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.
Click to expand...
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) 🤦‍♂️
 
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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.
 
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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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mas985 said:
The original pump PSI and suction in-hg you posted were 30 PSI and 9" HG respectively. This would indicate a total head loss of close to 80' of head. From the pump curve, flow rate is right at 180 GPM (DMJ curve). There may be an issue with your flow meter.

1747773869804.png
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The suction side reading has changed slightly (see below). How does this change the calculation of "head loss"? How do you calculate total head in feet from those two gauge readings? What gpm do these two measurements indicate now? Not sure if it matters, but remember... that suction side gauge does not go to zero when the pump is off because the gauge is about 2' above water level (see third pic below).

We meet with the PC on June 3rd to discuss their proposed solution(s). All the information that you have all provided will be very helpful in that discussion. At this point it sounds like figuring out the discrepancy in the flow rate between the flow meter and what is indicated by those readings at the pump is key before anything else is done. I will definitely have them pull apart the pump and check the impeller. Since we did have that impeller replaced in the past two years, it's possible that the wrong size impeller was installed. How can I get the part number for the original impeller on our pump?


IMG_9204.jpgIMG_9205.jpg1748020346070.png
 
Not sure if I asked this question before... If I bypass the filters, i.e., put the MPV is "Recirculate" mode and the flow rate at the flow meter doesn't change, does that eliminate the filter(s) and filter media as a potential source of the low flow rate? Should I expect to see any difference in the pump suction and pressure gauge readings when the system is running in that mode?
 

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JPMorgan said:
The suction side reading has changed slightly (see below). How does this change the calculation of "head loss"?
Click to expand...
What has changed on the suction side? For the suction level to change, some valve or other thing has changed.


JPMorgan said:
How do you calculate total head in feet from those two gauge readings? What gpm do these two measurements indicate now?
Click to expand...
Return Head Loss (ft) = Pressure (PSI) * 2.31 = 30 * 2.31 = 69.3'
Suction Head Loss (ft) = Suction (in-HG) * 1.13 = 10.8 * 1.13 = 12.2'

Total Head Loss (ft) = Return Head + Suction Head = 69.3'+ 12.2'= 81.5'

Then you look up the flow rate from the head curve: ~175 GPM

1748026854798.png

JPMorgan said:
Not sure if it matters, but remember... that suction side gauge does not go to zero when the pump is off because the gauge is about 2' above water level (see third pic below).
Click to expand...
That is ok and due to the height of the gauge over water level. The pressure side reacts in the same way but in the opposite direction so counters the suction side and nets to zero.

JPMorgan said:
We meet with the PC on June 3rd to discuss their proposed solution(s). All the information that you have all provided will be very helpful in that discussion. At this point it sounds like figuring out the discrepancy in the flow rate between the flow meter and what is indicated by those readings at the pump is key before anything else is done. I will definitely have them pull apart the pump and check the impeller. Since we did have that impeller replaced in the past two years, it's possible that the wrong size impeller was installed. How can I get the part number for the original impeller on our pump?
Click to expand...
It is usually stamped on the side of the impeller. Also, sometimes a clog in the impeller inlet or vane can also change the pump's head curve so it would have a different flow rate than what the pressure and suction would indicate. So while they have it apart and you confirm the part#, check the internal vanes for any clogs.
 
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mas985 said:
What has changed on the suction side? For the suction level to change, some valve or other thing has changed.
Click to expand...
The only valves I have adjusted are those ones for the heater bypass, Valves 9 and 10 are completely open again, but Valve 8 may not be in the exact same position. Should I tweak that valve to see if I can get a slightly lower reading on that suction gauge... back to where it was?
 
JPMorgan said:
The only valves I have adjusted are those ones for the heater bypass, Valves 9 and 10 are completely open again, but Valve 8 may not be in the exact same position. Should I tweak that valve to see if I can get a slightly lower reading on that suction gauge... back to where it was?
Click to expand...
It didn't really change things much so I don't think that is the real issue. Confirm the impeller part# and condition.
 
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Maybe you just need to replace the pump.

022035
WhisperFloXF VS Commercial Pool Pump
208-230/277-460V single-phase; 208-460V three-phase.


www.pentair.com

WhisperFloXF® VS 5HP Variable Speed Pump

The WhisperFloXF VS 5HP Commercial Pump is the first five-horsepower variable-speed pool pump that runs on single-phase or three-phase power.
www.pentair.com www.pentair.com

Drive Features
• Active Power Factor Correction
• High Drive Operational Efficiency
• Flow Control Capable when Paired with a 4-20mA Flowmeter (Pentair P/N 97014-4203KIT).
• Versatile Power Input:
– Single-Phase, 208-230/277-460V, 20-21/17-11A
– 3-Phase, 208-460V, 13-6A

 
JamesW said:
Maybe you just need to replace the pump.

022035
WhisperFloXF VS Commercial Pool Pump
208-230/277-460V single-phase; 208-460V three-phase.


www.pentair.com

WhisperFloXF® VS 5HP Variable Speed Pump

The WhisperFloXF VS 5HP Commercial Pump is the first five-horsepower variable-speed pool pump that runs on single-phase or three-phase power.
www.pentair.com www.pentair.com

Drive Features
• Active Power Factor Correction
• High Drive Operational Efficiency
• Flow Control Capable when Paired with a 4-20mA Flowmeter (Pentair P/N 97014-4203KIT).
• Versatile Power Input:
– Single-Phase, 208-230/277-460V, 20-21/17-11A
– 3-Phase, 208-460V, 13-6A

Click to expand...
Sounds like it might be a good option, but we will check out the impeller and other parts on the existing pump first to make sure there isn't something obviouly wrong there. If we are required to operate the pump at 170 gpm would we want a variable speed or a single speed pump?
 

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