SOLVED: Venturi tees are restrictive | Heater bypass next!

[matthewsunshineflorida]

SOLVED: Venturi tees are restrictive

SOLVED: Venturi tees are restrictive | Heater bypass next!

SOLVED: Venturi tees are restrictive https://www.troublefreepool.com/threads/solved-venturi-tees-are-restrictive-heater-bypass-next.269119/post-2358505 TLDR: At 1250 and 3450 RPM, I get 30 and 60 GPM in Spa mode (6 returns), but 45 and 105 GPM in Pool mode (3 returns), measured via a FlowVis...

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TLDR: At 1250 and 3450 RPM, I get 30 and 60 GPM in Spa mode (6 returns), but 45 and 105 GPM in Pool mode (3 returns), measured via a FlowVis 2x2.5" - why?

Going on 2 years with our pool and I've never once had algae, scaling, or corrosion of my plaster - thanks entirely to TFP principles. However, my 12" raised spa has never quite been at the pressure I would prefer - even at the maximum 3450 RPM of a 3hp intelliflo. I'm considering installing a heater bypass (learned it has its own intellivalve port) to boost the flow (I would divert say 30% of the water past it in heater mode and 90% in non heater mode)... but then I'm thinking WHY is the flow so different than the pool in the first place? I have removed the spa jets (no difference either way), turned off the venturi valve (no difference either way) bypassed the solar panels (big difference but that's the same pool vs spa). Ran some tests:
1) Spa mode (suction from spa, output to spa): 30 GPM at 1250 RPM and 60 GPM at 3450 RPM.
2) Spillover mode (suction from pool, output to spa): Same results as above.
3) Pool mode (suction from spa, output to 90% pool, 10% spa). 45 GPM at 1250 RPM and 105 GPM at 3450 RPM.
4) Pool mode but manually turn the returns 100% to pool. Same results as above.

The spa is raised 12" and 2" flex PVC was used because of the circular layout:


Any thoughts?

 

[ajw22]

Very simply, the spa return jet plumbing has greater "head" then the pool return plumbing.

The spa jet plumbing has many more twists and turns and smaller pipes then the pool returns.

Your problem is why I recommend two pump systems for spas to ensure adequate spa jet flow pressure.

What model Intelliflo pump do you have?

 

[matthewsunshineflorida]

Very simply, the spa return jet plumbing has greater "head" then the pool return plumbing.

The spa jet plumbing has many more twists and turns and smaller pipes then the pool returns.

Your problem is why I recommend two pump systems for spas to ensure adequate spa jet flow pressure.

What model Intelliflo pump do you have?

Thanks for your quick response! It's model 011056.

It's definitely 2" rigid from the pad and then 2" flex PVC going into the spa (compare the first photo to the 2" rigid for the known 2" wall suctions and a 2" overflow pipe).



The pad is on the spa side, so the two returns on the far side of the pool are going all the way around the spa and straight down the pool (i.e. at least 20ft more than the spa, plus more 90s to each fitting). Each of the 3 pool returns are also eventually reduced to small 3/4" eyelets. So the pool returns are further away, there's less of them, and they restrict down to a much smaller diameter, yet they have so much less head than 6 1.5" spa returns somehow?

Are you seeing this differently? Legitimately just trying to find either a fix or an explanation - because if the plumbing is inherently restrictive more than the water heater, a bypass is probably not going to make a huge difference, right?

 

[ajw22]

Bypassing the heater will lower the head in your system and improve the flow rate a bit.

At this point it is what it is. It is hard to fix basic hydraulics after all the plumbing is under concrete.

Please host your pictures directly on the forum. The way you link to them does not let them render properly in larger formats.

 

[matthewsunshineflorida]

Understood and my apologies - I got an error message of them being "too large" to upload here so I was trying to simplify with thumbnail links.

I guess I'm just trying to understand if this is normal - and how there's such a disparity without obvious restriction. Makes me wonder if gunite got into the line or something else I haven't thought of. I've had a hard time finding similar examples of pool/spa discrepancies when they're plumbed similarly.

 

[ajw22]

Plumbers are creative animals. No two seem to do things the same way. Many of them improvise with what they got unless specified differently.

Your plumber improvised with normal T's for the air/water interface instead of using one like this...

I doubt your plumber or builder did any hydraulic calculations on what was being built...

 

[matthewsunshineflorida]

Plumbers are creative animals. No two seem to do things the same way. Many of them improvise with what they got unless specified differently.

Your plumber improvised with normal T's for the air/water interface instead of using one like this...

Definitely agree on the creativity ha! However, they are definitely not normal tees - if they were, the water would shoot out the venturi valve on top of the spa, rather than sucking air in. I know it was a crappy photo upload so I compressed it to be able to upload the full size - see how one side of the T is shorter than the other - that's the same as in the attached photo.

I actually think you did inadvertently solve my problem though - the very principle of venturi IS the restriction! That explains why it makes virtually no difference whether the spinning jets with small holes are screwed in or not - the bottleneck is further back at the venturi tee. That didn't occur to me for some reason, so apologies if that's what you intended to say by "spa jet plumbing" having higher head!

Also found a thread showing around a 50% reduction in power consumption at a given flow rate with a heater bypass on a 3hp intelliflo, so I assume the principle remains true on the flip side - same RPM means significantly higher GPM. I'll post back with my findings for anyone curious.

Verifiable Benefits of a Heater Bypass Install

I found when considering a bypass, that there are primarily 2 types of responses I would get when inquiring about the pros and cons. 1. I don't see why you would want to install a heater bypass, but I cant see how it could hurt anything. (My builder was in this group as well) 2. It's a...

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