Technical Brief – Thermowell Considerations

A thermowell has a very important function, which is to protect your thermometers from damage. Although the device is fairly simple, choosing the right thermowell for your application requires careful consideration.

1.MATERIAL – The Longevity Factor

Corrosion resistance and strength are the primary considerations.

The standard materials listed for each well series will cover most requirements. A stock of special materials is carried at all times to ensure fast delivery on wells to be made of special grades of:

• Stainless steel

• Chrome-molybdenum steel

• Naval brass

• Hastelloy B or C

• Nickel

• Titanium

Consult the pressure-temperature ratings given for each well type. For example, a stainless steel well may be required for high pressure water service where otherwise a brass well would be satisfactory from a corrosion standpoint.

2.CONNECTION – The Installation Factor

Threaded wells are ideal for most industrial applications where removability is required.

Flanged wells are required for applications such as food and beverage manufacturing.

Socket Weld wells are welded in place for the best strength and durability.

3.INSERTION LENGTH – The Accuracy Factor

The insertion length is the distance from the end of the well to the underside of the thread, or other connection means, (also known as “U” dimension).

The primary concern with insertion length is accuracy.

Ensure the most sensitive portion of the thermometer or sensor is immersed far enough into the system. A medium is still will be inherently less consistent than a medium that is flowing.

Matching a Thermometer to a Thermowell:

Generally speaking, the application determines the insertion length of the thermowell. For accurate readings, the thermowell should be immersed into the process at a point where a representative temperature is present.

Once the thermowell insertion length is determined, the correct thermometer stem length can be selected. This measurement is the length from the top of the mounting threads to the tip of the stem. Industry standard stem lengths simplify the process, so just keep in mind the total thermowell length should equal the thermometer stem length plus ¼” for most applications.

4.BORE SIZE – The Interchange-ability Factor

The diameter of the bore has to match the type of thermometer you intend to use.

There are several standard sizes (such as .260 Diameter Bore, .385 Diameter Bore, etc), and the same thermowell can be used for Bimetal, RTD and thermocouple type thermometers.

5.TAPERED OR STRAIGHT SHANK – The Velocity Rating Factor

The straight shank is a cost-efficient option for general, low velocity applications.

However when higher velocity applications become a concern, upgrading to a tapered shank is recommended. These designs offer superior strength, with no loss of sensitivity

ACCESS Professional Viet Nam Limited Company is distributor of Tel-Tru Manufacturing Company manufactures USA.

Keywords: #Tel-Tru # thermometers # pressure gauges # temperature and pressure transmitters # digital thermometers #Thermowell

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