Prevent Pump Hose From Clogging

[Ratsima]

I guess I'm just a bit weary of all this. I appreciate the huge outpouring of both sympathy and help.

I still think that this is the most telling post:

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

Could it be the garden hose? That's the odd factor. I don't think many people use garden hose for pond hose, but I could be wrong.
Is it really the gunk slowing the water or is the hose collapsing because it's too soft?

You would think the force of the pump would keep the hose clear. Strange...

I remain unconvinced that a larger hose, or smoother hose inner surface, or any sort of filter will fix this.

However, to put the hose issue to rest in my mind, I'm going to fork out the bucks to buy the Alpine 1" hose from Amazon. It seems to be least expensive option for getting a flexible PVC hose. Odd as that seems.

[Aside: When building this pond I wanted to line it with EPDM. I couldn't buy it in Thailand. It is manufactured here. But, at the time, there was no consumer market for it. It was used mainly by farmers building huge ponds. The least I could find was a 100 meter roll. I ended up using HDPE instead. That lasted a few years and I ended up redoing the pond with ferro cement which has held up well. EPDM is now readily available in consumer quantities.]

 

[Ratsima]

For the past few days it has been cool and overcast with rain now and then. So, the fountain flow didn't get down to reaming rate until this morning. To do this I disconnect the hose from the pump, ream from the pump end and then again from the fountain end. I can generally see a certain amount of gunk that comes out (see previous photos) when pulling the reaming tool out of the hose. Reaming usually requires some force on my part.

This morning hardly any force was required and, almost no gunk came out on either end.

But, when I connected the hose to the pump, the fountain was again at full force.

For me, this just adds to the mystery.

I ordered this hose:

Takara Knitting Plus Series PVC

It's only twelve bucks (US) and seems to have a smooth inside. It's not as flexible as the flex PVC, but since I've eliminated the only kink point, I think it should be OK. Should arrive in three or four days. I'll post the results.

 

[GBBUDD]

NO clue on that one good luck

 

[Ratsima]

An engineer on a general interest Thai forum asked me to take some measurements of my pond and hose. Here they are if of any interest:

Clean hose flow rate: 5 liters in 20 seconds
Dirty hose flow rate: 5 liters in 103 seconds
Length of hose: 8 meters (ID 5/8")
Static lift: 35 cm
Immersion depth of pump: 9 cm
(intake and output are the same depth)

 

[Ratsima]

An engineer on a general interest Thai forum asked me to take some measurements of my pond and hose. Here they are if of any interest:

Clean hose flow rate: 5 liters in 20 seconds
Dirty hose flow rate: 5 liters in 103 seconds
Length of hose: 8 meters (ID 5/8")
Static lift: 35 cm
Immersion depth of pump: 9 cm
(intake and output are the same depth)

Here is the detailed analysis done by a member of the HuaHin (Thailand) forum:

That's quite a drop! To make a simple model, I took various 'new condition' hose diameters, 28 C temperature, 0.25 mm abs rougness for the hoses, 1 of 90 degree bend + some other minor losess. about twice of the bend. Pump shutoff head = 3.50 m, and the QH curve is simply a straight line from that point to the 5000 l/h (83.3 l/min) point on the Q (x) axis at zero head. This type of linear QH curve is typical for similar submersible pump pumps. To save effort I used software, and got IMO reasonable figures as shown below:

ID inch  ID mm.       Flow l/min    Velocity m/s
1"       25.40         42.5          1.40
3/4"     19.05         24.87         1.45
5/8"     15.88         16.60         1.40
1/2"     12.70          9.70         1.28
3/8"      9.53          4.65         1.09
          8.00          2.94         0.97
1/4"      6.35          1.65         0.87

Thus, about 16. 6 l/min flow is predicted by the model for the 8 m long 5/8" hose with 0.35 m static lift, quite close to 15 l/min measured value. The flow is turbulent (needed for the model) though at relatively low Reynolds numbers.
The dirty stage corresponds to a clean hose with about 8 mm (internal) diameter in the same conditions. In other words, the effect of biofilm growth corresponds to about a halved 'clean' diameter.. that's quite significant.
I stop there since predicting flow conditions for visco-elastic biofilm deposits with the obtainable data only would be wild guesswork. Btw, the software is abadonware (since 2015), too bad if one licensed it then tried to use it in 2016 on a new PC having a different hard disk serial. If someone is interested im playing with it, PM and I can give a link to the setup+fix+the model files (it runs under Windows).

It can be seen that using a simplistic model could be very wrong. Like only relying on the the continuity equation, which states that the flow rate (velocity x cross sectional area) is constant along a pipe. Then halving the pipe diameter would increases the velocity 4 times, which is a way out of the measured value.

