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I'm happy to see this one stay on target. I agree on the reduction....I'd try to feed and discharge at 100% pipe diameter without any fittings for at least 15" for best hope. The pumps are going to cavitate....how much and how it affects the downstream piping will be dependent on how fast the pumps are ate up and how the actual flow ends up settling in. Buying yourself 5-10 pipe diameters of straight run piping is your first line of defense. There may be opportunity to reduce the cavitation by changing pump rpm, introducing flow or suction stabilizers....etc. Interesting info here, https://www.hindawi.com/journals/sv/2019/8768043/
I would not buy something that runs on any kind of primer given the possibility of primer shortages and even regulations. In fact, why not buy a flintlock? Really. Rocks aren't going away anytime soon.
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The blue wax mixing valve is front and center. As it sits it receives hot water (165) from boiler on the left and mixes it with incoming (80) pool water on the right to send tempered water down to the pump and into the boiler. It’s purpose is to reduce condensation in the boiler combustion chamber.. Point is it’s all 2 1/2 and is the mixing valve is supplied by the seller of these “systems”... If you follow the pipe going away from the right side you can see back where it reduces down from 4 to 2 1/2, so in regards to increasing suction side.. it technically could be done. But I’m not convinced that would accomplish anything? ![[Linked Image from i.postimg.cc]](https://i.postimg.cc/wj38vqHS/8-D21-FFCE-D97-B-44-A0-A62-F-73-E564-F784-CE.jpg) post imagesThe 3 – 2.5 reducer on top of the B&G manifold receiving the water from the mixing valve is your problem. It is causing a pressure drop as the water transitions from the 2.5 dia piping out of the mixing valve into the larger 2.5/3.0 reducer. The pressure drop is allowing the oxygen in the water to expand and create air bubbles as the pressure drops. It is essentially doing the exact same thing as what happens in a refrigeration system right at the metering device, where liquid refrigerant (Your case – liquid water) transitions from high pressure to a lower pressure and changes from a liquid state to a gaseous state (liquid > liquid w/bubbles > gaseous state). Your pump is getting that (liquid w/ oxygen bubbles), and possibly a lot of bubbles. The mixing valve is mounted too close to the pump for the water to settle back down to a solid column of water after coming out of the 3.0 dia. opening of the reducer, and before entering the pump intake. Think holding a water hose with a solid stream of water into a tank, and creating bubbles below the surface. The bubbles eventually dissipate into the surrounding water, and some rise to the surface. The pump is too close to the 2.5/3.0 reducer, and not giving the liquid enough time to settle back down. You might need 5-10 ft of 3.0dia. transition piping entering that pump, to allow for blending back into a solid state of water after coming out of the 2.5/3.0 reducer, which would be mounted back around the mixing valve. Looking at the layout, I highly doubt you have enough room presently between the mixing valve and manifold to accomplish what you need to. That means mounting the mixing valve further back overhead between the two supply feeds (back over above the first boiler with the SS impellor), and putting the 2.5/3.0 reducer further back and running 3.0 dia from there to the pump manifold. You’ll need to relocate both mixing valves. Also, in the installation instructions there should be a section discussing piping lengths when transitioning from one size to another and how far away the fitting needs to be from the entrance side of the pump manifold. If you don’t find it in the instructions (Might look on line at their site if you don’t have them on site) I would call tech support at B&G, and get one of their brains on the phone, and text them your pics, and see if they don’t agree with what I just said. I just looked on B&G site. It looks like they don’t make a 2.5 dia. pump. Looks like they go from 2.0 – 3.0, so you have to use a 2.5-3.0 reducer. Copy and paste this analysis I just wrote and send it to the tech support guy in an email, so they can get their head wrapped around what I just said, so you don’t have to reread it to them. ElkSlayer, this has been my thought also from the beginning. My hat is off to you for being so Vocationally astute in being able to describe the process of cavitation. Again, very good explanation.
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Here’s the fix for you, that will save you guys a few thousand on time and material I’d bet. Just need to figure out what volume tank needs fabricated.
Instead of rerouting everything, I believe you could have a tank fabricated to put between the mixing valve and the intake manifold of the pump. Have them put a baffle on the intake side of the tank, to divert the water from just being a straight shot across the diameter of the tank, and into the 3.0 opening on the pump manifold.
Just picture a expansion tank being there.
Essentially what it would do is allow the pump to grab water out of the tank without the pressure drop immediately in the pipe at the mouth of the pump intake, as is right now. The volume of the tank would be where the pressure drop takes place.
"He is far from Stupid"
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– DocRocket (In reference to ElkSlayer91)
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Here’s how to figure the volume of the tank.
