Tags: Thermostatic Traps

Float and Thermostatic Traps


A float and thermostatic trap (see Figure 10-23) has both a thermostatic element to release air and a float element to release the condensation. As such, it combines features of both the float trap and the thermostatic trap.

float thermostatic trap Float and Thermostatic Traps

These traps are recommended for installations in which the volume of condensation is too large for an ordinary thermostatic trap to handle. Float and thermostatic traps are also used in low-pressure steam heating systems to drain the bottom and end of steam risers (see Figures 10-24 and 10-25). Other applications include the draining of condensation from unit heaters, preheat and reheat oils in air conditioning systems, steam-to-water heat exchangers, blast coils, and similar types of process equipment.

low pressure steam Float and Thermostatic Traps

Check the trap-seat pressure before installation to make sure its rating is equal to or greater than the steam supply of the boiler.

If the trap is operating properly, it will immediately and continuously discharge condensation, air, and noncondensable gases from the system that enter the inlet orifice of the trap.

low pressure steam drain Float and Thermostatic Traps

The condensation is handled by the ball float, which is connected by a level assembly to the main valve head. Condensation entering through the trap inlet causes the ball float to rise, moving the level assembly and opening the valve for discharge.

Air and noncondensable gases are discharged through the thermostatic air vent. The thermostatic element is also designed to prevent the flow of steam around the float valve.

Float and thermostatic traps operate under pressures ranging from vacuum to a maximum pressure of 200 psig; however, the great majority of them are designed for 40 psig or less.

Thermostatic Traps


The operation of a thermostatic trap (see Figure 10-20) is based on the expansion or contraction of an element under the influence of heat or cold.

Thermostatic traps are of the following two types: (1) those in which the discharge valve is operated by the relative expansion of metals and (2) those in which the action of the liquid is utilized for this purpose. The latter is probably the most commonly used thermostatic trap found in modern steam heating systems. Thermostatic traps of large capacity for draining blast coils or very large radiators are called blast traps.

Modern thermostatic traps consist of thin, corrugated-metal bellows or discs enclosing a hollow chamber that is filled with a liquid or partially filled with a volatile liquid. When steam comes in contact with the expansive element, the liquid expands or becomes a gas and thereby creates a certain amount of pressure. The element expands as a result of this pressure and closes the valve against the escape of the steam.

thermostatic trap Thermostatic Traps