Losing / poor prime

[Jpadie]

Hello

First time on here. Hello everyone!

I've just converted (tried to) my in ground magiline cartridge pool to a more standard set up with a pool house, pump and sand filter.
It didn't go smoothly. Happy to expand on that if useful....

Anyway the new pump I have (a polish clone of a Hayward super pump) seems not to prime properly. The inlet is about 30cm above the water line. There is a non-return valve in line. It's a 63cm suction line.

The pump is 1.5hp. and the sand filter is sized to match. Pool is just under 100m3. There are two main returns plumbed with 50cm lines. A third is a jet with a 50cm line and the last is a 25mm line passing through a booster for a Polaris 280.

Whatever the scenario, with pump at full speed and the prefilter filled with water, I end up with the bucket only half to two thirds full.
If, after ensuring all air has escaped, I turn down the speed, by the next day the bucket will be filled only under the inlet. There will be precious little flow. And lots of air in the sight glass area of the chlorinator.

I have done and redone the joints on the suction lines. Sprayed with foam and no dimpling. When I say redone, I've junked the whole line and rebuilt it. Twice. There is no leak there.

The pump itself seems ok. I've taken it to bits and regreased and seated the joints. The prefilter I've cleaned and regreased most days. The exhaust port for the pump likewise.

The pump manual says it's good for 8ft of self priming. It's got 30ish cm to cope with and fails.

The suction lines come from (perhaps) the main drain and a large side port in the pool. This floods a reservoir about 1m deep and 75cm diameter. There's a hole in the bottom which is attached to the suction like. I can't see what's going on with the plumbing there as it's under concrete and the constructor isn't forthcoming with plans. I have not been successful at threading an endoscope either. It's not impossible that it's blocked but not likely either.

I'm really not sure about the main drain. There's no feeling of suction but I can't see what else it would be connected to.

But just in case this causes confusion, the skimmers are not not not connected to the suction line. They work via Bernoulli effect caused by the return jets. It's a rubbish system.

Going back to the pump:. Is the thing junk? Or am I missing a trick?

Looking forward to your collective wisdom.

Thanks in advance
Justin

 

[cowboycasey]

Welcome to TFP Justin

Is there any way you can upload some pictures of your setup and what is happening, it would give us more to work with...

If the suction side is clogged can you run something back to the pool to see if it is clogged or maybe it gets unclogged... Did this setup work before with the pump you changed out?

We will see if we can get something going...

 

[Jpadie]

thanks for the welcome @cowboycasey

I will indeed upload some photos in about an hour.

in the 'old' setup, the pump was under the water line and had no suction line. But I have spliced into the 'flow' to install the new kit. Difficult to visualise I'm sure, so I will upload a diagram with the photos.

I have thought of plumbing the suction into the return and dropping a hose into the pool for the suction line. see whether that dislodges anything. but the plumbing would be a headache. I don't have a drain-king here either and haven't found a decent looking alternative in France. But I have snaked down a karcher unblocker. from where the pump suction line is exposed to the pump I have snaked about 6m and there's no blockage. from the other direction I can't get beyond a foot - but I think this is because there may be a manifold there. I agree that a good blast of pressure might give some great insight though!

I have a port near the pump suction for a suction side cleaner. difficult to prime as it's above the water line and supple pipe. But it is 50mm so some decent flow can be obtained. with this in place I definitely do get suction at the end of the vac - but not what I'd expect from a barracuda or similar. and after an hour of that I have no prime left. Relevant because this is plumbed about 12 inches from the entry to the pump.

I've been trying to persuade friends to let me borrow their pool pump for an hour too ... so far I just get sypathetic shaking of the head in reply!

back later!

 

[Jpadie]

to add to the previous message - the setup is new. so there is no previous history of the setup in its current state. but the suction line is *unchanged* save that. I have cut it, installed a shut off and non-return valve and connected to the pump. ie. if it has a break before the plumbing then it has always had a break (and i've got no leakage). I've checked the suction plumbing as best I can and can find no leaks.

right. here are some photos. I've yet to get the diagrams done but the important thing to get across is that in a magiline system the skimmers have no flow lines. just return. the return jets create a low pressure area that sucks the water through the skimmer, the leaf-basket and the filter cartridge.

however there used to be a chlorine filter in the loop. i took the(63mm) flow into this as my suction line and the output (which split into 3* 50mm returns) as my returns.

general photos of the pool:




this is one of the two skimmers. the 'box' on the right is mainly taken up with pebbles. but the bulge on the left of the right box is where the return jet comes out and mixes with a moulded pipe that connects with the bottom of the skimmer (about 1m deep).




