Orifice steam trap

Thermodynamic steam traps also rely on pressure differentials for their operation. They employ a control disc to open or close a discharge orifice. Both impulse and disc-type steam traps are used in medium-pressure (15-250 psig) steam delivery systems. 

If the trap orifice has been designed too large, the trap valve cannot open to discharge condensate, creating or amplifying serious plant problems. For any steam trap, for... 

Undersized condensate return-lines create one of the most common problems encountered with process steam traps. Hot condensate passing through a trap orifice loses pressure, which lowers the enthalpy of the condensate. This enthalpy change causes some of the condensate to flash into steam. The volume of the resulting two-phase mixture is usually many times that of the upstream condensate. 

On this basis, the selection of a group of steam traps to handle all steam tracing situations is possible. Actually this consists of a 3/8-inch nominal size trap but many steam trap manufacturers rate their traps by orifice size rather than by connection size. Suitable traps should have 150 psig steam condensate capacities from 350 to 600 pounds per hour at saturation temperature, and from 550 to 850 pounds per hour at 30°F below saturation temperature. Using 15 psig steam, the condensate capacity should range between 135 and 250 pounds per hour at saturation temperature and from 225 to 400 pounds per hour at 30°F below saturation temperature. 

The required orifice continuous flow capacity is determined at steam chest pressure to condensate system pressure at a flow 6 to 8 times design. If designed for normal flow the trap would have to be open 100% of the time. Then, as stated above, a body size is selected that can contain the required orifice (not be above the stated... 

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