Find out from the installation instructions or tech support how long of a piece of 3.0 dia. pipe needs to be from the 2.5/3.0 reducer to the pump.
Go to an online calculator, and punch in the length and radius of the pipe to get the volume of that length of pipe.
That volume of the length of pipe is the volume your tank needs to be, and I’d add 10-25% just for grins to be done with it.
Last edited by ElkSlayer91; 04/01/21.
"He is far from Stupid"
”person, who happens to have an above-average level of intelligence”
– DocRocket (In reference to ElkSlayer91)
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Do you run one boiler at a time, or both at a time(s)?
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The blue wax mixing valve is front and center. As it sits it receives hot water (165) from boiler on the left and mixes it with incoming (80) pool water on the right to send tempered water down to the pump and into the boiler. It’s purpose is to reduce condensation in the boiler combustion chamber.. Point is it’s all 2 1/2 and is the mixing valve is supplied by the seller of these “systems”... If you follow the pipe going away from the right side you can see back where it reduces down from 4 to 2 1/2, so in regards to increasing suction side.. it technically could be done. But I’m not convinced that would accomplish anything? post imagesThe 3 – 2.5 reducer on top of the B&G manifold receiving the water from the mixing valve is your problem. It is causing a pressure drop as the water transitions from the 2.5 dia piping out of the mixing valve into the larger 2.5/3.0 reducer. The pressure drop is allowing the oxygen in the water to expand and create air bubbles as the pressure drops. It is essentially doing the exact same thing as what happens in a refrigeration system right at the metering device, where liquid refrigerant (Your case – liquid water) transitions from high pressure to a lower pressure and changes from a liquid state to a gaseous state (liquid > liquid w/bubbles > gaseous state). Your pump is getting that (liquid w/ oxygen bubbles), and possibly a lot of bubbles. The mixing valve is mounted too close to the pump for the water to settle back down to a solid column of water after coming out of the 3.0 dia. opening of the reducer, and before entering the pump intake. Think holding a water hose with a solid stream of water into a tank, and creating bubbles below the surface. The bubbles eventually dissipate into the surrounding water, and some rise to the surface. The pump is too close to the 2.5/3.0 reducer, and not giving the liquid enough time to settle back down. You might need 5-10 ft of 3.0dia. transition piping entering that pump, to allow for blending back into a solid state of water after coming out of the 2.5/3.0 reducer, which would be mounted back around the mixing valve. Looking at the layout, I highly doubt you have enough room presently between the mixing valve and manifold to accomplish what you need to. That means mounting the mixing valve further back overhead between the two supply feeds (back over above the first boiler with the SS impellor), and putting the 2.5/3.0 reducer further back and running 3.0 dia from there to the pump manifold. You’ll need to relocate both mixing valves. Also, in the installation instructions there should be a section discussing piping lengths when transitioning from one size to another and how far away the fitting needs to be from the entrance side of the pump manifold. If you don’t find it in the instructions (Might look on line at their site if you don’t have them on site) I would call tech support at B&G, and get one of their brains on the phone, and text them your pics, and see if they don’t agree with what I just said. I just looked on B&G site. It looks like they don’t make a 2.5 dia. pump. Looks like they go from 2.0 – 3.0, so you have to use a 2.5-3.0 reducer. Copy and paste this analysis I just wrote and send it to the tech support guy in an email, so they can get their head wrapped around what I just said, so you don’t have to reread it to them. ElkSlayer, this has been my thought also from the beginning. My hat is off to you for being so Vocationally astute in being able to describe the process of cavitation. Again, very good explanation. Thank you, sir.
"He is far from Stupid"
”person, who happens to have an above-average level of intelligence”
– DocRocket (In reference to ElkSlayer91)
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Slayer.. thanks much for the input and suggestions. I’m following along with the concept you presented of pressure drop right as the water enters the pump due to the reducer.
Keeping it simple... you are suggesting the line leaving the mixing valve to the pump go from 2 1/2 to 3 immediately after leaving the valve, and only reduce to 2 1/2 at the last minute where it enters the boiler, yes..?
That keeps as much 3” in the loop as possible allowing the water to settle..
In essence.. that deals with the cavitation before the pump, so we aren’t dealing with the effects of it after the pump...?
She never made it past the bedroom door, what was she aiming for...?
She's gone shootin..
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HC.. appreciate the input and the vids, they certainly do illustrate what seems to be happening here..even if I do have an issue completely wrapping my simple mind around the why and how.
I realize pump and flow dynamics are a whole nother ballgame
She never made it past the bedroom door, what was she aiming for...?
She's gone shootin..
