Page 201 - Root Cause Failure Analysis

Steam Traps 189

Figure 15-2 Float-ad-thermostatic trap.

able gases. One disadvantage is the sensitivity of the float ball to damage by hydraulic
hammer.

Float-and-thermostatic traps are an economical solution for lighter condensate loads
and lower pressures. However, when the pressure and capacity requirements increase,
the physical size of the unit increases and its cost rises. It also becomes more difficult
to handle.

Thermodynamic or Disk Type

Thermodynamic, or disk-type, steam traps use a flat disk that moves between a cap
and seat (see Figure 15-3). On startup, condensate flow raises the disk and opens the
discharge port. Steam or very hot condensate entering the trap seats the disk. It
remains seated, closing the discharge port, as long as pressure is maintained above it.
Heat radiates out through the cap, thus diminishing the pressure over the disk, open-
ing the trap to discharge condensate.

Wear and dirt are particular problems with a disk-type trap. Because of the large, flat
seating surfaces, any particulate contamination, such as dirt or sand, will lodge
between the disk and the valve seat. This prevents the valve from sealing and permits
live steam to flow through the discharge port. If pressure is not maintained above the
disk, the trap will cycle frequently. This wastes steam and can cause the device to fail
prematurely.

The key advantage of these traps is that one trap can handle a complete range of
pressures. In addition, they are relatively compact for the amount of condensate