Cavitation issues

[warno]

I'm hoping some of you are still watching this thread and could help me out here.

My boiler has been idling ALOT lately, like it's not shedding the BTUs as it should. I know we all know my current plumbing and my current HX is less than ideal. But I'm at a loss because it seems the boiler is firing great but the storage just isn't taking it. I mean even worse then before. I pulled the screen on my boiler side strainer and it was, to my amazement, perfectly clean. I didn't pull the storage screen though. I'm getting a delta t of 40°+ on the boiler side and only 10°-15° on the storage. Boiler side pump on speed 2 and storage on speed 3. Boiler is pushing 185 as I'm writing and storage is at 140s. Storage should be climbing pretty fast right now but isn't.

Should i pull the storage screen and see if there's blockage that slowing flow or what should I check. I'm just trying to get through the rest of the season at this point.

 

[TCaldwell]

Descale the hx

 

[BoiledOver]

Delta temp of 40F says the btus are going somewhere. What is the flow temp going into the HX from the boiler? Is it close to the boiler out temp? If not, ouch.

Are you still running the monster circ on the boiler and the 15-58 on the storage? Do you know the flow rates of the two circulators at each speed? I do not know of the HX specs, but the 15-58 on high will probably push somewhere around 14 gpm with your short storage loop.

 

[warno]

Descale the hx

I was wondering this but it just started all of the sudden. I'd say within the last week or so.

Delta temp of 40F says the btus are going somewhere. What is the flow temp going into the HX from the boiler? Is it close to the boiler out temp? If not, ouch.

Are you still running the monster circ on the boiler and the 15-58 on the storage? Do you know the flow rates of the two circulators at each speed? I do not know of the HX specs, but the 15-58 on high will probably push somewhere around 14 gpm with your short storage loop.

Boiler temp in is ~180 and out ~140. Storage in is ~130 and out ~142-145. I used to see a 30° drop on boiler side to a 25° gain in storage. My temp readings were on the HX ports on both sides.

I'm still running the same circs. Nrf-36 boiler side, 15-58 storage side. My boiler side should be around 10 gpm on speed 2. My storage side is around 14 on speed 3.

Like I said it just started about a week or so ago. Could it be the warmer temps outside affecting it? We've been in the upper 30s to low 40s. 60 outside today.

 

[maple1]

That's weird. I was also thinking scale but the big boiler dt is a puzzler.

 

[warno]

Is it possible the storage side is scaled up? I know they're seperate from each other so I suppose one side could load up and not the other. I mean when I pulled a water sample for pH testing it was brownish water. No heavy sediment as nothing settled out in the sample but the water was brownish so there is something in it.

Should I pull the screen on the storage strainer just to check if it's full? If that screen is full I guarantee the HX has crap in it too.

 

[maple1]

Maybe the boiler side is scaled enough that it is restricting flow quite a bit on that side? The big dT could be from heat being pulled away on the other side, but it could also be from quite low flow on the boiler side. That is my first inclination, since it seems to have just started and nothing else has changed? Might not take much on that smallish HX?

 

[warno]

Maybe the boiler side is scaled enough that it is restricting flow quite a bit on that side? The big dT could be from heat being pulled away on the other side, but it could also be from quite low flow on the boiler side. That is my first inclination, since it seems to have just started and nothing else has changed? Might not take much on that smallish HX?

After I got to thinking more about it last night I'm wondering about the boiler side as well. The higher delta t would mean reduced flow on that side. Also the faster rising boiler temps would mean reduced flow through the boiler. But what I don't understand is the boiler water looks clear enough to drink, I'm not going to, and the strainer screen looked like the day it was installed. Is it possible enough very fine particulate finally got caught up in the HX it's causing issues?

When I checked it yesterday evening the boiler was idling at a temperature of 192, coming down from the 195 shut down limit. The storage was in the 150s throughout. When I checked my deltas at the HX. boiler side was 192 in and 162 out. storage was 152 in and 158 out. Huge delta on boiler side compared to storage. These temps were taking right on the HX ports again.

