Mas Grup
6
6.5.2. Suction Lines
To avoid air pockets which could affect pump priming, the suction line
must be as short and direct as possible. When operation pumped, if the
line slopes down to the pump at any point along the suction run, air
involves a suction lift, the line must always slope upward to the pump
from the source of the liquid being pockets will be created.
Installing Pipes
Suction line (top wiew)
Suction line (bottom wiew)
Suction flange
Suction flange
Figure 7:
Installing Pipes
6.5.2.1. Fittings
Suction lines should be the same size as the pump inlet. If reducers are
used in suction lines, they should be the eccentric type and should be
installed with the flat part of the reducers uppermost to avoid creating air
pockets. Valves are not normally used in suction lines but if a valve is
used, install it with the horizontal to avoid air pocket.
6.5.2.2. Strainer
If a strainer is furnished with the pump, be certain to use it; any spherical
solids which pass through a strainer furnished with the pump will also
pass through the pump itself.
If a strainer is not furnished with the pump, but is installed by pump user,
make certain that the total area of the openings in the strainer is at least
three or four times the cross section of the suction line and that openings
will not permit passage of solids larger than the solids handling capability
of the pump.
6.5.2.3. Sealing
Since even a slight leak will affect priming, head and capacity, especially
when operating with a high suction lift, all connection in the suction line
should be sealed with pipe dope to ensure an airtight seal. Follow the
sealant manufacturer’s recommendations when selecting and applying
the pipe dope. The pipe dope should be compatible with the liquid being
pumped.
6.5.2.4. Suction Lines in Sumps
If a single suction line is installed in a sump, it should be positioned away
from the wall of the sump at a distance equal to 1.5 times the diameter of
the suction line.
If there is a liquid flow from an open pipe into sump, the flow should be
kept away from the suction inlet because the inflow will carry air down into
the sump and air entering the suction line will reduce pump efficiency.
It is necessary to position inflow close to the suction inlet, install a baffle
between the inflow and the suction lines; it must be the rigid-wall,
reinforced type to prevent collapse under suction.
Using piping couplings in the suction lines is not recommended.
Suction inlet at a distance 1.5 times the diameter of the suction pipe. The
baffle will allow entrained air to escape from the liquid before it is drawn
into the suction inlet.
If two suction lines are installed in a single sump, the flow path may
interact, reducing the efficiency of one or both pumps. To avoid this,
position the suction inlet so that they are separated by a distance equal to
at least 3 times the diameter of the suction pipe.
6.5.2.5. Suction Lines in Positioning
The depth of the submergence of the suction line is critical to efficient
pump operation. Figure 7 shows recommended minimum submergence
vs. velocity.
Note:
The pipe submergence required may be reduced by installing a
standard pipe increaser fitting at the end of the suction line. The larger
opening size will reduce the inlet velocity. Calculate the required
submergence using the following formula based on the increased
opening size (area or diameter).
Figure 8:
Recommended Minimum Suction Line Submergence
vs. Velocity
𝑉𝐸𝐿𝑂𝐶𝐼𝑇𝑌 (𝑓𝑡 𝑠
⁄ ) =
𝑄𝑈𝐴𝑁𝑥(𝐺𝑃𝑀)𝑥0.321
𝐴𝑅𝐸𝐴
𝑉𝐸𝐿𝑂𝐶𝐼𝑇𝑌 (𝑚 𝑠
⁄ ) =
𝐹𝐿𝑂𝑊(𝑚
3
𝑠)
⁄
𝐴𝑅𝐸𝐴 (𝑚
2
)
6.5.3. Automatic Air Release Valve
The air release valve is going to permit air to escape through the bypass
line and then close automatically when the pump is fully primed and
pumping at full capacity.
Theory of Operation
The cross-sectional view of the air release valve is shown in open valve
position. During the priming process, air from the pump casing flows
through the bypass line and passes through the air release valve to the
wet well.
When the pump is fully primed, flow pressure compresses the spring and
closes the valve. The valve will remain closed, reducing the bypass of
liquid to 3.8 to 19 l/min until the pump losses its prime or stops.