Flexible PVC Pipe (solvent weld)

[Ratsima]

Thank you for the detailed analysis. I understand most of it. What's hard for me to understand is how 20 grams of biofilm can halve the diameter of the 5/8" hose in less than 48 hours.

I constructed the stream to be a bio filter. The total length is about 3 meters and it is about 30 cm deep and full of sand and gravel. I know that it works well, at least for some things, because when I had to replace the pond liner with ferrocement I removed the sand and gravel and thoroughly cleaned it. When I put the clean sand and gravel back in the stream the pond was a mess until the stream biota could grow back.

I have now replaced the old semi-rough interior garden hose with a 5/8" PVC hose with a smooth-as-glass interior. I don't hold out much hope, but it was a lot cheaper than importing the 1" flex PVC hose recommended by several on the pond forum.

I should know in a few days whether or not the smoother hose makes a difference. If not, I'll bite the bullet and import the larger hose.

Another thing I did was mostly eliminate the 90º bend making use of a cold chisel and Swiss Army knife saw. In doing so I found that the bend was actually 45º, not 90º. I've managed to remove enough of the old fitting that it is almost a straight shot for the hose from the surface down into the pond. I can put a length of rebar through without any problem.

Finally, I'm sure you're right about removing the sediment more frequently. It's not that hard and the compost heap seems to be happy with it.

Thanks again for taking the time to do such a detailed and thorough analysis of the situation. Most fascinating.

With your permission I'd like to repost on the Garden Pond Forum.

[laser]

<What's hard for me to understand is how 20 grams of biofilm can halve the diameter of the 5/8" hose in less than 48 hour.>

To put it more correctly, the hydraulic effect of the jelly appears to be equivalent of using a clean hose of 8 mm diameter.
Here we don't know the 'wet' volume of the gel (that has way much higher water content than the 20 g concentrated residual paste). For the given 5/8 " hose about 4 mm biofilm "thickness" (where water would not flow) is required to constrict the "free flowing" diameter to 8 mm. That seems to be excessive and unlikely. To make it more complicated, studies found that flow reductions by biofilms could not be well explained by wall roughnesses and/or diameter constrictions. Even relatively thin films increased the resistance quite significantly, sometimes. With the new hose in place, you will learn the cause, soon.

<I constructed the stream to be a bio filter. The total length is about 3 meters and it is about 30 cm deep and full of sand and gravel. I know that it works well, at least for some things, because when I had to replace the pond liner with ferrocement I removed the sand and gravel and thoroughly cleaned it. When I put the clean sand and gravel back in the stream the pond was a mess until the stream biota could grow back.>

That's fine but it has a given/limited uptake capacity, and needs periodic/regular cleaning. It's possible to remove only a fraction of the gravel filling (to avoid a major process upset), washing it then putting it back. But how often do you do that?

<Another thing I did was mostly eliminate the 90º bend making use of a cold chisel and Swiss Army knife saw. In doing so I found that the bend was actually 45º, not 90º.>
An assumed 90 degree bend caused very little headloss (in the order of centimeters), vs the hose itself, and the loss is even smaller for the 45 degree.

<With your permission I'd like to repost on the Garden Pond Forum>
No worries, feel free to use it any way.

[Ratsima]

To make it more complicated, studies found that flow reductions by biofilms could not be well explained by wall roughnesses and/or diameter constrictions. Even relatively thin films increased the resistance quite significantly, sometimes. With the new hose in place, you will learn the cause, soon.

Indeed I will.

One interesting thing is that none of the other enthusiasts on the garden pond forum report problems with reduced flow to the degree that I have. One member posted:

I'm just totally puzzled as to what exactly is causing it to clog.
How come no one here has ever had that problem?

As for the stream, all I do currently is run a garden claw through it from time to time to remove sediment. It's a bit of a hassle as I have to remove the decorative rocks from the stream to make way for the claw. It does stir up lots of sediment which clouds the water for a while. I assume that most of it ends up at the bottom of the pond from which I extract it by hand. I could make washing portions of the sand/gravel part of that process.

Thanks again for your detailed and interesting analysis.

[Ratsima]

Well, it's back to the drawing board. The new hose is a failure. After just 48 hours it went from a flow of 15 liters per minute (5 liters in 20 seconds) to 7.5 liters per minute.

I guess now I need to shell out the bucks to buy a larger (1") flexible PVC hose.

It's only money.

[Scout]

Well, it's back to the drawing board. The new hose is a failure. After just 48 hours it went from a flow of 15 liters per minute (5 liters in 20 seconds) to 7.5 liters per minute.

I guess now I need to shell out the bucks to buy a larger (1") flexible PVC hose.

It's only money.

Is it possible that the pump itself is the problem ? Perhaps it’s output declines several hours after it starts ?

[Scout]

Well, it's back to the drawing board. The new hose is a failure. After just 48 hours it went from a flow of 15 liters per minute (5 liters in 20 seconds) to 7.5 liters per minute.

I guess now I need to shell out the bucks to buy a larger (1") flexible PVC hose.

It's only money.

Is it possible that the pump itself is the problem ? Perhaps it’s output declines several hours after it starts ?

[centermid7]

How about creating a flow pathway that does not involve the pond for 12 to 24 hours or so? Fill a big ass container with water from a tap that then goes through the pump and then back to the container. Round and round she goes . . . ?

[Nereus]

Well, it's back to the drawing board. The new hose is a failure. After just 48 hours it went from a flow of 15 liters per minute (5 liters in 20 seconds) to 7.5 liters per minute.

I guess now I need to shell out the bucks to buy a larger (1") flexible PVC hose.

It's only money.

Is it possible that the pump itself is the problem ? Perhaps it’s output declines several hours after it starts ?

Exactly! It does not even take hours. All very well quoting all sorts of calulations, but nowhere has the pressure been mentioned.

Q1 = Q2 a simple equation that also does not consider pressure. I have stayed away from any further input, but there are a couple of other formulas that must be considered, including Bernoulli.

[Ratsima]

The pump is fine. As soon as I disconnect the hose to ream it out I can easily see that the pump is pushing water at full pressure.

At one point I isolated the pump from the pond to make sure nothing was getting lodged in the pump intake or outlet. There was nothing.

[Scout]

Have you solved this problem Yet ?

[Ratsima]

I ordered some PVC flex from RS. It was delivered to my home in Korat on Saturday. I’ll be back there Thursday to see if I can make it work.

[Ratsima]

2022-06-15_17.20.38.jpg

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The Hose Has Arrived

2022-06-15_17.26.56.jpg

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All The Fittings Fit

[Nereus]

I ordered some PVC flex from RS. It was delivered to my home in Korat on Saturday. I’ll be back there Thursday to see if I can make it work.

If I may; can you please tell me how you were able to order anything from RS. I am assuming that you mean RS in Bangkok. Thanks very much.

[Ratsima]

https://th.rs-online.com/web/

This website. I often order from them. Raspberry Pies (micro computers) tools, parts, etc.

[KhunLA]