Page 102 - Reciprocating Compressors Operation Maintenance

Design and Materials for Reciprocating Compressor Components 89

TAIL ROD PISTON DESIGN

Tail rod construction is required in those cases where reversal cannot
be obtained. This design has identical pressure areas on both ends of the
piston, resulting in load reversals at the crosshead pin. An additional
packing assembly is, of course, required.
This particular application is highlighted in Figure 2-48 where a suc-
tion pressure of 2800 psi and discharge pressure of 3100 psi is used with
a 6" bore cylinder (28 sq. in. area) and a 3" piston rod (7 sq. in. area).

PISTON POSITION PRESSURE A x P
28-7 3100 65tioo
Z8-7 2800 58,800
•LOAD DIRECTION 6300#
28-7 3100 65,100
28-7 2800 58,800
•LOAD DIRECTION 6,300#

FIGURE 2-48. Load on crosshead pin with tail rod design for specific exam-
ple conditions.

It can be seen that the frame and bearings have to withstand only 6,300
pounds; moreover, there is load reversal at the crosshead pin.
Using the same data, but omitting the tail rod, the resulting frame load-
ing is shown in Figure 2-49.

PISTON POSITION PRESSURE DIRECTION NIT PRESSURE AREA PRESSURE AxP

x _ m H8 3100 86,800
T_]=J
- 26-7 2800 -58,800
- — LOAD DIRECTION 28 , 800|
fi 1 28 2800 78,^00
lU 1
- 20-7 3100 65,100
— LOAD DIRECTION 13.300$

FIGURE 2-49. Load on crosshead pin without tail rod for the specific example
conditions listed in Figure 2-48.