n Keep the suction line as short as possible.
n The height h (see diagram) may only be smaller than or equal
to the suction lift of the pump P divided by the density rho of
the feed chemical:
h (in m)≤ P (in mWS) / rho (in g/cm
3
)
n The height h - see diagram - and the cross-section of the suc‐
tion line must be dimensioned in such a way that the negative
pressure created during the suction process cannot reach the
vapour pressure of the feed chemical being metered (cavita‐
tion!).
This can be seen in extreme cases by the dropping of the fluid
level or by an incomplete reciprocal stroke.
n Install a foot valve at the end of the suction line, in case the
pump is higher than the maximum fluid level in the storage
tank.
n Only shorten the free end of the suction line until the foot valve
is suspended just above the container base.
7.3 Information on the discharge-side installation
n Install a vacuum breaker if the feed chemical may not press
through the metering pump. Metering pumps are not absolutely
leak-tight shut-off units.
n Install the injection valve at the injection point to prevent
unwanted mixing of water and feed chemical in the discharge
line.
Length of suction line
Fig. 7
Height difference, suction side
Fig. 8
Avoid allowing the suction line to run
dry.
Fig. 9
With return from the main line
Fig. 10
Installation, hydraulic
23
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