UNIBLOC-PD Operation & Service Manual: PD600-677 9
3.2 System Design
When a pump is to be incorporated in a system, it is considered good practice to minimize the length of the pipes
and the number of fittings and any other restrictions to product flow. Always consider the following when designing a
system:
• Confirm the Net Positive Suction Head-NPSH available from the system exceeds the NPSH required from the
pump to ensure smooth operation and avoid cavitation.
• Avoid suction lifts and manifold/common suction lines for two pumps running in parallel, as this may cause
vibration or cavitation.
• Protect the pump from unintended blockage from nuts, bolts, welding slag, etc, by installing a strainer. Also
protect the pump from unintended operation against a closed valve by installing a safety/pressure relief valve.
Strainers and relief valves can be provided by Unibloc-Pump.
• Install monitoring equipment on suction and pressure side of pump for diagnostic purposes.
• Install shut-off valves on suction and pressure side to isolate pump when service is necessary.
• Make sure the pipes are well supported. Do not use the pump to support the piping. See figure 2.1
• Make the necessary piping arrangement if pump is supplied with a flushed seal or if the housing is jacketed
for heating/cooling.
• Do not expose pump to rapid temperature changes, this may seize the pump as a result from thermal shock.
• Allow at least 1m (3.3ft) free space around the pump for easy maintenance access.
Figure 3.3 shows a typical recommended design and required components for safe operation of the pump. All compo
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nents are available from Unibloc-Pump. Contact your supplier.
3.3 Flushed Seal Arrangement
The flushed seal arrangement cools and lubricates the shaft seal area. All flushed seals must be installed in a proper
system; otherwise the seal will NOT OPERERATE CORRECTLY. The flushing system also works as a barrier be
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tween the environment and the pumped media.
3.3.1 Single and Double Mechanical Seal Flushing/Cooling
DOUBLE MECHANICAL SHAFT SEALS MUST BE FITTED WITH FLUSHING SYSTEMS THAT WILL COOL AND
LUBRICATE THEM, OTHERWISE THE SEALS WILL BE DAMAGED.
The flushing system also provides a barrier of
protection between the environment and the pumped media. The fluid in this system must be flowing before or at the
same time the pump is engaged.
Flushing systems are normally not included with the pump. The piping arrangements and system components shown
in fig. 3.4, 3.5 and 3.6 are recommended for satisfactory operation of the seals and to insure containment of the
pumped liquid. Unless otherwise indicated, penetrations to the housing for flushing are 1/8” NPTF. The minimum flow
rate for the flushing system is 1 lpm (0.3 gpm) or a rate that will keep the temperature of the seals within
5°C (9°F)
of
the pumped media. The pressure of the flushing system is dependent upon the requirements of the pumping applica
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tion. As a guide, when the flushing system pressure is higher than that of the pumped media, the flushed liquid will en
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ter into the media if the seal fails. Likewise, if the pumped media has a higher pressure than the flushing system, the
media will enter into the flushing system if the seal fails. This is usually beneficial in cases when the pumped media is
extremely hazardous, as it may be safely contained and disposed of properly.
PRESSURE RELIEF VALVE
SHUT OFF VALVE
STRAINER
PRESSURE GAUGE
FLOW
FLOW
SHUT OFF VALVE
fig. 3.3