16
Details about dry running
What is dry running?
To seal the pump shaft against the pump casing the
mechanical seal needs lubrication between its rotating faces.
This lubrication is provided by the pumped liquid. If the pump
is fitted with a quench the lubrication for the quench must be
provided from an external source.
Dry running occurs when the lubrication fails. Dry running
destroys the mechanical seal in few seconds.
For example see fig. 5.
C A U T I O N
!
Dry running!
S
Damage to property.
Z
The suction line must be absolutely leak proof and laid in
such a way that no air pockets can form.
Z
Avoid tight elbows and valves immediately upstream of
the pump. They interfere with the incoming flow to the
pump and thus with the NPSH of the system.
Z
The head of the system may not be greater than the head
guaranteed by the pump.
Z
The nominal pipeline diameters of the system should be
equal to or greater than the DNS or DND connectors of
the pump.
Z
A foot valve should be used in suction mode.
Z
To prevent air pockets from forming, the suction line must
be laid so that it rises to the pump; a gravity feed line must
be laid with a slight downward gradient to the pump.
Z
If local conditions do not allow the suction line to ascend
continuously, install a venting device at the highest point
of the line.
Z
A shut off valve should be installed in the suction line near
the pump. This valve must be completely open during
operation and may never be used as a control valve.
Z
A shut off valve should be installed in the discharge line,
near the pump, to control the delivery rate.
Fig. 5
Lubrication between sliding surfaces
P - pump side
105 - mechanical seal
L - lubrication
A - atmosphere side
K.0
381V
1
P
A
105
L
