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IMMERSION WELLS AND COMPRESSION FITTINGS
7 68-0040—04
GENERAL INFORMATION
Immersion Wells
An immersion well consists of a metal tube, called the well
shell, closed on one end. A well spud externally threaded to fit
standard boiler tappings is welded or brazed on the open end.
See Fig. 1. The well is inserted into the tank and the
temperature sensing bulb is inserted into the well. The sensing
bulb never touches the controlled medium. Because the well
conducts heat rapidly, the bulb responds quickly and
accurately to temperature changes in the controlled medium.
An immersion well protects the temperature sensing bulb from
mechanical damage or damage due to chemical interaction
with the controlled medium. Also, a well permits removal of the
sensing bulb for testing or control replacement without draining
the system. The threaded fitting of the well spud provides a
tighter seal than a packing nut applied to the capillary.
Material Selection
The immersion well material must conduct heat readily and
resist corrosive and electrolytic action (especially in brine
solutions and when the well is a different material than the
container). The material must also resist fluid contamination
from chemical reaction with the well and withstand high
temperatures. Most Honeywell immersion wells are copper
because of its high conductivity. Stainless steel, mild steel and
Monel wells are also available for applications requiring higher
maximum temperature and pressure ratings or greater
corrosion resistance. Some copper wells are available with a
plastic sleeve over the tube to reduce electrolytic and corrosive
activity.
Well Sizing
Major factors in selecting well size are:
—
size of the boiler tapping.
—bulb diameter.
—insulation depth.
—insertion length.
Immersion wells are available to fit standard 1/2-14 NPT and 3/
4-14 NPT tappings. Sensing bulbs are 3/8, 1/2 or 11/16 in. in
diameter with well shells designed to fit these diameters. The
bulb should fit tightly in the shell. If the bulb fits loosely, fill the
space between the shell and bulb with heat-conductive
compound to ensure maximum heat transfer. Many Honeywell
temperature controllers ship with heat-conductive compound;
available in 4-oz cans and 1/2-oz single-application tubes. See
Table 4.
he nominal length of the spud, including the full length of the
threads and the hex, defines the insulation depth. Depending
on the characteristics of the tapping, 1/8 to 1/2 in. of the
Table 6. Accessories for Duct-Mount Applications
Description Application Size Part Number
Bulb shield assembly Shields bulb from weather;
less mounting screws and
split plug.
6 in. (152 mm) long; holds 3/8
in. and 1/2 bulbs.
Shields bulb from weather;
includes mounting screws
and 33578 Split Plug.
7 in. (118 mm) long, clip holds
3/8 in. bulb.
Pipe Strap Fastens bulb to outside of
pipe.
4-1/2 in. (114 mm) long; used
with up to 3/4 in. OD pipe.
M17284
107323A
M17285
34886A
M17286
105900