Submersible Pump

medium 138 / 138 models (Inspector)

A submersible pump has its motor sealed inside the same housing as the impeller and runs fully immersed in the liquid it moves, avoiding the shaft seal a dry-mounted pump depends on, but making the motor itself the point that fails if the seal lets water in.

Read more — Submersible Pump explained ▾

What defines this type

A submersible pump combines the motor and the pump end in one sealed unit designed to operate fully underwater, unlike a conventional dry-mounted centrifugal pump that sits above or beside the liquid with a shaft seal or gland keeping the liquid out of a dry motor. Because the motor itself is submerged, the design eliminates the mechanical seal as the usual failure point but shifts the risk to the motor's own watertight enclosure and cable gland. On ships this makes submersible pumps the natural choice for bilge wells, ballast tank stripping, and cargo hold or void space drainage, anywhere a dry-mounted pump would need long suction lines and priming.

Submersible pump cross-section — Section through a submersible pump standing in the sump liquid, showing the sealed motor housing, the shaft and mechanical seal down to the impeller in its volute casing, the inlet strainer below and the discharge outlet and sealed cable entry above.

Main components

Sealed motor housing with a double mechanical seal arrangement between the motor cavity and the pumped liquid, often with an oil-filled barrier chamber and a moisture sensor
Impeller and volute at the base of the unit, in vortex, semi-open or channel design depending on how much solids the liquid carries
Cable entry gland, one of the most common failure points, sealing the power cable where it enters the motor housing
Float switch or level sensor for automatic start/stop, common on bilge and drainage duty
Guide rail or portable base, letting the pump be lowered into or lifted out of a well without disturbing the discharge piping on fixed installations

Selection and sizing

Duty point: flow rate and total head including static lift out of the well or tank
Solids-handling capability if the liquid carries debris, sludge or fibrous material, which calls for a vortex or channel impeller rather than a closed impeller
Motor insulation class and moisture-sensor protection appropriate to continuous submerged duty, not intermittent dry-well use
Materials of construction against the liquid's corrosivity, particularly for bilge water carrying oil residue or ballast water with high chloride content
Portable versus fixed installation, since a fixed unit on guide rails needs matched coupling hardware in the well

Regulations and class

Bilge pumping arrangements, including submersible bilge pumps, fall under SOLAS Chapter II-1 requirements for bilge pumping systems and the number and capacity of pumps required by ship size and type. MARPOL Annex I governs the discharge of bilge water, requiring oil content monitoring before any overboard discharge regardless of which pump moved it. Class societies survey the pump as part of the bilge and drainage system, checking capacity against the required rules calculation and confirming remote start arrangements where fitted for unmanned machinery space operation.

Typical faults

Fault	Cause	Consequence
Motor failure from water ingress	Cable gland seal degraded or mechanical seal worn	Complete pump loss, often with no warning if the moisture sensor is not monitored
Impeller clogged or worn	Debris, rag or solids beyond the impeller's rated clearance	Reduced flow, and on vortex designs increased vibration from imbalance
Float switch stuck	Debris or oil residue fouling the float mechanism in a bilge well	Pump fails to start on rising level, or runs dry after the level drops
Bearing failure	Running dry for extended periods, or age	Increased noise and vibration, eventually seizure

What to look for in a supplier

Moisture sensor and double mechanical seal as standard, not an optional extra, for any well the pump cannot be easily lifted from
Impeller type matched to the actual solids content of the duty, not a generic clear-water rating
Guide rail and coupling hardware compatible with the existing well if replacing rather than a new installation
Spare parts kit availability for the seal and cable gland specifically, since those are the components that actually wear

A moisture sensor alarm on a submersible pump is an early warning, not a nuisance trip, so pulling the pump for a seal check at that point is far cheaper than replacing a flooded motor.

Inspector Mode Show All 138 / 138 with inspector value

6 manufacturers · 138 models

Grindex

35 ✓ 35 verified

Micro ✓ verified

Application

Drainage - Small portable

Common Failures & Inspection Points

Area: Verify pump impeller and suction strainer for wear, erosion, or cavitation damage. Compare with baseline per operating hours.
Check: Visual inspection of impeller surface, hard-iron coating integrity, and strainer perforations. Check for pitting in hydraulic surfaces.
Area: Confirm mechanical seal integrity (silicon carbide, tungsten carbide components) for salt-water/corrosive service. Seals degrade with abrasive particle contact.
Check: Run pressure drop test across seal cavity; measure leakage rate at discharge. Inspect seal chamber for contamination ingress.
Area: Verify stator housing insulation breakdown risk in Inox models during continuous operation. Material galvanic compatibility critical in marine bilge service.
Check: Megohm meter (insulation resistance test) across motor windings to ground at 500-1000VDC. Document baseline and trending.
Area: Check cable insulation degradation and connector corrosion, especially submersed 20m+ cable runs with salt spray exposure.
Check: Visual inspect cable jacket for cracks, UV damage, moisture ingress. Measure conductor resistance and insulation resistance annually.
Area: Verify bearing lubrication adequacy under continuous high-speed operation (2760+ RPM small models). Oil degradation accelerates in contaminated-water submersion
Check: Temperature monitoring of bearing housing (should not exceed 65°C). Visual inspection of oil color/clarity in accessible bearing cavities post-operation.

Typ-universelle Inspektionspunkte fuer Pumps (verifiziert, 2026-06).

Submersible Pump

What defines this type

Main components

Selection and sizing

Regulations and class

Typical faults

What to look for in a supplier

6 manufacturers · 138 models

Grindex

Tsurumi

DESMI

Hidrostal

Ebara

Grundfos Marine