this is a photo of the central 'pod'. the left is where the old pump went. just a flow. no suction. the right is a reservoir. see photo below for more info.




this is the the reservoir from closer. the side entry goes into the pool basin. I suspect that the bottom port is the main suction. although blocking it off seems to have little effect on the pump...




this is a photo of the pool shed area. shed to be built...
the suction line is 63mm and that diameter is maintained until the split into the individual returns. which are all 50mm except the flow to the booster pump, which is 25mm. this connects to a point on the pool wall for a polaris 280. when i turn this on, I loose most of the flow to the rest of the pool.



a close up of the returns.




a close up of the pre-filter. this was after 4 hours of running at full-tilt. there was almost no water left in the basket.



and lastly a close up of the pump spec. I thought it was Polish but in fact it is Spanish. my mistake.

 

[mas985]

When a pump fails to prime, there are usually one or more issues.

1) The pump lid gasket is broken or may just need some pool lube. Same for the pump drain plugs.

2) The impeller is clogged with debris. You may need to remove the motor from the wet end to inspect the impeller.

3) The suction line is clogged with debris. Back flush toward the skimmer to loosen.

Do you see the filter pressure changing at all during the priming process or is it always at zero?

Is there air coming out of the returns and is the flow strong?

 

[Jpadie]

Hello

For sure the pump lid is not the cause. Once prime is lost it is very difficult to remove the lid. And I regrease it frequently.
There is no link between the skimmers and the suction line unfortunately. So I cannot backflush towards the skimmers. As above, I do think it is possible that there is some clogging of the suction line at the pool end.

There is always air in the returns when the pump is first turned on. I have to purge it by allowing flow through one return at a time.

The impeller is not blocked. I disassembled the motor last week and found the gaskets were dry so lubed those.

The pressure in the filter when the pump is at first at full tilt is usually around 8psi. At this stage the prefilter is not full. (2/3 perhaps). It never fills, whether in recirculation mode or rinse etc.

I'm not confident about what the pressure does when the pump loses prime. I want to say that it drops to zero but I've never made a note

As an aside when I was checking the pool before bed last night I noticed that the waste line from the multi-port valve is leaking a little. In filter mode and recirculation mode there is definite change in pressure when I put my hand over the port. But I don't see this as being relevant to the priming issue as it is on the return side.

Today/tomorrow I will run a temporary hose from the pump's suction port directly to the pool. If that fully primes the pump then a problem in the main suction line is likely I think?

 

[Jpadie]

To confirm my guess, having checked the filter and pump this morning the pump ha almost its prime entirely and the pressure in the filter and multi-port valve is down to zero. There is no flow in the sight glass and the flow switch is, of course, off.

 

[cowboycasey]

It really sounds like there is something wrong with your pump, at 2 meters it should have no issues at all getting prime and keeping it... to troubleshoot can you connect 1 pipe to the suction side and 1 back to the pool taking all other pipes out.. does it work? if it does start connecting 1 piece at a time and see where the pump fails..

 

[Jpadie]

Thanks.

I'm trying with a pipe from the pool to the suction now. Just waiting for the cement to set.

I'm keeping the return as it is for now as I'm out of 63mm pipe. But as a question:is there anything on the return side of the pump that can cause loss of prime?

 

[cowboycasey]

If there are any leaks anywhere in plumbing "maybe" It is usually on the suction side or in the pump from what I have seen...

 

[Jpadie]

ok. good to know.

so there's now a pipe running straight from the top of the basin to the suction line. the pump would not prime at 49hz but did prime at 54hz. it's designed for 50hz ...


when I say 'prime' i mean that it has stopped sounding like it is sucking air and there is now flow and only limited air bubbles in the sight glass. the end of the pipe in the pool feels like it has excellent suction.

but the pre-filter is far from full. It's at about 50% of the entrance hole.

I have turned the pump down to 1.5Amps and will leave it running for a few hours to see what happens to the prime.

thanks!

 

[Jpadie]

So... A few hours later after pumping at 1.5A. The basket was down to about 1.5cm above the bottom of the inlet.

I plugged a flexible hose vac into the end of the temporary pipe in the pool after turning the pump up to 4.5A. good suction from the broom, but not good enough to suck an insect off the surface from 2 inches (vac submerged under the surface). But still good enough to pull on my hand strongly

At the end of the vac session the basket was quite low. Unplugging the vac helped and I'm back now at about a cm above the bottom of the inlet. I guess i must have gulped some air with the vacuum at some point.

