The filthy five and St valentines sump info?

[tdobson]

Looks awesome! Great job

Do we have a shorter length of 50mm mbpe to hand so we can test it?

 

[SamT]

Needs to be 40mm as that is the size of the connector.  I was just going to cut a couple of meters of the 50m roll, as and when it arrives, then take it to a river somewhere.  I reckon if it can push up to a meters head, then we're fine, as I'm confident that the height of the lip on the far side is less than that.  I'm hoping it'll only take a couple of strokes on the pump to get the syphon started.  Once it does start, it'll not take too long to drain. (I'm guessing about 10 to 15 mins).

My one concern is that I've made the stroke length too long and there might not be enough room in the deep bit of the sump to fully extend the pump.  We'll see.

 

[tdobson]

"I'm not an engineer but" - is silt getting sucked into it likely to be an issue or worth trying to protect against in some way?

 

[SamT]

Its kind of why it needs a big diameter pipe - so that pebbles etc dont get stuck.  Those holes are about 10mm across on the inlet, so nothing bigger than 10mm should get it, which in turn shouldn't get stuck in the 40mm pipe.  I guess a little sediment may fall out of the water and settle in the pipe - when its all static. But hopefully not enough to block it, and it should get flushed through easily enough when the syphon is running.

 

[Mark]

Just needs Eavis to get that 50m of black 40mm mdpe ordered and we're in business.

What length pipe do you need, Ive possibly got some in the lock up, will check later.

 

[SamT]

Eyup Mark.  about 30m I reckon.

I've fitted the pump together now with a 40mm (o.d.) connector.  (I could swap it out, but it'd be a faff to pull the pump apart).

Rob has just ordered some today so its not desperate, unless you do happen to have some lying about.

ta

 

[tdobson]

Hey Sam,

Is there anything I can do to help get this project moving again? Presumably we have various awkward things we need to get to SVS?

Eager to help,

-Tim

 

[Cantclimbtom]

being really nosy on someone else's thread (so tell me to clear off as necessary) but a "trick" I've seen that worked well with syphons and fresh water, is making the last bit a wider bore pipe. Suppose you have 40mm pipe then you have the last bit as water exits a metre of 50mm plastic waste pipe. The ideal coupling between the two would be a smooth gradual change in diameter (30 degree cone) just as water enters the wider pipe, but a sudden step using a coupling can also work. (Some diy skills with plastic 50mm waste and 40mm waste pipe needed if you want gradual/smooth flow). As the water flows it expands into the larger diameter creating suction. You don't get energy from nowhere and if you get anything out of this this depends on if you have enough flow speed on diameter-change, but in some cases a metre of oversize on exit can noticeably help a syphon. Dunno if relevant in your case as I don't know the flow speeds/head etc, so make of my waffle what you want.
Enjoy...

 

[pwhole]

So without getting too much into the physics here, which are probably esoteric, but is the idea that the 'tensile strength' of the water (assuming it's not exceeded) is sufficient to 'pull' more water through than would otherwise be possible by 'pushing' with gravity/atmos pressure alone? Or just that the greater volume ahead reduces the pressure required at the input end?

 

[SamT]

I think this will explain the reasoning.

https://en.wikipedia.org/wiki/Draft_tube#:~:text=Draft%20Tube%20is%20a%20diverging,the%20expense%20of%20its%20velocity.

increased pressure at the suction end.  less velocity at the exit, but I don't think any more or less water is shifted.

 

[Cantclimbtom]

Personally I'd have described it as the exact opposite of a rocket nozzle.
Trading energy that could be jet washing the bottom pool of your syphon in favour of a bit more suction in the pipe.

Edit: or for you mining types, look carefully at how the air exits the guibal labelled fig 6, it gets wider as it leaves to create suction

https://www.aditnow.co.uk/Photo/Guibal-Fan_43490/

 

[SamT]

Errr - that wasn't a rocket nozzle??  its a draft tube for a hydro turbine.

At the end of the day, extra suction at the intake still doesn't lead to an increase in the amount of water shifted, since it just slows the rate at the other then