Johnson Pump Top Wing Series Manual page 16

The NPSH available from the system must always exceed the NPSH required by the
pump. If the following guidelines are observed it should ensure the best possible suction
conditions.
• The suction line should have at least the same diametre as the pump connections.
• The suction line should be as short as possible.
• Use a minimum of bends, tees and pipework restrictions.
• The calculations to determine the NPSH available from the system should be carried
out for the worst condition, see vacuum table.
• If a filter is used on the suction pipe, check pressure drop at the actual flow.
This is important to avoid cavitation which can damage the pump.
Please contact your Johnson Pump distributor if you require information on the pump or
system NPSH characteristics.
Atmospheric
pressure
Absolute
vacuum
8. When installing a pump complete with drive motor and baseplate the following
guidelines must be observed:
a) The most suitable drive for the TopWing pumps is to use a motor with direct
coupling. Please contact your Johnson Pump distributor if using some other
method.
b) Flexible couplings must always be used and aligned correctly within the limits
recommended by the coupling manufacturer. Turn the shaft at least one full
rotation to control the alignment of the coupling and that the shaft rotates
smoothly.
c) Couplings must always be enclosed in a suitable guard to prevent contact with
rotating parts which could cause personal injury. Such guards must be of suitable
material - see point d - and be of sufficiently rigid design to prevent contact with
the rotating parts during normal operation.
14
For suction lift or
vacuum conditions
NPSH available
Suction lift
or vacuum
≅10 m
water
column
Suction line
friction loss
Vapour
pressure
Vacuum table
For conditions with
positive suction head
Suction
head
NPSH available
Suction line
friction loss
Vapour
pressure
A.0500.301/314.A – IM-TW/10.00 GB (0401)