Nova-Tech LMI Series G - SG Metering Pump - Manual (Page 14)

8
Suction Piping Considerations
• It is preferable to have the suction of the
pump flooded by locating the liquid end
below the lowest level of the liquid in the
supply tank. Installing the supply vessel on
the suction line close to the pump can help
ensure a flooded suction line. (Consult with
your LMI distributor or the LMI/Milton Roy
technical support team for assistance in
such applications.)
• Avoid negative suction pressure conditions
(suction lift), as such conditions adversely
affect metering accuracy. A lift of 8.2 feet
(2.5 meters) of water column is the maxi-
mum suction lift permissible.
• Series G Model G pumps are designed to
operate with process liquid supplied at or
above atmospheric pressure. Although
these pumps can move liquids supplied at
less than atmospheric pressure, in these
negative pressure applications it is impor-
tant that all connections be absolutely drip
free and vacuum tight, and that a foot
valve be installed at the bottom of the suc-
tion line (see Figure 5).
• When pumping a liquid near its boiling
point (max temp is 125 degrees F), provide
enough suction head to prevent the liquid
from “flashing” into vapor when it enters
the pump liquid end on the suction stroke.
Figure 5. Suction Lift Installation
• If possible use metal or plastic tubing for
the suction line because tubing has a
smooth inner surface and can be formed
into long, sweeping bends to minimize fric-
tional flow losses.
• A strainer should be used in the suction
line to prevent foreign particles from enter-
ing the liquid end. This and any other mea-
sures which prevent debris from entering
and fouling the ball-checks will give
increased maintenance-free service.
Check strainer frequently to prevent block-
age which could lead to cavitation.
• Keep suction piping as short and straight
as possible.
• Piping size should be larger than the liquid
end suction fitting to prevent pump starva-
tion.
• If long suction lines are unavoidable, install
a stand pipe near the pump in the suction
line.
• Suction piping must be absolutely airtight
to ensure accurate pumping. After installa-
tion, test suction piping for leaks with air
and soap solution.
Discharge Piping Considerations
• Install pipe large enough to prevent exces-
sive pressure losses on the discharge
stroke of the pump. Maximum pressure at
the discharge fitting on the liquid end must
be kept at or below the rated pressure
(Max. allowable working pressure shown
on the pump nameplate).
• The pump will not deliver a controlled flow
unless the discharge line pressure is 10 psi
greater than the suction line pressure.
There are a number of ways to create an
artificial pressure, such as by installing a
back pressure valve. (Please contact your
LMI distributor for recommendations to
increase back pressure in slurry applica-
tions.)
• When pumping water-treatment chemicals
directly into boiler drums, use one liquid
end assembly for each boiler drum. Dis-