Johnson Controls TopClean AS - Manual (Page 8)

6
IM-AS/02.00 GB (0412)
Fig. 1
NO YES
6.0 Non-permitted uses
Do not use the pump with a suction pressure greater than the specified value (0.5 times
the discharge head generated by the pump).
The pump must always be used in an environment appropriate to the level of protection
of the motor. Always check this on the motor plate before installation.
The pump may not be used in environments which require a higher level of protection or
a higher specification motor or electrical parts.
Components complying with the safety standards for the environment in question must
be used.
7.0 Installation
7.1 Suction and inflow conditions
(NPSH = Net Positive Suction Head)
NPSH of system (available NPSH)
In order to ensure that pump operation is free from cavitation, it is essential to observe
the maximum permitted suction lift ha geo max or the minimum allowable head hc geo
min. NPSH of pump (required NPSH)
The centrifugal pumps can operate correctly only if vapour has not formed inside. For
this reason the static head at the reference point for the NPSH is the centre of the
impeller, that is the point of intersection of the pump shaft axis with the vertical plane
that passes through the external points of the blade inlet corners.
NPSHnec. is the value required by the pump, expressed in metres, obtained from the
performance curve. In practice 0.5 m should be added to this value as a safety margin.
7.2 Piping
In order to prevent the creation of harmful stresses, the suction and discharge pipes must
be connected to the pump ports without the use of force. These pipes must also be
supported independently avoiding causing stresses on the pump. The internal diameter
must be the same size as the pump connections. It must in any case not be smaller to
avoid head loss and/or poor performances. Always use elbows with large radius. If the
pipe diameter changes along the line, use reduction cones, choosing the ones that are
most suitable for avoiding the formation of air pockets (Fig. 1).
The suction pipe must be as short as possible and rise as it moves towards the pump if it
is sucking from a tank, if on the other hand the pump is below the level of the liquid, the
pipe should descend slightly. If the pump is used for transporting hot liquids, fit expan-
sion joints to compensate any expansion of the piping. The maximum velocity of the
liquid in the suction pipe must not be greater than 3 m/s. Velocities between 1 and 2 m/s
are recommended.
The suction pipe must be designed in such a way as to prevent air from entering the
pump. For this reason, when sucking from a tank located at a lower level, the pipe must
reach below the free surface of the liquid. Avoid creating obstacles which could increase
suction losses disrupting smooth fluid flow. Make sure that there are no restrictions,