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Y/W, but if the 2.5 TACO wind up working w/ the specs, you solved it 100%, not me. I was concentrating on solving the pressure drop from a different angle (while multi-tasking here), and just assuming the pump had to be 3.0 to meet the specs for the boiler, and really didn't consider changing the pumps, but you still might have to stay with the 3.0 pump.

You need to look at the specs on that 2.5 mixer also to ensure it's GPM flow rate meets the boiler GPM requirements. You just don't know what is what in this situation now, when you have guys throwing packages together where they screw up the design, like here w/ the reducer to create a pressure drop. Sometimes you have to step back and reassess the complete package before moving back forward again.

If you have to stay w/ the 3.0 pump, that tank fab might still be easier, quicker, and cheaper than changing to a 3.0 mixer. You pretty much know your options now, and are back on the road to solving it.

Let us know if the 2.5 pump works.

Will do elks. Many thanks to you SC and everyone who had input here

Yep, and they didn't pickup on the reducer creating a pressure drop / problem in their hurry to keep inventory turning. It happens.....more and more.

30-40 years ago, this didn't happen. People took pride in their work at all levels, and watched out for their customer's better interests. Not today.

yeah, that should work. The Hydronic Laws for 2.5 pipe will tell you it will flow the required amount, and I can't see B&G under sizing the HP to where it wouldn't max out the flow for 2.5 dia piping.

Probably shortages like JOG just described.

It is bad right now across all sectors. You won't here it in the news, but it is bad, and everyone in the know does not see it getting better anytime soon.

You fellas might be in over your heads here. If you don't know what NPSH is, then you shouldn't be engineering projects with delicate running parameters. There is a gross lack of info here, to include lack of monitoring devices, (thermometers, flow recorders, pressure gages, etc.), unsufficient mention of psi and temp at various points of interest, whether suction pressure is positive or negative, and what is their values, the list goes on and on.

What you need to do is not replace parts, as it will possibly repeat at a cost, but find and correct the problem.

If the owner of this site is compassionate, or has deep pockets, s/he, or they might incur the cost of refinement, as it WILL be their equipment upon completion.

Just my thoughts at this point.

No sweat!

I'd love to be a fly on the wall, while Certifiable is standing there,

talking to the proper personnel,

ah, ya , I need another 10 grand in material and labor,

I think I know whats going on here, and how to possibly fix it,

guy on the internet told me so..........

Should go well huh?

One step at a time, first solve the pressure drop, and he is working on it and I believe pressure drop causing cavitation is what NPSH is all about, correct?

Next, run the boiler and check vitals, and check the barometric.

There's no re-design going on. All specs are being looked at to meet GPM needs to all equipment.

Well look who showed back up. Here's a troll who obviously wants to push this thread south.

Here kenneth, I'll step aside, and why don't you enlighten the audience with your brilliance on the subject matter......

[/quote]
One step at a time, first solve the pressure drop, and he is working on it and I believe pressure drop causing cavitation is what NPSH is all about, correct?

Next, run the boiler and check vitals, and check the barometric.

There's no re-design going on. All specs are being looked at to meet GPM needs to all equipment.



[/quote]

NPSH has multiple variables; suction head pressure, TEMPERATURE, flow demands/characteristics/variables extremes, velocity, density, specific gravity, you get the idea. The product being pumped and it's chemical levels and constituency within proper parameters (i.e. no slugging).

Perhaps minor corrections can resolve this issue. However, if it doesn't, then we are just parts changers, prone to repeat a failing process.

We know that a pump has failed, piping sizing might be suspect, NPSH is currently in question, impeller might be wrong material, discharge line has deposits and leaks, hangers and saddles and supports might be in need of redesign, thermometers and psi gages are needed, etc. I have seen butterfly valves that don't open properly. Any mechanical component might fail or be compromised.

Now then, back to a question I asked earlier: does only one boiler run at a time, or two at times?

If demand is high enough both boilers will run at once. The vast majority of the time only one runs.

They are not set up as a master/slave scenario and the only way to alternate which boiler carries the load is to change set points between the two

Good article talks about hot water and how it lowers NPSH . if some one can clean up the link please do.

https://www.pumpsandsystems.com/avoid-system-damage-when-pumping-hot-water#:~:text=Hot%20water%20systems%20tend%20to%20have%20low%20NPSHA%2C,pressure%20begins%20to%20increase%20and%20the%20bubbles%20collapse.

They wouldn't listen anyway! Just keep on guessing.

Kenneth..
It would be good for a laugh that’s for sure. Except there are no proper personnel. It’s just me here, trying to unfuqk a situation.

And SC you can assuredly place me in the over my head category, trying to save taxpayer dollars!

No troll at all, Not sure why you went there,

I've been in Cert's situation, trying to convince management on what, I think I know what the problem is, not sure but lets throw money at it and hope for the best.....Then explaining your going by info from some guy on the 'net.....Guaranteed to raise eyebrows.

And trying to request these funds from a school board. ain't that easy. been there, done that.

For Cert's sake, I hope your right, if he takes your approach, or he's the one that will face the music.

Later.

The boilers don’t usually run at the same time-

But both pumps run 24/7

Spoke to a B&G rep about the problem(s) and he didn’t feel the 2 1/2 reducers were the problem, but was focused more on the motor/pumps sizing. He speculated that the pump may be starving for water and causing the cavitation. Either because the pump is oversized (it’s not per the boiler GPM specs) or because of a restriction upstream.

This is exactly where my mind was going—why not swap down to 2-1/2" pumps, getting rid of the reducers between the mixing valve and the pump.

Tell whoever complains about paying the bill that the supplier they chose provide the systems included the wrong size pump relative to the rest of the system. This is evidenced by a failure to adhere to basic design standards and resulted in the pump having failed twice in two years.


I want to think there's got to be an obvious reason why the other pump didn't get destroyed. Are both boiler systems run in tandem or do they cycle back and forth or does one run as a primary with the second only kicking in when needed?

My experience is mostly with agricultural pumps, but am I wrong to think that this doesn't look like a pump that's been recently running constantly?

He's wrong. Going from 2.5 > 3.0 will create a pressure drop, which you don't want, air bubbles.



That restriction would be the 2.5 mix valve acting as a choke, like I mentioned above.

Simple fix is put the 2.5 pump in (99.9% It's going to flow enough, being the intake on the boiler is 2.5, just need to check the specs), and that will solve the pressure drop from the 2.5/3.0 reducer by removing it.

4.0 Feed > 2.5 mix valve > 2.5 pump > 2.5 boiler intake.

Being this job was just "added possibly" to the system, "without a load analysis performed on the water supply" to ensure the two boilers running at the same time (or even just one) do not overload the supply, and create a low water pressure situation, they need to perform one to eliminate that as a cause, even with the change to the 2.5 pump. Nobody knows what systems are on that branch coming off the main at this point.

This "repair" is at the point where you need to start from the beginning (drawings), and cover all bases.

ETA: and yes, there should be test points to attach meters, or permanent installed, so you know what's going on.

You need those anyway to adjust the barometric, so you know what your changes / adjustments are doing.