Changing pipework - does it increase flow

[Richard_S]

Not being a fluid engineer, thought I would ask here;

I have 1.5" piping and have just installed both a new chlorinator and VS Pump. The max speed for the pump is 3000rpm and the minimum is 600rpm. To a point I want to use the slowest speed that I can with the pump, subject to keeping the pool clean, to save on electricity.

My problem is that the minimum flow rate through the Pool Pilot seems to be 2100rpm - as below this it shuts down, which is therefore not benefiting my electricity bill much.

Would changing the pipework to 2" all around, as much as I can, help give a greater flow through the Pool pilot? Looking at the photo below, any thoughts or suggestions?

 

[mas985]

Larger pipe would help a little bit but may not be enough it make it worth the change. Is the bypass valve (red handled), completely off?

Did you have another post at one time? I think I remember the plumbing configuration.

Also, what is the filter pressure at 3000 RPM and 2100 RPM?

What is the filter gauge height relative to the water level?

Is the backwash valve 1.5" too?

What is the distance to/from the pool?

It appears you have two return lines, do they each feed only one eyeball or multiple eyeballs?

What is the eyeball diameter?

On typical 1.5" plumbing, you should be able to go down to 1200 RPM so there is clearly a high restriction somewhere in the plumbing.

 

[holubec37]

Re-plumbing with 2" would decrease flow rate (velocity) and lower discharge pressure. I know very little about the Pool Pilot, but I would have to assume that it's designed to run off of a certain flow rate which is why it's shutting down. Increasing the size of the plumbing would allow more water to bypass the cell due to less flow restriction in the 2", therefore even less flow through the cell. Although, depending on how much you replace, there still may be enough 1.5" plumbing to keep backpressure on the pump to where replacing only "some" plumbing would be negligible.

Maybe there are some fluid engineers on this forum that can correct me if I'm wrong.

 

[Richard_S]

Hi Mark thanks for your help, have taken each question separately for you...hope that helps?

Larger pipe would help a little bit but may not be enough it make it worth the change. Is the bypass valve (red handled), completely off?

Yes. Closed

Did you have another post at one time? I think I remember the plumbing configuration.

Yes, we talked about the Pool pilot before...I was having similar problems but have changed the pump to VS and this again shows the PP to not accept the lower RPM/flow rate...Still trying to work out if there is something wrong with the PP sensor.

Also, what is the filter pressure at 3000 RPM and 2100 RPM?

17 PSi and 9PSi respectively (I don't run at 3000rpm as this is too much for the sand filter)

What is the filter gauge height relative to the water level?

about 3ft vertical to bottom of sand filter then another 3ft approx to top of sand filter and gauge, so my guess is about 6ft.

Is the backwash valve 1.5" too?

Yes, believe so

What is the distance to/from the pool?

pump house is at the skimmer end of the pool, which is rectangular - this is about 15ft from nearest skimmer
return water inlet eyes are 50-60ft away

It appears you have two return lines, do they each feed only one eyeball or multiple eyeballs?

2 separate eyeballs

What is the eyeball diameter?

about 1 inch

On typical 1.5" plumbing, you should be able to go down to 1200 RPM so there is clearly a high restriction somewhere in the plumbing.

Pool Pilot shuts down below 2100rpm

 

[toofast]

Try putting in smaller eyeballs....you actually need more "pressure" I believe.

 

[Richard_S]

Try putting in smaller eyeballs....you actually need more "pressure" I believe.

I can close the return valves down, which would do the same thing, no? but this would simply put back pressure on to the system, it wouldn't necessarily increase the flow rate passing through the Pool pilot?

 

[toofast]

Try putting in smaller eyeballs....you actually need more "pressure" I believe.

I can close the return valves down, which would do the same thing, no? but this would simply put back pressure on to the system, it wouldn't necessarily increase the flow rate passing through the Pool pilot?

So I am not 100% sure, but I was told that even though you are having a low flow issue, it is really a pressure issue. I had the same issue with my Heat Pump, and I learned it was a pressure switch vs. a flow switch.

I am sure other SWG experts will chime in to confirm or deny.

 

[mas985]

I don't believe it is a pressure switch. This is in the manual:

Tri-Sensor Assembly
The Tri-Sensor Assembly is used to measure water
flow, salt level, and water temperature.
When the water flow reaches a minimum flow rate of
20 gpm (76 L/m), the flow paddle magnet closes a
micro-switch that is monitored by the Control Unit.
Note: The use of high strength magnet devices in the
close proximity of the Tri-Sensor can cause the flow
switch to function incorrectly.

That is a standard flow rate switch. A pressure switch would not be safe for a SWG as the unit would continue to produce chlorine when flow rate stops (e.g. dead headed pump).

But given the pressure, the return side plumbing (post filter gauge) has much higher head loss that what would be expected for that setup. If I calculate the head loss, it is about half of what you are experiencing so there is something in the plumbing that is causing higher than expected head loss. Has the filter been backwashed recently?

Also, if you open the bypass valve, what is the filter pressure at 3000 RPM?

 

[Richard_S]

I don't believe it is a pressure switch. This is in the manual:

Tri-Sensor Assembly
The Tri-Sensor Assembly is used to measure water
flow, salt level, and water temperature.
When the water flow reaches a minimum flow rate of
20 gpm (76 L/m), the flow paddle magnet closes a
micro-switch that is monitored by the Control Unit.
Note: The use of high strength magnet devices in the
close proximity of the Tri-Sensor can cause the flow
switch to function incorrectly.

