16 July 2024 Finishing Up my OB Pool

[ajw22]

We're lifting about 5.5' and the spec is 10' max so that shouldn't be a big issue. I've got 4" pipe to the pump suction where we reduce to 3" straight to the suction flange. I think part of the difficulty is that we've got about 50' of 4" pipe to lift through and the prime cycle isn't long enough to get water up to the check valve.

This lifts the water in the suction pipe about 6" each time.

50’ lift 6” at a time = 100 cycles?

Or

5.5’ lift 6” at a time = 11 cycles?

 

[JamesW]

The pipe should automatically fill to the same level as the water level in the trough.

The lift should be 5.5' or about 11 cycles.

 

[setsailsoon]

50’ lift 6” at a time = 100 cycles?

Or

5.5’ lift 6” at a time = 11 cycles?

Yep, I knew this was going to be a lot of work. That's why I came up with the "hose water injection" at the pump suction method... will be easier to leave the pump running and just open and close the valve~100 times.

 

[setsailsoon]

The pipe should automatically fill to the same level as the water level in the trough.

The lift should be 5.5' or about 11 cycles.

Don't I also have to fill up the 50' of pipe? It's mostly above the trough level.

 

[JamesW]

This whole pipe should be full of water.

The only lift should be about 5' near the equipment.

 

[setsailsoon]

Don't I also have to fill up the 50' of pipe? It's mostly above the trough level.

Oh, I get it...or does it fill with each cycle to the new level in the pipe?

 

[JamesW]

Each cycle will pull the water up about 6" in the pipe and you lock it in place with the check valve or regular valve like putting your finger on the end of a straw to hold it up in the straw.

 

[JoyfulNoise]

I didn’t really look carefully but I assume there’s no skimmer in this pool design? A skimmer would have put a source of water at or above the level of the equipment making the priming a lot easier.

Just a crazy idea here - Maybe temporarily connect a return line to the suction side of the pump so water can be pulled through a return?

 

[JoyfulNoise]

Or setup some temporary line that can be dropped into the top of the pool to pull water into the pump?

 

[JoyfulNoise]

A question for the hydraulics nerds - is there a minimum speed (suction head) that the pump will have to run at to keep the water in suction line moving and avoid losing head? I imagine if the pump speed is too low, and therefore not generating enough head, the weight of all that water in the pipe at that difference in elevation will cause the pump to lose prime.

Anyone do that calculation for this pump and pipe setup?

 

[mas985]

You shouldn't need to run these valve cycles to prime the pump. A self-priming pump recycles water from the volute into the suction side of the pump automatically and should continually build suction in the pump basket.

Part of the problem may be procedure.

When you close the suction valve, fill the pump basket, close the pump lid, turn on the pump first before opening the valve. Opening the valve first, will just drain the pump basket to the inlet because the pressure side of the pump is not primed so it will gravity drain out.

 

[mas985]

A question for the hydraulics nerds - is there a minimum speed (suction head) that the pump will have to run at to keep the water in suction line moving and avoid losing head? I imagine if the pump speed is too low, and therefore not generating enough head, the weight of all that water in the pipe at that difference in elevation will cause the pump to lose prime.

Once a pump is primed, it will only lose prime if there is entrance of air into the plumbing so no, there is no minimum RPM.

However, to prime the pump initially, there is a minimum RPM because the suction pressure has to be low enough so that the pool water pressure can push water up the pipe into the pump basket.

And yes you can calculate that minimum RPM to do so but if you want to prime as quickly as possible, then I would use full speed especially at this lift.

 

[mas985]

The manual says not to prime for more than 30 minutes. This seems like too long to run it dry to me. I don't think I have any suction leaks since when I run for a couple minutes and then stop I can hear a vacuum break when I remove the suction strainer lid.

How long are you allowing the pump to run in order to prime? Several minutes should be not an issue. You may just not be allowing the pump to run long enough. The recirculation mechanism in a self-priming pump takes a bit of time for high lifts. But it shouldn't take more than about 5 minutes. If it does, then there could be a leak in the plumbing somewhere.

