Borehole Water Tank - Remote Level Monitoring

[Alchad]

Our borehole is near the house and pumps to a tank at a higher ground about 600 to 700 metres away and probably 70 metres higher in elevation, the water then flows back via the same pipe to feed house, barns and various troughs around the place, pump is on a time switch set to pump a 2 to 4 hours per day depending on time of year - we share the system with a neighbour and usage varies with the amount of stock on his land.

Occasionally I get the time setting wrong and the tank runs virtually dry with the only indication when the house tap pressure declines.

I'd like to install some form of remote level indication and have seen some online which send a wireless signal from say an ultrasonic sensor back to a monitor, but there are two problems, the main one being that there is no "line of sight" between the tank and the house, and the second problem is the distance involved which seems to be too far for the systems I've seen advertised.

A solution I've thought of would be to fit some sort of (solar powered) repeater for the wireless signal on an old telegraph pole I have which would be installed in one of the fields between the borehole and the tank and the additional height would allow the signal to be transferred. Problem is that despite looking I've not come across anything that would act as this intermediate receive/transmit station.

Bit of a long shot but just wondered if anyone had this problem and found a solution.

Comments welcome.

Alchad

 

[Netherfield]

One way that comes to mind,

Have a ballcock fitted to the storage tank, a pressure switch fitted to the pump end, when the ballcock closes the pressure will increase and switch pump off, could also fit a delay timer set to say 3 hours, then the pump won't be constantly switching on and off when a small amount of water leaves the tank.

Obviously you need to experiment the pressure changes needed and an electrician to wire it up.

 

[Highland Mule]

Sounds terribly inefficient to pump water a mile (there and back) just to give the header tank some pressure. I'm sure a more modern design could be produced to have a local header tank that is held at pressure without all the extended distance.

 

[farmerm]

What about simply replacing the timer with a float switch?

There are various ways to generate a low level warning. If wireless transmission is difficult is there mobile phone coverage/affordable?

 

[Alchad]

Sounds terribly inefficient to pump water a mile (there and back) just to give the header tank some pressure. I'm sure a more modern design could be produced to have a local header tank that is held at pressure without all the extended distance.

Not really I don't think. The water is only pumped up to the tank. Gravity then does the work in pushing back down as required, it supplies 10 water troughs as well as the house on the way.

Alchad

 

[Alchad]

What about simply replacing the timer with a float switch?

There are various ways to generate a low level warning. If wireless transmission is difficult is there mobile phone coverage/affordable?

This probably is an alternative (and probably more efficient), but suffers from the line of sight wireless transmission problem. Phone signal at the tank is reasonable and is also an option - I did see that Kingspan had a system based on this, but it seems to have been discontinued.

Alchad

 

[Highland Mule]

Not really I don't think. The water is only pumped up to the tank. Gravity then does the work in pushing back down as required, it supplies 10 water troughs as well as the house on the way.

Alchad

Overcoming gravity is one thing, but there are a load of frictional losses in the long pipe run, plus a load of potential for leaks too.

 

[Alchad]

Overcoming gravity is one thing, but there are a load of frictional losses in the long pipe run, plus a load of potential for leaks too.

Yes I know, but as they say, "we are where we are", it's the system that was here when we moved in, the pump is a new replacement one last year and quite efficient, probably uses 5kw/day max. Modifying the system would be expensive and not economical.

Alchad

 

[Dry Rot]

Well, this is an interesting problem! Is there a way of using a pressure change in the water in the pipe to turn the pump on and off?

As the water in the tank drops, the pressure in the supply pipe will also drop due to the lowering of the head. Not much, but the decrease in pressure will continue all the way down the pipe to the pump.

Is there a pressure switch that can detect this very small change in pressure? Could that change in pressure be used to switch the pump on? The switch could be programmed to keep the pump running just long enough to refill the tank, then switch off. Oh well, it was just a thought.

 

[Highland Mule]

Well, this is an interesting problem! Is there a way of using a pressure change in the water in the pipe to turn the pump on and off?

As the water in the tank drops, the pressure in the supply pipe will also drop due to the lowering of the head. Not much, but the decrease in pressure will continue all the way down the pipe to the pump.

Is there a pressure switch that can detect this very small change in pressure? Could that change in pressure be used to switch the pump on? The switch could be programmed to keep the pump running just long enough to refill the tank, then switch off. Oh well, it was just a thought.

The dynamic pressure drops would be too significant and would dwarf the static. Effectively you’re trying to discriminate between 7 bar and 7.05, when there’s possibly a 2 or 3 bar variance due to friction. It’s not going to happen.

 

[e3120]

The dynamic pressure drops would be too significant and would dwarf the static. Effectively you’re trying to discriminate between 7 bar and 7.05, when there’s possibly a 2 or 3 bar variance due to friction. It’s not going to happen.

Agreed. A few hundred quid on a pressure vessel would completely automate the system. Just blank off the pipe at the tank. When we binned the tank on stilts here, the cottage inhabitants appreciated the cool, rust free water on a day like today.

 

[Alchad]

Agreed. A few hundred quid on a pressure vessel would completely automate the system. Just blank off the pipe at the tank. When we binned the tank on stilts here, the cottage inhabitants appreciated the cool, rust free water on a day like today.

The dynamic pressure drops would be too significant and would dwarf the static. Effectively you’re trying to discriminate between 7 bar and 7.05, when there’s possibly a 2 or 3 bar variance due to friction. It’s not going to happen.

