Figure 3-12.An inverted bucket trap.
BUCKET TRAP.There are two types of bucket
traps: the upright and the inverted. An example of the
inverted bucket trap is shown in figure 3-12.
During operation of the upright bucket trap, the
steam and water both enter the trap body. As the water
enters, it causes the bucket to float and the valve to
close. The water continues to rise; it overflows into the
bucket that sinks. When the bucket sinks, the trap valve
is opened and the steam pressure forces the water out.
When all of the water is expelled from the bucket, the
bucket again floats, the valve closes, and the cycle starts
During the operation of the inverted bucket trap, the
steam and water both enter under the bucket. The steam
makes the bucket buoyant, causes it to rise, and closes
the valve. When the steam condenses, the bucket drops,
opens the valve, and the steam blows the water out of the
Maintenance on bucket traps consists mainly of
cleaning and inspecting them periodically. If the trap
begins to leak steam, replace the valve disk and seat.
However, if the bucket fails to open the valve, the trap
usually becomes waterlogged. When a valve disk or
seat becomes damaged, the trap allows steam to leak
through. The condensate return line becomes
excessively hot when the trap is leaking steam. Bucket
traps contain some water at all times. Therefore, they
must be drained when the system is to be off during
Figure 3-13.A typical thermostatic trap.
trap is often used on radiators and is commonly known
as a radiator trap. It has a bellows that contains volatile
fluid that expands and vaporizes when heated. Pressure
builds up inside the bellows and causes it to lengthen
and close the valve. A typical thermostatic trap is shown
in figure 3-13.
When water collects around and cools the bellows,
the bellows contracts. This action opens the valve and
permits water to escape. As the water goes out, the
steam that enters contacts the bellows and causes it to
expand, closing the valve and preventing the steam
The most common trouble with the thermostatic
trap is that the bellows develops holes. So, the bellows
does not work and has to be replaced. The bellows and
lower valve seat can be removed for repair without
disconnecting any of the piping.
FLOAT THERMOSTATIC TRAP.The float
thermostatic trap operates on the principle of the float
trap and the thermostatic trap. Practically the same
maintenance is required. A typical example of the float
thermostatic trap is shown in figure 3-14. The
thermostatic bellows acts as an air eliminator.
IMPULSE TRAP.The operation of the- impulse
trap (fig. 3-15) is based on the principle that a portion of
hot water, under pressure, flashes into steam when its
pressure is reduced. The trap is operated by a moving
valve impelled by changes of pressure in a control
chamber. The valve has tiny orifices drilled through its
center that allow the continuous bypassing of
condensate from the inlet of the trap to the control
chamber. This bypassing reduces the chamber pressure
below the inlet pressure, so the valve opens and allows