Nozzle Stalled at a Bend
A municipal crew is jetting a 400-ft run of 24-in. storm drain that carries grease and roots. The jetter truck is rated 4,000 psi and 18 gpm, with 500 ft of 3/8-in. hose on a powered reel. At 150 ft, the nozzle stalls just ahead of a 90-degree bend. The operator raises pressure from 2,500 to 4,000 psi; the hose begins to pulse sharply, and the level-wind is misaligned so the hose is stacking on one side of the reel. A helper stands at the manhole edge, guiding the hose by hand and looking down the shaft. The truck's water tank is at one-quarter, and the site has no hydrant connection. The operator says he can 'power through' the bend if he holds the pressure and feeds hose.
1. Should the operator hold 4,000 psi and try to power through the bend? Analyze the decision.
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No. The truck is already at its maximum rated pressure, and the nozzle is stalled, so there is little or no forward flow to carry the jet energy away from the hose and fitting. The sharp pulsing indicates pressure spikes, likely from water hammer or intermittent blockage, and those spikes can exceed the gauge reading. A hose failure at the manhole would whip and could pull the helper into the shaft.
The water tank at one-quarter and no hydrant connection add a second constraint: if the tank runs dry, the pump will cavitate and lose the water column that helps control the hose. The correct decision is to reduce pressure, stop feeding hose, and diagnose the stall before resuming.
2. What do the stall at the bend and the hose pulsing indicate, and what immediate actions should the crew take?
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The stall suggests the nozzle has caught on a root mass, offset joint, grease plug, or the bend itself. The pulsing suggests intermittent blockage, air in the line, or the hose binding on the misaligned level-wind. The stacking on the reel can kink or crush the hose and also feed unevenly.
Immediate actions:
- Throttle down and stop the pump; relieve pressure before handling the hose.
- Pull the hose back 10-20 ft using the reel, not by hand at the manhole edge.
- Inspect the nozzle for debris and damage; clear it and, if roots are present, change to an appropriate root-cutting nozzle.
- Correct the level-wind so the hose spools evenly.
- Confirm adequate water supply before restarting; refill the tank or establish a hydrant connection.
- Restart at reduced pressure and feed slowly, keeping hands and body away from the manhole edge.
The reasoning is that a stalled nozzle plus maximum pressure converts the hose into a pressure vessel with no relief path at the far end.
3. Describe the safe setup for this manhole operation, including the helper's role.
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The setup should include barricades and warning signs around the manhole, a gas test before anyone leans over the opening, and continuous ventilation if the atmosphere is suspect. No one should enter the manhole for this work. The helper should stand back from the edge, use a hose guide or roller, and never grip the pressurized hose by hand at the opening. The reel operator should control hose feed from the truck, with two-way communication to the person at the manhole.
The water supply must be verified before the run: a one-quarter tank is insufficient for a 400-ft pull at 18 gpm, so refill or connect a hydrant. The pump relief and hose ratings should be checked, and the level-wind aligned so the hose does not stack or kink. PPE should include a face shield, hard hat, hearing protection, and gloves, but gloves do not make it acceptable to hand-guide a pressurized hose at the manhole edge.