Anyone here understand hydrodynamics (dripping tap)

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freddofrog

Likes Dirt
Ok, totally left field problem.

Who can explain why my dripper slows down???

In the picture you'll see I have attached a garden retic dripper beneath a container. Initial rate set to 40 drips per minute. A float valve keeps the water level constant +/- 10mm.

But for some unknown reason, the drip rate always slows down over time even though the water level is more or less constant.

Why does it do this? I need a constant rate +/- 5%

Any suggestion people?

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foxpuppet

foxpuppet

Eats Squid
How big is the dripper orifice?
Is the water filtered/pure or just tap water.
Could it be sediment slowly changing the size?
 
stirk

stirk

Burner
Hey buddy, I'll take an oz of buds when the plants bud.. pm to deal.



Define, over time. The only thing which should change the flow is the adjustable dripper, so what do you 'fix' to get the flow rate back at desired flow? That's a place to stare at until the answer comes to you.
 
Ivan

Ivan

Eats Squid
If the head pressure on the dripper (orifice) is constant, then the flow through the dripper should be constant.

As mentioned above I'd be looking for either sediment, scaling or biofouling of the dripper.
 
Kind_cir

Kind_cir

Likes Dirt
Gravitational forces change with time, hence the drip rate will change. Add in the change in tempreture, and friction, as well as surface tension, sediment levels in the water, and wind speed ect. Many things will have a bearing on the drip rate.
Is it not gravity that moves the earths oceans.
 
stirk

stirk

Burner
Kind_cir said:
Gravitational forces change with time, hence the drip rate will change. Add in the change in tempreture, and friction, as well as surface tension, sediment levels in the water, and wind speed ect. Many things will have a bearing on the drip rate.
Is it not gravity that moves the earths oceans.
Click to expand...
So when its a full moon the peak flow is crazy fast at 50 dpm while dark moon peak flow is only 30 dpm?
 
F

freddofrog

Likes Dirt
I tried mooning it but it didn't seem to do anything.

It's just tap water. It could be sediment but I doubt it. I do have a plumbed in water filter so I might connect that in and see if that makes a difference.
 
Calvin27

Calvin27

Eats Squid
Mate you need to stick some numbers and dimensions.

I have no idea what order of magnitude things are. Are we talking about a 10cm diameter cylinder with a 1L/s flow rate, or a 1000L tank with a 10ml/hr flow? Makes a world of difference in fluid dynamics.
 
stirk

stirk

Burner
Calvin27 said:
Mate you need to stick some numbers and dimensions.

I have no idea what order of magnitude things are. Are we talking about a 10cm diameter cylinder with a 1L/s flow rate, or a 1000L tank with a 10ml/hr flow? Makes a world of difference in fluid dynamics.
Click to expand...
Smoke a bud and get a grip, how big is a drip?
 
Calvin27

Calvin27

Eats Squid
Are you running a 12/12 lighting cycle or a 14/10? I'm a fan of the 14/10. Slower initial yield, but greater after the mother gets to size!

Anyhow, I suspect you floater thing is stuffed.
 
F

freddofrog

Likes Dirt
Calvin27 said:
Mate you need to stick some numbers and dimensions.

I have no idea what order of magnitude things are. Are we talking about a 10cm diameter cylinder with a 1L/s flow rate, or a 1000L tank with a 10ml/hr flow? Makes a world of difference in fluid dynamics.
Click to expand...
Cylinder is a 2L coke bottle filled 3/4 with tap water via the float valve. The dripper is initially adjusted to 40 drops/min (~120ml/hr) but will slow down to half that by 3-4hrs. I am aiming for 40d/m +/- 10%

The float valve actually works very well. I did have an expensive Philmac one which after 2 exchanges I discover had a design flaw. I ended up with a cheaper Kinetic from Bunnings which works much better.
 
pharmaboy

pharmaboy

Eats Squid
freddofrog said:
Cylinder is a 2L coke bottle filled 3/4 with tap water via the float valve. The dripper is initially adjusted to 40 drops/min (~120ml/hr) but will slow down to half that by 3-4hrs. I am aiming for 40d/m +/- 10%

The float valve actually works very well. I did have an expensive Philmac one which after 2 exchanges I discover had a design flaw. I ended up with a cheaper Kinetic from Bunnings which works much better.
Click to expand...
Stupid question, but is the Coke bottle open at the top ie equalised?

If it's sealed, or semi sealed, that's likely your problem
 
Calvin27

Calvin27

Eats Squid
You should probably measure the drip rate at maybe 15 minute intervals. this will determine the nature of the response. Without building a control model, it might just be a transient response. After 3-4 hours is it stabilised?
 
Rob_74

Rob_74

Likes Dirt
How does the dripper work? I suspect it not just a orifice but some tortuous path. Is this getting a little air trapped in it which after a few hours is flushed through and hence affecting the flowrate?
 
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