High pressure in sand filter

JamesW

TFP Expert
Mar 2, 2011
27,709
Just 1 more information : I hope that downgrading the impeler doesn't matter with this kind of pool (endless feature) which need water to overflow in a tank behind the pool.
It might be an issue depending on the amount of flow required by the feature.

Do you have a picture of the pool?

How much flow does the feature require?

You can go to a variable speed pump if you want or maybe try the smaller impeller to see if the feature still works.
And 1 last question : I understand everything about the "sizing" of all the equipments and I will do it following your recommendations. BUT, the high pressure problem began about 2 months ago. In your opinion could it have been caused by an unfavorable evolution of the badly dimensioned system or will it be necessary to look for another cause even after having changed impeler and diffuser?
If the pressure problem started only recently, then I would suspect a configuration problem or a defective piece of equipment.

Since your system is more complicated than a regular residential system, you will probably need an onsite visit so that a qualified technician can carefully go over everything to see what the actual problem is.

Maybe a valve is set incorrectly or maybe a failed check valve or maybe something else.
 

Stefany

Member
Jun 29, 2021
24
Thailand
Pool Size
200000
Chlorine
Salt Water Generator
SWG Type
Astral Viron V45
Update


It might be an issue depending on the amount of flow required by the feature.

Do you have a picture of the pool?

How much flow does the feature require?

You can go to a variable speed pump if you want or maybe try the smaller impeller to see if the feature still works.

If the pressure problem started only recently, then I would suspect a configuration problem or a defective piece of equipment.

Since your system is more complicated than a regular residential system, you will probably need an onsite visit so that a qualified technician can carefully go over everything to see what the actual problem is.

Maybe a valve is set incorrectly or maybe a failed check valve or maybe something else.


A very busy week carrying out the operations recommended by JamesW and replacing some spare parts.



1st step: THE PUMP: The brand’s engineer told me that the current 3HP pump is barely sufficient for the volume of water to be treated, the entire pool having to be renewed once, according to him. every 4 or 6 hours. For him : Pool volume (200 cubic meters) / 3HP pump flow (36 cubic meters per hour) = about 6 hours, so just normal. When converted to gallons, this gives pool volume (53,000 gallons) / pump flow (9,510 gallons / hour, or 158 GPM). So he told me the pump was properly sized.

Anyway, I forgot that I had exactly the same pump model but an 1HP one for a jaccuzzi which is totally separate from the pool. So it was easy to switch the pumps and see what happens with a 1HP pump connected to the pool system.

Result: absolutely no change. With a 1HP pump the pressure is as high as with a 3HP pump !



2nd step: replacing the filtrer lid which had exploded as well as spare parts to kiw the lid and the gasket as JamesW tough they seemed damaged. I emptied all the sand from the filter since it was not possible to change the gasket (under screws). Before restarting (I was already with the 1HP pump and had not restarted the 3HP pump) I decided not to put the sand back in the filter for testing.

Result: absolutely no change. With the 1HP pump and the sand filter empty of sand the pressure is still very high (a little more besides but this is due to the change of pressure gauge which was delivered with the new lid).



3rd step: full return to service. I put the sand back in the filter, ran the 1HP pump.

Result : absolutely no change, the pressure is exactly the same with and without sand (or a really tiny difference).

So I restarted the 3HP pump and it didn't really change anything .



So now, the system has been examined in almost all its elements and these tests show no defect to explain the high pressure.



After explaining to the brand’s engineer again :

. that the filter did not seem to be the cause since (in addition to having been completely dismantled and checked), in RECIRCULATE mode (where water does not circulate in the filter - I even carried out the test while the filter was completely disconnected from MPV) the pressure was also high

. that the MPV was new and appeared to operate normally after being disassembled and checked

. that the RETURN line did not seem to be the cause since in RINSE mode (where water circulates in the filter but does not go into the RETURN line since I can close the line valve without problem) the pressure is also high,



He wanted to test the filtration mode by discharging the water elsewhere than in the RETURN line. For me this is equivalent to the RINSE mode but anyway I did, by flooding the technical room for a few moments : it did not change the high pressure.

He is going to have the matter studied by another engineer, but between us I have little hope.



Some additional information: by changing the pump and therefore interested in the operation of the jaccuzzi which is quite similar to the swimming pool, I see that the jaccuzzi pump is located 4 meters below the water (compared to 7 meters for the swimming pool). When I stop the jaccuzzi pump, the gauge drops to 0. A few weeks ago when I had no high pressure problem on the swimming pool system, it was the same for the swimming pool: pump stopped the gauge was at 0. Now the pressure with the pump off is 5 to 7 PSI.



