York YD A, Эксплуатация и техническое обслуживание, Страница: 46 / 52

JOHNSON CONTROLS
46
FORM 160.69-O2
ISSUE DATE: 9/30/2020
SECTION 6 – MAINTENANCE
ACID CLEANING OF TUBES
If the tubes are fouled with a hard scale deposit, they
may require acid cleaning. It is important that before
acid cleaning, the tubes be cleaned by the brushing pro-
cess described above. If the relatively loose foreign ma-
terial is removed before the acid cleaning, the acid solu-
tion will have less material to dissolve and flush from
the tubes with the result that a more satisfactory cleaning
job will be accomplished with a probable saving of time.
Acid cleaning should only be performed
by an expert. Please consult your local
water treatment representative for as-
sistance in removing scale buildup and
preventative maintenance programs to
eliminate future problems.
COMMERCIAL ACID CLEANING
In many major cities, commercial organizations now
offer a specialized service of acid cleaning evaporators
and condensers. If acid cleaning is required, YORK
recommends the use of this type of organization. The
Dow Industries Service Division of the Dow Chemical
Company, Tulsa, Oklahoma, with branches in principal
cities is one of the most reliable of these companies.
TESTING FOR EVAPORATOR AND
CONDENSER TUBE LEAKS
Evaporator and condenser tube leaks in R-134a sys-
tems may result in refrigerant leaking into the water
circuit, or water leaking into the shell depending on the
pressure levels. If refrigerant is leaking into the water,
it can be detected at the liquid head vents after a period
of shutdown. If water is leaking into the refrigerant,
system capacity and efficiency will drop off sharply. If
a tube is leaking and water has entered the system, the
evaporator and condenser should be valved off from
the rest of the water circuit and drained immediately to
prevent severe rusting and corrosion. The refrigerant
system should then be drained and purged with dry ni-
trogen to prevent severe rusting and corrosion. If a tube
leak is indicated, the exact location of the leak may be
determined as follows:
1. Remove the heads and listen at each section of
tubes for a hissing sound that would indicate gas
leakage. This will assist in locating the section of
tubes to be further investigated. If the probable
location of the leaky tubes has been determined,
treat that section in the following manner (if the
location is not definite, all the tubes will require
investigations).
2. Wash off both tube heads and the ends of all tubes
with water.
Do not use carbon tetrachloride for this
purpose since its fumes give the same
flame discoloration that the refrigerant
does.
3. With nitrogen or dry air, blow out the tubes to
clear them of traces of refrigerant laden moisture
from the circulation water. As soon as the tubes
are clear, a cork should be driven into each end
of the tube. Pressurize the dry system with 50 to
100 PSIG (345 to 690 kPa) of nitrogen. Repeat
this with all of the other tubes in the suspected
section or, if necessary, with all the tubes in the
evaporator or condenser. Allow the evaporator or
condenser to remain corked up to 12 to 24 hours
before proceeding. Depending upon the amount
of leakage, the corks may blow from the end of a
tube, indicating the location of the leakage. If not,
if will be necessary to make a very thorough test
with the leak detector.
4. After the tubes have been corked for 12 to 24
hours, it is recommended that two men working
at both ends of the evaporator carefully test each
tube – one man removing corks at one end and
the other at the opposite end to remove corks and
handle the leak detector. Start with the top row of
tubes in the section being investigated. Remove
the corks at the ends of one tube simultaneously
and insert the exploring tube for 5 seconds – this
should be long enough to draw into the detector
any refrigerant gas that might have leaked through
the tube walls. A fan placed at the end of the evap-
orator opposite the detector will assure that any
leakage will travel through the tube to the detec-
tor.
5. Mark any leaking tubes for later identification.
6. If any of the tube sheet joints are leaking, the leak
should be indicated by the detector. If a tube sheet
leak is suspected, its exact location may be found
by using a soap solution. A continuous buildup of
bubbles around a tube indicates a tube sheet leak.