Learn how tanker crews confirm cargo pump priming before discharge, check suction and discharge lineups, use fitted priming systems, and recognise loss of suction. A cargo pump may be ready to run mechanically but still be unable to move cargo. If gas or vapour occupies the casing or suction line of a conventional centrifugal pump, its impeller may fail to establish a steady flow. Priming means ensuring that the pump and its suction path contain the liquid needed for the pump to operate.
On an oil tanker, this is part of a larger discharge preparation. The crew must also confirm the correct cargo route, a safe receiving path ashore, adequate liquid at the tank suction, and clear communication between the cargo control room (CCR), deck team, pump room where fitted, and terminal. A non-self-priming centrifugal pump requires priming before start; running a centrifugal pump without adequate liquid can damage its components.
Training scope: The sequence below explains the checks and decisions involved. Valve positions, venting arrangements, drive controls and start limits differ between ships. The vessel’s approved cargo plan, piping diagram, pump-maker instructions and safety management procedures determine the actual operating sequence.
First, identify the pump arrangement
“Cargo pump” does not describe one universal installation. A tanker may have conventional centrifugal pumps in a cargo pump room, submerged pumps inside individual cargo tanks, or another arrangement. The distinction changes how the crew prepares the pump.
| Pump arrangement | What the crew needs to establish |
|---|---|
| Pump-room centrifugal pump | Confirm that the selected tank and suction line can supply liquid to the pump and that the casing is filled or vented through its approved arrangement. |
| Submerged cargo pump | Follow its specific start and minimum-liquid-level requirements. A separate pump-room casing priming sequence may not apply. |
| Self-priming or specially equipped pump | Confirm the conditions its manufacturer requires; “self-priming” does not mean it can be started in any dry condition. |
| Pump with a vacuum or gas-extraction system | Identify whether that system assists initial priming, manages vapour during discharge, or supports final stripping. These are different functions. |
For example, a manufacturer’s automatic unloading system uses vacuum pumps to remove gas that accumulates as tank levels fall after the cargo pump has started. Its controls should not be assumed to be an initial priming procedure for every tanker.
Who does what before discharge?
The chief officer is normally responsible for planning and supervising the cargo operation. The plan identifies which tanks and lines will be used, the intended pump sequence, transfer limits, and how the ship will communicate with the terminal.
The officer at the CCR checks tank levels, valve indications, pressures, alarms and pump controls against that plan. A pumpman or designated deck crew member may verify local valve positions, line condition and equipment status, reporting findings to the CCR. An engineer or other authorised specialist assists with drive or machinery faults within their responsibility.
These roles depend on the ship’s manning and procedures. The useful principle is that a remote valve indication and a local observation should agree where both are available. No one should start the pump while the team is uncertain which tank it will draw from or where its discharge will go.
How to confirm a cargo pump is primed: the operating sequence
1. Complete the ship–shore preparations
Before pumping, the ship and terminal need an agreed transfer plan and reliable communications. Confirm the manifold connection, intended receiving line, initial transfer rate, pressure limit, emergency signals and shutdown arrangements. The International Safety Guide for Oil Tankers and Terminals, Sixth Edition (ISGOTT 6), includes ship–shore checks covering these matters, as well as supervision, spill response and tank venting.
Priming a pump does not by itself make the shore line ready. The discharge path must be confirmed before cargo flow is established.
2. Check the selected tank and suction path
At the CCR, identify the tank designated to feed the pump. Confirm that its cargo level provides the liquid supply required by the ship’s discharge procedure. Trace the route on the approved piping diagram from the tank suction, through the relevant valves and suction line, to the pump.
Check that the necessary valves are in their planned positions and that cross-connections to other tanks, incompatible cargoes or unintended destinations are secured. Compare remote indications with local checks where the procedure calls for them. Also confirm that the tank atmosphere and inert-gas arrangements, where applicable, are in the required condition for discharge. ISGOTT’s ship–shore checklist includes checks on cargo tank atmosphere and positive pressure for ships using inert gas. ocimf.org
3. Check the pump and its support systems
Review the pump’s condition and any outstanding alarms. Depending on its design, checks may include seal or gland arrangements, bearings, lubrication, drive readiness, cooling or sealing services, and the status of temperature and leakage monitoring.
Where the ship has a cargo pump room, confirm that its ventilation and gas monitoring are functioning. A request for a local visual check is not permission to enter automatically: pump rooms can contain hazardous atmospheres. Entry must follow the ship’s assessment, testing, authorisation, communications and rescue arrangements. The IMO’s revised enclosed-space recommendations explicitly address pump rooms and advise against single-person entry.