So I'm thinking 3 options on the boiler side

1) HX scaling
2) impeller on circ has damage from cavitation and not flowing good enough
3) other blockage I'm not thinking of

 

[Marshy]

After I got to thinking more about it last night I'm wondering about the boiler side as well. The higher delta t would mean reduced flow on that side. Also the faster rising boiler temps would mean reduced flow through the boiler. But what I don't understand is the boiler water looks clear enough to drink, I'm not going to, and the strainer screen looked like the day it was installed. Is it possible enough very fine particulate finally got caught up in the HX it's causing issues?

When I checked it yesterday evening the boiler was idling at a temperature of 192, coming down from the 195 shut down limit. The storage was in the 150s throughout. When I checked my deltas at the HX. boiler side was 192 in and 162 out. storage was 152 in and 158 out. Huge delta on boiler side compared to storage. These temps were taking right on the HX ports again.

So I'm thinking 3 options on the boiler side

1) HX scaling
2) impeller on circ has damage from cavitation and not flowing good enough
3) other blockage I'm not thinking of

My vote is #2.
If you speed up the boiler circ is it still cavitating like it use to? Maybe performance is dropping from damage due to cavitation.

 

[warno]

My vote is #2.
If you speed up the boiler circ is it still cavitating like it use to? Maybe performance is dropping from damage due to cavitation.

Oh yes cavitation is terrible at speed 3 sounds like gravel going through there. Speed 2 is bad enough.

I would just shut it down and drain the boiler if I knew it wasn't going to freeze anymore. I'm draining my boiler water into drums to put it back in after my replumbing takes place. I can't see wasting the treated water.

 

[maple1]

Ya, never thought about the impeller being damaged. Which should have been the first suspect given the thread we're in.

 

[warno]

Ya, never thought about the impeller being damaged. Which should have been the first suspect given the thread we're in.

Could it get to a point where it "all of the sudden" quits pumping enough flow? Its literally been within the last week or so that's it's been having this issue.

 

[Marshy]

If it's been cavitating for the whole time I believe it could have caused damage to the impeller to the point where performance has dropped. The ends of the impeller get erroded and the pump moves less and less water. It's a real possibility and matches the symptoms.

 

[warno]

I guess I'll fight through this week and maybe pull the pump this weekend and check it out. I suppose if it's beat to crap I'll shut 'er all down and drain the boiler to start replumbing. Not really what I wanted to do at this time but I can't see sending perfectly good wood up the stack in a cloud of smoke.

I could throw a new impeller in the pump but then as soon as it starts cavitating, due to the current plumbing set up, I'm just trashing a new impeller.

 

[warno]

I called supplyhouse.com today and they told me that they cannot get a impeller for my NRF-36. Should I try B&G directly to see if a factory direct replacement is available?

If I can't rebuild it I'm going to need a new circ for my new plumbing setup. Should I go with a single speed pump or run another variable? Once I get to replumbing I'll have my head loss figured so sizing shouldn't be an issue.

 

[leon]

Hello Warno,


if you go to the B+G web site they have dealer links. I am sure you can either get a new circulator and 2 impellers and new gaskets.

I was able to purchase new springs for the couplers on my single speed B+G circulators that were over 30 years old.

www.bellandgossett/sales-service/


Go to the find your local rep button and then type in your zip code and go from there and they will help you find a stocking B+G reseller.

 

[warno]

I haven't had a chance to pull the circ apart to check on the impeller but I've been thinking about my hat dump zone. With the idea that it may never get used I've been wondering about using my current garage heating loop as the dump zone instead of a dedicated WAHX.

I'm thinking about running a line from my diverter valve up and tie into my current heating loop. The diverter valve only opens in the event of over heating situation. I'm going to use the controller that controls the diverter and tie it in parallel with the garage loop pump and fan on that line.

So if boiler is over heating, diverter valve opens, garage fan and pump kicks on. My thought is the garage pump would be in series with the storage charging pump to help with the added head of the garage loop.

Here's my sketch of what i think the plumbing would be. Would this work for my heat dump?

Does this make any sense? Lol