Homebrewed Electricity > Hydro
Air Vents Again
camillitech:
I had similar issues with my system 70M of head and 900M long 90mm MDPE penstock. Drilling a small hole at the high spots certainly cured the problem but then people kept reporting the leaks. This was fine when it was to me but I became concerned when I was approached by the local water company because some concerned tourist had spotted the 'leak' in my black pipe. This was despite it being some 7 or 8 miles from the nearest mains water pipe and in the middle of nowhere. Consequently I fitted 'automatic air bleed valves' for water irrigation systems at the high points. Sorry my Internet is pish at the moment and I can't find the link. They were plastic around £20 each ,1/2" BSP threaded and have been doing their thing for about ten years.
I also see you have bother with peat lining the penstock, me too and I recommend you 'pig' it. Works a treat, I was always frightened of doing it and the 'pig' getting stuck but I've done 3 or 4 now on penstocks of 450 and 900M with no issues, piece of cake ;-) https://lifeattheendoftheroad.wordpress.com/2022/01/22/pigging-the-penstock/ Good luck
camillitech:
Here is the valve I used at last ;-) https://javelindirect.co.uk/product/1-kinetic-air-release-valve/
Vortechs:
camillitech! That's really great info thank you :)
Is there a minimum distance or height down from the filter for the bleed hole/valve? I cant get over the feeling it would just suck more air in there at the top. Obviously it must be at a lower point than the level of the intake filter as it says: "This can also be used in pipelines to avoid siphoning. Once the pressure drops in the line, the valve opens and lets air back into the pipe, breaking the siphoning action."
Nice blog! I salvaged about half of my 250 meters of 3" (90mm OD 75mm ID) black HDPE pipe from beaches around here, it's apparently used by the salmon farms as a float around the tops of the cages. Had some great fun trying to get it into a roll small enough to tie on my car trailer, ended up with a 12 foot roll tied vertically on the trailer - got some strange looks on the way back home :)
I was terrified of the 'pig' pushing a big sausage of peat down the pipe and blocking it solid. After 18 years running continuously most of the pipe had about a quarter inch coating the insides, so I made up a scraper for drain rods that would allow the water and peat to pass the scraper, that meant I could do it while the pipe was still partially running. Here's a picture of the scraper I made. With thirty 1 meter drain rods I was able to do it with a connector at least every 60 meters, which meant I only had to put one extra one in. How did you get the rope through the pipe to pull the pig through, that was my other worry about using one of those foam ones?
bigrockcandymountain:
Usually a pig is just pushed by the upstream pressure. No rope or anything required. They work pretty good. All the gas fields use them for keeping water and sludge out of their buried pipelines.
If you think about a 3" pig with even 30psi behind it, that is 212lbs pushing it down the tube. Hook an air compressor up behind it and up it to 120psi and your over 800lbs of force.
I would probably do a series of pigs starting with quite a loose fit for the first cleaning. After that, a quick pass here and there should keep the pipe happy.
SparWeb:
No direct experience with hydro but I am wondering if this has been tried: A settling tank?
If a tank is installed near the upper end (but not too close to the intake) then the velocity of material passing through the tank would be slow, allowing solids to drop to the bottom before the water flowed out the other end. Air would rise into a head space. If the tank is lower than the water intake, a riser would keep the head in balance. I could see this looking a lot like a septic tank but adapted in ways to allow much more flow. Even the pump-out of accumulated debris could be done with the typical suck-truck.
Just seems like it would help both of your problems at the same time, but I wouldn't know if it has a fatal flaw that hydro users would know about.
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