The Wiper Ring

When analyzing the effectiveness of a wiper ring installation on reciprocating compressors,
the following considerations must be addressed:
1. The ring design must incorporate the efficient removal of crankcase oil from the piston
rod surface with a light tight interface.
2. The oil, when wiped must be rapidly removed from the rod surface and directed back
into the crankcase. Rapid oil removal from the surface is accomplished by large
oil ports on the ring's deep stripping edge and a large area around the ring for oil flow
away from the wiping surface. In addition, the drainage holes in the wiper gland should
be located at the bottom of the assembly. These draIn holes should be as large as
possible within space limitations.
3. Wiper ring material must be compatible with the piston rod and maintain a sharp
wiping edge. Our experience has indicated that Class 40 open grained cast iron with
a 150-220 Brinnell is the most effective wiping material in standard applications and
the most cost efficient. Bronze ring material is normally specified where piston rods
have special coatings or low RMS finishes. Babbitt is normally restricted for chrome
or stainless rods and in oxygen service. AAVOLYN recommends metal rings over
plastic. The plastic ring has a tendency to rapidly lose its wiping edge on
reciprocating compressors, expecially on high speed units.
4. The wiper ring material must be compatible with the gas being compressed. The
following table lists our recommended ring material in different gas services.
Ring Material Application
Cast Iron Standard Applications
Bronze Specialty Gases
Babbitt Chrome Rods
Stainless Rods
Oxygen Rods
5. Side Clearance - The amount of clearance between the set of oil wiper rings and the face
of the gland is critical to maintain high levels of performance from your wiper installation.
There is no face pressure to the oil rings against the crank side of the installation. The rings
must move freely in the case. However, excessive side clearance will allow oil to flow over
and behind the ring and be pumped along the rod into the distance piece and the pressure
packing. Each ring in the set should have .001/.0015" side clearance to function properly.
6. Spring Tension - The tension of the spring holding the ring together must be sufficient for
the ring to wipe oil from the rod. Each ring is held together by a garter spring. This spring
must be of sufficient tension to create a wiping action at the piston rod surface. No other
force acts on the wiper ring to provide this action.
TROUBLE SHOOTING
* Check the piston rod diameter in the wiper area. If more than .003" undersized repair or
replace.
* Verify groove depth. If more than +- .003" off remachine to standard depth.
* Check rod finish or surface condition. Rough finishes or scoring may cause leakage.
* Rework the piston rod.
* Check oil wiper rings on a gage bored to rod size to ensure there is no light at the bore.
* If open replace. Exception: AAVOLYN TYPE 495 where a plain face faces the crank.

* The oil rings should be installed with the oil ports facing the crankcase. If they are
reversed reinstall properly. Be aware that some wiper ring manufacturers do not
furnish rings with a true tapered stripping edge primarily because of the difficulty in
manufacturing. These rings may be required to be installed with the oil ports facing
away from the crankcase. This type of installation is not as effective but may be
necessary because of the ring design. AAVOLYN wipers, with their 7 degree tapered
stripping edge are designed to be installed with the oil ports facing the crankcase for
maximum efficiency.
* Check spring Tension. If the pressure of the ring on the rod is not sufficient, the ring may
not wipe. The tension of the spring holding the ring together must be sufficient for the
ring to wipe oil from the rod.
* Make sure that the wiper gland is installed with the drain holes on the bottom, so the oil
can drain away rapidly.
*Each ring is held together by a garter spring. This spring must be of sufficient tension to
create a wiping action at the piston rod surface. No other force acts on the wiper ring to
provide this action.

AAVOLYN CORP

AAVOLYN COMPRESSOR ENGINEERING BULLETINS

AAVOLYN CORP

	The Wiper Ring
	Engineering Bulletin # 35 Oil Wiper Design and Function