Figure 3-14.A float thermostatic trap.
Figure 3-15.An impulse trap.
free discharge of the condensate. The temperature of the
remaining condensate rises and flashes back to steam.
The flow through the valve orifice is choked and
pressure builds up in the control chamber, closing the
About 5 percent of the rated capacity of the trap
flows through the valve orifice. The pressure on the
discharge side of the trap should not be over 25 percent
of the inlet pressure if the trap is to function properly.
Very little maintenance, except some periodic cleaning,
is required for the impulse trap. The trap may be
disassembled for cleaning or repairing without
disturbing any of the piping.
THERMODYNAMIC TRAP.A typical ther-
modynamic trap is shown in figure 3-16. It contains
only one moving parta disk. This disk is operated by
changes in steam pressure. Pressure under the disk
raises it to allow the condensate to be discharged.
Droplets of condensate form on top of the disk. Then
steam enters at high velocity and creates a low pressure
under the disk; the droplets of water above the disk then
flash into steam and create a high pressure above the
disk. (You recall that water expands to as much as 1,728
times its volume when it changes to steam.) The high
pressure against the top of the disk overcomes the lower
pressure of the incoming steam, so the trap closes. As
more condensate collects in the trap, the steam above
the disk condenses and relieves the high pressure and
the cycle is repeated.
The most common trouble is that the trap becomes
plugged and has to be disassembled and cleaned. The
thermodynamic trap can be cleaned or repaired without
disturbing any of the piping. Very little other
Figure 3-16.A thermodynamic steam trap.