Another very surprising thing about the swimming pool for the pressure observed at the MPV (and not at the filter): pump stopped, pressure at 5PSI. I close all the inlet valves, put the MPV in the closed position. Due to the handling of the MPV which releases the pressure to the sewer, the pressure drops to 0. But a few hours later, the pressure rose to 5PSI. I relieve the pressure by letting the water escape from the MPV through a purge until the pressure is at 0. A few hours later, the pressure 5PSI is back up. As my whole system was dismantled, I took the opportunity to examine where this pressure could come from by gradually dismantling all the piping elements and valves connected to the MPV. To see that water was flowing from the pump to the MPV. All the inlet valves to the pump being properly closed (very serious verification made no leaks), the pressure is created in my opinion by the water or the air present between the 3 valves coming from VACUUM, TANK and MAIN DRAIN and the pump outlet. However, the problem can hardly come from the pump since when I switched the pumps between 1HP and 3HP, there was always overpressure.



Maybe a minor detail, but since I have this high pressure problem, the pump lid gasket is frequently damaged (it slackens). Likewise, I can no longer fully close the lid (to get the marks perpendicular to the pump as indicated in the manual and as it works very well on the jaccuzzi pump). The lid seems tightly closed but something has happened, I don't know what. I bought a new cover and new gasket that I tried: I can't close it perpendicular anymore.


Stefany, maybe a silly question but ....... those two gray valves that are used before and after the salt generator, are they always on that position? I know the red handles everywhere are currently closed because your filter is broke, but those grey valves are partially closed as well. That would increase your filter pressure.

TEXAS SPLASH when you said the problem was probably right after the filter: The problem still exists when I disconnect the RETURN line and connect a temporary pipe to see what the filtration pressure is when the water is drained from the filter.



Can we agree that the problem cannot come:



. the water inlet: the high pressure exists regardless of the source of the water (VACUUM, MAIN DRAIN, TANK)

. filter: Since I tried without the sand, by disconnecting the filter from the MPV and there is still an overpressure (noted on the MPV since by definition there is no longer a gauge connected to the circuit since the filter is disconnected)

. of the RETURN line since when I disconnect this line the high pressure is still thre (RINSE position or even direct discharge after the filter without piping)



I know this is difficult to understand, but I am wondering if it is possible that the high pressure is being caused before the filter. That is to say on one of the following 5 elements I tried to describe with pictures attached :

1) pipeline which centralizes the 3 water inlets,

2) pump,

3) check valve just after the pump,

4) pipe connecting the pump valve to the MPV,

5) MPV.



Knowing that the pump has been checked and that even with a 1HP pump the overpressure exists and that the MPV is new ... What do you think? You are my only hope because I really have no idea how to find a solution.


Merci beaucoup !
 

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Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2014
33,424
Texas, San Antonio/Marion, South-Central Area
Pool Size
17888
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-45 Plus
You certainly have done some exhaustive work - well done. I just want to be sure of something I mentioned earlier and that is when you are referring to the main issue here (high pressure) you are referring to the filter gauge correct? Not the MPV gauge you installed? Maybe @JamesW will have a theory for the purpose of the MPV gauge you installed, but we generally focus on the filter gauge. I just don't want us to get confused when troubleshooting.

Near the end of your post you mention the five items that might apply, items 3-5 would seem to result in a lower filter pressure if something was wrong. Items 1 & 2 .... seem unlikely as well, but perhaps James sees something from a hydraulic standpoint I don't.

Earlier you mentioned one of the gauges not going to zero when off, which one was that? Was that teh filter gauge?
 

JamesW

TFP Expert
Mar 2, 2011
27,709
With a 1HP pump the pressure is as high as with a 3HP pump !
You have a blockage somewhere.

It will really require someone on site to go through everything to find it.

As far as turnover goes, there is no reason to get a specific turnover unless this is a commercial pool that has to meet turnover requirements or a very high use pool.
 

Stefany

Member
Jun 29, 2021
24
Thailand
Pool Size
200000
Chlorine
Salt Water Generator
SWG Type
Astral Viron V45
I just want to be sure of something I mentioned earlier and that is when you are referring to the main issue here (high pressure) you are referring to the filter gauge correct? Not the MPV gauge you installed? Maybe @JamesW will have a theory for the purpose of the MPV gauge you installed, but we generally focus on the filter gauge. I just don't want us to get confused when troubleshooting.
Yes it's right. I always referre to the filter gauge. Only when we talk about the recirculate ou closed mode, means when the filter is out of order I referre to the MPV gauge, to check what happens.

