Couldn't find an answer to this specific question, hoping there's a ninja that can help - I had an idea for a closed gravity feedirrigation system with a ram pump.
What I don't know is, in reference to the attached image - if the gravity feed draws from the holding tank and creates vacuum suction on the pump end (being a closed system) - would this be able to start the ram pump up again?
Though I haven't tried it, my guess would be no. I believe the impetus that drives the pump comes from the falling water off the left side of your pic. If it were suction from the opposite end, it would be a siphon. Though if the gravity feed lines go to a lower elevation than the ram pump is located, I think it could siphon the water (and maybe start the pump). I do wonder if the gravity feed lines might give issues if the resistance through all is not perfectly balanced, though.
Hopefully someone with more experience will come along.
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When a ram pump stalls, it generally does so with the valve shut. In order to get it pumping again, the valve needs to be freed. Since there is pressure coming down the drive pipe, I do not think suction on the delivery pipe would be sufficient unless it was strong enough to depressurize the whole drive pipe for an instant.
Also, if I am understanding you correctly, you want the tank on the top of the hill to be closed? That means it will need to be a pressure rated vessel - like a heavy steel well tank or something. If it were something like the size of a rain barrel (lets say 36" in diameter) the lid would have an area of about 1000 sq inches. A ram pump can easily produce 40 psi. If the hill accounts for half of that pressure (lifting about 45 feet) your lid would still need to hold down 20,000 lbs of pressure. Also, since the system is closed, you are not really gaining anything by way of gravity feed. The tank could be placed anywhere in the system, and the overall output pressure would still be the same (ignoring pipe losses).
Using an open tank at the top of the hill works fine, though, and a properly tuned ram pump will not need to be fussed with very much.
Ok awesome, thanks for the feedback - the holding tank would actually be a series of 4 5000L tanks in stepped arrangement to allow any sediments to settle in the first. the feed from the pump to the tanks will be about 160m and the gravity feed pipes will be a main line of about 100m @ 50mm with several off-shoots.
This thought experiment was to determine if the system can self-regulate but its not a major train-smash to have to go start the pumps every day or two.
Yeah, ok, with an open tank at the top of the hill, the whole system should run swimmingly. I ran my ram pump for only 1 summer, but even with a completely home-built job, it really did not need much babysitting. Mine had a rubber gasket on the waste valve, and it was shot after a couple months. I doubt I had to restart it more than once every couple of weeks, if that. When I was out in the garden I could hear it going clunk-clunk-clunk and know that all was as it should be. The sound carried a good 500 feet.
If you wanted to try and be really clever, you might try a solenoid valve somewhere in the drive pipe. The waste cycle is initiated by a momentary drop in pressure as the shockwave heads up the drive pipe - in theory diverting some water out the bottom of the drive pipe might be enough start it up. Not sure how big a valve you would need, and if it would even work; but I do like dreaming up wild ideas, so you can have it at cost.
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