Yes, a pressure switch to turn the borehole pump on at low level in the reservoir and off when full would need a very accurate pressure switch - the tank (it's actually a concrete circular pit in the ground) is only about 4 metres in depth, so say 3metre change from low level switch on to high level full is about a 0.3 bar change in pressure. As the static head (70 metres) is 6.85 bar I suspect 0.3 bar difference would be asking too much for a normal pressure switch?? Also, don't think the dynamic pressure drop would come into this because the flow out of the tank/reservoir under normal circumstances would be quite small and the dynamic pressure loss similarly small. Agreed that when the pump is operating to fill the tank the dynamic pressure loss would be quite high - as you say 2 to 3 bar.

Regarding the pressure vessel. Haven't come across these, will investigate.

Thanks all for the input.

Alchad

 

[Highland Mule]

Also, don't think the dynamic pressure drop would come into this because the flow out of the tank/reservoir under normal circumstances would be quite small and the dynamic pressure loss similarly small.

You'd be surprised.

Just running a quick calculation, plastic 32mm pipe of 700m length would lose between 1 and 1.5bar, for 2cube per hour of flow.

Pressure Drop Online-Calculator

www.pressure-drop.com

 

[chipchap]

Just install a pressure vessel and forget the concrete reservoir.
Modern borehole systems all operate like this.

By the way, your pressure calculations above are wrong, if you install a ball valve on the reservoir, in conjunction with a small pressure vessel, you could wait for the pressure at the pump to get to 15 bar before turning off, assuming your pipe work will stand it. Remember to check your pressure relief valve is set right

 

[Alchad]

You'd be surprised.

Just running a quick calculation, plastic 32mm pipe of 700m length would lose between 1 and 1.5bar, for 2cube per hour of flow.

Pressure Drop Online-Calculator

www.pressure-drop.com

OK, before retiring I earnt my living as a chemical engineer for 25 years, so am pretty familiar with design of pipework systems. We have a system which pumps up to a tank/reservoir for a couple of hours a day. When it is pumping the pump has to overcome the head difference between the pump (static pressure difference) and dynamic pressure drop created by the flow. So yes when the pump is operating there will be the pressure drop you quote, and in actual fact it will be a lot more because I think the pipe is only 25mm. BUT when the tank is just sitting there with a few metres of water in it and feeding say the house when we flush the loo or a trough when the sheep have a drink, the flowback down the pipe will be very small and dynamic pressure drop will be very low.

Perhaps we are misunderstanding each other?

Alchad

 

[Highland Mule]

OK, before retiring I earnt my living as a chemical engineer for 25 years, so am pretty familiar with design of pipework systems. We have a system which pumps up to a tank/reservoir for a couple of hours a day. When it is pumping the pump has to overcome the head difference between the pump (static pressure difference) and dynamic pressure drop created by the flow. So yes when the pump is operating there will be the pressure drop you quote, and in actual fact it will be a lot more because I think the pipe is only 25mm. BUT when the tank is just sitting there with a few metres of water in it and feeding say the house when we flush the loo or a trough when the sheep have a drink, the flowback down the pipe will be very small and dynamic pressure drop will be very low.

Perhaps we are misunderstanding each other?

Alchad

I’m not yet retired

I was guessing at the backflow during use, but I don’t have the system knowledge that you do. If you have the skills, modelling should be fairly easy.

Pressure vessels should be right up your street too, and are certainly worth a look. As far as I can tell they use an inflated bladder to allow for expansion and pressurisation - something like a megaflow hot water tank.

 

[Alchad]

Just install a pressure vessel and forget the concrete reservoir.
Modern borehole systems all operate like this.

By the way, your pressure calculations above are wrong, if you install a ball valve on the reservoir, in conjunction with a small pressure vessel, you could wait for the pressure at the pump to get to 15 bar before turning off, assuming your pipe work will stand it. Remember to check your pressure relief valve is set right

Not sure which calculations are wrong? As I said not familiar with pressure vessel borehole systems but installing a pressure vessel and ball valve at the reservoir would presumably subject the whole system to the dead head of the pump and stressing any underground joints?

Alchad

 

[Alchad]

I’m not yet retired

I was guessing at the backflow during use, but I don’t have the system knowledge that you do. If you have the skills, modelling should be fairly easy.

Pressure vessels should be right up your street too, and are certainly worth a look. As far as I can tell they use an inflated bladder to allow for expansion and pressurisation - something like a megaflow hot water tank.

Retirement has mixed blessing, learning stopped many years back, I still think in psi and moving with the times to modern new fangled ways takes me out of my comfort zone (apart from IT type of things, hence my original quest for a level signal transmitted back from the tank - that would be fun, a pressure vessel not so.

Regards

Alchad

 

[Hjwise]

I fill a 20,000l tank with the bore pump using two float switches that kicks in when the level drops to 10,000l (so I have backup if pump fails) and stops when full. I then have a small pump drawing from this tank controlled by an inverter that maintains a constant pressure (usually 1.1 bar).
This means the bore pump is not start/stopping frequently as it would on a pressure vessel system and is only running at a pressure needed to fill the tank. The cheaper small pump is only running at the speed necessary to maintain system pressure (via a small expansion vessel), so is efficient. It works well.

 

[defender]

Probably the simplest option is to put a ball valve on the tank and fit a pressure switch at the pump so it stops when tank full, fit a start timer delay that can be any delay you want , the pump could be alarmed so it sends signal if it hasnt started for a period of time