4. Establish liquid in the pump and remove trapped gas by the approved method
On a conventional non-self-priming centrifugal installation, the objective is a continuous liquid supply at the suction and a liquid-filled pump casing. Depending on the ship’s design, cargo may flood the pump from the selected tank, or a fitted, closed priming or venting arrangement may be needed to remove trapped gas. Observe the specified indication or other confirmation in the vessel’s procedure before treating the pump as ready. KSB
Do not improvise a “manual priming” method by opening a cargo line, casing or vent to the pump room or atmosphere. Use only the connections and destinations approved for that cargo system. Keep the cargo system closed where the operating procedure requires closed handling.
5. Confirm the discharge path and start conditions
Recheck the path from pump discharge to manifold and shore. The pump’s discharge valve position at start is equipment-specific: it may be controlled manually, automatically, or as part of a recirculation or minimum-flow arrangement. Follow the maker’s start sequence and the vessel’s procedure; do not apply a blanket instruction to start every cargo pump against a fully closed or fully open discharge valve.
Pump rotation direction should already have been verified after installation or relevant maintenance under an authorised procedure. It is not a reason to briefly run an unprimed pump. If rotation or drive status is in doubt, stop the preparation and have the responsible engineer investigate.
6. Start at the agreed initial rate and verify flow
Once the ship and terminal have confirmed readiness, start the pump as instructed and increase discharge gradually within the agreed limits. The CCR should look for a coherent set of indications: the expected suction and discharge pressures, stable flow, an appropriate fall in the selected tank’s level, and a corresponding quantity received ashore.
The deck and pump-room team, where assigned and safely positioned, should report leaks, abnormal noise, vibration, overheating or other unusual conditions. The CCR should also monitor the manifold pressure and confirm that the terminal is receiving cargo as expected. ISGOTT’s pre-transfer agreements provide for maximum transfer rates, maximum manifold pressure and pressure-surge controls. ocimf.org
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What does a failed prime look like?
A pump that does not establish or maintain suction may show little or unstable flow, abnormal suction pressure, fluctuating discharge pressure, unusual vibration or noise, or a pump temperature alarm. The selected tank may show no credible level change despite a running indication.
Do not keep increasing speed to “force” an uncertain pump to pick up cargo. Reduce or stop it in accordance with the ship’s procedure, inform the chief officer and terminal as necessary, and investigate the cause before another attempt.
| Possible cause | What to verify |
|---|---|
| Insufficient liquid at the selected suction | Tank level, trim, suction location and the discharge plan |
| Incorrect valve lineup | Selected tank, suction and discharge valves, and unintended cross-connections |
| Gas trapped in the casing or suction line | Approved venting or priming indication and any fitted extraction system |
| Air or vapour entering during pumping | Suction conditions, changing tank level and relevant alarms |
| No clear receiving path | Manifold and terminal line status, with ship–shore confirmation |
| Pump or drive fault | Relevant machinery alarms and checks by authorised personnel |
A falling tank level can eventually allow gas to enter the suction even when the pump started correctly. Some installed systems manage this during final discharge, but their control logic and stripping limits are specific to that equipment. The operating team must recognise when to change tanks, reduce rate or move to the ship’s planned stripping method. shinkohir.co.jp
Safety points to remember
- Keep the cargo route deliberate. Check the tank, suction, discharge and manifold as one connected path.
- Protect the pump from loss of liquid. A running indication alone does not prove that cargo is flowing.
- Maintain ship–shore communication. Rate changes, pressure concerns and shutdowns affect both sides of the manifold.
- Treat pump-room entry as a separate safety decision. Ventilation or a normal fixed-gas reading alone does not replace the ship’s entry procedure.
- Use the installed system as designed. Vacuum extraction used for late-stage unloading may serve a different purpose from pre-start priming.
- Stop and investigate abnormal indications. An uncertain prime can become equipment damage, a spill or an unsafe transfer condition.
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Frequently asked questions
Does every oil-tanker cargo pump need manual priming?
No. The required preparation depends on pump type, its position relative to the cargo, and the fitted venting or priming arrangements. Determine the pump type before using any step-by-step procedure.
Can a vacuum pump be used to prime the main cargo pump?
Only if the vessel’s installed system and operating instructions provide for that use. A vacuum pump fitted to remove vapour during final unloading should not automatically be treated as a pre-start primer.
Can the cargo pump be started briefly to check its rotation?
Do not use an unprimed cargo pump for an informal rotation check. Rotation verification belongs in the authorised equipment or post-maintenance procedure.
What is the first response if flow does not establish after starting?
Follow the ship’s stop or fault-response procedure, communicate with the cargo team and terminal, and check the tank supply, valve lineup, priming indication and pump alarms before restarting.
Final takeaway
Successful priming is confirmed by the right liquid supply, the right cargo route and a stable response when pumping begins. The chief officer’s discharge plan sets the operation; the vessel’s pump instructions set the equipment sequence. Crews should understand both before starting cargo transfer.
Reference guidance: ISGOTT 6 and its ship–shore checklists; IMO revised recommendations for entering enclosed spaces aboard ships.