QUANTECH
142
FORM QWC4-NM1 (221)
ISSUE DATE: 02/28/2021
SECTION 7 - MAINTENANCE
Be sure the vacuum indicator is valved off
while holding the system vacuum. Open
the valve between the vacuum indicator
and the system when checking the vacuum
after eight hours.
6. If the vacuum does not hold for eight hours within
the limits specified in Step 5, find and repair the
leak.
CONDENSERS AND EVAPORATORS
MAINTENANCE
General
Maintenance of the condenser and evaporator shells is
important to provide trouble free operation of the unit.
The waterside of the shell tubes must be kept clean
and free from scale. Proper maintenance, such as tube
cleaning, is covered on the following pages.
Chemical Water Treatment
Since the mineral content of the water circulated
through evaporators and condensers varies with almost
every supply source, the water being used may corrode
the tubes or deposit heat resistant scale in them.
Reliable water treatment companies are available in
most large cities who can supply a water treating pro-
cess, which will greatly reduce the corrosive and scale
forming properties of almost any type of water.
As a preventive measure against scale and corrosion
and to prolong the life of the evaporator and condenser
tubes, a chemical analysis of the water should be made,
before the system is installed. Consult a reliable water
treatment company to determine if water treatment is
necessary, and if so, to furnish the proper treatment for
the particular water condition.
CLEANING EVAPORATOR AND CONDENSER
TUBES
The condenser and evaporator tubes in a QWC4 chiller
are made of copper with mild carbon steel waterboxes.
If the equipment is located in an unheated
area susceptible to freezing, drain the wa-
ter from the condenser and evaporator to
prevent the tubes from freezing.
Condenser Tubes
Proper condenser water treatment can eliminate or sig-
nificantly reduce the formation of scale on the water-
side of the condenser tubes.
Maintain a minimum condenser water flow rate through
the tubes of at least 3.33 ft/s (1 m/s).Tube water veloc-
ity should not exceed 12 ft/s (3.6 m/s).
Condenser tubes must be maintained to provide proper
chiller operation. The condenser approach temperature,
which is the difference between the condenser leaving
water and the saturated condenser temperatures, is a
useful tool to monitor the performance of the condens-
er. Recording and logging the condenser approach tem-
perature, as part of the chiller maintenance program,
warns the operator that the waterside condenser tubes
are fouled and require cleaning.
If the approach increases more than 4°F (2°C) above
the approach when the tubes were clean, or during the
annual condenser inspection the tubes are observed to
be fouled, the tubes require cleaning.
In a condenser, a problem due to fouled tubes is usually
indicated by:
• A steady rise in head pressure over a period of
time
• A steady rise in condensing temperature
• Noisy operation
Tube Fouling
Fouling of the tubes can be due to two types of
deposits:
1.
Rust or sludge –
which finds its way into the
tubes and accumulates there. This material usu-
ally does not build up on the inner tube surfaces
like scale, but does interfere with the heat transfer.
Remove the rust or sludge from the tubes using a
thorough brushing process.
2.
Scale –
due to mineral deposits. These deposits,
although thin and scarcely detectable upon physi-
cal inspection, are highly resistant to heat transfer.
Remove the scale by circulating an acid solution
through the tubes.
Summary of Contents for QWC4
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