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Most pump issues are suction side of pump!
kk alaska
Alaska 7 months of winter then 5 months of tourists
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Also.. I don’t want to seem like I’m looking for the easy way out but there’s the possibility that’s what I’m going to be told to do..
Seems to me using 3x21/2 brass reducer bushings in and out of the pump flanges would greatly reduce that area of expansion being created by the 3” male adapter and fitting reducer?
The nature of the fitting would ensure a straight shot of 2 1/2 directly into the pump
Just a thought...
She never made it past the bedroom door, what was she aiming for...?
She's gone shootin..
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One more thing, have the tank manufacturer use flanges with slotted holes on the tank, so you don’t have to mess with being slightly off-alignment from the bolt holes in the outer flanges you will be bolting the tank up to.
If you have it fabricated on-site, the above doesn’t matter, and that might be a quicker option to get it back together, depending on the tank fabricators workload.
"He is far from Stupid"
”person, who happens to have an above-average level of intelligence”
– DocRocket (In reference to ElkSlayer91)
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The blue wax mixing valve is front and center. As it sits it receives hot water (165) from boiler on the left and mixes it with incoming (80) pool water on the right to send tempered water down to the pump and into the boiler. It’s purpose is to reduce condensation in the boiler combustion chamber.. Point is it’s all 2 1/2 and is the mixing valve is supplied by the seller of these “systems”... If you follow the pipe going away from the right side you can see back where it reduces down from 4 to 2 1/2, so in regards to increasing suction side.. it technically could be done. But I’m not convinced that would accomplish anything? post imagesThe 3 – 2.5 reducer on top of the B&G manifold receiving the water from the mixing valve is your problem. It is causing a pressure drop as the water transitions from the 2.5 dia piping out of the mixing valve into the larger 2.5/3.0 reducer. The pressure drop is allowing the oxygen in the water to expand and create air bubbles as the pressure drops. It is essentially doing the exact same thing as what happens in a refrigeration system right at the metering device, where liquid refrigerant (Your case – liquid water) transitions from high pressure to a lower pressure and changes from a liquid state to a gaseous state (liquid > liquid w/bubbles > gaseous state). Your pump is getting that (liquid w/ oxygen bubbles), and possibly a lot of bubbles. The mixing valve is mounted too close to the pump for the water to settle back down to a solid column of water after coming out of the 3.0 dia. opening of the reducer, and before entering the pump intake. Think holding a water hose with a solid stream of water into a tank, and creating bubbles below the surface. The bubbles eventually dissipate into the surrounding water, and some rise to the surface. The pump is too close to the 2.5/3.0 reducer, and not giving the liquid enough time to settle back down. You might need 5-10 ft of 3.0dia. transition piping entering that pump, to allow for blending back into a solid state of water after coming out of the 2.5/3.0 reducer, which would be mounted back around the mixing valve. Looking at the layout, I highly doubt you have enough room presently between the mixing valve and manifold to accomplish what you need to. That means mounting the mixing valve further back overhead between the two supply feeds (back over above the first boiler with the SS impellor), and putting the 2.5/3.0 reducer further back and running 3.0 dia from there to the pump manifold. You’ll need to relocate both mixing valves. Also, in the installation instructions there should be a section discussing piping lengths when transitioning from one size to another and how far away the fitting needs to be from the entrance side of the pump manifold. If you don’t find it in the instructions (Might look on line at their site if you don’t have them on site) I would call tech support at B&G, and get one of their brains on the phone, and text them your pics, and see if they don’t agree with what I just said. I just looked on B&G site. It looks like they don’t make a 2.5 dia. pump. Looks like they go from 2.0 – 3.0, so you have to use a 2.5-3.0 reducer. Copy and paste this analysis I just wrote and send it to the tech support guy in an email, so they can get their head wrapped around what I just said, so you don’t have to reread it to them. ElkSlayer, this has been my thought also from the beginning. My hat is off to you for being so Vocationally astute in being able to describe the process of cavitation. Again, very good explanation. +100 The comparison to refrigerant through a metering device is a good one and helps with visualizing what the water is doing when it hits that 3".
4 out of 5 Great Lakes prefer Michigan. 
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Slayer.. thanks much for the input and suggestions. I’m following along with the concept you presented of pressure drop right as the water enters the pump due to the reducer.
Keeping it simple... you are suggesting the line leaving the mixing valve to the pump go from 2 1/2 to 3 immediately after leaving the valve, and only reduce to 2 1/2 at the last minute where it enters the boiler, yes..?
That keeps as much 3” in the loop as possible allowing the water to settle..
