Sequential or random switching

[Engineer54]

If asked id build a small panel PLC controlled, water level, flow switches and alarm status... Pumps would work as requested if flow switch failed to monitor water flow the pump in question would be locked out and other pump takes over. Alarm would be raised.

A little bit more money but you won't get a call out in the middle of the night saying its flooded because one pump failed.

If were talking about rainwater harvesting, the tanks will be outside, so i can't see a problem with flooding to be honest.

Seen the system using three or four tanks being used for this very purpose all over Southeast Asia, and none of them needed a PLC controlling 3 pumps. If anything, you stand more chance of the PLC going ---'s up, than a pump... Bit different if this system was for an industrial process, i'd certainly agree with you in that instance... I'd be keeping this rainwater system as simple as possible...

 

[Darkwood]

If were talking about rainwater harvesting, the tanks will be outside, so i can't see a problem with flooding to be honest.

Seen the system using three or four tanks being used for this very purpose all over Southeast Asia, and none of them needed a PLC controlling 3 pumps. If anything, you stand more chance of the PLC going ---'s up, than a pump... Bit different if this system was for an industrial process, i'd certainly agree with you in that instance... I'd be keeping this rainwater system as simple as possible...

You make a good point, im blinkered a bit here wasn't thinking too much about the general set-up and what its actually doing and was just looking at control options available.

 

[tazz]

Can see with external sensing were the cost can come in......from a circuit side, now its just a case 16 inputs and 16 outputs, and a good programmer sorts out all the requirements, to control it actions, and user input and safety inputs...with less components i did a the quick design for op......life is a lot easier now...lol

 

[Paul2011]

What Marvo is asking, ...is ''WHY'', because basically it makes no sense??

If the the 3 tanks are linked, they will self level themselves (the larger the linking pipes, the faster the self leveling will be), and only one pump will be required rather than three pumps. Oh, and motorised pumps, be they submersible or otherwise, are very reliable bits of kit today and not something you need to constantly watch over....

The answer to this is that my understanding is that for this to work the tanks have to be linked near the base. As they are buried this would involve excavating a 2 metre plus deep trench between them. As I also want a way of isolating the tanks so that for example one could be cleaned out whilst still using the others, isolating valves would need to be fitted and some means of access provided. None of this is particularly practical.

Thanks to everyone for their contribution. Really interesting - I was hoping for a very easy and cheap solution. Might well go with the tazz design, but a bit beyond me so would need to get someone to make it up for me.

One idea that has just occurred to me since starting to write this is that I could just have three cheap programmable timers - one for each pump- set up so that only one pump was in use at any one time. Not exactly what I asked for but close.

 

[Engineer54]

See, that now explains WHY!! It would have been better if you had explained the situation in your opening post. Though why anyone would bury rainwater tanks is a bit obscure to me ...lol!! I had a feeling that Tazz's drawing was going to be a bit beyond most electricians comfort zone to sit down and make. A simple exercise, is now going to be well and truly over complicated.

 

[Paul2011]

See, that now explains WHY!! It would have been better if you had explained the situation in your opening post. Though why anyone would bury rainwater tanks is a bit obscure to me ...lol!! I had a feeling that Tazz's drawing was going to be a bit beyond most electricians comfort zone to sit down and make. A simple exercise, is now going to be well and truly over complicated.

I did say in my opening post that changing the configuration of the tanks was not possible, but if I post again I will try and give more detail if that is what is required.

As for burying the tanks two good reasons are it stops them freezing up in the winter, and it's aesthetically much better in a small garden not to be looking at large tanks.

 

[Darkwood]

Lol.... my over complex idea now seems to be a consideration as the OP has slowly drip fed us the set - up well i'd be inclined to go with one pump up top (2 if you want redundancy) and a valve system which works off 3 separate 4-20mA level sensors so if one tank gets drawn off too quickly a percentage marker will be exceeded in comparison to the other tanks and the valve will swap over. PLC wise simple operating principle but will be more complex on the number crunching side.

Where are you based?

 

[Paul2011]

Lol.... my over complex idea now seems to be a consideration as the OP has slowly drip fed us the set - up well i'd be inclined to go with one pump up top (2 if you want redundancy) and a valve system which works off 3 separate 4-20mA level sensors so if one tank gets drawn off too quickly a percentage marker will be exceeded in comparison to the other tanks and the valve will swap over. PLC wise simple operating principle but will be more complex on the number crunching side.

Where are you based?

Suffolk, England.

 

[Darkwood]

Well out of my catchment area sorry to say but maybe we have a more localised Engineer within the forum... and i personally would be one to go the whole hog ....cheaper systems may be fine if consequences are low in a fault or failure. I've done a similar set-up although not to the same requirements where the operator had full LCD screen overview of tank levels it was fully automated and as it was 24hr monitoring it had multiple redundancy with auto fault clearance. It cost a bit but has already excelled in its use and earned its money by avoiding 2 plant shutdowns.

Its down to really asking what your customer needs, what would happen if say the only pump fitted failed... what this affects and what the inconvenience and cost to anyone, then and only then can you recommend the best set-up for the job.

