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I'm designing a small system where typically a ball valve is used to divert water through a heater when desired. I've noticed the ball valves designed for this situation result in a hard 90 degree turn when diverting the flow, and also lowers the diameter of the pipe by approximately 10%. The inside of the valve is manufactured such that it will create a significant amount of friction and turbulence even when it's in the straight/bypass position.

Three way valve design.

I'm considering an alternate plumbing approach that uses a standard ball valve and tee wye bend fitting. When the ball valve is closed, water will be diverted through the tee wye bend. I suspect this will result in less resistance and higher flow than the aforementioned three way valve will allow, but I'm unsure if I need to be worried about turbulence or other factors that will constrain flow while the system is in either of the two possible states.

Ball valve with tee wye bend design

The valve will be open to bypass the heater the majority of the time. Will the tee branch lead to a significant amount of friction or turbulence that will impede the flow in any considerable amount?

Can someone with a better understanding of the fluid dynamics at play here verify that my alternate approach is more efficient (or at least not significantly less efficient) in terms of flow than the design with the three way valve?

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    $\begingroup$ Are you sure that the pressure loss through the valve is higher than the pressure loss through the heater? That would be the only reason to worry about the design of the value. Also, the alternative diagram does not prevent fluid from going through the heater. There would always be some fluid going through the heater (inversely proportional to the pressure loss through the straight branch versus the heater). The alternative is not a design I would expect to see, depending on whether the heater needs to be fully isolated from the main line or not. $\endgroup$
    – JohnHoltz
    May 10 at 3:25
  • $\begingroup$ To make your second option work would need two valves, as per the isdue raised in the other comment. $\endgroup$
    – Solar Mike
    May 10 at 6:12
  • $\begingroup$ @JohnHoltz No, the pressure loss through the valve is certainly lower than the loss through the heater. Most times the heater will be bypassed. I'm looking to optimize the flow through the valve when the heater is not in use. Good catch on the need for another valve at the entry of heater. I will be including that neglected to include it in the diagram. Q: Will the tee wye branch will create a significant amount of turbulence when the heater is bypassed, and is the resulting turbulence negligible or not. Also curious for impact of tee wye when heater is in use vs. three way valve. $\endgroup$
    – Chris
    May 10 at 13:47
  • $\begingroup$ It can be calculated. Search for "head loss in bends". But if you care about the flow with heater off, I'd think it is the diameter reduction in ther valve that matters. I would guess negligible effect, if ball valve sized properly $\endgroup$
    – Pete W
    May 10 at 14:08

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