Packing
Cases & Rod Rings
The broadest line of sealing products from
the most respected name in the industry.
Rod Rings and Packing Cases
As the inventor of floating mechanical packing over 110
years ago, Cook packing has performed successfully in thousands
of applications worldwide.
Today,
rod ring design options and material choices from bronze
to high-performance non-metallics assure the optimum ring
for your applications. Technical expertise extends to packing
case design as well, which is demonstrated by the patented
VORTEX® cooled packing
case.
Rod Rings
Pressure Breaker Rings
Pressure Breaker rings are not used for a direct seal, but
are designed to slow the flow of gas back down the rod on
the intake stroke. Without buffering, this back flow could
blow the rings off the rod, damaging the garter springs
and/or breaking the ring. Pressure Breaker rings may be
constructed with any currently available material, but those
materials with a low thermal coefficient of expansion and
high stiffness are preferable for a stable orifice area.
Metal is usually superior to TFE, but Pressure Breakers
can be made successfully from some high strength plastics.
P RINGS
P rings use three cuts in the ring as the flow paths for
gas. With zero clearance over the rod, the flow controlling
orifice in the P ring is the gap that is formed at the segment
ends.
PA RINGS
PA rings are similar in function to P rings. However in
the PA ring, the flow controlling orifice is formed by the
clearance between the ring bore and rod. Clearance at the
ring segments is zero when installed over the rod. The PA
ring provides lower rod loading than the P, but has a more
difficult-to-control orifice area.
Wiper packing acts to maintain oil in the crankcase. Seal
rings in the wiper packing also minimize the flow through
the packing caused by the pumping action of the crosshead.
EM-4 is the standard wiper arrangement that combines a BD
seal ring and a 3RWS wiper ring.
3RWS WIPER RINGS
The 3RWS is the basic and most commonly used wiper
ring combination. The only function of the 3RWS is
to wipe the rod and drain the fluid away. The 3 indicates
that the RWS ring configuration is doweled to prevent
alignment of cuts.
560 WIPER RINGS
The 560 wiper ring set is made up of two wiper rings
and a butt tangent seal ring that combines the wiper/seal
function into one groove. The 560 wiper rings are
installed with drain notches of one wiper toward the
oil source.
561 WIPER RINGS
The 561 wiper ring set is identical to the 560 wiper
ring set with two wiper rings and a butt tangent seal
ring that combines the wiper/seal function into one
groove. The difference is that the 561 wiper rings
are installed with the flat face of one wiper toward
the oil source.
RWS-BT
WIPER RINGS
The RWS-BT is a wiper/seal combination ring installed
with drain notches facing the oil source. This is
utilized where space is limited.
Packing
Case
Without an effective seal,
liquid or gas emissions could flow along the rod and
leak into the distance piece area. C. Lee Cook
offers a variety of packing cases that resist wear
and excel in specific pressure environments. When
it comes to lubrication, venting, purging, cooling
or heating,
C. Lee Cook delivers proven quality in sealing
products.
NON-LUBRICATED PACKING
Non-lubricated packing consists of non-metallic rings
or, if the operating pressure is high, non-metallic
rings with additional back-up rings. The back-up,
pressure breaker and vent rings may be metal, but
high strength plastics are also used in many applications.
Rod and Case Material
Most ring materials can be abrasive when no lubricant is
present. Therefore, a harder rod material and a finer rod
finish are required. Nitrided or tungsten carbide coated
rods are the most common materials used with nonlubricated
packing. The choice of rod material, as with packing case
material, may also be dictated by corrosive elements in
the gas stream. Packing cases may be plated for corrosion
resistance, but are usually made of corrosion-resistant
cast iron, bronze or stainless steel.
Cooled Cases
One particular problem in non-lubricated conditions is the
high frictional heat generated by the packing at the ring
bore. This heat must be removed by conduction through the
case or rod.
C. Lee Cook has developed a cooled case that is cooled
by circulating coolant through channels in the individual
packing case cups. Channels can be formed internally in
the cups so that no O-ring seals encircling the rod are
required.
Coolants
Almost any "heat transfer fluid" can be used as coolant,
but water or water/anti-freeze mixtures are the most effective.
Oil offers advantages, such as corrosion resistance or deposit
prevention, but is less capable of carrying away heat than
water. Some compressors incorporate liquid or gas coolant
circulated directly against and around the rod. Keeping
friction low and removing the generated heat is crucial
to long life for non-lubricated packing.
STATIC-PAC
Rod packing will leak more when the rod is stopped than
when it is moving. This is due to the loss of oil which
filled the leak paths, changes in the ring shape as the
ring cools and changes in the rod alignment as the temperature
changes. To eliminate leakage through the packing rings,
Static-Pac is available in kit form from C. Lee Cook
to adapt to the existing cases or it can be supplied as
part of the original design.
Minimize Gas Escape
Static-Pac is an uncut, conformable ring which is forced
against the rod by a piston when the compressor is stopped.
Static seal actuation occurs when pressurized gas is admitted
to the piston, wedging the seal ring inward against the
motionless rod. The shape of the seal is designed so that
pressure within the cylinder will cause the seal to move
away from the rod when actuating pressure is lowered. Static-Pac
is especially useful during compressor shutdown to minimize
the escape of dangerous or expensive gases.
HYPER PACKING
"Hyper" generally refers to pressure greater than 10,000
psi. But compressor or pump discharge could go up to 50,000
psi. At these high pressure levels, gases tend to act like
liquids with low compressibility, so packing cases must
be built heavier and of stronger steel. The type of seal
rings used by C. Lee Cook in hyper packing are able
to withstand the stress at these higher pressures.
Highest Strength Steel
A common problem in most hyper packings is the containment
of very high cyclic pressure within the thick-walled vessel.
Cyclic stresses require compound construction for the cups,
autofrettaging and/or pressure loading on the outside of
the case to ensure high fatigue strength. C. Lee Cook
hyper packings have been successful in meeting these sealing
and life requirements of high-pressure packings by utilizing
proven technology and the highest strength steel available.
WIPER PACKING
With the increase in non-lubricated applications and
the use of incompatible oils in the same machine,
oil wiper packing must be highly effective. This packing
is essential in keeping oil to one side of the bulkhead
to maintain separation from the rest of the crankcase.
Wiper ring material must be conformable in order to
mate to an imperfect rod, but also be of sufficient
strength to maintain a sharp wiping edge. C. Lee
Cook has found that using nonmetallics with the
right combination of flexibility and hardness has
proven to be the best approach toward solving wiper
problems.
