Figure 13-37 shows the assembly of an orifice-type steam trap. Constant-flow drain orifices may be used in systems of 150 psi and above where condensate load and pressure remain near con-stant. The constant-flow drain orifice operates on a thermodynamic principle-the variable den-sity of condensate. The density of any fluid changes with temperature. As the temperature of the condensate decreases, its density will increase, as will the flow of condensate through the orifice. The reverse is also true. As the temperature of the condensate increases, its density will decrease, as will the flow of the condensate through the orifice.

Because of the difference in densities between the steam and the condensate, the condensate will flow through the orifice at a faster rate.