Valves; Discharge Piping; Air Release Line - ITT MARLOW Serie Manual De Instalación, Operación, Mantenimiento

required NPSH of the pump. (Refer to pump perfor-
mance curve for the value of the NPSH required by
the pump at the operation point.)
3. Suction piping should be the same size as the pump
inlet.
4. Any reducer should be of the eccentric type. If a re-
ducer is used in the horizontal run of suction piping,
it must be used with the fl at part of reducer on the
top to avoid air pockets.
5. A horizontal portion of the suction line must have
a gradual rise to the pump from the source of the
liquid being pumped. Any high point in the suction
line will create an air pocket, and will prevent proper
pump operation and inhibit priming capability.
6. An installation requiring long pipe lines handling hot
or chilled liquids, requires provisions for relieving
the expansion and contraction of the pipe to elimi-
nate any pipe stress from acting on the pump casing.
7. It is recommended to use long radius elbows and
eccentric reducers whenever possible. These types of
fi ttings reduce friction loss. Tapered reducers should
only be used in vertical suction piping.
8. If a suction strainer is used, it should have mesh size
equal to or less than the solid handling capability of
the pump, and open mesh area equivalent to a mini-
mum of eight times the area of the suction pipe size.
9. The size and length of the suction pipe, the number
and type of pipe fi ttings, and the height of the static
suction lift will determine the total dynamic suction
lift of each piping system. This system characteristic
should be calculated so that it does not exceed the
design capacity of the pump causing reduced fl ow
and/or cavitation.
10. Before tightening the suction pipe connection fl ange,
align it exactly with the pump suction fl ange. Do not
pull a pipe into place by tightening the fl ange bolts
and/or couplings. All pipe lines near the pump must
be rigidly supported to avoid strain on the pump,
which may cause excessive vibration, decreased
bearing life and/or increased shaft defl ection and seal
wear.
11. Leaks in the suction line can adversely affect both the
pump's priming, and performance; especially when
the pump is operating at high suction lift. To prevent
leaks, make sure all piping connections are tightly
sealed. The piping gasket sealant used should be
compatible with the liquid being pumped.
12. If a single suction line is installed into a sump, it
should be installed away from the sump wall at a
minimum distance equal to 1½ times the diameter
of the suction line. If more than one suction line is
installed in the same sump, separate the suction lines
from each other by a minimum distance equal to
three times the diameter of the largest suction line.
13. If there is a discharge from an open pipe into the
sump, the fl ow should be kept away from the pump's
suction pipe. This infl ow usually carries air down
into the sump with the liquid. Liquid with entrained
air will increase priming time and reduce pump
effi ciency. If the discharge into the sump is close to
the suction pipe, install a baffl e between the infl ow
4
and suction pipe at a distance of at least six times the
diameter of suction pipe away from the suction pipe.
The baffl e will allow the air to escape from liquid
before it is drawn into the suction pipe.
14. Recommended are the use of bell type increasers at
the bottom of the suction pipe to reduce inlet veloc-
ity. If this can't be done, cut the bottom of the suc-
tion pipe at a 45º angle to avoid swirling of liquid.
15. Refer to Hydraulic Institute Standards general
guideline for sump design.

VALVES

ITT does not recommend the use of valve on the suction
line EXCEPT:
a) In case where positive suction heads are present in
the system or
b) Where it is possible for a positive head to develop
due to fl ooding conditions.
c) Sometimes it is advisable to have valves on suction
and discharge so that the pump may be isolated
during repair.
In any case if suction valve is used, install with stems in
horizontal position to avoid air pockets.
1. If throttling valves are necessary in the discharge
line, use a valve size equivalent to the largest pipe
size in the line to minimize friction loss. Never install
a throttling valve in the suction line.
2. Gate and check valves may be used on the discharge
side, but it is not necessary in low discharge head
applications.
3. It is recommended to use a throttling valve and
check valve in the discharge line to protect the pump
from excessive shock or water hammer and reversed
rotation when pump is stopped.

DISCHARGE PIPING

1. To minimize piping friction losses:
a) Keep discharge line as straight as possible.
b) Use the minimum number possible of elbows and
other pipe fi ttings.
c) Use long radius elbows and/or eccentric reducers.
2. Do not terminate the discharge line at a level lower
than that of the liquid being pumped, unless a
siphon breaker is used in the discharge line.
Siphoning action may cause damage to the pump.
3. If there is a high discharge head, slow repriming
may be encountered requiring the use of an air
venting device. If a discharge check valve is used, an
air release line must be incorporated between the
discharge check valve and pump to insure priming.
4. If the system has a long discharge line it is
recommended to install a siphon breaker to avoid
siphoning out the liquid from pump casing.

AIR RELEASE LINE

It is essential to allow the air to escape from the discharge
line to atmosphere during the initial priming and reprim-