How to Identify Your Pump’s Mechanical Seal (NZ)

Why is my pump leaking water underneath?

A pump leaking water from underneath, at the join between the wet end and the motor, almost always has a failed mechanical seal. The mechanical seal is the spring-loaded pair of polished faces (typically a rotating carbon face against a stationary ceramic seat) that stops water travelling along the spinning shaft and into the motor. The tell-tale signs are a steady drip or puddle under the pump body while it runs, rusty streaks radiating from the shaft, white crusty mineral deposits around the seal housing, or water inside the motor’s fan cowl. A leak from a hose fitting, barrel union or housing O-ring is a different fault, so wipe everything dry and run the pump briefly to confirm where the water first appears. A leaking seal never heals itself, and every hour it runs pushes water towards the motor bearings, turning an inexpensive seal into a dead motor.

Mechanical seal, shaft seal, pump seal, water seal: on a centrifugal pump these all name the same assembly, sitting on the shaft behind the impeller.

How do you identify a pump mechanical seal in 5 steps?

To identify a pump’s mechanical seal, work through five facts in order: pump make and model, shaft diameter, seal dimensions, face materials, and the OEM part number. The fastest route is the OEM number: Onga, Davey, Waterco, Astral and DAB all publish seal part numbers such as Onga 702789, Davey 48802SP or Astral 75508, and a stockist can cross-reference those directly. If there’s no number to be found, measure the shaft with vernier callipers: Australasian-built pumps (Onga, Davey, Waterco) mostly use imperial shafts of 3/8″, 1/2″, 5/8″, 3/4″ or 1″, while European brands (DAB, Grundfos, Pedrollo, Lowara) use metric shafts of 12-18 mm. Note the face materials too; carbon/ceramic is the standard pairing, silicon carbide the heavy-duty one, and confirm everything against the old seal in your hand, because two seals for the same shaft size can still differ in seat diameter and working length.

In practice:

1. Find the model. It’s on the motor nameplate (e.g. Davey Prime Jet, Onga Homemaster HM150).
2. Look up the OEM seal number. Owner’s manuals and exploded parts diagrams list it: Davey seal numbers usually end in “SP” (48800SP, 48802SP, 49771SP), though older ones like 47863 don’t; Onga’s are six-digit numbers starting 70 (700270, 702789).
3. Measure the shaft. Pull the old seal off and measure the shaft where it sits. Be precise: 12 mm and 1/2″ (12.7 mm) are different seals, and the 0.7 mm matters.
4. Measure the old seal. Outside diameter of the rotating head, the seat diameter, and overall length. Two seals for the same shaft can differ in all three, so keep the old seal until the new one is confirmed. Where a documented cross exists, use it. Our Waterco Hydrostorm/Supatuf/Aquamite seal, for example, replaces Waterco part 6340162 on a 3/4″ shaft.
5. Check the faces. A dull dark-grey rotating face is carbon; a white or pale-grey seat is ceramic; a mirror-hard gunmetal pairing is silicon carbide.

What shaft sizes do NZ pumps use?

The pattern: pumps designed in Australasia use imperial shafts; pumps designed in Europe use metric. Across the seals we stock, the spread looks like this:

Shaft size	System	Typical pumps	Seal
3/8″ (9.5 mm)	Imperial	Onga Homemaster HM10-HM150, HJ pressure pumps	PSL-130
1/2″ (12.7 mm)	Imperial	Onga LeisureTime LTP400-LTP750, Davey X-series jet and spa pumps	PSL-110
5/8″ (15.9 mm)	Imperial	Davey Prime Jet 90-150, engine-drive pumps	PSL-115 (Davey 48801SP)
5/8″ (15.9 mm)	Imperial	Davey HS50/HS60, Silensor	PSL-140 (Davey 49771SP)
5/8″ (15.9 mm)	Imperial	Davey Dynaflo	PSL-155 (Davey 47863)
3/4″ (19.1 mm)	Imperial	Onga/Astral CTX and Poolrite pool pumps, Onga LTP1100	PSL-120
3/4″ (19.1 mm)	Imperial	Waterco Hydrostorm, Supatuf, Aquamite	PSL-150
1″ (25.4 mm)	Imperial	Onga 185, Davey Mukmova and Prime Jet 200-240	PSL-125
12 mm	Metric	DAB/Pedrollo/Pentax small jets	PSL-160
12 mm	Metric	Grundfos JP5/JP6, Lowara, Saer	PSL-170
13 mm	Metric	DAB Jet and Jetinox, Grundfos JPF2/JPF3	PSL-165
15 mm	Metric	DAB K-series, Grundfos JPF4-7, Ebara pressure and farm pumps	PSL-175
16 mm	Metric	Davey PowerMaster, Power Ace, Power Chief CR (the Davey exception)	PSL-180
17-18 mm	Metric	Larger DAB jet and centrifugal pumps; Davies and Pedrollo	PSL-185

Some seals have no OEM cross-reference at all: the 12 mm seal for Grundfos JP5/JP6, Lowara and Saer pressure pumps is matched purely on shaft size and dimensions, which is why step 3 matters.

Which OEM part numbers cross to which seal?

