Screw Plug Immersion Heaters

Typical Heating Applications

• PROCESS WATER HEATING
• HEATING OILS, WAX, TAR, ASPHALT, PARAFFIN
• MILD ALKALINE & ACID SOLUTIONS
• FREEZE PROTECTION
• EQUIPMENT WARM-UP
• HEATING GASES
• FOOD PROCESSING

Selection tips for screw plug heaters

Screw plug immersion heaters have a wide range of applications. It is essential to take several factors into consideration in order to select a heater that has features that match the requirements of a specific application and suitable to the environment where the heater will operate. The following are a number of criteria that should be taken into consideration:

• Besides the heating capacity required, a heater should operate at a temperature and a watt density that is adequate to the fluid heated. Tables 2 and 3 provide maximum sheath temperatures and watt densities that are recommended for heating various fluids.
• In order to select proper materials for screw plug heaters, general selection guides that are based on common experience in industrial usage could be used. However, this selection should always be based on a user’s experience and knowledge in a specific application. Table 3 provides recommended sheath and screw plug materials for different mediums.
• It is important to note that at all times the temperature of the sheath material should not exceed the following temperatures:

• Taking the environment within which the heater will operate into account, safety issues should be taken into consideration.
• Adequate temperature controlling devices, temperature and pressure high limit switches, low liquid level and flow controllers and other control/safety devices should be used. These instruments will control the heating process and protect the heater from excessive heat.
• The classification of the electrical terminal box should match the application (NEMA 1, NEMA 4, NEMA 7, NEMA 12 etc.).
• The amount of contamination that the heater will be exposed to should be taken into account.
• Electrical safety codes should be considered.

For more information, please contact our technical specialists.

• NEMA 4 (MOISTURE PROOF) TERMINAL BOX
• BUILT-IN THERMOWELL
• BUILT-IN SINGLE OR DOUBLE POLE THERMOSTATS
• PASSIVATION FOR STAINLESS STEEL AND INCOLOY HEATERS
• BUILT-IN PROCESS OR HIGH LIMIT THERMOCOUPLES
• SPECIAL PLUGS OR NON-STANDARD THREAD SIZES
• NEMA 7 (EXPLOSION PROOF) TERMINAL BOX

Thermostats and thermocouples

Thermostats that are utilized in screw plug heaters are the bulb and capillary style. These thermostats operate by the principle of expansion and contraction of a heat sensitive liquid found inside the bulb and capillary assembly, which controls the activation of an electrical switch inside the thermostat.

Thermostats in most cases open the electrical circuit when the desired temperature is attained (open on rise). The table below shows available ranges of thermostats.

A pilot duty thermostat can always be used when the ampacity of a heater is higher than the available thermostat amperages shown below.

It should be noted that thermostats are only temperature controllers and should not be used as fail-safe high limit switches.

Built-in thermocouples could be utilized inside screw plug heaters to give more accurate temperature indications. Thermocouples could also be attached to one of the heating elements and utilized as high-temperature limiting devices.

Terminal Boxes for Screw Plug Immersion Heaters