Weird that I thought the 4" suction line would help with flow could be causing the prime difficulty because it holds more water.

Actually, the size of the inlet pipe does not matter that much. What matters is the pressure differential in pump basket which determines the lift. Having a bit more air because of the pipe size will just increase the priming time a bit.

 

[ajw22]

5 minutes can feel like a very long time when waiting to see the pump prime.

IntelliFlo VS pumps have a prime cutoff where it shuts down if it senses no prime. Let the pump do its own thing priming for as long as it wants and protect itself if it decides to shutoff.

 

[setsailsoon]

How long are you allowing the pump to run in order to prime? Several minutes should be not an issue. You may just not be allowing the pump to run long enough. The recirculation mechanism in a self-priming pump takes a bit of time for high lifts. But it shouldn't take more than about 5 minutes. If it does, then there could be a leak in the plumbing somewhere.


Actually, the size of the inlet pipe does not matter that much. What matters is the pressure differential in pump basket which determines the lift. Having a bit more air because of the pipe size will just increase the priming time a bit.

Thanks for the reply, I'm probably being too cautions and not running long enough to protect the seals. After I stop and wait a few minutes I still hear the vacuum suck into the basket as the top comes of so I'm pretty sure I don't have a leak. Just to be on the safe side I did the water drip test on all joints above ground. The pressure test held for several weeks at 30+ psi so I think the pipe run from the basin to the pad is good.

Chris

 

[mas985]

I believe the max prime time is a settable parameter:

Max Priming Time

Default: 11 minutes

The maximum priming time can be set from 1 - 30 minutes. This setting is the amount of time the pump will try to prime before it gives a priming error. If this occurs, fill the pump basket with water and restart the pump.

 

[mas985]

Thanks for the reply, I'm probably being too cautions and not running long enough to protect the seals. After I stop and wait a few minutes I still hear the vacuum suck into the basket as the top comes of so I'm pretty sure I don't have a leak. Just to be on the safe side I did the water drip test on all joints above ground. The pressure test held for several weeks at 30+ psi so I think the pipe run from the basin to the pad is good.

Chris

Remember than once you fill the pump basket up to the top of the impeller inlet, the seal is fully covered with water and remains so during the priming process. The only issue with running too long is the water heats up but that only occurs after a very long time which is why the maximum prime time is at 30 minutes so technically you are safe to that point.

You are actually probably doing more damage to the pump by shutting it on and off. Just let it run and it should prime.

 

[setsailsoon]

Remember than once you fill the pump basket up to the top of the impeller inlet, the seal is fully covered with water and remains so during the priming process. The only issue with running too long is the water heats up but that only occurs after a very long time which is why the maximum prime time is at 30 minutes so technically you are safe to that point.

You are actually probably doing more damage to the pump by shutting it on and off. Just let it run and it should prime.

Right now, I'm running max rpm continuously for 4 min then opening the garden hose up to the suction side of the pump. I'm also carefully monitoring the bowl surface temp and nothing other than warm. I open the hose up for about one minute till the suction port is liquid full then stop for 4. minutes. When I add water there are massive bubbles coming out of the pool returns so the pumps definitely doing some work... been through 4 cycles so far.

 

[mas985]

Right now, I'm running max rpm continuously for 4 min then opening the garden hose up to the suction side of the pump.

Why are you doing that? You are adding pressure to the suction side of the pump which is exactly the opposite of what you are trying to accomplish. The point of priming is to lower the pressure in the pump basket.

Just fill up the pump basket, close the lid and start the pump. But let it run for longer than 4 minutes until the pump shuts off itself.

 

[JoyfulNoise]

Right now, I'm running max rpm continuously for 4 min then opening the garden hose up to the suction side of the pump. I'm also carefully monitoring the bowl surface temp and nothing other than warm. I open the hose up for about one minute till the suction port is liquid full then stop for 4. minutes. When I add water there are massive bubbles coming out of the pool returns so the pumps definitely doing some work... been through 4 cycles so far.

You could try opening the air relief valve on the top of the filter. That way any air drawn in will be blown out the air relief rather than run through the plumbing. It will shoot water too but at this point it doesn’t matter.