As Tazz brought up before a lot of the extra's can be done at low cost i.e. because you would have multiple tank monitoring of levels it doesn't take much to write in a monitor watch on fill rates so if one filling grate/channel got blocked to one tank then it would fill up unequally and be left low while other tanks filled normally - this can all be set to alarm up just by having a simple logic model written.

Again we can easily over-complicate this but we lack info and requirements.

 

[Engineer54]

I did say in my opening post that changing the configuration of the tanks was not possible, but if I post again I will try and give more detail if that is what is required.

As for burying the tanks two good reasons are it stops them freezing up in the winter, and it's aesthetically much better in a small garden not to be looking at large tanks.

So what are these buried rainwater tank being used for, watering the garden or for something else?? If watering the garden you wouldn't need the tanks operational during the winter, plenty of rainwater in the UK during winter. Though aesthetics i can understand...lol!! Though if as you say, it's a small garden, why do you need 3 large rainwater tanks??

This control system is going to cost in terms of both materials and time, more than it's worth. Why not just pump the water as and when required with the flick of a switch, rather than trying to keep all three tanks at the same level?? I still don't quite understand the thinking behind that stipulation??

 

[Engineer54]

Well out of my catchment area sorry to say but maybe we have a more localised Engineer within the forum... and i personally would be one to go the whole hog ....cheaper systems may be fine but it all about what happens if this fails or that fails etc. I've done a similar set-up although not to the same requirements where the operator had full LCD screen overview of tank levels it was fully automated and as it was 24hr monitoring it had multiple redundancy with auto fault clearance. It cost a bit but has already excelled in its use and earned its money by avoiding 2 plant shutdowns.

There you go again!! lol!!

Would you really go the whole hog as above, if this set-up is say, just to water a garden in summer?? lol!!

 

[Darkwood]

There you go again!! lol!!

Would you really go the whole hog as above, if this set-up is say, just to water a garden in summer?? lol!!

I did carry on to say (with edit) we lack info and consequence list... you never know it might be for his prized competition grade Giant Marrows or simply the back up for the local allotment in dry times ...but yes too much of my career designing fail safe that prevent high cost failures

 

[Paul2011]

I did carry on to say (with edit) we lack info and consequence list... you never know it might be for his prized competition grade Giant Marrows or simply the back up for the local allotment in dry times ...but yes too much of my career designing fail safe that prevent high cost failures

Sorry guys. When I posted this I thought an off the shelf easily available piece of kit would be available, and I just hadn't come across it.

For those who are interested we are talking about 3 x 1,500 litre tanks fed by 300+ square metres of roof, to be used for flushing toilets, washing machine, gardening etc. The water to the tanks is pre-filtered and the tanks fill evenly from the roof.

 

[Darkwood]

I take it the toilets use the tanks as primary water source but can be switched back to mains water?
What is the nature of the building (domestic, commercial, industrial) and its use?

 

[Paul2011]

I take it the toilets use the tanks as primary water source but can be switched back to mains water?
What is the nature of the building (domestic, commercial, industrial) and its use?

It's domestic. Large house. Toilets can be switched back to mains but only with a manual intervention.

 

[Darkwood]

Keep it cheap and cheerful then i can only assue you have some sort of header tank in the house thats isolated from the mains system id just implement a secondary water overlevel sensor to ensure you don't get the pump flooding the house if the level switch fails again not enough in ...could go on for days at this rate questions and answers before we get the whole set up.

 

[Knobhead]

I’ve been following this. I was thinking of a PLC that can handle “drum control”. Now I know it’s to flush the bogs I don’t know whether to laugh or cry.

KISS*

*Look it up.

Bath/shower water is a good source of grey water.

 

[DPG]

Hope you can work this out...each time the contacts are closed on your time switch it latches an on/off function......so sequence is
off / pump1 on / off / pump2 on / off /pump3 on/off / then pump1 on again.......hope this helps

View attachment 23629

4017 - an excellent chip. Done many a circuit with those. Still got my Knight-Rider light somewhere - forward/backwards direction using diode logic on the 4017 outputs. And large caps to give the 'trailing' effect. Daz

 

[Darkwood]

I’ve been following this. I was thinking of a PLC that can handle “drum control”. Now I know it’s to flush the bogs I don’t know whether to laugh or cry.

KISS*

*Look it up.

Bath/shower water is a good source of grey water.

Only Fools and Horses sketch -- When you said you had land to furrow i was thinking of acre's not an allotment!

 

[Marvo]

Having the tanks unconnected is making you life very complicated and expensive. I'd seriously reconsider your decision not to connect them together at the bottom, below ground level if necessary.

The advantages are;

• You only need one pump instead of three.
• You only need one low-level safety switch to protect the pump from dry run.
• You don't need a complicated ladder/sequence control to operate the three pumps in order.
• One third of the wiring and cabling, one third the size of control panel and one third of the controls and switchgear.
• More flexibility ie all the collected water is available for all tasks simultaneously.

If your only reason for not connecting them is to be able to isolate tanks individually for cleaning then rather look at just pumping the entire system dry and cleaning all the tanks together. If you really need to isolate individual tanks you could also fit standard 2" plastic ball valves on the balancing pipes and make up some extension handles so they can be operated from above ground level. You also get 12v/24v electrically operated ball valves but the price of these for an IP66 version may be prohibitive.