An electric device that stops electricity when no water is flowing, or preferably, when the water reaches a certain height, in which case it could also automatically restart at a set height.
There are many times where a float cannot be used to control the pump, especially in external (non submersible) pumps, where the fluid is stored in a location that has only a small opening such as a sealed barrel that only has a small opening on the top. Also, a float can be non sensitive and get stuck.
I'm thinking in the line of a pressure gauge (cost's less than one dollar) and a bit of electronics to set it.-- pashute, Jul 24 2013 Baked http://www.ia.omron...roducts/family/241/Floatless Level Controller [MechE, Jul 24 2013] Different Approach http://pumps.stanco...controlle/item-1141 [MechE, Jul 24 2013] Pressure Sensor http://www.sjerhomb...-Level_Features.pdf [MechE, Jul 24 2013] More https://www.sparkfun.com/products/10221varistor type [MechE, Jul 25 2013] What's the first link. I don't understand the product.
I didn't see anything on the market so didn't even think of googeling for 'floatless''. Thanks Meche!
The third link uses the exact method that I'm proposing, but seems like its geared towards large fuel tanks or such.
I meant a SIMPLE (or say - simpler) gadget that has an electric plug and socket, and stops the electricity accordingly. Anybody who makes such, it will sell next to all the none-submersed pond and wine pumps, in all hardware stores. (There are close to 1 million sold every year, so you'll be making a nice profit.
The flaw with the second link's approach is that it runs the pump on an empty tank, so pump protection may not be so good.-- pashute, Jul 24 2013 The first is still a simple level sensor, it runs a low voltage electric current through the liquid. If there's liquid over the upper point, you get a closed circuit and it triggers the pump.
The second will put a little more wear on your pump, but it isn't intended to run the pump completely dry, and not for very long once it reaches that stage. As long as it's only running in that state for brief periods, it shouldn't greatly shorten pump life. I'll admit I don't think I would implement it in a situation where there wasn't a reasonably steady level of flow, such that the timed turn on almost always found more liquid to be pumped.
Based on the scale of the 2" mounting bracket in the PDF image (and assuming even vaugely to scale), that looks like a fairly standard sump or septic tank application to me. The sort of bare bones PLC control it appears to have is kind of the minimum you'll find for purchased control systems these days.-- MechE, Jul 25 2013 Added one more.
If you need a variable level reading, you can also do it with an ultrasonic distance sensor in a lookdown position, or a laser distance sensor, as long as it's one that can detect your liquid (simple if it's milk, more difficult if it's water).
If you just need a simple on-off at height, it's possible with a retroreflective or thru-beam with an opaque liquid. Feasible but not simple with a clear liquid. More practical might be an capacitative proximity sensor, which will work fine as long as you have a non-metallic window to look through (they can work through thin metal, but they're touchy at best).-- MechE, Jul 25 2013 Use guilt. Put a caged kitten and a mini-cctv camera in the tank, with a monitor where people can see it.-- not_morrison_rm, Jul 25 2013 not - you meant to post that on my cat-a-pull idea.
MechE - thanks!! I was working two years back on a fuel theft prevention device, and should have remembered this solution.
The lasers are extremely expensive, even for the simplest use. Pressure gauges are extremely cheap, and not much less sensitive or accurate.
That last one looks fantastic! I sent the link to some of my friends.-- pashute, Jul 25 2013 The thin strip liquid sensor from SparkFun looks interesting until you look at the price. A capacitive solution is much more economical. If you want to prototype it, I'd recommend a "PSoC 4 Pioneer Kit". It's got way more features than you need (including ARM processor), but for $25 it's got everything you need except a length of wire to use as the capacitve level sensor. For a simply binary level detect, just fold a wire in half so there are no exposed contacts in the liquid, attach it securely inside the tank so it can't move relative to anything except the water level and hook one end of the wire to a capsense pin. When the water gets high enough to touch the wire, the capacitance will change and the chip can detect that.
If you want to transition the design to small scale production, the chip is less than $2. For mass production I'd switch to a lower cost capsense specific part, but the dev kits for those are more expensive.
That's all you need to connect to a PC, but if you want to control some power directly, you'll need a relay. I easily found a 150VAC Arduino compatible relay shield for $8 that should plug in nicely.-- scad mientist, Jul 25 2013 thanks scad!-- pashute, Jul 26 2013 There are off the shelf solutions to this, using optical or ultrasonic probes. But they cost rather more than a dollar.
You might be able to make a device using standard IR LEDs for about USD$5 … the works out of a standard computer mouse with quadrature encoders using IR LEDs would be a good starting point.-- 8th of 7, Jul 26 2013 random, halfbakery