Just Better Copper Capillary Tubing - Manual

EXTRA
LONG
LENGTHS
CRITICAL
POINT "L"
OPTIMUM
LENGTH RANGE
5 to 16 FT.
SHORT LENGTH
ACTS LIKE ORIFICE
OPTIMUM FLOW
RANGE
FLOW
LENGTH
CRITICAL POINT "S"
Typical flow curve showing
changes in flow of
refrigerant through a
capillary tube with a
change in the length of the
cap tub.
The size of the cap tube is fairly critical.
Unlike orifices, such as expansion valve seats,
capillary tubes depend on their length as well as
their diameter to determine their total restriction.
The relationship between these two factors are
shown in the following charts. A change in
diameter on a percentage basis can change the
flow more than an equal change in length. To
illustrate, changing the diameter by .005" as
between .026" I.D. and .031" I.D. can double
the flow.
Restriction can also be changed by length-
ening or shortening the cap tub. The longer the
tube, the slower the flow; the shorter the tube, the
faster the flow. The general flow curve graph
(right) shows what happens to the flow of
refrigerant through a cap tube as the length is
changed. This curve is not meant to give specific
flows but to simply illustrate what happens with
all cap tubes so that the general flow pattern can
be understood.
By following the flow curve from left to right it
can be seen that for the very longest length the
flow is the smallest. Then as the cap tube length
is decreased, the flow increases slowly until
critical point "L" is reached.
At this point the flow increases more rapidly
with each reduction in length until critical point "S"
is reached. From this point on, further decrease in
DIAMETER AND LENGTH
FACTORS AFFECTING REFRIGERANT FLOW
APPLICATION AND ENGINEERING DATA
Copper Capillary Tubing
For Refrigeration and Air-Conditioning
SHORT COIL 100 FT. COILS 10 COILS DESCRIPTION
TC-26-16 TC-26-100 TC-26-100-101 .026 ID x .072 OD x 16'
TC-31-12 TC-31-100 TC-31-100-101 .031 ID x .083 OD x 12'
TC-36-12 TC-36-100 TC-36-100-101 .036 ID x .087 OD x 12'
TC-42-12 TC-42-100 TC-42-100-101 .042 ID x .093 OD x 12'
TC-44-12 TC-44-100 TC-44-100-101 .044 ID x .109 OD x 12'
TC-49-11 TC-49-100 TC-49-100-101 .049 ID x .099 OD x 11'
TC-50-11 TC-50-100 TC-50-100-101 .050 ID x .114 OD x 11'
TC-54-11 TC-54-100 TC-54-100-101 .054 ID x .106 OD x 11'
TC-55-11 TC-55-100 TC-55-100-101 .055 ID x .125 OD x 11'
TC-59-10 TC-59-100 TC-59-100-101 .059 ID x .112 OD x 10'
TC-64-10 TC-64-100 TC-64-100-101 .064 ID x .125 OD x 10'
TC-70-12 TC-70-100 TC-70-100-101 .070 ID x .125 OD x 12'
TC-75-9 TC-75-100 TC-75-100-101 .075 ID x .125 OD x 9'
TC-80-10 TC-80-100 TC-80-100-101 .080 ID x .145 OD x 10'
TC-85-9 TC-85-100 TC-85-100-101 .085 ID x .145 OD x 9'
TC-90-7 TC-90-100 TC-90-100-101 .090 ID x .145 OD x 7'
TC-100-10 TC-100-100 TC-100-100-101 .100 ID x .156 OD x 10'
length causes ever increasing flow. From the
study of this typical curve, certain pertinent
conclusions can be reached that directly affect
the field application of capillary tubes.
On the graph, the section above the critical
point "L" is marked as extra long lengths.
Attempting to increase restriction (i.e. reduce
flow) by increasing length into this region is not
only uneconomical but frequently hopeless. In
addition, tubes in this range may not be respon-
sive enough to changes in head pressures during
operation. All in all, tube lengths in this range
should be avoided where possible.
Continuing down the graph, the section
below critical point "S" should be avoided like the
plague. In this range, the tube is so short that
even small changes in length will cause very
large increases in flow. This is caused by the fact
that the length no longer affects the flow and the
tube now beings to act more like an orifice than a
capillary tube. But, without the other components
necessary to control an orifice, such as are
present in an expansion valve or high side float, a
very short cap tube will give wildly erratic opera-
tion under varying ambients and loads.
All of this would be meaningless without
some definite way to use this information. Al-
though the critical points will vary depending on
the I.D. of the cap tubing being used, a very safe
operating rule-of-thumb can be offered. Keep the
cap tube no shorter than 5 ft. and no longer
than 16 ft.
© COPYRIGHT 2007 J/B INDUSTRIES INC.