In essence.. that deals with the cavitation before the pump, so we aren’t dealing with the effects of it after the pump...? Yeah, the problem is before the pump. You don't have enough room as it stands between the mix valve and pump to solve the problem. Your only option is to relocate the mixer further back, and run the correct length of 3.0 dia to the pump or fab a tank. You guys will waste time and money to rig it like you're talking, and you will be back and it will damage your brand of your company. Fix it right, and be done with it. Call B&G tech, and talk to an engineer, and they will confirm my two options. The pitting on the output will be solved once you correct the entering cavitation issue, but since you're having all of this fun, I'd put the 2.5/3.0 reducer right at the boiler intake and run 3.0 from pump to boiler.
"He is far from Stupid"
”person, who happens to have an above-average level of intelligence”
– DocRocket (In reference to ElkSlayer91)
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Also.. I don’t want to seem like I’m looking for the easy way out but there’s the possibility that’s what I’m going to be told to do..
Seems to me using 3x21/2 brass reducer bushings in and out of the pump flanges would greatly reduce that area of expansion being created by the 3” male adapter and fitting reducer?
The nature of the fitting would ensure a straight shot of 2 1/2 directly into the pump
Just a thought... Nope, won't work. There is a reason it "transitions" smoothly into the impeller. Putting a 2.5 brass bushing / choke in will still create a pressure drop right at the pump when it comes out of the 2.5 opening and into the 3.0 area on the backside of the bushing. It will also create a "void" and create even worse turbulence in the water where it should smoothly transition into the impeller.
"He is far from Stupid"
”person, who happens to have an above-average level of intelligence”
– DocRocket (In reference to ElkSlayer91)
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I would not buy something that runs on any kind of primer given the possibility of primer shortages and even regulations. In fact, why not buy a flintlock? Really. Rocks aren't going away anytime soon.
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The more I look at that pic the easier it gets. Man, have a guy come build a tank on-site. You guys provide the material. I bet a good fab guy could build both tanks in place in one day. Maybe cost you guys 3K total, tops for both.
It'd cost you way more than that rerouting and relocating the mixer. That'd be 2-3 days on each minimum, I'd bet looking at it.
"He is far from Stupid"
”person, who happens to have an above-average level of intelligence”
– DocRocket (In reference to ElkSlayer91)
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This is a school job. Did you guys build it out as per the plans were stamped?
And where is the service manager of your company on, this? Why isn't he overseeing this to make the right decisions?
Just curious. I can't believe your company has you out on the internet looking for the right next move to solve the issue.
Fill me in. Are you the service mgr?
"He is far from Stupid"
”person, who happens to have an above-average level of intelligence”
– DocRocket (In reference to ElkSlayer91)
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Also.. I don’t want to seem like I’m looking for the easy way out but there’s the possibility that’s what I’m going to be told to do..
Seems to me using 3x21/2 brass reducer bushings in and out of the pump flanges would greatly reduce that area of expansion being created by the 3” male adapter and fitting reducer?
The nature of the fitting would ensure a straight shot of 2 1/2 directly into the pump
Just a thought... Nope, won't work. There is a reason it "transitions" smoothly into the impeller. Putting a 2.5 brass bushing / choke in will still create a pressure drop right at the pump when it comes out of the 2.5 opening and into the 3.0 area on the backside of the bushing. It will also create a "void" and create even worse turbulence in the water where it should smoothly transition into the impeller. Ok elk in retrospect I agree that’s true..I’ll stuff that idea back where it came from
She never made it past the bedroom door, what was she aiming for...?
She's gone shootin..
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Did the 2.5 flange mixing valve come with the boiler package?
Last edited by ElkSlayer91; 04/01/21.
"He is far from Stupid"
”person, who happens to have an above-average level of intelligence”
– DocRocket (In reference to ElkSlayer91)
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This is a school job. Did you guys build it out as per the plans were stamped?
And where is the service manager of your company on, this? Why isn't he overseeing this to make the right decisions?
Just curious. I can't believe your company has you out on the internet looking for the right next move to solve the issue.
Fill me in. Are you the service mgr? Damn elks.. this both made me literally laugh out loud while at the same time felt like I was getting kicked in the balls!!🤣 If you could be in my shoes you’d be laughing too. I’m just a $hithouse plumber whose problem is he cares too much about finding out the why, when something fails.. There is no service manager. If there is to be any right decisions made they’re going to made be me, with the help of you generous and knowledgeable people. I’m on my own here. Guaranteed if I ask I’ll be told just replace the impeller and the damaged pipe. You know what I’m saying? Also I have 23 other sites I’m 100% responsible for any and all plumbing issues, so this is taking me away from all that
She never made it past the bedroom door, what was she aiming for...?
She's gone shootin..
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