maintenance is required for this trap because of its simple construction. Too, the trap is usually constructed of stainless steel.

THROTTLING TRAP. - The operation of the throttling trap (fig. 3-17) is based on the principle that the flow of water through an orifice decreases as its temperature approaches that of the steam used. The rate of flow of the condensate may be adjusted by raising or lowering a stem (needle valve) that fits into a tapered seat. This throttling trap has no moving parts.

Condensate that is slightly cooler than steam enters the trap, travels up through a baffle arrangement, and is discharged through an orifice. If the condensate discharge rate is higher than the inlet rate, the water (condensate) level in the chamber drops. This allows steam to enter the baffle passage and heat the condensate.

The amount of water flashing into steam increases; so the volume of steam-water mixture handled by the orifice increases and thereby reduces the capacity of the orifice. The reduced flow through the orifice permits the level of condensate in the chamber to rise until the heater water in the baffle passage has been completely discharged and replaced with water that is slightly cooler. Then the cycle is repeated. Air is vented from this trap through the same passage as the condensate.

The throttling trap can be replaced without disturbing any of the piping.

Figure 3-17. - A throttling trap.

BIMETALLIC-ELEMENT TRAP. - The bimetallic-element trap, as shown in figure 3-18, contains bimetallic elements that bend when heated. The metals in the bimetallic strip generally are Emvar and copper. The copper expands rapidly when heated, but Emvar expands very little. Therefore, the bimetallic strip bends when it is heated. This trap may be used for higher or lower steam pressure by increasing or decreasing the number of bimetallic leaves in the trap.

This trap works basically the same as the thermostatic trap. When steam enters the trap, the element is heated and bends, thus closing the valve. As steam condenses, the elements cool and straighten out to allow the valve to open and let the condensate escape. The bimetallic trap can be repaired without disturbing any of the piping.

Pointers on Operating Procedures

To help ensure trouble-free service of steam traps, follow the proper operating procedures carefully. Some important factors involving operating procedures are furnished below.

Steam traps should be operated within the capacity rating and pressure differentials recommended by the manufacturer. Use traps for the correct pressure and temperature. If operating pressures change, it may be necessary to change trap sizes, or internal parts, to fit the new pressure conditions.

Traps should be insulated where heat must be conserved. Some types of traps, which depend on the cooling effect of the condensate for operation, should be left bare. Check the manufacturer's instructions regarding insulation.

Where continuity of service is a requirement, a three-valve bypass is usually provided to permit drainage while the trap is being overhauled. Bypasses are also used to speed up the discharge of condensate and air when you are starting a system. In normal operation, however, the bypass valve should be kept closed to prevent steam from being wasted.

Check valves, located in the discharge line, are important in parallel installations to prevent the discharge of one trap from backing up into that of another. Also, when condensate from the trap must discharge to a higher elevation, a check valve prevents backflow of condensate.

Inverted bucket traps must be primed for operation by providing a condensate seal in the bottom