Now, hydraulics is useful to estimate discharges but says nothing abut the cause. The biofilm topic is complex, but with some simplification one can state that most algae are phototrophic microorganisms, use CO2+light, hence cannot live in dark hoses. Ergo, killing algae would not help. In contrast, many other microorganisms, such as aerobic bacteria only can use organic carbon as food (measured as BOD/COD or DOC) and oxygen to grow and typically do not need light energy.
Biofilms are ubiquitous, present in living water and difficult to get rid of. Besides, they be utilised, see, for example, trickling filter in sewage treatment and various biofilters in drinking water treatment. The jelly-like nature of the deposit (biopolymers, mainly polysaccharides) is an good indicator of aerobic bacterial origin (there are patents to produce biopolymers similar ways). Even if the stream and pond look “clear” to the eye, they have plenty of biofilms. The question that why they like the hose? The explanation is the good food supply. In stagnant water, mass (food) transport is controlled by diffusion, whereas in the hose the flow/mixing enhances the delivery and uptake of the food. Of course, increasing the water velocity increases shearing, and removes some of the film, thereby creatings a dynamic balance.

For the new pond a small hose & pump was good enough, right? But with the gradual accumulation of organics and nutrients, the increased food supply has created an issue. The solution is obvious: reduce the available food supply. Frequently removing the sediment from the pond and diluting the pond water with fresh water make it sustainable/manageable, and even can provide regular activities and exercise. But if those are becoming a pain then consider installing a small, home-made biofilter to provide a better place for slime growth. For this small system a plastic storage box or drum would suffice, adding some piping and suitable filter material (sponge, non-woven textiles, rings cut from an old hose.)

The following from a subsequent post:

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.

 

[Ratsima]

I ordered this hose:

Takara Knitting Plus Series PVC

It's only twelve bucks (US) and seems to have a smooth inside. It's not as flexible as the flex PVC, but since I've eliminated the only kink point, I think it should be OK. Should arrive in three or four days. I'll post the results.

Well, it's back to the drawing board. The new hose (5/8") is a failure. After just 48 hours it went from a flow of 15 liters per minute to 7.5 liters per minute.

I guess now I need to shell out the bucks to buy a larger (1") flexible PVC hose. Installing that will involve some pond and fountain reconstruction.

It's only time and money.

 

[combatwombat]

I’m concerned your problem is not the hose. Seems you have a small feature. What happens if you do a full clean out and water change?

 

[Ratsima]

I’m concerned your problem is not the hose. Seems you have a small feature. What happens if you do a full clean out and water change?

What would I be looking for or trying to accomplish in doing that?

 

[combatwombat]

What would I be looking for or trying to accomplish in doing that?

To see if something about your water chemistry is producing the film that is clogging your hose. Do I misremember that you already tested a larger hose and did not see meaningful improvement?

 

[Ratsima]

To see if something about your water chemistry is producing the film that is clogging your hose. Do I misremember that you already tested a larger hose and did not see meaningful improvement?

No, I’ve never tried a larger hose. The current 5/8” is the largest I’ve used.

What concerns me is that there is no visible or feel-able biofilm or algae anywhere in the pond. The only exception is the stream where string algae sometimes forms if the stream receives full sunlight.

I’m willing to try most anything, but draining and removing everything from the pond would be a huge and time consuming task. Last time I did it was when I replaced EPDM lining with ferrocement. That took many days of hard work.

 

[Ratsima]

I reamed out the new hose this afternoon. Same old slimy junk came out. It sure grows fast and seems to stick even to smooth-as-glass PVC.

Here's what I know didn't work:

• A larger hose: ½" to 5/8"
• A smoother interior PVC hose
• A pump with a greater flow 2700L/h to 5000 L/h

I'm ready to just resigning myself to having to ream the hose every few days. Trying to fix this has been a lot more stressful than just putting up with it.

 

[SarahT]

The problem with a clear or transparent hose is if exposed to sunlight, it will clog with algae quickly.

I threaded my clear hose through a larger size of the not-great black corrugated hose which hid and protected it from sunlight. No algae formed and it worked well for many years (for a smaller fountain waterfall feature).

 

[poconojoe]

I would buy a cheap 1 inch I.D. hardware store hose and just run it temporarily on the outside. See if that helps. If so, then spend the money and get the better 1 inch flex PVC.
As I stated previously, most hardware or big box stores carry hose on reels where you cut what you need.

 

[Ratsima]

I threaded my clear hose through a larger size of the not-great black corrugated hose which hid and protected it from sunlight. No algae formed and it worked well for many years (for a smaller fountain waterfall feature).

The hose I've been using is completely opaque, so no light can get in to support photosynthesizing organisms.

I would buy a cheap 1 inch I.D. hardware store hose and just run it temporarily on the outside. See if that helps. If so, then spend the money and get the better 1 inch flex PVC.
As I stated previously, most hardware or big box stores carry hose on reels where you cut what you need.

Perhaps I'll try that. Easier said than done though. This is Thailand after all. I couldn't find the 5/8" PVC locally so ended up ordering it online. I went to two nearby hardware stores last weekend (Thai Watsadu and Home Pro) and neither had anything more than a few spools of that thick-walled plastic transparent hose and a few packages of cheap garden hose.

 

[mrsclem]

What size hose is this pump set for? I have never seen a pond pump designed to use garden hose.