arlier you mentioned one of the gauges not going to zero when off, which one was that? Was that teh filter gauge?
To be clear, a few months earlier, when I hadn't any pressure problem, I remember when the pump is off the gauge (filter gauge) is going to zero. Last week when I replaced the 3HP for a 1HP used for the jaccuzi as James told, I saw that on the jaccuzi system, when I turn off the pump the gauge went to zero too. But now, with this high pressure problem, on the pool system, when I turn off the pool pump, the filter gauge (as the MPV gauge) went to 5 or 6 PSI. It is the same when I start the system with no pressure, all valves closed. The gauge (filter as MPV) is at zero and when I open a valve (either the main drain valve tank or vacuum, or the return line valve, or both) the pressure rises to 5 or 6 PSI. I start the pump, the pressure rises to 20 or 22 PSI. I shut off the pump, the pressure drops to 5 or 6 PSI.

And I guess the cause of the problem is linked with this fact. Why the pressure is the pool system is now so high, even when the pump is off. It is not only the static pressure because before it didn't happen and because on the jaccuzi system (even if the height is lower - 4 meters/7 meters) the gauge goes to zero. Can an obstruction in the succion line cause such an high pressure in the system even if no air or bubbles can be seen in the pump basket? High pressure problem is usually caused by an obstruction in the return line but there, when the return line is not used (I connected an other pipe on the return line to test) the pressure is still high. As I answer to James, it's now sure there isn't any blockage on the return line because when I bypass this return line the high pressure is still there. So, for me, the blockage is probably only in a very small area : the 5 items I described in the last message. Or, may be (new idea) caused by something in the succion pipe which make the pressure rise jsut before the pump (cause pump off the pressure is more than 5PSI). It's for what I wonder if something in the succion line can cause this high pressure.

Thanks
 

Stefany

Member
Jun 29, 2021
24
Thailand
Pool Size
200000
Chlorine
Salt Water Generator
SWG Type
Astral Viron V45
You have a blockage somewhere.

It will really require someone on site to go through everything to find it.

As far as turnover goes, there is no reason to get a specific turnover unless this is a commercial pool that has to meet turnover requirements or a very high use pool.
Alright. I understand about the pump and I will clear it when the high pressure problem will be solved.
And about the blockage I cannot find any area where it can be. As I told, when I disconnect the return line and install a temporary pipe the pressure is still high (as in the rinse position). It seems it cannot be the return line, cannot be (?) the MPV, cannot be the pipe connecting pump to MPV (?). So now the only other idea is a blockage in the succion line (but in this case it means a same blockage in 3 pipes at the same time (!) why not?

But to test this idea, I have first to know if a blockage in a pipe can increase the pressure? What I saw in hydraulic website let me doubtful.

It will really require someone on site to go through everything to find it.
Yes for sure. But at this moment, due to the covid-19 situation, nobody from the capital city can come here, and there are only 3 pool shops with very poor knowledge of hydraulic problems. They came, couldn' understand and proposed to change sand, so change MPV, ... No way. It is for what I'm so insisting searching for a solution.
 

JamesW

TFP Expert
Mar 2, 2011
27,709
A blocked suction will not cause high pressure in the filter.

Can you show some more pictures of the equipment with the entire system in a single picture?
 

Stefany

Member
Jun 29, 2021
24
Thailand
Pool Size
200000
Chlorine
Salt Water Generator
SWG Type
Astral Viron V45
Thanks. So I stop searching solution in the suction line.

Please find attached 2 pictures of the entire system in one shot.

I send an other one with reference number to follow the water from the pool to the pool

1. 2. 3. water comes from the pool by 3 ways (1. vacuum, 2. tank, and 3. main drain which is standard mode). Below 3 ball valves for each number, and for pipes 1. and 2. check valves.
4. pipe collecting the 3 pipes and going to the pump
5. pump
6. check valve
7. MPV
8. filter
9. return line
(between 7.9. the pipe going up is connected to the MPV for the waste water)
10. electrolyser with bypass
11. return line
12. small pipe connected on 16a to collect water from the pool for ph regulation 13. can, 14. acid pump, 15, acid injection, 16. going to the return line
17. small filter for nothing because after the filter so the water is clear.
When I tried to filter the water with the return line disconnected, I opened this small filter and connected a pipe to go outside. So the water passed through the pump, the MPV, the filter, then arrived at this small equipment, passed into a new pipe and was therefore connected neither to the RETURN LINE nor to the electrolyser.

I hope this can be helpful to understand the system. I noted today the pressure keep on rising (now in filtration mode, the pressure is about 22PSI in the filter.

Thanks for your help.
 

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JamesW

TFP Expert
Mar 2, 2011
27,709
I don't know what else to check.

I suspect that you will have to go through everything and take it apart until you find the problem.
 
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