Marsh Bellofram Thermo-Couple Products Division Thermowells Overview Sheet - Marsh Bellofram - #1

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www.tcproducts.com a division of Marsh Bellofram www.marshbellofram.com Thermo-Couple Products Co. 1-800-727-5646 Material - The Longevity Factor In general, the thermowell material chosen for the installation is governed mainly by the corrosion conditions to which the well is exposed. Recommended materials for various services are given in the corrosion table on pages 67 to 69. The high mirror polish given to all stainless and monel wells provides maximum corrosion resistance. Sometimes the major consideration is strength rather than corrosionresistance. For example, a high pressure water service may require a stainless steel well, while from a corrosion standpoint, a brass well would be satisfactory. Connection - The Installation Factor In these pages you will find standardized wells of threaded, flanged (A.N.S.I. and Van Stone), and socket welded types with standard bore sizes. Threaded wells are all made in readily welded or brazed materials for installations requiring seal welding or brazing. The pipe thread provides the mechanical strength, the weld merely seals. Flanged wells other than Van Stone type) consist of a bar-stock well which is permanently welded to a top quality flange. Standard construction uses a primary “J” groove weld and a bevel groove secondary weld. Both welds are machined to produce a clean fillet. this double welded construction eliminates possibility of crevice corrosion since no open joints exposed from either inside or outside the installation. Socket welding types of wells are simple to install - merely welded into place.These wells fit A.N.S.I. standard socket weld coupling of flanges. The resulting installation is clean and tight. Insertion Length - The Accuracy Factor The distance from the end of the well to the underside of the thread, or other connection means, (designated as “U”) is the insertion length. For best accuracy, this length should be long enough to permit the entire temperature sensitive part of the well to project into the temperature medium being measured. A properly installed thermowell will project into the liquid and amount equal to its sensitive length plus at least one inch. In air or gas, the bulb should be immersed into the sensitive length plus at least three inches. Thermocouples and thermistors have short sensitive lengths and therefore can use the smallest insertion lengths. Bi-metal thermometers, resistance thermometers, and liquid-in-glass thermometers have bulbs with sensitive portions between one and two inches long. Therefore, the minimum standard insertion length of 2-1/2" must be entirely immersed in liquid for proper accuracy. Filled system thermometer bulbs may have sensitive portions from one to several inches in length. Determine the sensitive length of bulb before choosing an insertion length. Above all - be sure that dead length i.e. - that required to pass thru wall, pipe fittings, etc. is taken into account when choosing the necessary well insertion length. Bore Size - The Interchangeability Factory Several types of temperature measuring instruments are used in most installations. The selection of a standard bore diameter provides extreme flexibility; the same well can accommodate thermocouple resistance thermometer, bi-metal thermometer, or test thermometer. The bore size of wells shown in this catalog cover the most commonly used temperature sensing elements as follows: .260 Diameter Bore: Bi-metal Thermometers (1/4" stem) Thermocouples - (#20 Gauge) Liquid-in-glass Test thermometers (Unarmored) Other elements having .252" maximum diameter. .385 Diameter Bore: Bi-metal Thermometers (3.8" Stem) Thermocouples - (#14 Gauge) Liquid-in-glass Test thermometers (Armored) Other elements having .377" maximum diameter. Tapered or Straight Shank - The Velocity Rating Factor Tapered shank wells provide greater rigidity for the same sensitivity. The higher strength to weight ratio gave these wells higher natural frequency than for equivalent length straight shank wells, thus permitting operation at higher fluid velocity. Typical Thermowell with Flange Extension Nipple Terminal Head