Chiller supply pump leak, for the second time...

[YSBrewer]

Hi guys, i've got a 5 ton unit with a 1HP Scot pump that has been replaced previously when it started leaking at the rear pump seal. Now the new one is doing the same thing... Our glycol loop bypasses at 30 psi and is 1" sch. 80 PVC. It's no longer than 100' and feeds three 7bbl fv's and our HX when we're knocking out. We do have an inline strainer and I cleaned it out last time I changed out the pump. There was nothing in it to raise flags... Is it possible the pump is undersized and can't take the use?

[jimvgjr]

Hi Nate,

In addition to debris that can cause wear on the mechanical seal, another leading cause of seal failure is from "dead heading" the pump- or completely eliminating flow for an extended period that results in the pump head heating up and eventually damaging the seal. You mention having a bypass @ 30 PSI, it should be easy to confirm that with all of your tank jackets closed, the bypass is opening and that you are indeed bypassing and a "dead head" is not experienced.

You mention the "new one" is leaking too, did you completely replace the pump or just the seal? If it was just the seal that was replaced, you could have a defect with the pump housing or motor, like a bent shaft, that is causing the premature seal failure.

Good luck, if one of our customers had a second seal failure I'd replace the entire pump and have the failed pump evaluated by our pump supplier. Hope you get this resolved soon.

Thanks

Jim
Pro Refrigeration Inc.

[Starcat]

I hp

A 1 HP pump should in no way be undersized for that size of system but possibly the other direction.
Its always a necessity in my shop to have spare seal kits on hand for all pumps in the house.
Every critical system needs a back up plan, or you could be down in a bad way.
Redundancy and overlap on all critical systems.
The pumps we buy do not come set up off the shelf. You have to install the seal when they are brought into service.
Some of the tolerances right out of the book are off and also do not match how the pumps were set up in the past for seal tension.
Whatever the brand, I would become familiar with how to tear down and re-assemble the unit to get at the root of what may be going on.
Aside from the set up instructions being " off " you will often find engineering weakness in many products that you are charged to work around, because no one else will.
It definitely keeps things interesting.
Just pulling up stainless pumps from the MFG. you mentioned. They tout " long seal life."
I would also talk to one of their Engineering Techs. They can parse your system over the phone and often times get you on the right track for a soultion.
A full 30PSIG may be a high bypass for that small system. There are some others more versed in pump dynamics on the forum. Possibly they can advise on the pipe sizing and so forth.

[lhall]

I would make sure that you are actually bypassing when none of the fermenters are calling for flow. The pump may be deadheading and killing the seal. If not, look for wear or scoring on the pump housing where the seal rides. You can usually have any scoring turned down by a machine shop without having to replace the housing or backplate.

[YSBrewer]

Thanks for the input guys!

To further answer your questions. The replacement was a new pump and motor. So I have a back up when things go south. My glycol loop has a gauge at the front and back of the loop on the supply side so I will see 30 psi at the head and around 25 psi at the by-pass. It's by-passing because it cycles much less when tanks aren't calling for glycol. Although I will watch for that. I suppose I could build a manual by-pass just to be sure when we aren't cold crashing or finishing beers...

The manufacture sent new EPDM seals that are much better for low temps, although I didn't have them installed just yet because the company that rebuilt the pump this time used there own that's supposed to hold up to my conditions... We shall see! It's up and running again so let the test begin!

I would totally love to know how to break one of these pumps down! I see no way to hold the shaft while trying to get the impeller off so I took it somewhere this time. There is some tell tale marks on the end cap of the motor so I'm assuming you pry the cap out to put a wrench on the shaft to get the impeller loosened... In the future I will be doing the work myself!

[YSBrewer]

So the pump with new seals started leaking, now the other is in with new seals... That made me check my by-pass valve and it is not adjusting anymore. So what are your thoughts on just a simple ball valve cracked open as a by-pass valve? Or can you guys recommend a 3/4" by-pass valve that I can implement? My brass by-pass valve certainly didn't last long!

This is the by-pass valve i've got - 9763K12
http://www.mcmaster.com/#catalog/119/489/=n2nhof

[YSBrewer]

So far no leaks with the new upgraded seals - it's been in service for a week. Knock on wood!