Off-Grid water, pump fail safe help

[Old Guy in Tenn]

We got our water running a couple of weeks ago. A 300 gallon tank down by the spring, with a 1HP submersible pump inside the tank to pump the water up 160 feet with a 500 foot run to the house. We have a bladder tank up at the house, which is where it switches the pump on/off as water is used. The switched 220 then powers the pump. It is working very well, so I could leave it alone, but...

I am worried that we could somehow run the tank dry, and damage the pump. I want some simple way to turn off the pump if the water in the tank gets too low. We ran an extra wire pair down to the spring to connect to a float switch or whatever, in case that helps.

Looking forward to hearing your suggestions.

Thanks.

 

[DuckSlayer1017]

Use the float and probably a relay to power the pump. If the float is up pump runs. If the float is down pump won’t run. Use your extra pair of wires to turn on a light at the house if the float is down. Also, make sure you check the float periodically, we’ve burned up plenty of pumps at work because floats stuck.

Maybe one of the electricians or EE’s on here could draw the circuit for you. I’m just a ME and let the pros do the circuit design for me.

 

[Fallon]

Thermal sensor on the pump near the seal & latching relay. Might be hard to tune so it trips in time without to many false positives.

Redundant float switches wired in series. More likely to leave you without water if any one of the float switches failed.

 

[fried1765]

We got our water running a couple of weeks ago. A 300 gallon tank down by the spring, with a 1HP submersible pump inside the tank to pump the water up 160 feet with a 500 foot run to the house. We have a bladder tank up at the house, which is where it switches the pump on/off as water is used. The switched 220 then powers the pump. It is working very well, so I could leave it alone, but...

I am worried that we could somehow run the tank dry, and damage the pump. I want some simple way to turn off the pump if the water in the tank gets too low. We ran an extra wire pair down to the spring to connect to a float switch or whatever, in case that helps.

Looking forward to hearing your suggestions.

Thanks.

You can buy a "PumpTec" or "Pump Saver Plus".
When they sense the pump running out of water, they will shut the pump off, and can be set for automatic time delay, to allow water recovery.
Works great.

 

[gary49]

You can change your pressure switch to a low pressure cut off type switch. Square D makes one. It cuts the pump off if the pressure falls to 12 PSI. That will be the simplest, cheapest way to do it. If the cut off is activated, there is a lever on the switch that you have to use to reset the switch.

 

[Egon]

There are options:
Low level! Low flow, temperature sensor, low discharge pressure, pump run time. Pick one that suits you equipment and situation best.

For awareness a low pressure at the house should be all that is required.

 

[CobyRupert]

You can change your pressure switch to a low pressure cut off type switch. Square D makes one. It cuts the pump off if the pressure falls to 12 PSI. That will be the simplest, cheapest way to do it. If the cut off is activated, there is a lever on the switch that you have to use to reset the switch.

I have the "low pressure cut-off" version of the pressure switch at the input of my ballast tank that controls submersible pump, as I have house, barn and a few apartments on well and always feared somebody would leave a faucet on, or a pipe break, etc.. when not home and pump would burn up. ...
The down side is if the power goes out for an extended period of time and too many people flush toilet etc.. and reduce pressure to below cut-off point. When the power comes back on you're still without water until you manually hold reset lever on switch and pressure builds back up to above the cutout pressure. For me, that means climbing down through an outdoor manhole into a dark cramped underground vault. And if I've been away at work all day or on vacation, nobody has water until I get there.
It's like paying for insurance.

If you go with float switch wired directly in the wire between the pressure switch and pump, make sure it's rated for 220V and horsepower rated for the motor. That is, switch is not just rated for motor's full amps, but can handle motor overload and motor starting amps too. Generally a (general use AC/DC) switch's ampere rating should be twice the motor's full load amp rating if a horsepower rating is not given. [For an AC (only) general use switch, 125% or greater of the motors rating is ok]

If wired directly, float switch should be 2 pole, that is, it interrupts both wires / legs (L1 & L2) of the 220V circuit and not just one leg, which would leave voltage through the motor even when off.
If float switch operates (drops out) a relay whose contacts interrupts pump's power circuit from pressure switch, relay's contacts should be rated for pump hp/amps as mentioned above. Relay (coil) & float switch will then need to operate on the separate 120V circuit.

(Note: there are ways to operate the float/relay off the existing 220V circuit from the pressure switch, but that gets more complicated. That is, you either need a (white) neutral conductor (in addition to (green) ground conductor) run with your 220V so you can get 120V for the relay coil and float switch, or you have a 220v relay coil and float switch. Also in these scenarios, the relay would be starting the pump every time the pressure switch calls for water rather than just stopping the pump in an low water situation.)

 

[mrmikey]

You can change your pressure switch to a low pressure cut off type switch. Square D makes one. It cuts the pump off if the pressure falls to 12 PSI. That will be the simplest, cheapest way to do it. If the cut off is activated, there is a lever on the switch that you have to use to reset the switch.

What he said...works great, no extra moving parts.........Mike

 

[hawkeye08]

You can change your pressure switch to a low pressure cut off type switch. Square D makes one. It cuts the pump off if the pressure falls to 12 PSI. That will be the simplest, cheapest way to do it. If the cut off is activated, there is a lever on the switch that you have to use to reset the switch.

