"Donald R Smith" wrote in message
...
I believe I may have a problem with my system here. Now that the water
table is receding thew pump has difficulty in producing enough flow to make
the pop-ups pop.

Probably due to the suction head increasing therefore getting close to the
maximum head rating of the pump.

A friend peered in to the depths of my bore liner and was able to tell me
that the inlet to the pump was far smaller than the delivery pipe to the
system. This he claimed would cause a vast reduction in the back pressure.

Changing the suction line probably wouldn't improve things as you would still be
trying to lift the same head of water.
Unless it is too small which would increase the restriction to flow, this would
cause cavitation (read footnote) to the pump and eventually destroy it.
If it has been ok in the past, I wouldn't be too concerned. Look at other
things first.

Actually, a larger delivery line is better, giving less restriction to flow you
would get increased flow to the take off points for the pop ups and better back
pressure.

I would like to see the science of all this and hope that someone can point
me in the right direction.

Do you have one line and a foot valve down the bore?

Or do you have a jet pump at the bottom (2 lines going down the bore, 2
different sizes) for self priming.

I did not want to call in a contractor because that will cost me heaps of
dollars.
Is there a simple answer to all this?

Honestly, there is no simple answer, But, because the water level has dropped,
the ability for the pump to lift (actually, the ability for the pump to create
enough vacuum to allow the air pressure (atmospheric pressure) to push the water
up the line and into the pump) has reduced.

Maybe a larger capacity pump might be the answer.

Do you know the distance from the pump to the water level (Not the length of the
suction line, which would be longer), compare that with the rating of the
pump.....

Oh, Another thing, what is the condition of the pump inside, any sign of
cavitation, are the impellers ok, is there a buildup of any rust, calcium, etc
inside the pump. If the fittings are galvanised fittings there may be a buildup
inside the fittings reducing the capacity of the pump

Good luck!
Gerard


Footnote:
Cavitation is the formation of vapour bubbles within a liquid at low-pressure
regions that occur in places where the liquid has been accelerated to high
velocities, as in the operation of centrifugal pumps, water turbines, and marine
propellers. Cavitation is undesirable because it produces extensive erosion of
the rotating blades, additional noise from the resultant knocking and
vibrations, and a significant reduction of efficiency because it distorts the
flow pattern. The cavities form when the pressure of the liquid has been reduced
to its vapour pressure; they expand as the pressure is further reduced along
with the flow and suddenly collapse when they reach regions of higher pressure.
The sudden growth and collapse of these vapour cavities cause the extreme
pressures that pit the metal surfaces exposed to the cavitating liquid.