Hi guys, I'm on a project that requires protecting a 1/2 HP water pump out of working without water. I thought on a water flow sensor at the output of the pump, but they're quite expensive and they work with a propeller, so sooner or later they're going to fail.
So guys, I need a low cost solution and easy to install in order to protect the pump, I don't need to meter the flow rate, I just need to know if the pump it's receiving water. Thanks for your attention.
What kind of pump? Submersible sump pump? Well pump? Irrigation pump? ? ?
Is it a submersible pump?
Can the source reservoir water level be measured?
DC/AC pump?
outsider:
What kind of pump? Submersible sump pump? Well pump? Irrigation pump? ? ?
AC 220V Irrigation pump.
larryd:
Can the source reservoir water level be measured?
No, we can't measure the reservoir water level, It's a quite deep well.
It's not submersible.
So, (assuming a centrifugal pump), if the pump is running and the discharge pressure is near the same as suction pressure, would that qualify as running dry?
Instead of flow meter, you can use a flow switch. That's all you need. No rotating bits, just a switch that gets triggered when there's flow, which is what you're after. They're easier to read (a simple on/off signal) and pretty cheap to boot.
wvmarle:
Instead of flow meter, you can use a flow switch. That's all you need. No rotating bits, just a switch that gets triggered when there's flow, which is what you're after. They're easier to read (a simple on/off signal) and pretty cheap to boot.
I wasn't able to found a properly water switch, the only ones available on Ebay were quite small (30l/min, or 8g/min), the only thing similar to that was a "water paddle switch", still expensive ($17 usd) but it looks a lot more reliable than the spinning one.
outsider:
So, (assuming a centrifugal pump), if the pump is running and the discharge pressure is near the same as suction pressure, would that qualify as running dry?
The pressure it's always the same, because you can't compress water, and when the pump runs dry there's no water on both sides, so the pressure is still the same.
Just because water is incompressible doesn't mean you can't have pressure differences. In fact, the whole reason a pump pumps is because it produces a (possibly really large) pressure difference!
Also while we say it's incompressible, in fact water (like all materials) DOES compress when placed under pressure. It's just so little that you don't normally see it, which is why for most practical purposes this compression can be neglected.
blueribbon:
I wasn't able to found a properly water switch, the only ones available on Ebay were quite small (30l/min, or 8g/min), the only thing similar to that was a "water paddle switch", still expensive ($17 usd) but it looks a lot more reliable than the spinning one.
I see them sold on Taobao at the equivalent of USD 4-5 a piece - excl shipping of course. Try Aliexpress, they must be available there as well.
Even USD 17 (especially if that includes shipping to you) is not that big a sum to reliably protect your pump. I bet that pump costs a lot more than USD 17!
Most people use a low pressure cutoff switch, like this one, available in every home improvement center.
jremington:
Most people use a low pressure cutoff switch, like this one, available in every home improvement center.
That is the exact device I have on the output of my irrigation system It not only provides protection when the pump runs out of water, it also protects when something breaks in the distribution piping.
Paul
jremington:
Most people use a low pressure cutoff switch, like this one, available in every home improvement center.
I know, but the project requires to be low-cost and also easy to implement, the cutoff switch costs twice as the entire board with it's sensors.
blueribbon:
I know, but the project requires to be low-cost and also easy to implement, the cutoff switch costs twice as the entire board with it's sensors.
Lets see. Mine has been working fine for 10 years. A "T" in the pump output pipe, a nipple and elbow to the pressure switch and two wires between the switch and the control box. How many years will your electronics operate?
Paul
wvmarle:
I see them sold on Taobao at the equivalent of USD 4-5 a piece - excl shipping of course. Try Aliexpress, they must be available there as well.Even USD 17 (especially if that includes shipping to you) is not that big a sum to reliably protect your pump. I bet that pump costs a lot more than USD 17!
Yeah, I know it. It looks like the best solution right now.
Also it's not "my pump", it's something for a project on which I'm working.
Paul_KD7HB:
Lets see. Mine has been working fine for 10 years. A "T" in the pump output pipe, a nipple and elbow to the pressure switch and two wires between the switch and the control box. How many years will your electronics operate?Paul
I know that exists extremely good and reliable commercial solutions for this, this is just an optional feature that I want to add to this project, but at the same time it needs to be sufficiently reliable to add it.
If the installation will be out of doors and/or exposed to a damp environment, any electronics you put together will fail due to corrosion, within weeks to months.
Guaranteed.
blueribbon:
I know that exists extremely good and reliable commercial solutions for this, this is just an optional feature that I want to add to this project, but at the same time it needs to be sufficiently reliable to add it.
What is your experience with pump controls and working with the electric power driving the pump?
Paul
Paul_KD7HB:
What is your experience with pump controls and working with the electric power driving the pump?Paul
I've worked with variable-frequency drives on three-phase motors, also with contactors, no big deal, but this project is giving me a headache.
jremington:
If the installation will be out of doors and/or exposed to a damp environment, any electronics you put together will fail due to corrosion, within weeks to months.Guaranteed.
Probably I'll need to sink the pcb's on epoxy solution or something like the washing machines pcb's, and obviously it's going to stay into a plastic enclosure and under a roof.