If you have a part number from a manual or parts diagram, this table crosses the documented OEM references to the seals we stock:

OEM part number(s)	Typical pumps	Shaft	Faces	SKU
Onga 702789, Davey 48802SP	Onga LeisureTime LTP400-750, Davey X-series (pool & spa)	1/2″	Carbon / Ceramic	PSL-110
Davey 48801SP	Davey Prime Jet 90-150, engine-drive, Poolrite Dominator	5/8″	Carbon / Ceramic	PSL-115
Onga 700270, Astral 75508	Onga/Hurlcon/Astral CTX, Poolrite	3/4″	Carbon / Ceramic	PSL-120
Onga 700274, Davey 48800SP	Onga 185, Davey Mukmova, Prime Jet 200-240	1″	Carbon / Ceramic	PSL-125
Onga 700273K	Onga Homemaster HM10-HM150, HJ	3/8″	Carbon / Ceramic	PSL-130
Davey 49771SP	Davey HS50/HS60, Silensor, ProMaster	5/8″	Carbon / Ceramic	PSL-140
Waterco 6340162	Waterco Hydrostorm, Supatuf, Aquamite	3/4″	Carbon / Ceramic	PSL-150
Davey 47863	Davey Dynaflo	5/8″	-	PSL-155
DAB 61M/16	DAB Jet/Jetinox, Grundfos JPF2/3, Davies	13 mm	Carbon / Ceramic	PSL-165
DAB 100M/16	DAB K-series, Grundfos JPF4-7, Ebara	15 mm	Carbon / Ceramic	PSL-175
Davey 49021, 49021SP	Davey PowerMaster, Power Ace, Power Chief CR	16 mm	SiC / SiC	PSL-180
DAB 200M/6	DAB Jet 200/300, Davies, Pedrollo	17-18 mm	Carbon / Ceramic	PSL-185

Treat the table as a cross-reference starting point, not a fitment guarantee. Manufacturers change seals between production runs, so always confirm shaft size and seal dimensions against the part you removed. For pool pumps, two documented crosses are the 3/4″ Onga 700270 / Astral 75508 seal and the 5/8″ Davey Dynaflo seal (47863); for Prime Jet 90-150 pressure pumps and engine-drive firefighter pumps it’s the 5/8″ Davey 48801SP.

Should you replace the bearings at the same time?

If the seal has been leaking for a while, yes, the escaping water runs straight into the front motor bearing, and a rumbling pump after a seal leak is usually that bearing dying. Most pool pump motors use standard sealed, pre-greased deep-groove ball bearings, and a bearing kit for the Onga Pantera and LeisureTime LTP1100 is NZ$68.95 with both bearings in the bag.

The test: with power isolated, spin the motor shaft by hand and rock it side to side. Grinding or sideways play means the bearings go in the same session. The pump is already apart.

Can you fit a mechanical seal yourself?

Mostly, yes. Replacing a mechanical seal is a mechanical job, not electrical work. On a typical NZ pump you isolate the power, undo the through-bolts or barrel nuts joining the wet end to the motor, unscrew the impeller off the shaft (hold the shaft at the fan end), and the two seal halves lift out. If your pump plugs into a socket, unplugging it is all the isolation you need. If it’s hardwired (most pool pumps are) switch it off at the breaker before you start, and leave the wiring itself alone. If you’re not confident working on mains equipment, have a registered electrician do it.

Three rules make the difference between a seal that lasts years and one that fails in a week:

1. Never touch the polished faces. Skin oil is enough to make a carbon/ceramic pairing leak. Handle the seal by its edges.
2. Lubricate rubber parts with soapy water only. Petroleum grease swells the elastomer bellows and seats.
3. Never run the pump dry. The faces are water-lubricated; even 30 seconds dry can wreck a new seal. Fill the pump before restarting.

While the motor end is open, check the run capacitor for bulging or leaking oil. A pump weeping water over its motor often takes the capacitor with it.

Frequently asked questions

How much does a pump mechanical seal cost in NZ?

The mechanical seals we stock run from NZ$91.95 to NZ$103.95 depending on shaft size and face materials, and our motor bearing kits are NZ$68.95. Tracked NZ delivery: each product page shows the delivery time for that part. Browse the full range of seals and bearing kits in the shop.

Can I keep running a pump with a leaking seal?

Not for long. The leak only travels one way, along the shaft into the front motor bearing, and a rusted bearing or flooded winding costs far more than the seal. Fix it when you first see the drip.

Are pump mechanical seals universal?

No. Seals differ by shaft diameter (3/8″ to 1″, or 12-18 mm), seat diameter, working length and face materials, and a 12 mm seal will not seal on a 1/2″ (12.7 mm) shaft. Always match dimensions or a documented OEM number off your own pump.

What’s the difference between carbon/ceramic and silicon carbide faces?

Carbon/ceramic is the standard pairing on domestic pool and pressure pumps. Silicon carbide on silicon carbide is much harder and handles heat, grit and heavy duty better: that’s why the Davey PowerMaster range uses an SiC/SiC seal (Davey 49021).

Why did my new mechanical seal fail within weeks?

Dry running is the usual cause: the faces are water-lubricated and burn in seconds without it. The other culprits are fingerprints on the faces during fitting and petroleum grease on the rubber parts. Fit it clean, lube with soapy water, prime the pump, and it should last years.

Do you stock a seal for my exact pump model?

We stock mechanical seals across the ten shaft sizes above, plus motor bearing kits for common Onga and AstralPool pool pumps, covering the Onga, Davey, Waterco, Astral, DAB and Grundfos fitments in the tables. We can’t guarantee fitment from a model name alone (pumps get revised), so check the OEM number or shaft size against your old seal first, and send us your measurements via the contact page if it’s not in the table.