Solar hot water pump failure

[MillWeld]

After 3 years my TACO 009-BF5 hot water circulator pump failed apparently because of a frozen bearing. I had the pump replaced with a stainless version but kept the old one in an attempt to repair it. The BF5 is no longer available but I can get the "cartridge" for it ($100) which is a sealed unit and has bearings within it. I'm trying to decide if it is worth buying a new cartridge. A new pump is $300. One of the windings of the motor apparently overheated and is discolored (see pic); the motor was very hot when I discovered it wasn't working so I expect the winding is still OK.

Does anyone have experience with this pump/motor? The cost of replacing it just about negates the gain I have gotten from the collector. It is an AET collector system installed by Southern Energy Management who says some pumps go out in 1.5 years and some have lasted more than 10.

 

[Raspy]

I have a lot of experience with these. They can either fail by the bearings wearing out or the windings burning out. In your case the bearings probably failed and the pump seized, causing it to just sit there and get very hot. They can survive this, but it can also toast them. They fail far more often by wearing out the bearings to where the armature rubs the inside of the cartridge and stops them. Also running dry ruins them.

The best thing is probably a whole replacement pump, if you are not sure. Another trick is to buy an iron one and use its motor and cartridge on your bronze body.

You don't mention if potable water is going through the pump or if it's a closed loop system. If it's closed loop you don't need bronze and cast iron would be the best choice. They are a lot cheaper. Also, you can often get a Grundfos pump for less.

The critical decision on changing models or brands is the head pressure required. The 009 is a very high head pump and unless you really need that feature it is a poor choice. A 008 might be a good choice or a Grundfos 2664, or 1558 three speed. Grundfos pumps are not necessarily better, but sometimes make sense, and they bolt right in. I used to use a lot of them, but then switched to Taco. Now I use a lot of both.

If you give some more information about your system, I can help further.

 

[MillWeld]

Thanks for the info, Raspy. The pump is used for a closed loop glycol circuit for 1st floor rooftop collectors. The storage tanks are in a crawl space so I guess it is about 20 feet of head and probably 50 feet of piping. If the armature is rubbing the cartridge then I doubt I will try to repair it but just the same I'd like to know the resistance of the winding(s) to see if they are still good. Do you have ant info on that?
Bob

 

[Raspy]

I don't have the resistance value to check the windings.

Here is another point I'd like you to ponder. When you have a closed loop glycol system, in other words, full all the time with an expansion tank and no draining back to a holding tank, you don't consider the head pressure in your pump calcs. There is no standing head, only the resistance of the piping, collectors and heat exchanger. And since that's the case you don't need a pump like the 009 which is a very high head pump designed to push water all the way to the roof while the return line is empty. That pump is good for drain back systems. With closed loop there is no standing head to overcome.

Also, glycol is an excellent corrosion inhibitor and bronze or stainless is not needed. Use and iron pump.

If you only have two collectors, for instance, you should be using a 008 or a Grundfos 1558. They would probably be fine up to four or even five collectors depending the pipe sizing and roof layout. They might last longer and would use less energy to run.

For example, the system at my place uses a 007 (even lower head) for two 4X10 collectors and works very well.

 

[MillWeld]

Actually, my system is a drainback one. I asked why they used drainback with glycol and got the impression they went for overkill on the freeze prevention.

 

[Raspy]

Got it.

In that case the 009 is a good choice. I don't know why they would use both freeze systems either. I consider drain back to be the absolute best and the only time it might be a problem is in extremely cold climates where even the holding tank might freeze, or there might be a bit of trapped water in the piping, or the draining process is very slow. But in milder climates and with good installation work, simple drain back is pretty much fool proof. It also allows single wall heat exchangers with no health issues.

Is it propylene or ethylene glycol?

Your pump may have suffered from too much air bubbling through it with occasional very hot water, or constant high head. Be sure the drain down vent, if it has one, is NOT at the top of the system on the return line. If the system is open to the atmosphere and drains to a non pressurized tank, the vent should be down closer to the tank. If it's closed loop drainback it needs no vent at all.

Good luck.