OT : Water reservoirs - Hydraulic logic

Hi,



We have to rehabilitate a pumping station.

As per tender documents we have to keep in working condition old reservoirs (having in total 4000m3) and build a new one with 10000m3.



Old pumping station was feeding by gravity in one supply zone and by pumps in second supply zone.



OK.



They start build the new reservoir and meantime asked me to wrote the automation philosophy as to be approved. I have been provided with a P&I diagram.
OK so far BUT in reality is not so nice.

They started to build the new reservoir with a elevation 5 meters higher than old ones (do not ask me why), so no matter what I am doing old
will overflow trying to fill up new one.

In supply pipe we will have 1.5bar but we will feed from top of reservoirs, meaning old reservoirs will be fed with 1.5bar, new 1 bar.


Solutions can be
a. Obvious = quit on using old reservoirs
b.Stupid = use new reservoir only at half capacity
c.expensive = use a proportional valve at entrance of old reservoirs as to handle flow, and a equalizing pump at exit as to cover the 1/2 bar difference between
all reservoirs

Anyone encountered this kind of problems?
Any thoughts on how this problem can be handled?

All the best
marian

sounds to me that you need a filling pump assigned to each reservoir and seperate PI settings for each tank depending on which one your filling drawing from. I take it you changed the software for the new PI and now when you fill the old one it overflows?

When filling a lower reservoir from a higher reservoir the best solution is often to simply use a hytrol valve (or valves in parallel depending upon required flow) with a mechanical level/float control pilot.

This solution does not require any electrical or PLC controls at all.... no wires to run, no electrical or electronic level sensor......

It's not glamorous.... It's not high-tech........ but it works. You will simply set the float control to regulate the level of the lower reservoir at the desired level. Works just like a toilet tank......



Stationmaster

I think you've got the best scheme at the moment... use the lower tank to fill the higher tank whenever the higher tank is low.

The line which feeds into the higher tank should ofcourse have a non-return valve on it. It should be a one way system, this path should only allow water to be pumped from the low (old) reservoir to the new high reservoir.

If you also want to be able to balance out levels in the opposite direction then you could have a control valve which bypasses both the pumps and the non-return valve. This would be interlocked against the pumps (so both don't operate at once).

You could utilise one flow meter on a common pipe section between the two reservoirs to meter water between them (for fill rate control).

A manual ball valve at each end of the fill line would ofcourse be practical, as would low flow monitoring of the pumps (ie when pumps are running at X% flow should be > Y m3/s otherwise alarm and interlock pump operation)

Regards,
Bevan