Repeating Ceramic Seal Failures

[Jimmy_from_NZ]

Hi all,

Long time reader, sporadic poster. I run a pool shop in New Zealand and am having a problem that I have never come across before... Maybe someone might have some advice and can point me in the right direction?

Part of our work is that we do pump warranty work for a NZ based pump manufacturer. About 4 weeks ago we got a service job to replace a leaking ceramic seal on a pump. The pump is a 1HP Power Plus (a local NZ Brand) and is installed on a concrete plaster pool that is 5 months old. A fairly standard job, we expected perhaps the pump had been run dry. However when we visited site the water was flowing well with no obvious heat damage to the plastic internals or motor. The pump is installed on a 36,000L pool. 1x Skimmer and 1x Drain line both run in 50mm pipe to the front of the pump. Distance between the pool and pump pad is 11m. The pump feeds into a 650mm (25") sand filter, to a Rainbow 320 Tri-Chlor feeder and then back to the pool via 3 return jets. Very standard. Note: the pool was not installed by us, we are just contracted to fix the leaking pump. I personally wouldn't have installed the Tri-Chlor feeder, we steer people away from stabilized chlorine.

We replaced the ceramic seal, reinstalled and tested. Everything ran fine. 3 days later it started leaking again. Very unusual we thought, because we replace a lot of these seals and it's rare that one fails after a few days, but maybe we stuffed up something.

Over the last 4 weeks we have replaced 3 ceramic seals into the original pump. We have swapped out the original pump for a different unit of the same model. We then switched out that pump for a different brand pump, which also leaked after about 3 days. We have now installed a WaterCo 1.0HP which also leaked after 3 days. So this is not an issue with the quality of the ceramic seals, or the installation of them. Some other factor must be causing the seals to fail, but what?

Water/ chemical imbalance? We have been testing the water regularly as part of trying to solve this issue. Most recent test results:
FC: 5.5ppm
TC: 5.8ppm
pH: 7.42
CY: 32ppm
Alk: 75ppm
CH: 380ppm
Temp: 19 deg C
System Pressure 80kpa / 11.25PSI

Nothing in that seems to shout out at me as abnormal. Could the Tri-Chlor feeder be leaking concentrated chlorine backwards to the pump housing while the system is turned off? It seems unlikely to me because the pump holds it's prime very well when turned off, so there is no reverse flow of water through the system. The only time the system loses prime is when the Tri-Chlor feeder is opened once a week by the home owner. The system fully primes back up within 30-40 seconds.

Vibration? The pump is in a wooden pump shed housing all the equipment. Plenty of air flow. The PVC pipes are neatly screwed with clips to the inside of the shed, so perhaps the vibration of water flow through the pipe is transferring through the wooden floor into the motor, causing the shaft to wobble or something? But this style of installation is not unusual here so if this were true I would have thought it a more regular occurring problem. To be sure we have installed a rubber pad under the pump to reduce any vibration through the wooden base.

So I'm a bit lost at what other causes there could be, considering I have ruled out the issue as being isolated to a particular pump or pump brand.

Could there be a bonding issue? I don't see how that would affect the ceramic seal?
A water hammer issue? The pump doesn't seem oversized for the system and 2" pipe throughout. I could install a flow meter to get more accurate readings if that would help?

Any ideas/suggestions on what to look for or test for would be very much appreciated!

Love the forum, especially the build threads

 

[CJadamec]

You've done your home work to rule out pump housing and seal supplier issues. Excess chlorine shouldn't affect the carbon or ceramic. Maybe the rubber but that doesn't sound likely. If you have one of the failed seals around inspect the faces and look for pitting and cracking. There maybe ultrafine suspended solids in the water ruining the seal faces. I wouldn't think pump vibration would be an issue as the housing and motor are bolted together. Any chance they have a DE filter.

 

[Jimmy_from_NZ]

Hopefully that picture attaches.

Thanks CJadamec, I've just opened the most recent leaking pump up, and yes there is considerable wearing. Perhaps you are right and there is fine debris getting between the carbon and ceramic faces? The filter is just using plain filter sand.

The water itself is visually very clear. I could try using some skimmer socks and a coagulant to bond the particulates together?

 

[CJadamec]

Did you change out the motor when you swapped pumps? Or was it just the pump bodies. From the picture it looks like the wear on the carbon face is located just in one area. A motor bearing issue could be causing a misalignment. If you changed the motors when you changed the pump heads double check the pump base to make sure its supported and flat and nothing has broken underneath. Has the pool owner done anything recently before the first seal failure that was out of the ordinary? Like changed chemicals or any other service or repairs? When mechanical seals fail the wear pattern on the seal is a good place to start looking to figure out why they failed.

 

[Bama Rambler]

It's really strange that they've all leaked around 3 days. The wear in the picture above looks like the seal faces are separating allowing debris between them.

When the pump is running is the pressure steady? Is the needle on the gauge bouncing around?

 

[JamesW]

I would suspect that something abrasive is in the water. Perhaps quartz aggregate dust from the plaster being vacuumed up. Try using a filter before the pump to catch debris for inspection.

Put a skimmer sock in while vacuuming to catch debris.

Other than that, maybe there's some reason that the pump is intermittently running dry. Perhaps a sticky weir.