Service manual

14
D.7.6 System Filtration
In systems that recirculate pumped liquid, downstream (pressure and/or return side)
filtration should be installed. Downstream filters may also be required to protect
components such as servo valves in hydraulic systems or high-pressure fuel nozzles
and flow dividers in fuel oil supply systems for gas turbines. System’s most
contamination-sensitive component determines its liquid cleanliness requirement. For
optimum Imo pump life when running on fuel oil, light lube oil, hydraulic oil and other
relatively low viscosity (thin) liquids, a high efficiency 10 micron “absolute” or finer filter
is recommended. This same filter rating is recommended for pumps running at extreme
operating conditions and/or in harsh environments. For pumps running on relatively
clean, more viscous (thicker) liquids, filter ratings as high as 25 micron “nominal” may be
acceptable as long as operating conditions and the operating environment are
moderate. Imo should be contacted for filtration requirements for pumps running
on very low viscosity (water thin) and low lubricity as well as for those with an
unusually large quantity of contaminants.
System builder determines filter size (dirt holding capacity) by amount and size of
contamination expected to be produced by system and other external contamination
sources, by allowable pressure drop across filter and by acceptable frequency for
cleaning/replacing filter elements.
D.7.7 Outlet Piping
In general, outlet piping should be sized to accommodate pump’s flow rate while
minimizing pipe friction losses. It should also be designed to prevent gas and air
pockets. Piping downstream of pump should include a vent at highest point in system to
allow air to escape during priming.
D.8 SHAFT PACKING AND SEAL LEAKAGE
Pump should be installed so any leakage from shaft packing or shaft seal does not become a
hazard. Packing leakage should be about 8 to 10 drops per minute. A small amount of liquid
may also leak from mechanical or lip seals (usually less then or equal to 10 drops per hour).
Provisions should be made to collect leakage from packing or shaft seals.
WARNING
DANGER
If not appropriately collected, packing leakage may make floor slippery or expose
personnel to hazardous fluids.
D.9 QUENCHED SHAFT SEALS
Some pumps include quenched mechanical shaft seals. For these pumps, a low pressure
stream of steam, nitrogen, or clean water is supplied from an external source to atmospheric
side of seal faces.
Quenching is used in selected seal applications to:
• Heat or cool seal area.
• Prevent build up of coke formations by excluding oxygen.
• Flush away undesirable material build-up around dynamic seal components.
• When quenched mechanical seals are part of pump assembly, an appropriate quenching
stream must be supplied by user.