Product Overview

IMMERSION WELLS AND COMPRESSION FITTINGS
7 68-0040—05
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 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 temperature controllers ship with heat-conductive
compound; available in 4-oz cans and 1/2-oz single-
application tubes. See Table 4.
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