I've put the pump back to 1.5A to recheck in a few hours but I'm at a bit of a loss now.

On the one hand this is definitely an improvement over before in terms of suction and the ability to prime. This suggests that the non return valve on the "normal" suction is leaky or my plumbing is sub par.

On the other hand i would expect a 63mm hose with only 25cm of head and one 90°angle to cope with to provide plenty of water for the pump to be able to fill itself completely.

I'm trying to get hold of the pump manufacturer to ask whether this pump is designed to be happy without being full. I cannot imagine why but I do read other people feeling that their pumps are behaving normally without the water level being fully over the inlet. Incidentally the manufacturer (Fluidra) is the company that owns lots of pool brands such as Polaris and Zodiac etc. They are in Spain and perhaps they will reply.

I have the option of breaking out a few metres of concrete and putting the pump below the water line. But I'm loathe to do this unless it is going to be a necessity for all pumps.

 

[mas985]

Are you sure this is a self-priming pump? 18m max head is fairly low.

Exactly how high is the pump inlet above water level? Does the pump spec support that lift?

Are you running that pump off a VFD? If so, is the motor inverter duty?

Also, if there is very high restriction on the return side, that could also prevent the pump from fully priming. Given the multi-port is leaking and the pressure in the filter is low, that might be an area of concern.

 

[Jpadie]

Hello

The pump inlet is about 25cm above the water line. I don't know much about the pump's design but it is marketed as self priming and the indication is 8ft )as it is a drop in replacement for the Hayward superpump. The manual says that if the pump is to be installed above the water line the pressure differential must be less than 0.02MPa which it says is the equivalent of 2mH20. I've little idea what that means.


Yes the pump is running off a vfd. It's rated for 3HP and has not run hot in the last six weeks since I started the pool up. The pump is three phase and I've wired it in delta formation. I can hook it up to a single phase with a shifting cap but realistically that can't be the issue as it's drawing the right number of amps at the right number of rotations (within 10% wiggle room).

I don't think there is material restriction on the return. The behaviour is broadly the same in recirculation or filter mode (obviously there is a difference but explainable by the filter medium). The returns are all clear and are 50mm pipes.

The pressure in the filter with the new plumbing direct to the top of the poop basin is about 11psi when the pump is at full speed. The filter is oversized for the pool so I've not seen it get much higher than that.

 

[mas985]

What was the filter pressure with the old pump?

Have you checked the pump unions for leaks?

 

[Jpadie]

There were no measurable filters in the previous installation. The pump was a special magiline fxv2 unit and the filters were cartridge, built in to each skimmer. The pump had very little to do but was still 1.5hp and very expensive to run.

I've checked the pump unions in that there is no water escaping and no dimpling of shaving foam. But I've also, just in case, removed cleaned and re-teflon'd them a couple of times. No change in behaviour.

 

[mas985]

Just to confirm, the test you did earlier bypassed most of the suction side plumbing correct? Where the TEE and valve are located in the picture above. Does this line completely bypass ALL of the suction side plumbing? If not, is it possible for it to do so? I am having a hard time visualizing the bypass. Perhaps a few pics would help.

 

[Jpadie]

Hello.

It's indeed probably easier if I post a photo of the current set up. See below




The blue flex hose in the water connects to the solid pipe (I didn't have enough of either) and then into an elbow directly into the pump. There is nothing else on that line. The lift is 25cm.

I'm sorry for the abject mess. I'm still in the process of building the shed and I can't see the point in tidying up until the plumbing is done and the pump correct. I think I will have to break out all the concrete to the skimmer (to make the magiline skimmer into a "normal" skimmer. So that's more mess. I do appreciate it's difficult to see what's going on though!

I lost prime earlier. And then I could not get it back whether on recirculation or filter. I eventually regained prime by holding the end of the flex hose about 1m20 up in the air with a garden hose shoved down in at full blast. Then when I heard the motor change I dunked the whole thing. Terribly heath Robinson.

But I do wonder at a pump that cannot achieve prime 'normally' on 4m of pipe with a 25cm lift.

Anyway the water is now at the top of the strainer and a couple of inches from the top of the prefilter glass. That is the best it's been in 6 weeks. I've left the pump on filter and at 1Amp and will see how dire it all is in the morning.

I fear that a change in pump is nigh...

 

[mas985]

It really does sound like it is an issue with the pump. You have eliminated pretty much everything else.

 

[cowboycasey]

I agree, sounds like that pump is not able to do what it is supposed to... if it only primes with a garden hose above the pump I believe it is an above ground pump and has no priming ability or at least very little ability...