Page 155 - Reciprocating Compressors Operation Maintenance

Operation and Maintenance of Reciprocating Compressors 141

Reed Valves

Reed valves are similar to feather valves in that the sealing element is
the spring. One end of the reed is fixed so that it deflects as a cantilever
beam. The stop is either contoured or a bumper that limits the deflection
of the free end of the reed. These valves are used in small horsepower,
intermittent-duty compressors.

Concentric Ring Valves

These valves use one or more relatively narrow metallic or nonmetallic
rings arranged concentrically about the center line of the valve. Spring is
provided by either wave springs or, more commonly, coil springs. There
are many variations of springing configuration, but the most popular in
use today features multiple small coil springs on each ring.
In many cases of oil-free applications, a nonmetallic "button" main-
tains a separation between the spring and ring.
Lift is controlled by a flat stop that limits the ring motion. In some
cases, the ring grooves merge into a close clearance groove that provides
fluid damping. (See Figure 3-15).
Concentric ring valves have a wide application range and are used in
low- to high-speed applications. Lifts are as high as .160". Experience
has shown that the top end of application speed is in the area of 1200
rpm. Lifts are approximately .100". The flow efficiency of these valves is
not as good as straight element valves, but it is good for the pressure
ratios generally used.
These valves can easily be used with plug-type unloaders by eliminat-
ing one or more of the inner rings.
The rings have either a rectangular cross section as shown, or a more
aerodynamically streamlined shape (Figure 3-16).
Valves that use a rectangular ring are easier to manufacture and main-
tain. This, plus dynamic considerations, favors the rectangular configura-
tion in most applications.