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which conditions may vary widely. If such variations can put
an excessive vacuum on the blower, overloading can often be
avoided by installation of a pilot operated vacuum relief valve
near the blower inlet. For further protection, a dependable
pressure sensitive device can be installed to provide alarm
and/or shutdown action.
At the first opportunity, stop the blower and clean the tempo-
rary protective pump inlet screen. Depending on the amount
and type of debris found, judgement can be made as to how
long the screen should remain in place. unfavorable condi-
tions may lead to repeated and frequent clogging or loading.
Installation of manometer in such cases will reveal the need
for cleaning by indicating an increase in pressure drop
through the screen. during this shut-down period verify level-
ing, anchor bolt tightness, alignment of shaft coupling, or
tension of drive belts.
After VJ2 is in operation it may be found that only a small
vacuum can be produced. this operating condition should be
avoided, since the second stage blower will be running idle
and doing no work, and the by-pass check valve may be flut-
tering against its seat. one solution could be to remove the
second blower from the system and thus eliminate excessive
maintenance problems. The preferable choice should be to
increase pumping capacity in order to bring the vacuum to
the desired level and make normal use of both blower stages.
When a vacuum blower is taken out of service it may require
internal protection against rusting or corrosion. The need for
protection must be a matter of judgement based on existing
conditions, protection probably will not be needed if shut-
down is not longer than one day. Under conditions likely to
produce rapid corrosion the blower should be protected
immediately. Following is a suggested procedure.
Remove the vacuum load from the blower and vent the inlet
to atmosphere, if possible. With the sealing water shut off at
valve (C), run the blower until the interior surfaces are judged
to be dry. Remove inlet and discharge piping at the blower
connections and inspect the interior. If any moisture is pres-
ent, run the blower again until drying is completed. Coarse
screens should be placed over both connections to avoid
damage or personal injury.
Now coat all finished surfaces of cylinder, headplates, and
impellers with a protective compound. Amount suitable com-
mercial products is Motorstor, marketed by Daubert Chemical
Company. This material is best applied by spraying at, but
may also be brushed on. Special care should be taken to
insure good coverage between the end of the impellers and
the headplates. before doing this work make sure the blower
cannot be started accidentally. After completing the applica-
tion, seal all blower opening with vapor barrier paper and
tape.
This type of protection is normally effective for about one
year if seals are not broken. When blower is to be returned to
service, remove tall seals and inspect the internal surfaces. If
dirt of any kind is found clean with all surfaces with a good
petroleum solvent. If cleaning is not required for dirt removal
the blower may be reconnected and a check run made to veri-
fy normal operation. Before operating under power, turn the
drive shaft several revolutions manually to verify that
impellers turn freely at all points, with no scrapping or or
bumping. Also make sure that tape is removed from the
drain/vent holes near the bottom of each headplate.
Scale build-up
A basic principle of the ROOTS VJ unit is that there is no
internal contact of moving parts. To satisfy this concept and
still maintain maximum pumping efficiency, there must be
small but definite clearances between the impellers and
between impellers and case. Any scale build-up due to miner-
al deposits from the water or process residue, which tend to
close these clearances is intolerable. Loss of clearance will
case the impellers to rub the case and each other, which may
cause the unit to stick while in operation or to freeze when
shut down.
There are two methods of preventing scale build-up. one
method is to use de-mineralized water for sealing and to filter
any process residue ahead of the unit. The other method is to
de-scale the unit at regular intervals, such as weekend shut-
downs. The latter method is the simpler and more economi-
cal, unless shut-down periods are infrequent.
it is recommended that a sample of the build-up material be
sent to the scale removal supplier for analysis so the proper
agent can be selected for the removal. Scale deposits in dif-
ferent processes and localities may require variations in con-
centration or type of removal agent.
Following are two recommendations received from scale
removal suppliers who examined samples of build-up
deposits from a particular installation. They are listed in order
of preference based on effectiveness, estimated cost of solu-
tion, cost of equipment, ease of applying, and possibility of
damage to the blowers from the solution
1. Magnus 61-C alkaline stripping compound - Magnus
Chemical Co., Inc., Garwood, N.J.
Fifteen pounds of Magnus 61-C dissolved in 40 gallons
of water can be fed into the blower before shut-down
and allowed to soak as long as possible before flushing.
For weekend shut-downs, the start up of the blower after
shut-down can be considered as the flush.
The solution may be made up in a 55-gallon steel drum
and fed into the blower by attaching a hose from the
drum to a threaded connection at the inlet to the blower.
A valve should be placed in the line near the blower for
shutoff during normal operation. On two-stage blowers,
feed the solution into the inlet of the first stage. The seal-
ing water flow should be shut off immediately after start-
ing to feed the Magnus 61-C solution. Shut down the
blower as soon as the solution has been fed into the
blower.
2.
Calgon Micromet phosphate product – Calgon, Inc. 323
Fourth Ave., Pittsburgh 30, Pennsylvania. A Micromet
feeder should be installed in the sealing water line ahead
of the blower. The feeder should be sized for an initial
charge of 4 to 8 pounds of Micromet per gpm of water
flow. The Micromet dissolves at a slow rate, and the
feeder should be recharged regularly.
Micromet discourages scale build-up, but is not effective
as a de-scaler. The scale should be removed by other
methods before the Micromet treatment is used.
The above recommendations apply generally where the
