Originally Posted by ElkSlayer91
Originally Posted by Certifiable
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?
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The 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.