Yep, I accidentally got one of these and the it does shutoff when pressure drops too low and has to manually reset.

https://smile.amazon.com/gp/product/B000FKBY8W/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

[Old Guy in Tenn]

You can change your pressure switch to a low pressure cut off type switch. Square D makes one. It cuts the pump off if the pressure falls to 12 PSI. That will be the simplest, cheapest way to do it. If the cut off is activated, there is a lever on the switch that you have to use to reset the switch.

OK. If this type of switch is installed, and the pump goes dry after the faucet/toilet/whatever is turned off but before the OFF pressure is reached, wouldn't the pump keep running? It seems it would go off only when more water was used and the pressure finally dropped below the low-pressure cutoff.

 

[Industrial Toys]

Personally, if I did it, and I automate stuff like that all the time, I would want a heads up BEFORE it runs out of water. But still the out of water limit switch as well.

I like the small stainless float switches. They are low current and need to run a solid state relay or go into a low level input. What I used would also depend on the hardness of the water. If it was too hard, I might just go with the large plastic float that has a contact in it. I used one of those into a high quality (supervised) INNOVONICS transmitter to go about five hundred feet to a friends house, as a low level warning in a hillside spring fed well that he used for his heat pump. It was just a low level warning but could have controlled anything you wanted.

 

[gary49]

I assume the 300 gallon tank is basically a springbox and is gravity fed by the spring, so there is some water flowing into it all the time. If you have an average sized pressure tank, say a 40 gallon nominal tank the actual drawdown between switch off and switch on is roughly 7 gallons. So if the switch is on, even a 1 gallon/minute flow into the system with no water being drawn from said system would result in the pump running 7 minutes before it reached cut out pressure. Not great for the pump,but they're pretty tough. More likely scenario is somebody leaves the hose on, the pump pumps out the springbox, pressure falls, and the switch cuts out. The Pumptec is safer, but considerably more money, I think the switch will do the job for you, but you pays your money and you takes yer choice.

 

[Industrial Toys]

If the level switch controls the pump, yes, the pump and cycle too frequenly. I bought some junky little logic board from E-Bay that has a upper and lower limit/float switch input to address just that. The pump can't start again until the high limit is activated. Board probably cost two and a half bucks!

 

[CobyRupert]

I assume the 300 gallon tank is basically a springbox and is gravity fed by the spring, so there is some water flowing into it all the time. If you have an average sized pressure tank, say a 40 gallon nominal tank the actual drawdown between switch off and switch on is roughly 7 gallons. So if the switch is on, even a 1 gallon/minute flow into the system with no water being drawn from said system would result in the pump running 7 minutes before it reached cut out pressure. Not great for the pump,but they're pretty tough. More likely scenario is somebody leaves the hose on, the pump pumps out the springbox, pressure falls, and the switch cuts out. The Pumptec is safer, but considerably more money, I think the switch will do the job for you, but you pays your money and you takes yer choice.

Lets look at another scenario:
Say switch normally turns pump on at 40 psi, pumps ballast tank to 60 psi and turns pump off. My understanding is there is a check valve between pump and ballast tank.
What happens if source tank runs out of water when pump has raised ballast tank to 50 psi? Assume nobody is drawing water (or pressure) off of ballast tank.
Wouldn't the pump continuously run until it burns itself up because the pressure switch never sees any pressure less than 50 psi even though pump is dry? Or run until enough spring water enters source tank that pump can fill ballast tank to 60 psi, whichever comes first.
Is this a "perfect storm" / low probability scenario?

 

[Industrial Toys]

I both like and don't like designing such things. It's rarely as straightforward as you had first thought. And later, you won't be able to figure out what you did, or why.

 

[Fallon]

I both like and don't like designing such things. It's rarely as straightforward as you had first thought. And later, you won't be able to figure out what you did, or why.

Yup. It's even worse for somebody trying to figure out what it why you designed & built it that way.

 

[gary49]

Lets look at another scenario:
Say switch normally turns pump on at 40 psi, pumps ballast tank to 60 psi and turns pump off. My understanding is there is a check valve between pump and ballast tank.
What happens if source tank runs out of water when pump has raised ballast tank to 50 psi? Assume nobody is drawing water (or pressure) off of ballast tank.
Wouldn't the pump continuously run until it burns itself up because the pressure switch never sees any pressure less than 50 psi even though pump is dry? Or run until enough spring water enters source tank that pump can fill ballast tank to 60 psi, whichever comes first.
Is this a "perfect storm" / low probability scenario?

I haven't seen the OP's set-up, I'm making some assumptions such as, it's a springbox with a continuous flow of water coming in, it has a submersible pump with a check valve built into the top of the pump section, and the pump is likely lying on it's side in the springbox. If that's the way it is, the motor section will still be mostly underwater when the pump starts to suck air, which will keep the motor cool enough to not burn up, and it will pump whatever water comes into the springbox. If there's no water flowing out of the pressure tank, the system will pump up to 60# and the switch will cut out. If there is water flowing out of the pressure tank faster than the flow into the springbox, the low pressure cut off switch will soon cut the pump off. The check valve is to keep the pressurized water in tank from flowing back into the springbox. If it is a jet pump, it will lose it's prime as soon as it sucks air, that's a bit different, that might burn up the impeller in your scenario. I'm not a fan of jet pumps because they aren't self priming, the pumptec would cut it off, but possibly not the low pressure switch. Pump would need to be re-primed, even with a pumptec. Jet pumps are a PITA.

 

[Egon]

Flooded suction jet pump should not have to be primed.