MACHINERY LUBRICATION- INDIA SEPTEMBER-OCTOBER 2019 | Page 23

MLI
Heat Exchanger Flushing
and Cleaning
In a shell-and-tube type of heat
exchanger, oil flows over the tubes.
Water flow is ported through the tubes
in the opposite direction. The heat in
the oil is transferred from the oil to the
water. To achieve the most efficient heat
transfer, the water flow should be 25
percent of the oil flow. The water flow
can be controlled by manual valves, a
water-modulating valve or an electrical
solenoid valve. Circulating hot wash oil
or light distillate through the tube or
shell side can effectively remove sludge
or similar soft deposits. Soft salt
deposits may be washed out by
circulating hot, fresh water. A mild
alkaline solution such as Oakite or a
1.5-percent solution of sodium
hydroxide or nitric acid can be used.
The tubes should be flushed in the
opposite direction that the oil normally
flows.
If an air cooler is employed, verify that
the cooler fan is turned on at
approximately 120 degrees F and turned
off at about 105 degrees F. Keep the fins
clean so daylight can be seen through
them. If necessary, combs should be
utilized to straighten the fins on the
unit. When cleaning the fins with an air
hose, care should be taken so as not to
damage them.
drain line, then the pump should be
changed. An excellent method of
monitoring the case drain flow while
operating is to permanently install a
flow meter in the case drain line.
Fixed-displacement pumps can be
tested by checking the flow through the
relief valve. Turn on the pump and
record the flow out of the relief valve
tank line for one minute. Next, reduce
the setting of the relief valve to its
minimum setting. There should be less
than a 10-percent difference in flow
rates between the two tests. If a pump
is badly worn, the flow will be
considerably less at the highest pressure.
Accumulator Testing
An accumulator that is used for volume
should be pre-charged with dry nitrogen
to one-half to two-thirds the pump’s
compensator setting. When the
hydraulic system is turned off, a
charging rig with a gauge can be utilized
to check the pre-charge level.
To confirm an accumulator is operating
properly, check the side of the shell with
a temperature gun or infrared camera.
The bottom half should be hotter than
the top half. If heat is only indicated at
the bottom, the accumulator may be
overcharged. If there is no heat, the
bladder may have ruptured, the piston
seals may be bad, the pre-charge may
be above the compensator setting or all
the nitrogen may have leaked out. If
heat is felt all the way to the top, the
accumulator is undercharged.
Another check that can be made is to
watch the system pressure gauge while
the system is operating. The pressure
should not normally drop more than
100-500 pounds per square inch (PSI)
when the accumulator is properly
pre-charged.
If piston accumulators are used, the
charging rig should be installed when
the system is down and the oil bled off
the top of the piston. With the pump on
and the bleed valve open, there should
be little or no flow out of the bleed
Pump Testing
On variable-volume pumps, check the
flow out of the case drain line by porting
the line into a container and timing it.
This test should be made with the outlet
pressure at the maximum level. It is not
recommended that the line be held
during this test. Secure the line to the
container prior to starting the pump.
The normal case flow is 1-5 percent of
the maximum pump volume. Vane
pumps usually bypass more than
piston-type pumps. If 10 percent of the
maximum volume flows out of the case
Test a fixed-displacement pump by turning on the pump and recording the flow out of the relief
valve tank line for one minute.
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