Low flow and low pressure. What is wrong?

[Monomial]

Situation:

 

I was away for 2 months and nobody took care of the pool. In fact, the pump was simply left on 24/7. No salt was added. Rain came.Eventually, the salt water chlorinator turned off the pump due to low flow.

 

The bottom of the pool had some nice green/brown slimy areas.

 

There was clearly no salt in the water.

 

Anyway, I have shocked the pool and killed everything that was in there. I restored the salt level. The pool looked good except for a small amount of the green/brown slime, which I thought I could simply vacuum up.

 

Build up to the problem:

 

I backflushed the sand filter because I had no idea when the last time it had been done. It seemed to work normally in that I got a decent flow out of the waste pipe and the dirty water eventually cleared. I then tried to vacuum. After about 15 minutes the suction seemed to quit. I stopped and cleaned out the cyclone filter at the ingress to the pump. The problem remained. I tried to backflush the sand filter again. I can only get a trickle of water to come out the waste pipe, despite the fact that the filter is below the level of the pool, and gravity alone should be pushing water through it.

 

Then I tried to put it back into filter mode,  and I had absolutely no pressure on the sand filter at all. Unless I closed the return valve to the pool, in which case the pressure would build (so not a gauge problem). I thought I must have channeling in the sand filter, so I opened it up and mixed up the sand. Yes, the sand was very slimy on the top, but nothing extreme and no obvious channels.

 

I put everything back together and turned on the filter. Only  a marginal improvement.

 

The problem:

 

Now I have a few PSI on the sand filter, but still very low volume.

 

Troubleshooting:

 

I have redundant pumps on this pool, and I switched pumps. There is no difference, so I don't believe the pump is the problem. I tried all 3 water sources from the pool. Vacuum port, overflow tank, and main drain. All of them give low flow, so I don't think it is a blockage in the system, unless it is in a very short section of PVC that is common to all 3 right before the water enters the pump. But I discount that possibility because if it was a blocked pipe before  the pump, then the water level in the pump should fall as it is starved for water. That doesn't seem to happen.  The cyclone filter before the pump impeller has a clear lid which clearly shows the water level is full.

 

So I'm left with a conundrum. I believe there is no issue with air or blockages from any of the pool drains up to and including the pump, and I believe there are no issues with the pump itself. But I still clearly have very low pressure on the filter, combined with very low water volume.

 

What else could be wrong?

 

The only thing I can think of is that maybe the multi port valve is clogged somehow?  Does this sound reasonable? I am a bit hesitant to try and take this apart if I don't have to, because I have a great talent for taking things apart and then being unable to reassemble them.

 

Can anyone else think of something that might be causing the problem. I have attached a marked up graphic of the filter setup. Remember, this is all below the level of the pool, so there is positive water pressure at the ingress to the pump.

 

Summary of the facts:

 

Both pumps show the same problem -- conclusion? Not a pump issue.

All 3 water sources show the same problem -- conclusion? Not a PVC leak issue

Pump water level remains full during use -- conclusion? Not a block on the common PVC line

 

What else can cause simultaneous low pressure and low volume?

 

Any suggestions appreciated. My children will thank you if you can help me get this working.

 

 

[sappersrest]

Ok the  solution to your problem may be very simple and have witnessed this probably a hundred times in my career.

 

The lid to the pump strainer has not been fitted correctly

the white basket has a small notch at the bottom and should correspond , with a small lug at the bottom of the pump strainer box, once you have located this correctly the basket should be flush  with the top of the housing, then replace the lid preferably applying silicon grease.

be careful not to over tighten as you may distort the o ring.

What you have describe is the result of air ingress on the suction side of the pump.

If this fails to work you may have to file the lug or the notch as you may have damaged both in your previous attempt

Good luck

[sappersrest]

EDIT

 

The basket should be  below the top of the housing or sometimes flush  with the top of the housing,Not above.

[Monomial]

Thanks for answering sappersrest. A good night's sleep and your response inspired me to do some more digging.

 

I don't think the basket is out of place (there is a very clear notch where it sits, and it is firmly seated in place), but a more thorough analysis convinces me there is definitely a leak in the system.

 

It is hard to see through the plastic lid on the pump when the water is spinning, but I was finally able to catch it. The water level in the cyclone filter in the pump was definitely down about 4 cm from the top when it should have been completely full.

 

That means there is a leak. I just need to figure out where. I'll go ahead and get some silicone grease and see if it is due to the lid. That would certainly be the easiest fix. I suppose over time and extended use grease could be slowly pulled away from the seal by moving water.  That pump was running for nearly 3 months continuous. And the other pump I opened before turning it on. I did not regrease either O ring before putting the lid back on.

 

If that is not the problem though, I am not sure where to check next. 

 

Thanks for your help. If you have any further advice please let me know.

[sappersrest]

Do you have water in the balance tank, if your pump is drawing from this and it is empty ???? no flow

 

Top the pool up to normal levels i.e. over flowing then top the balance tank up about half full   ..... then try pumps

 

 

" tried all 3 water sources from the pool. Vacuum port, overflow tank, and main drain."

You may have a float valve in the balance tank that feeds from the bottom of the pool ensure this is not stuck.

are you are able to isolate these 3 sources.

try shutting the valve from  balance tank and vac point ......then try pump

 

 

To check wether the basket is seated correctly .

