Fixed Tank Cleaning Nozzle

What makes a fixed nozzle different from portable cleaning gear

A fixed tank cleaning machine is permanently installed inside the cargo tank, plumbed to a cleaning medium supply line that runs through the deck, and driven either hydraulically, by a turbine in the water or chemical stream itself, or by a small electric motor. Because its position and throw pattern are fixed by the installation drawing, each unit only has to cover its own assigned zone of the tank's internal surface, and the tank's full set of machines is designed as a group to leave no shadowed area. This differs fundamentally from a portable machine lowered through a Butterworth hatch, which one crew member repositions between cleaning passes to reach areas a single fixed unit cannot.

Main components

Nozzle head and drive gearing

Internal gearing steps down the rotation of the jet in two planes - a slow indexing rotation and a faster jet spin - so the wash pattern covers the tank surface in a repeating, overlapping sequence rather than tracing the same path continuously.

Supply line and isolation valve

Each machine connects to a dedicated branch of the cleaning medium main, isolated by a valve on deck so individual units can be taken out of service without shutting down the whole system.

Mounting and tank penetration

The machine passes through a gas-tight deck or bulkhead fitting; the seal at this penetration is a frequent point of leakage if disturbed during tank entry work or repair.

Selection and sizing

Coverage is set by throw distance and jet pattern against tank height and internal structure (stringers, heating coils, swash bulkheads), and by the number of machines per tank needed to avoid shadow zones. Flow rate and pressure at the nozzle determine cleaning effectiveness for a given cargo residue and wash medium - hot seawater, fresh water, or a chemical cleaning agent - and must match the capacity of the ship's tank cleaning pump and heater.

Typical faults

• Worn drive gearing inside the head - the machine slows or stalls partway through its cycle, leaving an uncleaned band on the tank wall that is easy to miss during a visual check from the tank top.
• Blocked or damaged nozzle tip - cargo residue or scale reduces jet reach and pattern accuracy, shrinking effective coverage without any obvious external sign.
• Leaking deck penetration seal - cleaning medium or tank vapour passes the seal, risking contamination on deck or loss of tank gas-tightness.
• Isolation valve seized or leaking - the unit cannot be taken out of service cleanly for maintenance, or continues to pass fluid when the tank should be dry for entry.
• Incorrect indexing after reassembly - a machine rebuilt without matching the original gear timing sprays an already-covered zone twice and leaves another zone untouched.

What to look for in a supplier

• Original coverage diagrams and duty cycle data for the specific model, so a replacement machine reproduces the tank's approved shadow-free wash pattern.
• Spare gear sets and seal kits sized to the actual installed model rather than a generic equivalent.
• Materials compatible with the cargoes the tank actually carries, since chemical tankers in particular need nozzle and seal materials resistant to the specific cargo range.
• Documentation suitable for supporting the ship's tank cleaning procedure and any gas-freeing or inerting sequence tied to it.

After any repair to a fixed machine, check the indexing sequence against the original coverage diagram before relying on it - a machine that turns is not proof that it is covering the whole zone it was installed to clean.