhole access |
| Structurally failed or badly cracked pipe | Low-pressure jetting or no cleaning until repair | Impounded head or high-pressure jets can complete the collapse |
| Dead-end main with stagnant flow | Flushing | Restores velocity and suppresses odor |
The variables the criteria names are the deciding ones:
- Debris type — grease, grit, roots, and scale each defeat a different tool.
- Pipe diameter — nozzle and ball sizing must match; an undersized ball simply floats through.
- Grade — a flat line will not transport dislodged debris downstream, so it must be vacuumed at the receiving manhole.
- Pipe type and condition — review the CCTV record first. Vitrified clay with open joints and deteriorated brick sewers do not tolerate high impact.
- Level of flow — heavy flow limits how much additional head can safely be impounded and may require bypass pumping first.
A crew is balling an 18-inch grease-fouled sewer main. Which pre-cleaning check most directly prevents a customer basement backup?
Why is a poly pig used on a force main rather than on a gravity sewer segment?
A CCTV record shows a 60-year-old vitrified clay sewer with multiple open joints, longitudinal fractures, and one section of missing pipe wall. The line is also grease-fouled. What is the appropriate cleaning decision?