35
6.7
Utilizing a Low-Production
Water Source
6.8
Installing the Pump Under a
Windmill or Hand Pump
Cylinder
PS-Pumps
can make the best of a limited
water source, even if the pumping rate can
exceed the recovery rate. You want to draw
the most water possible, without running dry.
PS-Pumps
can handle this in two ways.
The low-water probe
The low-water probe
allows the pump to work to its full potential
until the water level drops (see Section 5.9).
This is a good strategy because you get all
the water you can while the sun shines.
Place the pump near the bottom of the well to
utilize the storage of water in the well. When
the pump is stopped by the low-water probe,
it re-starts after a 20 minute delay. The Low
Water OFF light will slowly flash even after
the water recovers and the pump restarts, to
indicate that the level got low at some time
during the day. See Section 5.9, Low Water
Probe. It may be feasible to hang the probe
independently and use it to locate the water
level at any moment. See Section 6.3, Safety
Rope and Binding.
Reduce the Maximum RPM setting
If the
well has little storage capacity, the supply may
recover before the 20-minute restart delay. In
this case, reduce the “Maximum RPM” setting
in the controller. See Section 5.6.
WARNING Do not use a valve
as a means of reducing the
flow
. With a helical rotor pump,
excessive pressure may result.
Use the Maximum RPM setting
instead.
PS-Pumps
can be combined with a classic
water-pumping windmill or hand pump, to
utilize both energy sources automatically. The
following system is often used with a conven-
tional AC pump, so a generator can be used
for backup. The AC pump is placed immedi-
ately below the cylinder, and connected to the
cylinder’s threaded intake. When power is
applied to the AC pump, it pushes water up
through the cylinder, pushing its valves open.
When the windmill draws water, it sucks it up
through the AC pump with little resistance.
(The centrifugal pump end of the standard AC
pump allows water to flow through it when it is
stopped.) When both pumps operate, each
one is relieved of its load, more or less.
This system can be employed with
PS-
Pumps.
A centrifugal model (one with a “C” in
the model number) will allow water to flow
freely through it and does NOT require any
special precautions. For helical rotor models,
the following warning applies.
To use a helical rotor
pump
under a cylinder,
you must build a bypass assembly with a T
fitting and a foot valve (a check valve with
intake screen). When the cylinder’s flow
exceeds that of the solar pump, water is
sucked in through the foot valve. When the
solar pump’s flow exceeds that of the
cylinder, the foot valve closes and allows the
solar pump to work normally and push up
through the cylinder.
Question How is a pump damaged
from “dry run”?
Answer If the pump runs completely
dry, parts will overheat and be
damaged. However, if water is only
trickling into the pump, it will usually
provide enough lubrication and
cooling to prevent damage.
WARNING
helical rotor
models (those
without a “C” in
the model
number) will
NOT allow water
to flow freely
when stopped. A
bypass foot
valve must be
used. If it is not
used, the result-
ing suction can
cause an uplift
on the rotor
which will cause
damage and
void the war-
ranty.
Bypass foot valve assembly with offset
elbows to fit a drilled well casing
windmill or hand
pump cylinder
foot
valve
PUMP
To make this system for a casing
6" (150 mm) or smaller, an offset
using 45° elbows must be
carefully constructed, as illus-
trated. Copper fittings must be
used for the bypass assembly
due to the limited space in the
well casing. Do not use any iron
fittings in this assembly.
