leaks, improper operation of air ejectors, insufficient
flow of seawater, or ineffective use of heat transfer
surface in the distilling condenser.
Many distilling plant troubles are direct results of
air leaks. Air leaks in the shells of distilling plants cause
a loss of vacuum and capacity. You must take extreme
care when making up joints, for they must be kept tight.
Periodically test the joints under pressure for leaks.
When the plant is in operation, use a candle flame to test
all joints and parts under vacuum. When the plant is
secured, you can use air pressure or soapsuds for testing.
Air leakage may also be detected by hydrostatically
testing the various parts of the plant. You should take
the necessary precautions not to exceed the maximum
limit of the test pressure specified by the manufacturer.
Defective tube(s) on the heat exchangers can be
located by means of an air or a hydrostatic test. You
should follow the recommended procedure according to
the manufacturers instructions.
The steam pressure at the nozzle inlet of the air
ejector must not be less than that for which the ejector
is designed (stamped on the nameplate). Pressures at the
air ejector nozzles may be 10 to 15 psig higher than the
minimum specified by the manufacturer.
The primary causes of air ejector problems are low
steam pressure, wet steam, an obstructed nozzle, or a
clogged steam strainer. Problems are usually indicated
by a failure to obtain or to maintain the required vacuum.
If a problem is due to low steam pressure or wet steam,
you should increase the steam pressure, install a
drainage trap, or devise a manual solution. A clogged
nozzle or strainer must be removed and cleaned. You
should use special reamers to clean the air ejector
nozzles. You should NEVER use a sharpedged tool to
clean nozzles! Improper tools will damage the nozzle
surfaces and impair the efficiency of the air ejecter.
Procedures for testing air ejectors can be found in
the manufacturers technical manual. In general, the
same maintenance procedures should be followed for
distilling plant air ejectors as for air ejectors for the main
You should inspect the air ejector strainer according
to the PMS. Failure to keep the strainer clean will cause
a reduced or fluctuating vacuum. When a strainer or a
nozzle becomes damaged, you should replace it.
Insufficient Circulating Water
An insufficient flow of circulating water is indicated
when the temperature of the water rises more than 20°F
while passing through the condensing section of the
distiller condenser. The last-effect shell pressure is
directly dependent upon the distiller condenser vacuum.
The vacuum is dependent upon the temperature and
quantity of the circulating water and the proper
operation of the air ejectors. Too low an overboard
discharge temperature of the distiller condenser
circulating water is accompanied by efficiency losses in
the distilling plant. The overboard discharge
temperature should be kept as high as possible, without
exceeding the desired 20°F temperature rise through the
distiller condenser. In addition, limiting the quantity of
circulating water tends to prolong the service life of the
tubes and tube sheets. When troubles occur which are
not caused by improper operating procedures, you
should inspect the condenser circulating water system
to determine the true cause of the faulty operation.
You must carry out preventive maintenance
procedures to ensure that the circulating water pump is
maintained in good material condition. You should also
carry out routine procedures to ensure the proper setting
and maintenance of the back-pressure regulating valve.
A regulating valve that is not working properly must be
disassembled and repaired before its faulty operation
interferes with the operation of the distilling plant.
You should inspect the condenser circulating water
system pipings at regular intervals for cleanliness as
well as for scale or foreign matter. The operators of the
distilling plant should
according to the PMS.
inspect and clean the strainers
If the distilling plant fails to produce the designed
output when the pressure above the orifice is 5 psig and
the first-effect tube nest is several inches of mercury,
this is an indication of improper drainage of the distiller
condenser or of one of the evaporator tube nests
subsequent to the first effect. Complete flooding of the
flash chamber gauge glass is also a positive indication
of improper draining of the condenser. Because the level
appears to be in the gauge glass or below is not
necessarily an indication of improper drainage. Air leaks