Page 184 - Reciprocating Compressors Operation Maintenance

1 7O Reciprocating Compressors: Operation and Maintenance

COOLED PACKING TYPE

Cooled packing includes the following:

1. Oil cooled. The packing cups contain internal and external passages
for circulation of coolant through and around the cups in the stuffing
box. An O-ring is contained in the circumference of the outer cup to
confine the coolant within the stuffing box. The source of the coolant
may either be the frame cooling system or a separate system.
2. Water cooled. This type of packing provides passageways through
the cups between the packing rings for circulating cooling water. The
coolant completely encircles each cup and first travels to the hottest
point of the case, then travels progressively to the cooler points.
The possibility of leakage is eliminated with precision cup manu-
facture and O-ring seals between each cup. The coolant must be free
of any foreign material and deposit-prone chemicals. The required
coolant flow through the packing is small and should be regulated
by a needle valve. The flow must be adjusted to provide an outlet
temperature only slightly greater than the inlet coolant temperature.
Excessive flow is neither necessary nor helpful. A rate of one to
three gallons per minute is adequate.
3. Thermosyphon. This type of packing is similar to water-cooled
packing with passageways through the cups also. Circulation of
the coolant through the packing is by convection. Heat is dissipat-
ed by ambient air passing over externally mounted finned tubes.
Coolant level must be maintained within limits indicated on a
sight flow gauge.

PACKING MINGS

Packing rings are the heart of the packing assembly, sealing along the
piston rod and between themselves and the packing case (see Figure 3-29).
The tangent ring is cut into three segments so that each cut lies on the
side of an equilateral triangle. The cuts of this ring maintain sealing con-
tact regardless of variations of the ring's inside diameter. As wear occurs,
the ring segments will close radially to compensate while still maintain-
ing sealing contact at the tangential joints, Figure 3-30 and Figure 3-31.
The clearance provided at the end of each tangent joint to allow for
such compensation allows a direct leakage path. To seal these joints, a
ring cut radially into three segments is paired with and pinned to the tan-
gent rings so that its segments form a seal along the rod at the edge of the