Repairs & how-to
How to change a mechanical seal
A steady drip from underneath the pump, where the motor meets the wet end, is the usual sign of a worn mechanical seal. It’s a wear part, and on many pumps you can replace it yourself with a seal kit and some patience. Here’s what the job involves so you can decide whether to tackle it.
What a mechanical seal does
Where the motor shaft enters the water, a mechanical seal keeps water in and air out while letting the shaft spin. It has two very flat faces, one that spins with the shaft and one that stays put, pressed together. Over years, or after a dry run overheats them, those faces wear and it starts to weep.
Before you start
- Confirm it’s actually the seal, a drip from the motor-to-pump-body joint, not from a pipe fitting.
- Get the correct seal kit for your exact pump model.
- You’ll need basic tools and, often, a puller for the impeller.
The job in outline
- Isolate power and drain the pump.
- Separate the motor from the wet end (undo the through-bolts or housing).
- Remove the impeller to reach the seal, this often means holding the shaft and undoing a central nut or screw.
- Press out the old stationary seat and remove the rotating half.
- Clean the surfaces spotlessly. Never touch the new seal faces with bare fingers, skin oil ruins them.
- Fit the new seat and rotating half per the kit, lubricated only as the kit says.
- Reassemble in reverse, refit the impeller, prime, and test.
When to hand it to a pro
If the pump is seized, the impeller won’t budge, or you aren’t confident splitting the motor from the wet end, a pump service agent will do it quickly. And if the seal failed from a dry run, fix that cause too, or the new one will go the same way.
Safety: Isolate power and drain the pump before you start. This is mechanical work, but if the motor terminal box is opened for any reason, that part is for a licensed electrician.
Common questions
Why did my seal fail?
Age and dry running are the big two. Even a brief dry run overheats the seal faces and can ruin them, which is why priming matters so much.
Can I just tighten something to stop the leak?
No. A mechanical seal isn’t adjustable, once it weeps it’s worn and needs replacing. A weep that’s actually from a loose pipe union can just be tightened, so rule that out first.