Hey all. I've recently installed a nice big rain collection system, and have run into a small issue I hope to solve easily.

Basically, the rain barrel is connected to a pump that in turn feeds a hose manifold, and I have a bunch of hoses that go to various gardens.

The problem is that the rain barrel is located at a point higher than the gardens, and I'm getting gravity flow-through when the pump is off. When I look at anti-siphon valves, they are (apparently) not what I need - they are for preventing backflow into the water supply, I want to prevent low-flow forward into the system, which drains the tank, floods the garden and so on.

I've looked at check valves with adjustable cracking pressure, that's not quite what I need. Can someone tell me what to search for? I want a valve that only opens when the inward pressure is above 2 or 3 psi (ideally adjustable).

What is that thing I need called?

How about looking for a solenoid valve and wiring it to come on with the pump. Power up the pump and the valve opens, shut off the pump and the valve closes.

- Eric

I assume this is an automated watering system (on a timer)?

I wonder if it would be simpler to add a loop on the pump outlet that stands above the water line in the tank. End of siphoning problem.

Think what you are looking for is a vacuum breaker. But it has been a long time since I sold hardware so I might be wrong. Do you have a plumbing supply or irrigation supply company nearby? Usually the help at a business that supplies other businesses have help that are more knowledgeable than the big box type stores. If I were looking that's where I would start.

That is a common enough issue for water systems, and an easy enough issue to fix.

What you need is a loop of pipe raised above the maximum water level and a anti-siphon valve installed at the high point. This should be located on the discharge side of the pump.

If you want to save a little money it is simple enough to avoid having to buy an anti-siphon valve and simply drill a tiny hole in the top of the loop. The hole only has to be big enough to allow air in and you can get creative with the tiny fountain coming off the top of the loop when the pump runs.

An interesting variation is to install hose barb at the top instead of just having a hole. From there you run a bit of vinyl hose to something that needs watering. Or even just back to the tank. If you do use some tubing you will have to make sure it drains by gravity without any bellies or obstructions so it will allow the air to flow back up and break the vacuum on the loop and stop the siphoning.

Pardon my poorly-thought-out reply above . A higher-than-source loop alone will not help; it must be combined with some sort of air intake into the piping to break the siphon effect. So, a valve that closes under pump pressure but opens to admit air under siphon (slight vacuum). But that doesn't give you a name.

EDIT: Art beat me to it.

Wouldn't it just be easier to put a hose spigot on the manifold and shut it off when you don't need it? Then treat it like a regular hose outlet.

What you're looking for is something similar to a pressure relief valve, but I imagine those aren't really designed for that kind of application and would restrict the flow quite a bit.

That's the solution! I will pop a 1/8" hole in the discharge line, run a bit of tubing back to the tank, and that will solve the problem easily. Thanks Art.

Art, that idea worked like a charm. I put a t fitting in and a small return line after a check valve that holds the prime in the pump and connected a 1/4" tube from the t up to the tank. A small amount of water flows back into the tank, and when I shut down the pump, the line quickly breaks the siphon - problem solved...now on to the timer switch and to find another 350 gallon tank to sit next to the first one (which I found being thrown out - it was a brine tank for a school water softener and they had let the salt harden into a single 500 lb block, but I was able to get the salt out by cutting it with a pressure washer set to 0 degrees)

No way! Did you save any of the salt =D? Would be a great resource for The end of the world so you could cure meats =P