E-Mail: aavolyn@bellatlantic.net

Discussion - The introduction of FILLED TEFLONŽ materials for use as piston rings in
reciprocating compressors was initially to allow compressors to run without lubrication in the
cylinder area. This design enabled the gases to be compressed successfully without
introducing any oil into the compressed gas. In order to prevent the metal to metal contact
of the piston and cylinder wall, a rider or carrier ring was necessary to also be installed
around the piston. The clearance between the piston and cylinder was increased to allow the
rider ring to have acceptable wear and ring life.

DESIGN CONSIDERATIONS - The width of the rider ring was determined by a series of
considerations including the wear factor of the TeflonŽ material, weight of the piston,
designed operating O.D. of the rider ring and the cylinder wall to ensure that the rider ring did
not act as a sealing ring since the rider ring had much more surface area than the piston ring
and would develop more frictional heat. Heat is a major factor in determining the life of the
TeflonŽ installation.

LUBRICATED APPLICATIONS - Design engineers and operating personnel soon realized the
benefit of the rider ring to prevent cylinder wear and provide a safety factor in case of loss of
lubrication. It is fairly common now for rider rings to be installed on compressor pistons in
both lubricated and non-lubricated applications.

DESIGNED TEFLON RING LIFE - For standard NON-LUBE installations using
conventional FILLED TEFLONS, a ring life expectancy of 8,000-10.000 hours can
be anticipated. As pressures increase past 250PSI and operating temperatures
exceed 275 degree Fahrenheit, ring life will decrease. In LUBRICATED installations,
ring life is normally doubled. Although rider rings are normally replaced with the piston
rings, you can expect them to last through (2) two changes of piston rings.

PERFORMANCE VARIABLES - As mentioned above, temperature and pressure affect ring
life. In addition, solids and liquids in the gas stream are detrimental to ring life. For gases
such as NITROGEN, THE DEW POINT of the gas can have an effect on the performance of
the rings.
The addition of SPECIAL FILLED TEFLONS combined with Pressure Balanced ring
designs can increase the life of the installation. These improvements should be considered
where they have an application.

PREVENTIVE MAINTENANCE - To ensure the optimum performance is obtained from your
ring installation and damage to piston and cylinder surface is prevented, the clearance
between the piston and cylinder wall should be checked at least every (6) months. If you are
not seeing at least 8000 hours operating normally for your piston rings and riders, inspections
should be increased proportionately. Using these inspection procedures, you can eliminate
any cylinder and piston damage. A MINIMUM of .030 inches CLEARANCE should be
maintained between the piston and cylinder wall. When this minimum is reached, the rings
should be replaced.

616 ORANGE ST.

P.O. BOX 1097

MILLVILLE, NJ 08332

Telephone: 856-327-8040

Fax: 856-327-9595

E-Mail: aavolyn@bellatlantic.net