and out ports, an inlet pressure gauge, a dump trap, and
a sump drain port. There is also a pipe plug located in
the top for testing the dump trap.
Air flows through the in-port and a down-
coming tube, and is exhausted into the tank. It then
reverses its direction, flows upward to the top of the
out-port tube, and reverses direction again to reach the
Centrifugal forces at the two points of reversal and
the slowing of the flow within the tank extract the
entrained droplets of liquid. These droplets collect at
the bottom of the tank and drain into the dump trap.
When the liquid level in the trap rises sufficiently, a
float (through a connecting linkage) opens a valve to a
waste line, and the collected liquid is blown out. When
the float drops, the valve closes and liquid collects until
the float automatically initiates another disposal
Operation of the float maybe observed through a
transparent trap bowl. The trap is also equipped with a
manual drain, which is operated by pulling a button on
the bottom of the trap.
Telltale Oil Filter and Dump
The telltale oil filter and dump trap are
located downstream from the fluid separator and dump
trap. It is designed specifically to remove oil from
compressed air and to indicate by color the state of the
oil removing material. This unit further purifies the air
by removing small oil droplets that escape the fluid
As shown in figure 2-3, the filter employs
two direction changes of airflow and impingement
surfaces to mechanically remove droplets; a mist
separator to help small drops become larger and drop
out; and an absorbing material to remove the
remainder. The absorbing column, which is visible
in a transparent tube, changes color from pink to
dark red as it absorbs oil. Before the color change
reaches a redline indicator, the filter element should be
Liquid oil drains are collected into an automatic
dump trap for discharge into a waste line. This trap is
identical to that used on the fluid separator; therefore,
the same explanation and comments apply.
The combination of the fluid separator and the
telltale oil filter removes entrained water and oil and
some of the oil vapor from the supply air, provided that
these units are properly maintained. Water vapor and
any remaining oil are removed in the dehydrator (fig.
2-1), which follows further downstream.
Figure 2-3.-Telltale oil filter.