Focus on the Filter (Pentair Sand)

[ksquared]

I have narrowed my choice for the filter to the Pentair Tagelus 60D. I eliminated the Pentair Sand Dollar because the tank is thermoplastic. I'm thinking the Tagelus 60D should be fine, but a few of experts much prefer the Triton II, although both Tagelus and Triton II are made with a fiberglass reinforced tank. I thought the main difference was the Triton II is side inlet/outlet, but the Tagelus is on top. The Triton II needs a valve purchased separately, which seems counterintuitive to me, since any filter will need a valve, but it becomes very expensive once everything is included. I don't know that the benefit is there though.

One point is that I'm not sure about is if The Triton II TR60 inlet/outlet is 2" pipe or 1.5", as the Tagelus 60D is 1.5". All the plumbing for the pool is 2", but from my research reading the experts' opinions, cutting down to 1.5" for the filter shouldn't be an issue, as it makes sense to me that the filter is going to be a restriction anyway, but what do I know.

The help here is always greatly appreciated.

 

[mas985]

There is a very large difference in head loss between 1.5" and 2" MPVs (2x) so given a choice, I would always go with a 2".

 

[ksquared]

Thank you for that insight. It does make sense, I'd even be willing to go the extra cost for the 2" inlet/outlet on the bigger valve, but I'm still confused.

Doesn't both the 2" inlet valve and the 1.5" inlet valve go down the same pipe into the sand filter? Or is the 2" inlet the major consideration for doing the required backwash, as indicated, reaching back to 10/2/2013, mas985 said,

For example, a multi-port 2" backwash valve will have 50' of head loss at 182 GPM which is not really realistic. For a flow rate of 80 GPM, a backwash valve will have a head loss of about 10' of head (per Pentair spec sheet). Still high but not 50'. At 20 GPM, the head loss drops to 0.6' of head.

I understand, 2", like a four-lane expressway, straight, traffic moving without problems. Cut it back to three lanes, and yes, everything slows down, and a much bigger traffic jam if everybody is trying to go 100 rather than 30. But what I don't understand, isn't the 1.5" inlet somewhat just an extension of the filter? Which I'd think of the filter inlet pipe as going down to two lanes, so much more traffic impediment. Won't the 2" system's head loss, due to the filter, with a 2" Multi-port valve or a 1.5" Multi-port valve, be very close to equal? Or is the actual filter not the major cause of the loss?

Edit: OK, I did more research, it seems if you get a 2" valve you also must replace the inlet pipe which will be larger to fit the 2" valve. So learning that, I do understand more that 2" remains throughout the system. I just don't know if the "very large difference in head loss" is critical or just a detail that the pump will overcome.

 

[mas985]

It is a series of head losses that add together for every fitting and every piece of equipment. So yes, the sand media also adds head loss but it is independent of other features of head loss. Just envision a packet of water traveling from the pool, through the skimmer, pipe, fittings, valves, pump, fittings, filter, fittings, valves, pipe, and finally through the return eyeballs. EVERYTHING the water touches adds head loss and it does not matter where in the chain it might be. The major determinants of head loss are water velocity and plumbing geometry.

A transition from 1.5" to 2" adds head loss but the water traveling through the MPV also has head loss that is proportional to the diameter^4 of the fitting diameter it is traveling through. So a 2" vs 1.5" fitting, assuming exactly the same geometry scaled to a different diameter would have a theoretical head loss ratio of ~3:1. This is why diameter is very important.

Edit: OK, I did more research, it seems if you get a 2" valve you also must replace the inlet pipe which will be larger to fit the 2" valve. So learning that, I do understand more that 2" remains throughout the system. I just don't know if the "very large difference in head loss" is critical or just a detail that the pump will overcome.

You don't have to use 2" pipe with an 2" MPV, you can use bushings with a 1.5" pipe although I would not recommend that.

The largest impact of head loss is pump efficiency. For the same flow rate, it will cost more to run a pump on 1.5" plumbing that it will for 2" plumbing. Or another way to look at it is that for the same RPM, you will get more flow rate with 2" vs 1.5" plumbing.

 

[ksquared]

I appreciate your help and knowledge! I've spent a few hours reading, and the most informative ones have been yours. Now I'm thinking I'm understanding a bit more.

A filter's main purpose is to trap debris that gets by the skimmer and pump basket. It will pretty much do that at nearly all flow rates below the rating. Some tiny debris can be pushed through with too much flow rate but that is usually only an issue with dead algae and maybe pollen. Most pool debris is large enough to be caught by the filter regardless of the flow rate.

But there is an optimal flow rate for your Intelliflo for energy efficiency. This would be the lowest RPM where water still travels over the weir door in the skimmer so you still get skimming action at the lowest possible flow rate. With a single skimmer, this would be around 15-20 GPM. But usually, there is no need to go much below about 800-1000 RPM because the power draw of the pump starts to level out at that point. This operating point would also be a good thing for the filter as it is low enough flow rate to trap nearly all debris.

Looking at the chart in the "Have you lost your head" thread, the Pentair Quad DE with 2" valve loses 1.5 @ 25 GPM, and 6.1 @ 50 GPM, vs. the 1.5" valve loses 2.5 @ 25 GPM, and 9.8 @ 50 GPM. So at 25 GPM, the difference seems fairly small, but at 50 GPM, is losing 3.7 ft of head a major loss, and economically what is a reasonable price to mitigate this difference? I'm thinking a small difference over many years though will add up to a big difference at some point. Can you run the pool at this lower 25 GPM all the time to mitigate? If I run at 20 GPM that will give 15K gallon turnover in 12 hours, which I thought would be OK for a 15K gallon pool.

 

[mas985]

Is there really that much of a difference in cost between 1.5" and 2" to be concerned about it? Especially when you compare it to the total cost of the pool.

 

[ksquared]

Especially when you compare it to the total cost of the pool.

Yes, I do agree. The price difference is about $240, so small percentage in the overall scheme of things. I like the better size going forward for all those years.

But, this is more of a supply question, as I can get easily get the one with 1.5" but the 2" one is harder to find locally.