Page 171 - Improving Machinery Reliability

Machinery Reliability Audits and Reviews 143

Table 3-10
Comparison of Vendor Standings (Illustrative Example Only)
-
Rank Value x Rank
Value I VendorX VendorY 1 VendorX VendorY
Technical backup 3 4 8 12 24
Frame Rating 2 4 5 8 10
Packing cup experience 2 4 4 8 8
Piston or plunger failure 3 8 8 24 24
Leakage disposal 3 I I 21 21
Spare parts supply 2 I 5 14 IO
Erection coverage 1 5 5 5 5
Turnaround time 1 6 6 6 6
Auxiliary systems I 6 6 6 6
Hydraulic tensioning I 6 I 6 I
Piston speed conservatism 2 4 5 8 10
Cylinder alignment ease 2 6 8 12 16
Valve experience 2 6 6 12 12
Winterizing experience 1 8 5 8 5
Bearing material and design 2 I 9 14 18
Pnspection and quality control 2 6 9 12 18
Cooling oil system I 4 8 4 8
Total 180 208
Value scale: 3 = very important Ranking scale: 10 =perfect, no
2 = average importance improvement possible
1 =below average 5 = average quality
1 = barely acceptable

the one shown in Table 3-10. Factors to be considered in compressor selection are
assigned values ranging from 3 (very important) to 1 (below average). These values
are then multiplied by ranking numbers from 10 (perfect, no improvement possible)
to 1 (barely acceptable) and the resulting products added for the various offers under
consideration. The total summation can be used as an indication of relative standing
among competitive offers.

Typical Component Strength Analysis for Hyper Compressors

Assume a 214 rpm machine, with moving components weighing 4,000 kg:
1. Determination of instantaneous gas pressure in cylinder, P.

Where
Ps = suction pressure in cylinder
PD = discharge pressure in cylinder
E = clearance volume in cylinder
Sf = fraction of total stroke (at instant of calculation)
S =total maximum stroke length
k = polytropic exponent at compression
k‘ = polytropic exponent at expansion