That is a standard flow rate switch. A pressure switch would not be safe for a SWG as the unit would continue to produce chlorine when flow rate stops (e.g. dead headed pump).

But given the pressure, the return side plumbing (post filter gauge) has much higher head loss that what would be expected for that setup. If I calculate the head loss, it is about half of what you are experiencing so there is something in the plumbing that is causing higher than expected head loss. Has the filter been backwashed recently?

Also, if you open the bypass valve, what is the filter pressure at 3000 RPM?

Ok, so bypassing the PP by opening valve makes no difference on the filter pressure at 3000rpm( also closing off PP, leaving it open, makes no difference with bypass valve open)

I have backwashed (i did it yesterday too) just now to check pressure. After backwash and rinse pressure in the filter is 15psi @ 3000rpm and at 8psi @2100rpm

 

[mas985]

Ok so that probably means it isn't the SWG that is causing the high head loss.

The extra head loss is either downstream in the return pipes or it could be in the backwash valve or maybe in the filter itself. With the old pump did you ever notice a sharp increase in pressure at any point or was the pressure fairly consistent throughout the time you owned that pump?

Have you ever inspected the backwash valve and/or the sand/laterals in the filter? Does the filter have a recirculate mode and can you drop the pump RPM when it is in that mode?

Also, if you close off each of the return lines, does the pressure increase to the same amount for both lines or does one line have much higher pressure than the other?

Just trying to eliminate some possible causes.

 

[Richard_S]

Ok so that probably means it isn't the SWG that is causing the high head loss.

The extra head loss is either downstream in the return pipes or it could be in the backwash valve or maybe in the filter itself. With the old pump did you ever notice a sharp increase in pressure at any point or was the pressure fairly consistent throughout the time you owned that pump?

No, apart from the slow build up of pressure over a period of a week/2weeks or so as the filter got "dirtier" - which was cured by doing a 30sec backwash followed by a similar time in "rinse" mode.

Have you ever inspected the backwash valve and/or the sand/laterals in the filter?

No but I'm getting a feeling in ma waters....

Does the filter have a recirculate mode and can you drop the pump RPM when it is in that mode?

And that's the kicker, just tried this in recirculate mode and I can run the pump down to 800rpm before the Pool Pilot shuts off - so something either in the filter or the selector switch is killing the flow....

Also, if you close off each of the return lines, does the pressure increase to the same amount for both lines or does one line have much higher pressure than the other?

and that didn't work out too good...closing down one of the valves to the return forced a leak at the join of the PP with the grey 1.5 piping....The PP seems to swivel around it's 2" to 1.5" white connectors...sure that shouldn't happen....should be glued in the vertical position no? Anyway, a little gentle adjustment and I have got the leak down to a drip - which I will have to fix tomorrow... Need to go back to that one to work out if there is a blockage on the return, but more likely a problem with one of the eyeballs....which I already know about....

thanks for all the help by the way, definitely getting somewhere....I think the next step may be dealing with the sand filter....

 

[JasonLion]

The AutoPilot SWGs only need about 15-18 GPM to work, and I find it difficult to believe that this setup can't produce 18 GPM even at very slow speeds.

Have you checked the strainer inside the SWG manifold to see if it is dirty? It is easy to overlook that strainer.

Another possibility is that the bypass ball valve is actually open a little, despite the handle being in the closed positions. That isn't exactly a common issue, but you do see it now and then.

Hum, your latest info suggests neither of these are the issue, still worth a quick check.

 

[Richard_S]

Have you checked the strainer inside the SWG manifold to see if it is dirty? It is easy to overlook that strainer.

Another possibility is that the bypass ball valve is actually open a little, despite the handle being in the closed positions. That isn't exactly a common issue, but you do see it now and then.

Hum, your latest info suggests neither of these are the issue, still worth a quick check.

yes, had already checked the strainer a couple of days ago. Seems the guy who fitted the PP didn't bother putting it in so am currently awaiting a new strainer which I ordered as soon as I realised it was missing. Needless to say I cannot get hold of pool guy...Probably scared him with the "where's the strainer that should be in the PP gone??"... Either way a bit worrying, because if something has gone into the tri sensor I don't suppose that will do it much good. Having said that, recirculating tends to suggest that it's working fine....at the mo....

 

[mas985]

If it works down to 800 RPM in recirculate, it is definitely the filter/backwash valve. Either laterals, caked sand, or perhaps something stuck in the backwash valve (less likely). Hate to say it but if you don't find something wrong with the valve, it might be worth it to remove the sand in the filter and check the laterals. A big job but it should reveal the issue. First, you could try an extra long backwash and see if that helps any.

 

[Richard_S]

Whohey!!

5 minute backwash seems to have done the trick. The only thing that stopped me was that the pool water level went below the skimmers!

Anyway, seems that the pressure is now down to 12psi on 3000rpm and I can run the speed of the pump down to 1000rpm on filter mode, before the PP shuts off.. which is a great result. The pool was built and commissioned in 2008 so has had 5.5 summers' of use. Probably about time I changed the sand? Just unfortunate that it's 250kg of sand each way....

Thanks for all the help Mark and others, glad we seem to have got to the bottom of this one.

Just out of interest on the photo below of the pool pilot, should this joint be glued? It isn't on my set up and now that it's leaking both water (and I think letting in air) I can't believe that this should not have been welded together when the PP was installed.

 

[mas985]

And yes, the joint should be glued unless it is threaded.