Backwash procedure for pool with 2 filters

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Lake Placid said:
You can do it with the pump running. Mandatory to open valve 8 all the way first. It shouldn’t technically matter the sequence of the other 2, but closing 9 first will stop flow through the heater before closing the outlet side. You won’t put un-necssary pressure on the heat exchanger vs closing 10 first which would allow pressurized water to get trapped in the heat exchanger. Always close and open the valves slowly.

Reverse the sequence when opening. Open 10, then 9, then tweak 8. Although depending on what happens to flow with the heater bypassed, valve positions may need to be tweaked to get the desired flow rate.
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I will try this today and see if flow rate improves at all. Will post results shortly.
 
Lake Placid said:
You can do it with the pump running. Mandatory to open valve 8 all the way first. It shouldn’t technically matter the sequence of the other 2, but closing 9 first will stop flow through the heater before closing the outlet side. You won’t put un-necssary pressure on the heat exchanger vs closing 10 first which would allow pressurized water to get trapped in the heat exchanger. Always close and open the valves slowly.

Reverse the sequence when opening. Open 10, then 9, then tweak 8. Although depending on what happens to flow with the heater bypassed, valve positions may need to be tweaked to get the desired flow rate.
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I adjusted valves as you said. Unfortunately, there was no increase in the flow rate with Valve 8 fully open and 9 and 10 closed, so I returned the valves to their original positions. Sounds like I can pretty much rule out any valves and lack of by pass for heater as the source of the low flow rate reading. That leaves me with the following potential issues causing the low reading at the flow meter:
  1. Faulty Flow Meter (Remedy: Install new digital flow meter to improve visibility/accuracy of flow rate reading and to see if rate increases)
  2. Improper Position of Valves (Fix: Have pool company inspect and make sure all valves are set correctly)
  3. Heater by-pass (Fix: If no bypass, install heater by pass)
  4. Hydraulically Inefficent Plumbing (Remedy: Replace sections of plumbing that may be restricting flow.) (Recommended by pool company.)
  5. Leaky MP Valves: (Remedy: Not likely the cause of the problem, but should be addressed. Water flows out of backwash line in "Filter" mode. Replace spider gasket or install new MP Valve (Recommended by pool company.)
  6. Filters Restricting Flow Rate (Remedy: Replace media (sand) in filters or replace both filters. (Recommended by pool company) Note: when filters are put in "Recirculate" mode, there is no increase in flow rate.
  7. Pump not meeting required output (Remedy: Inspect impeller. Replace impeller with larger one(?). (Impeller was replaced less than 2 years ago.) Consider new pump.)
Re: #4 above, the photo below is the section of the pipe that I believe the PC is saying is "hydraulically inefficient". Does that make sense? Are we likely to see any increase in flow rate with changes to that section of the plumbing? If MPVs are replaced would that plumbing need to be cut anyway? Is addressing the items above (in that order) the best way to proceed? Anything else to consider or rule out? The Big Question seems to be.... why are the gauges at the pump indicating a flow of 180 gpm, but the flow meter is reading 120 gpm?

Here, again, is the assessment of the problem by the PC and the three options they propose (along with my comments):

Assessment
  • The largest problem is the failing multiport, although it is unknown how many GPM will be gained in that repair. Since the plumbing will need to be cut apart to change the multiport valve it is an opportune time to correct any hydraulic flow issues.
  • Since the filters themselves are quite old (the filters have a date of 2018 on them) and the fiberglass is known to warp and leak, the best solution is to completely replace the filters at this time and eliminate possibilities for future needed repairs.
Options
Complete System Upgrade
  • Remove 2 existing filters. (7 year old filters should not need replacing, right?)
  • Supply and install 2-TR100C filters including new multiport valves and media. (Not sure why they would replace TR-140C filters with TR-100C filters, unless it is a matter of space and plumbing.... maybe getting the larger filters into the room is also an issue.) Would 2 TR-100C filters be adequate to handle the required flow? Would the smaller filters run at a higher pressure?
  • Reconfigure inlet and outlet piping for filter system.
Rebuild Existing System
  • Remove existing filter media and replace.
  • Remove faulty multiport valves and multiport configuration.
Multiport Valve Only
  • Remove and replace 2 existing multiport valves.
 

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Simplest/least expensive solution is to replace your flow meter to verify its accuracy. Unfortunately it may be good money after bad as we don’t know that the current flow meter is actually malfunctioning. If you see the same result in flow after that, digging in to deeper solutions is necessary. (Yes call me captain obvious) 🤦‍♂️
 
JPMorgan said:
Hydraulically Inefficent Plumbing (Remedy: Replace sections of plumbing that may be restricting flow.) (Recommended by pool company.)
Click to expand...
The concern I have is what does that actually mean? Is it hydraulically inefficient because it should be 4”, 6”, 8” in diameter?….. or because it has too many restrictive fittings….or because anything? They have not defined the actual root cause, which leaves you with a potential fix that could mean re-plumbing everything depending on the knowledge/expertise of the diagnostician….Call me pessimistic but their diagnosis/proposed solution leaves me feeling a bit queasy.
 
Before replacing any plumbing I would try to reconcile the disconnect between the flow meter and pump pressure/suction measurements. They each indicate different flow rates.

Either one or both may be incorrect but if both are correct then there is something wrong with the pump because it does not match the published head curve.

I would separate the wet end from the motor and get a part number off the impeller to verify it is the correct one.
 
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