Taco 009-F5 oversized for my application?

[Joacchim]

I have a Central Boiler CL5036 in service since October, 2010, with 2 Taco 009-F5 cast iron circulators, one going 30 feet (60 round trip, Central Pex 1") to my barn mixing valve and a single zone pump for hydronic heat there. The other pump goes about 300' round trip direct to a heat exchanger in the house forced air furnace system.

Problem is with the barn pump discharge flange - it recently sprang a leak, and my current CB dealer says it looks like pump turbulence caused the inside of the flange to erode (see photo, after I epoxied it, but got a new flange and installed it) . I ran this pump without a bypass at the mixing valve for about 6 years, destroying 2 of the valves before my previous dealer pointed out my error. Anyway, fixed that, but I suspect operating like that may have eroded the pump flange as well.

My new dealer thinks the 009 pump has much more flow capacity than is needed for that 30' run to my barn, and that's what caused the flange failure. If you agree the pump is the problem, any suggestion for a pump replacement? I'm open to a multi-speed pump (to save energy) but also important is flange to flange dimension of ~6-1/2" - I do not want to replumb the pump connections. The current 009 pump was installed new in October, 2022 - if I can keep it, that'd be great.

Thanks in advance.

 

[sloeffle]

Where is the circulator physically located. On the back of the boiler or in your shop ?

 

[Joacchim]

Where is the circulator physically located. On the back of the boiler or in your shop ?

Back of the boiler.

 

[sloeffle]

Back of the boiler.

Couple folks on Facebook have had similar issues because the circulator is in a basement and there isn't enough pressure on the inlet side and it causes cavitation.

I'm probably grasping at straws at this point. I know on the older CB's they had problems with spot boiling because you were told to pull from the top vs the bottom. Do you have any problems with spot boiling ? I wouldn't think it could get that hot to cause the metal to melt / deform.

To answer your question, a Grunfos 15-58 would probably fit the bill for that small of a run. I was told by someone who knows more about OWB's than what I do to not use a Alpha 1 or 2 in the back of the boiler cabinet because it gets too hot and fries the electronics out. You will need to figure out the head though to make it would work based off of the pump curve.

 

[PassionForFire&Water]

as Sloeffle wrote, your pump is cavitating.

You need a pump with a very small Net Positive Suction Head (NPSH).
Only a few feet.

The Grundfos UPS 26-150 has a very small NPSH
But it's probably way to big for your application.

I don't know of anything smaller and less money.

An other approach would be to select the smallest pump available for you application and replace it each time it breaks.
Less money upfront, much much more money in the long run of course.

 

[Joacchim]

Thanks guys. Can't say if spot boiling is occurring, max indicated temp runs about 177 normally (175 setpoint) . Suction does pull from near the top of the boiler so there's not much inlet pressure to begin with.

Assuming 10gpm, google says 60' of 1" pex is about 4' head. The run to the barn has about a 2' drop in elevation (and subsequent rise on the return trip), not sure how that affects head. It looks like the grundfos 15-58 might be good at speed 1, but I don't know how to interpret the pump curve (attached screenshot). Also the low inlet pressure might be a problem for this pump, as the spec says minimum at 190F is 4psi, and at 140F is 1.3psi. My dealer suggested I might not even need a circ pump with that short run but last year when it crapped out (impeller disintegrated), the downstream zone circulator pump didn't work - no heat to barn. Maybe circ pump was plugged up with impeller pieces...

The Grundfos UPS 26-150 has a high flow rating, seems like that would increase the possibility of cavitation - I'm by no means a pump expert, though. Plus, it's pretty expensive compared to other options.

Bottom line is I ran with this pump for 13 years without issue. Maybe just keep going as is, see what happens?

 

[hedge wood]

I have several short runs on my Garn system and I run Grundfos 15-58 pumps and some Taco 007 pumps. Both have last well most have been in since 2009. Make sure your water level isn't getting to low. Menards have those pumps in stock in my area for $135.00. I usually run the Grundfos on the second speed.

 

[sloeffle]

8GPM is max for 1" PEX. With 4 feet of head, if you wanted to push 8 GPM you could easily do it on speed 2 based off of the pump curve and the amount of head you calculated.

I would think the 100+ gallons of water in the OWB reservoir would provide enough pressure to meet the above PSI requirements, maybe not due to the way CB wants you to plumb the boiler up. Some folks on the Facebook group I'm on have moved theirs to the bottom because they were having similar cavitation issues. My boiler pulls from the bottom. @PassionForFire&Water thoughts on the PSI requirements for the 15-58 ?

My dealer suggested I might not even need a circ pump with that short run but last year when it crapped out (impeller disintegrated), the downstream zone circulator pump didn't work - no heat to barn. Maybe circ pump was plugged up with impeller pieces...

Do you have a plate exchanger "separating" your in floor heat from your OWB ? I put an Rusco spin down filter in my setup just for this reason.

 

[sloeffle]

An old thread talking about cavitation. The scenario seems very similar to yours.

Wood Boiler Circulation Pump

A friend of mine made a homemade wood boiler. He has basically two loops, one for the house and one for his shop. The shop loop consist of a copper coil in the boiler and in floor Pex tubing. He has been using taco pumps with plastic impellers. He has gone threw two or three of these. The...

www.hearth.com

 

[Joacchim]

The pump suction is just 15" below the operating water level - that's a little over 0.5psi. Seems low for the Grundfos' minimum inlet pressure requirement.

No plate heat exchanger - boiler water gets temperature reduced to ~105F before going to a zone circulator which feeds the floor directly.

@sloeffle - That's a good reference. I may have done damage in the early days when I created a high differential across the pump by not having a bypass around my mixing valve. Very little flow and probably a lot of cavitation. Surprisingly the pump held up (until last year) but the outlet flange finally failed, even though the problem was corrected about 6 years ago. I'll probably leave the 009 pump in place for now.

To everyone: Thanks for all the input

 

[PassionForFire&Water]

if the pump worked for 13 years, I would not worry too much about this.
Just replace it with the same model and go for another 13 years.

 

[Joacchim]

I need to add something I discovered yesterday. First, note that one of the two bypass tees I installed in 2017 (and which both see the same flow the discharge flange is exposed to) sprang a leak this past March. At the time and up until yesterday I thought it was because I distorted the brass tee while installing it - I was holding it with a vicegrip to muscle it into position. With all this forum discussion, I finally decided to take a closer look  inside the tee, and lo and behold, it looks like cavitation was occurring there as well. These tees were not easy to replace and I'm not looking forward to doing it again, so tomorrow I'm visiting my CB dealer to pick up a new, smaller capacity (?) pump. Hopefully it will stop any further cavitation. Stay tuned for what pump he sells me (thanks for all the suggestions but I still didn't feel confident buying anything myself without benefit of his experience).

 

[sloeffle]

If your dealer instructed you to install in your in floor heat without a plate exchange separating the two then I wouldn't trust his opinion on what pump to buy. He's probably going to route you to a pump that he's going to make some kind of commission on. You could order a pump from Supplyhouse and have it in a day or two.

 

[Joacchim]

Well, I very seriously considered buying one myself, probably the Taco 007 or 007e, but just didn't feel confident. My original dealer has retired so can't blame this guy, but you're probably right, he'll get a commission. My original dealer's prices weren't out of line with street prices, though. I want to keep on good terms with the new guy and making an occasional purchase will help. I agree, SupplyHouse is great - the replacement flange I ordered came in less than 24 hours.