Compressor Package Design Requiremen...

1. The skid/pedestal should transmit shaking forces to the foundation and provide adequate structural

support with proper tie-down under piping, and other critical components.

2. Provide sufficient skid stiffness and strength so the compressor mounts flat without bending or

twisting the compressor frame, crosshead guide, or cylinder. All frame and crosshead guide

mounting points should be supported by full depth cross members.

3. When installing equipment to the skid, ensure all mounting points are flat and parallel to compressor

feet to avoid angular and parallel soft foot and to facilitate ER-82 compliance (see

Appendix H). The mounting method depends heavily on packager ability to duplicate skid flatness

at installation. Methods to mount the frame to the skid include:

• Grouted sole plates

• Grout chocks

• Careful rail or full bed grouting

• Welded steel chocks

NOTE: Flatness and parallelism can be difficult to achieve using this method. It is recommended

to machine steel chocks after welding to avoid angular soft foot, which requires

the use of step shims or re-machining in the field. Step shims create point loading and will

not provide adequate contact between the foot and chock.

• Threaded adjustable chocks

NOTE: Though threaded adjustable chocks have been used with success under smaller

frame classes, they are not permitted under JGC:D:Z:U:B:V and KBZ:U:B:V frames. Keep

in mind the compressor frame is to be the stationary component of the alignment train.

4. Provide compressor hold down bolting in accordance with Ariel ER-26 (see Appendix A). Bolt

lengths extending through only the compressor foot and I-beam flange are typically insufficient to

prevent loosening.

5. Support crosshead guide feet not only to provide vertical support, but also to prevent horizontal

movement perpendicular to the piston rod. Attaching any support to the deck plate alone is insufficient.

Ariel recommends A-frame supports attached directly to a full depth skid member. Ariel

offers crosshead guide supports for JGW and larger frames. Use of threaded adjustable chocks

to support the crosshead guides requires a careful mechanical study to validate their use.

6. JGC:D and larger 2-throw frames require a full width compressor pedestal (wide enough

to include the guide support mounting feet) to control unbalanced forces and couples.

Ariel recommends a reinforced concrete-filled pedestal of common height and use of Ariel crosshead

guide supports.

7. Each crosshead guide deflects an amount relative to the weight of the cylinder mounted on that

throw. See the Ariel Performance Program for estimated crosshead guide foot deflection. This

estimate accounts only for cylinder weight. Account for the weight of attached bottles and piping

if correcting after bottle mounting. For JGR:J:W and smaller frames, cylinder weight will not

deflect the guide, but bottle weight still requires consideration. After mounting the frame and

torquing the frame mounting bolts, shim the crosshead guide to achieve zero deflection when the

guide support bolts are tightened. Loosen the guide support bolts, lift the cylinder, then add shims

equaling the deflection value as calculated by the Ariel Performance Program to the shim pack

under the crosshead guide to level it. Tighten guide support bolts per ER-63. Shims may need

adjustment so crosshead top and bottom clearances and piston rod run out are within tolerance

(see Ariel Maintenance and Repair Manual). Except for KBZ:U frames, shim crosshead guides

between the guide feet and the support; shim KBZ:U guides under the support. On JGZ:U

frames equipped with long two-compartment (L2) crosshead guide extensions, use the outboard

feet under the guide extension to support the guide. Leave feet under the guide unsupported.

8. Provide sufficient skid stiffness to prevent twisting due to torque reaction between the driver and

compressor. Provide enough stiffness so shipment or relocation minimally affects driver/compressor

alignment. Always check and correct coupling alignment after package relocation.

9. Every installed compressor package has several mechanical natural frequencies (MNF), usually

in scrubber/bottle/cylinder system groupings. Each frequency is a function of the stiffness and

mass of the entire system, including the foundation or deck.

If the system first MNF is within the operating speed range or twice the operating speed range of

the package, resonant vibration occurs. Ensure the first MNF of the skid package mounted on the

user foundation or deck is either less than 0.8 times the minimum compressor operating speed,

or more than 2.4 times the maximum operating speed. Coordinate with the foundation or deck

designer.

Although not recommended, to tune a major cylinder MNF between 1 and 2 times the operating

frequency, maintain the cylinder MNF above 1.5 times operating frequency. The high excitation of

1 times compressor forces combined with low level amplification up to 1.5 times the operating

frequency can cause excessive vibration.Forward maximum/minimum speed and normal operating speed range to the end user along with

a caution to examine off-skid structure, piping, instrumentation, and equipment for resonance.

10. Provide skid beams with gussets at anchor bolt locations. Anchor bolt locations should also be

supported internally by cross members.

11. Well-designed crosshead guide supports provide high axial (parallel to the crankshaft) and vertical

stiffness that usually eliminate the need for head end cylinder supports (HES). If a mechanical

analysis predicts interference with a cylinder/guide combination MNF in the operating speed

range, HES may be recommended. Use HES to supplement well-designed crosshead guide supports.

• The mechanical analysis provider should provide detail drawings of the cylinder support of

appropriate stiffness to shift the MNF.

• It is a good practice to design provisions for HES into a skid, even if HES are not recommended.

It is relatively inexpensive to fabricate and correctly install HES if considered in the

design phase.

• HES require careful adjustment and may hinder maintenance access. Improperly adjusted

HES can cause high stress on cylinders and fabricated process piping that can result in failure.

• HES are also recommended for vertical support of cylinders weighing over 10,000 lbs.

• Some cylinders have a small pad on the bottom of the head end of the cylinder. This can be

used when only vertical support is required.

Head End Support Required Features

• HES must be adjustable to avoid cylinder stress. Adjust HES with the compressor at operating

temperature.

• HES must be very stiff vertically and as stiff as possible parallel with the crankshaft.

• HES must not be excessively stiff horizontally (parallel with the rod). They are not intended to

restrain rod load forces.

• Ariel recommends “clamp” style supports for most Ariel cylinders. “Clamp” style supports grip

the flange of the head end head or clearance pocket. For clamp style HES, it is critical to

machine the inside diameter of the clamp to a very tight tolerance to provide as much contact

area as possible.

• Attach the vertical support of the HES to the skid beam web section, not to the flange. Gussets

are required between the beam flanges.

NOTE: Supports that use gas containment bolting to attach to the cylinder require Ariel

approval.

Head End Support Adjustment

Adjust the HES with the system heat-soaked and immediately after adjusting the bottle supports in accordance with the start up checklist and the maintenace schedule. Shim or otherwise adjust the support to hold the current position of the cylinder.

NOTE: Piston rod run out and crosshead running clearance checks will confirm guide/cylinder

alignment has not been compromised.