is no single solution to this problem, but some
specific guidelines will be discussed below.
Pulsation dampeners serve as pulsation and
noise mufflers by providing acoustical chambers
with the dampener. Manufacturers generally pro-
vide dampeners to a specified discharge pulsation
peak of ± 2 percent of line pressure. Figure 11-19
shows several typical pulsation dampeners. These
units should be used whenever reciprocating and
centrifugal compressors serve the same com-
pressed air main, because the pulsations of the
reciprocating compressor can transmit to and
disturb the operation of the centrifugal com-
pressor. Pulsation dampeners may not completely
solve downstream resonance, but they will reduce
the vibration amplitudes.
Several other ways to decrease noise and
amplification caused by discharge pulsation are
available. Surge chambers can be used to change
the equivalent length of the piping and increase
the pulse-absorbing volume of the pipe. A surge
chamber can be as simple as an increased diameter
of discharge piping near the compressor discharge.
An orifice plate or plates may be installed in
conjunction with surge chambers to change the
acoustical resonant frequency of the piping
system. Piping support is also important at the
compressor. They must not only be supported
from top or bottom but also have lateral support.
When piping is large, provide spring-loaded two-
Compressor control systems generally include
one or more controlling devices, such as safety
controls, speed controls, and capacity controls.
Such devices function in the system to regulate
the output of the compressor as it meets the
demand for compressed air.
On some small compressors the simple
Bourdon tube-type pressure switch serves as a con-
troller by actuating the prime mover on and off
over a predetermined pressure range. More com-
plex compressors require control systems that load
and unload the compressor as air demands
change. The CONSTANT-SPEED type of con-
troller used with many compressors decreases or
increases compressor capacity in one or more steps
by the use of unloading devices, while allowing
the prime mover speed to remain constant.
Another type, referred to as the DUAL-
CONTROL, is a combination of the constant-
speed and an automatic start-stop control. It
permits constant speeds when demands are con-
tinuous and an automatic stop or start when
demands are light. There is still another system
that enables the prime mover to idle and
compressor suction valves to remain open when
air pressure reaches a set maximum. As the
pressure drops below a set minimum, the prime
mover speed is increased, suction valves are
way lateral supports to absorb vibration.
closed, and air is compressed.
Figure 11-19.Pulsation dampeners.