If any of these types of pumps
are mounted in a horizontal position,
then a shallow-well float-type control
may be used. Pumping efficiency is
greatly reduced, however. Generally,
one of the following types of control
is used: Diaphragm-type air control; Water-displacement control; or the
When the pump stops, all the
suction is removed from the diaphragm,
and the spring forces the diaphragm
to the left. This action forces the new
charge of air through the small opening
into the tank.
If the water level in the tank is
below the water control, then air moves
form the tank into the control instead
of from the snifter valve. When the
pump stops, the air is then forced back
into the tank, no new air is added.
This type of control must be
matched with the tank size. Also, the
pump must turn on and off frequently,
because air is added or re-moved only
at the beginning or end of each pumping
cycle.
When the pump stops, the water
pressure equalizes amongst the pressure
tank, the pump, and the pump suction
line. Water moves from the pump suction
line back into the air-control cylinder.
The air- control float valve is lifted,
and the cylinder fills with water. The
new charge of air from the air-control
cylinder is forced into the tank.
When too much air accumulates for
proper tank operation, the air is released
through an air-release mechanism shown
in the figure. This type of control may
be used with ant of the centrifugal or
turbine pumps.
Diaphragm-type Air Controls (2)
As the pump starts, water
is removed from the right side of the
control by pump suction causing
a partial vacuum. This causes the
diaphragm to move to the right against
a spring. The sudden action causes a
partial vacuum to form in the control
on the left side of the diaphragm if
the water in the pressure tank is
above the opening connecting the tank.
At the same time the partial
vacuum causes outside air to force
open the sniffer valve, and a charge
of air enters the control.
Water-displacement Controls (2)
When the pump starts, there
is an immediate difference in pressure
between the point where the control
connects to the pressure tank and the
point where the suction tube connects
to the pump suction line. The highest
pressure is at the tank connection. If
the water level in the tank is above
the opening to the control, water from
the tank passes through the jet into
the air-control cylinder. As a
result, suction develops at the snifter
valve, and air is carried with the water
into the air-control cylinder until the
air-control float valve seats in the
charger. This stops further water removal
from the cylinder.
If, when the pump starts, the water
level is below the tank connection to
the control, air flows into the cylinder
from the tank. The air movement from
the tank into the cylinder does not
develop enough suction to open the
snifter valve. As a result, no new air
is added to the tank. Other designs
for the same operating principle can be
found in.
Venturi-and-Air-Release Controls (2) (2)
The venturi unit is placed
between the pump and the pressure tank.
The pressure-drop adjuster valve is
closed enough to force some water through
the venturi as it passes from the pump
to the pressure tank. Water passing
through the venturi causes a partial
vacuum at the snifter valve. This
partial vacuum is enough to draw water
into the water line and into the pressure
tank.
Return to Pressure-tank Air-volume Controls
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