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Installation
Installation
Location
Pumping unit should be placed as close as practical to the source of supply. Floor space and
head room allotted to the unit must be sufficient for inspection and maintenance. Be sure to
allow for crane or hoist service.
Installation
Model 3935 pumps are multi-stage pumps, closecoupled to the driving motor. The pump
should be supported only at the bearing frame (at the motor on pumps with Y frame) and pump
foot. The unit should be bolted to a substantial, rigid base to prevent distortion of the pump.
Pumps should not be hoisted in the air for mounting purposes with the motor bolted to the
frame. Motors should be mounted after the pump is securely installed on its permanent base.
Oh high temperature service, a gap should be left between the pump foot and end of the
casing, or shoulder of the discharge head, to allow for thermal expansion. The pump foot bolt
(371U) should not be tightened down until pump has reached operating temperature.
The discharge head should never be loosened or tightened to make up piping downstream of
the pump.
On pumps with flanged suction and discharge connections, the pump foot fits over the casing.
Oil lubricated pumps must be installed in the horizontal position. Grease lubricated pumps may
be installed in the vertical position, but should have the motor above the pump. The Model
3935 should never run dry. If there is any possibility that the pump's source of liquid might fail, a
protective device should be incorporated into the system to shut the pump down.
Piping
The pump should not run with a closed discharge for more than a few minutes, such as during
startup or shut-down. Sufficient heat can be transmitted to the fluid causing the liquid to
vaporize and allow the pump to run dry and fail. The suction pipe should never be of smaller
diameter than the pump suction. Use of suction pipe one or two sizes larger than the pump
suction, with a reducer at the pump suction, is desirable. The pump should never be throttled
on the suction side. Quick closing valves should be avoided in the discharge line to protect the
pump from damage due to surging and water hammer.
For operation at low flow, or to insure liquid will always be flowing through the pump, a bypass
line should be installed. The bypass line should be returned to the liquid source and injected
below minimum liquid level to prevent air entrainment.
If a bypass line is not used, it is recommended that precautions be taken to insure that the
pump will not run dry, run at closed discharge, or handle pumpage of excessive temperature at
pump suction. Devices which can protect the pump from the above problems are flow switches
or high temperature switches.
When handling liquids at elevated temperature, it is suggested that expansion loops or joints be
installed in the suction and discharge so that expansion of the piping will not impose excessive
strain on the pump.
Additional information on piping can be found in Hydraulic Institute Standards.
Alignment procedures
Pumps which have NEMA C-flange motors directly mounted to the bearing frame do not
require pump and motor shaft alignment. Jog motor to be sure rotation is correct before
connecting coupling. Rotation is counter-clockwise when viewed from the coupling end.
4
Model 3935 Installation, Operation and Maintenance Instructions
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