Coupling and Drive System

1. The maximum coupling size for each Ariel compressor frame model is predetermined by most

coupling manufacturers or torsional providers. The crankshaft stub shaft length shown on the

outline drawing matches a standard industry coupling size. Do not use a coupling hub design that

does not completely engage or overhangs the compressor stub shaft length unless it is thoroughly

checked by torsional and stress analyses.

2. For all direct drive units (engine or motor), use a torsionally rigid, flexible disc coupling similar to

the Thomas or Formsprag types, unless thoroughly checked by torsional analysis.

3. Do not use couplings that grow and shrink axially due to torque loading.

4. See the coupling manufacturer instruction manual for specific coupling installation and operation

requirements.

5. Determine the appropriate interference fit between the coupling hub and the compressor shaft to

transmit torque at all operating conditions. The torque load is considered a "heavy" or "heavy

alternating" load. Ensure the coupling hub and shaft are clean and dry before installation. If a

shrink disk or other externally applied interference mechanism is used to ease hub removal, the

packager and component vendor must verify the coupling can transmit the required torque without

slipping or embedding into the compressor stub shaft.

6. Perform an on-site torsional vibration measurement on compressors driven by variable speed

electric motors. Test through design speed ranges and anticipated cylinder unloading steps as

soon after start-up as possible to confirm theoretical analysis results.

7. To ensure parallel and concentric

drive train alignment, position connected

equipment so total indicator

reading (TIR) is as close to zero as

possible on the coupling hub faces

and outside diameters at normal operating

temperature. Do not exceed

0.005 inches (0.13 mm) on the face

and outside diameter, except for coupling

hub outside diameters above 17

in. (43 cm). The angular face TIR limit

is 0° 1’ (0.0167°). See Fig. 5-1.

Hub O.D. >17 in. x 0.00029 = angular

TIR, in. max.

Hub O.D. >43 cm x 0.0029 = angular TIR, mm max.

Center the coupling between the driver and compressor

so it does not thrust or force the crankshaft

against either thrust face.

For cold alignment, account for the difference in thermal

growth height between the compressor and

driver. See Table 5-1 for compressor centerline

height change based on 6.5 x 10-6/°F (11.7 x 10-6/°C)

and a differential temperature of 100°F (55.6°C).

Obtain driver thermal growth predictions from the

driver manufacturer