Vilter VSM 71-701 Operation And Service Manual Download

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Page 2

/ BULLETIN 10-11

Liquid subcooling is provided by the following
methods:

1. In the condenser

2. Suction – liquid heat exchanger

3. Special devices

Method 1

– will provide sufficient subcooling for the simple short-

coupled system that has only moderate liquid line pressure drop.

Method 2

– will usually not provide more than 20°F subcooling on

air conditioning systems operating at normal head pressures. The
amount of subcooling will depend on the design and size of the heat
exchanger and on the operating suction and discharge pressures.

Method 3

– may be used to provide considerable subcooling

required for systems with excessive vertical lift. The following
special devices are the most commonly used methods:

■

Water coils in heat exchange relationship with the liquid line.

■

Separate refrigeration system.

■

Special heat exchanger which uses a portion of the refrigerant to
cool the main body of liquid. See Figure 1.

Ordinarily the conventional suction-liquid heat exchanger is installed
near the evaporator, where the suction vapor is the coldest, to re-
condense any vapor in the liquid line. When the primary purpose of
the heat exchanger is to prevent the formation of flash gas – particu-
larly on systems that have a long liquid line or excessive vertical lift
– install the heat exchanger near the receiver

before the vertical

lift occurs

. (This also applies to the special devices described in

Method 3). Because vapor in the liquid line considerably increases
friction losses, the total pressure drop available across the expansion
device on these types of systems is reduced. Also, the suction line and
liquid line should be carefully insulated to minimize heat gain if
subcooled below ambient temperature.

Important

Preventing the formation of vapor in liquid lines having high pressure
losses does not eliminate the requirement that an adequate pressure
drop must be available across the TEV. The capacity tables show
valve capacities at pressure drops lower than normal. For TEV
application data and capacities at pressure drops below those listed,

consult Sporlan Valve Company

Solder Techniques

It is not necessary to disassemble solder type valves when soldering
to the connecting lines. Any of the commonly used types of solders,
e.g., 95-5, Sil-Fos, Easy-Flo, Phos-Copper, Stay Brite 8 or equiva-
lents may be used for copper to copper connections. When soldering
a brass refrigerant distributor to the valve, appropriate solders for
these connections, such as 95-5, Easy-Flo, Stay Brite 8 or equivalents
must be used. It is important however, regardless of the solder used,
to direct the flame away from the valve body and avoid excessive
heat on the diaphragm, Figure 2. As an extra precaution, a wet cloth
may be wrapped around the body and element during the soldering
operation.

This precaution will prevent overheating the valve body which could
damage the superheat spring and result in flood back problems. In
addition, the Type O, EBF/SBF, and EBS valve contain synthetic
parts which can be damaged due to overheating, resulting in poor
valve performance.

Bulb Location and Installation

The location and installation of the bulb is extremely important to the
proper performance of the system and care should be taken with its
final location.

Accepted principles of good suction line piping should be followed
to provide a bulb location that will give the best possible valve
control. When system manufacturers have piping recommendations
that differ from the general industry recommendations and Sporlan’s
suggestions shown in this section, those recommendations should be
used. When specific recommendations are not available, the sugges-
tions below should be used.

The bulb should be attached to a horizontal suction line at the
evaporator outlet (See Figures 3, 4, and 5) If the bulb cannot be
located in that manner, it may be located on a

descending

vertical

line only (as shown in Figure 5 for “pumpdown control”). The bulb
should never be located in a trap or downstream of a trap in the
suction line. Liquid refrigerant or mixture of liquid refrigerant and oil
boiling out of the trap will falsely influence the temperature of the
bulb and result in poor valve control.

On suction lines 7/8” OD and larger, the surface temperature may
vary slightly around the circumference of the line. On these lines, it
is generally recommended that the bulb be installed at 4 or 8 o’clock
on the side of the horizontal line, and parallel with respect to the
direction of flow. On smaller lines the bulb may be mounted at any
point around the circumference, however locating the bulb on the
bottom of the line is not recommended as an oil-refrigerant mixture
is generally present at that point. Certain conditions peculiar to a
particular system may require a different bulb location than normally

Figure 2

To Compressor

Main Liquid Line

Insulation

Main Suction Line

Receiver

Figure 1