Remove basket refit lid.

Start pump again if this works the the problem is that the basket has been fouling the perspex lid causing it not to seal correctly. this needs very careful examination.

[Monomial]

This is becoming very frustrating. I can not find anything wrong.

But first, finding silicone grease is incredibly difficult. Silicone sealant, easy. Grease? Impossible. I went to 4 hardware stores (MegaHome, Thai Watsadu, HomePro, and Global House) and the local pool supply. Nobody carries it. Where do you guys find it?

 

In any case, after careful examination I do not believe this is the problem anyway. I turned on the pump while holding incense sticks around the lid. There was absolutely no suction of air through the lid. Zero. Not even a puff.  I proceeded to do the same thing around the remainder of the common PVC piping. Again. Absolutely no leak of air that I could find. I would still like to find the grease and rule it out completely though.

 

What else could be wrong? Blockage in the pipe?

 

Again, the same low flow situation happens no matter which water source I select, and with the other sources turned off. Also, the same problem happens even when I change pumps.

 

And the first manifestation of the problem was when the pump was left on continuously for 2-3 months while the pool was not maintained, the salt became depleted, and green slime and algae formed in the pool. The balance tank was selected at this point, and while it got very low it did not actually run dry. It was just barely above the level of the intake port.

 

What does this suggest to anyone?

 

Where could the problem be if not the lid?

 

 

 

[sirmud63]

ok , heres one to try out . check the intake in the middle of the impellor in both pumps . somtimes they can block up with leaves and rubish .iv found this to be the problem many times . so maybe worth a look.

[sappersrest]

Ok

Another thing to look at is the valve on the suction side of the pump even though you are turning the handle is the valve open?

these type of valve handles have a tendency to  to either round off or split giving the impression you are opening or closing the valve.

 

Two easy ways of checking first one ... with the valve in the open position try to push a pice of hose 1/2  dia or less from the pump through the suction pipe it should go through until you hit the elbow. if it does the valve is ok.

Second..... pull off the red handle of the valve and check that is not rounded or split......if that is the case you will have to check the valve spindle is in the correct position. you will have to do this using an adjustable spanner move it 1/4 turn and see if you can put the hose through it.

DO NOT USE PLIERS.

Are you in Chiang  Mai?

[grollies]

Start from the suction side and work through your pumps and filter to the pool return.

Ensure balance tank and pool are full.

Close pump suction and discharge valves.

Remove top from strainer on both pumps.

Open suction valve (as Sappersrest says, check the valves are operating OK) to each pump in turn. You say the pumps are below water level so the suctions should  free-flood quickly proving no blockage on the suction lines. If the suctions flood really slowly then you have debris in the suction lines.

If OK then using the valves on the suction side fully flood the baskets, close the valves and replace the lids (use Vaseline if you cant find the right grease).

Now your pumps are partially primed and your suction lines are OK.

Next, remove the pipework between the pump discharge valves and filter multiport valve.

Open the suction lines.

Open the pump discharge valves until water flows and all remaining air is displaced.

Fully close the discharge valve to one pump.

Half close the discharge valve to the other and start the pump. You should get good flow and pressure. (Note, never start a pump against a closed valve).

Slowly gag-in the discharge valve against the pump. You should see an increase in pressure from the pump by the increase in distance the water 'squirts'. (If you can fit a temporary bend to the pump discharge this saves getting very wet!). Repeat on second pump.

At this point if you get a good pressure indication from the pump discharge the next step is to look at your multiport valve. Take it out and flush through. Replace.

If no good pressure from your pump the impellors may be excessively worn.

Disconnnect the pool return pipe from the multiport valve.

Set the multiport valve to by-pass and start the pump(s).

If flow is good stop the pumps, change muliport valve to filter and re-start the pump.

If no flow your problem is the filter medium.

If flow is good re-connect the pool return line and re-start the pump.

It is unlikely your return line is blocked as it has always been run through the filter and you'd get pressure back-up on the filter gauge.

Sounds like a priming issue 

 

 

[grollies]

How're you getting on?

[sappersrest]

Come on give us a clue to how it is progressing please.

[grollies]

On 16/12/2016 at 0:30 PM, sappersrest said:

Come on give us a clue to how it is progressing please.

Reminds me of a joke we told as kids:

''how do you keep an idiot in suspense?"

[grollies]

PS the use of vaseline on the pump strainer lids is a temporary fix only for testing your pumps while you source a silicone-based sealant. Once you finish testing your pumps clean off all vaseline.

[Monomial]

The mystery is finally solved, and I was a bit shocked at what it was.

 

An Intex Dive Stick had managed to get sucked all the way through the plumbing and blocked at the final elbow. I guess the pump suction was simply not enough to pull it through the final vertical section into the pump.

 

Anyway, all that remains now is to rebuild the common section of the PVC pipe back to the pumps and find someplace that sells silicone grease.  Anybody with a source for that in or around northern Bangkok (or online) please let me know.

 

Attached is a picture of an Intex Dive Stick for anyone who doesn't know what it is, and also the markup of exactly where we finally found it lodged in the plumbing.

 

Thank you for all the advice.

 

[grollies]

<deleted>! How on earth did that get there???

 

Anyway, nice one, glad you resolved your issue :-)