Vogt HEC-10, Руководство по обслуживанию

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HEC-Series Service Manual
MAINTENANCE
10/21/01
7-3
Proper operation of cooling towers will increase the interval between cleaning considerably. The
tower overflow rate should be checked frequently. If a tower is operated with insufficient overflow,
nominal 1-1/2 to 3 GPH bleed depending on water quality, the resulting mineral concentration in the
water can cause rapid and heavy flooding inside the condenser tubes, requiring excessively frequent
cleaning. Also, these conditions often lead to severe corrosion.
Chemical additives, including those to stop algae and related growths, should be obtained only from a
reputable, established supplier, and used specifically according to directions. Excessive treatment of
the water can cause more harm than good: and the condensers, pumps, piping, and the towers
themselves may be damaged.
It is advisable to double check the system to make sure that fouling is actually causing the trouble.
High head pressure alone does not mean a fouled condenser. The following possibilities should
always be checked before cleaning is undertaken:
1. Non-condensables in system or faulty head pressure gauge? Check standby pressures against
refrigerant tables.
2. Incorrectly set or defective water regulator valve? Check its setting and operation.
3. Partly closed compressor discharge service valve? Check its setting. Stem should be backseated.
4. High water temperatures entering condenser? Check tower fan and system.
After the above possibilities have been eliminated, determine the temperature difference between the
water leaving the condenser and the refrigerant condensing temperature (saturation temperature, from
pressure-temperature chart, corresponding to head pressure). If this difference is more than 10
°
F,
cleaning is indicated because this difference indicates a good heat exchange is not being made. If this
difference is less than 8
°
F, something other than a fouled condenser may be causing the high head
pressure. In normal operation, this difference will stay between 5
°
F and 10
°
F regardless of water
inlet temperature when the water flow is regulated by a pressure operated water valve. If this
difference is less than 5
°
F, restricted water flow or a low supply pressure is indicated. A restriction
can occur with foreign matter in the condenser, but it is also likely to be somewhere else in the
system.
Draining. Draining of water cooled condensers is recommended in preparation for the winter cold
where units may be left exposed to ambients below 32
°
F. Theoretically, it is easy to drain a
condenser. In practice, the problem can be complex.
Despite the fact that a condenser my have vent and drain fittings, the opening of these fittings is not
sufficient for a natural gravity flow. Water will be retained in a tube due to (1) surface tension and
(2) the normal curvature between tube supports. Our experience shows that as much as 20% of the
water in the condenser can be retained. To break the surface tension on the tubes and to drain all
tubes completely, it is necessary to remove the back plate and actually tilt the condenser a minimum
of 5 degrees. Whether water left in the tubes will cause damage during a freeze-up will be dependent
upon how quickly the freeze occurs and the location of the water inside the condenser.
In the field it is recommended that the tubes be blown out individually with air. Alternatively, a
minimum of 25% ethylene glycol in the system will also prevent a freeze which can rupture the tubes.