Page 156 - Root Cause Failure Analysis

144 Root Cause Failure Analysis

compressors can be mounted on a foundation just large and rigid enough to carry the
weight and maintain alignment. However, most reciprocating compressors require
larger, more massive foundations than other machinery.

Depending on the size and type of unit, the mounting may vary from simply bolting it
to the floor to attaching to a massive foundation designed specifically for the applica-
tion. A proper foundation must (1) maintain the alignment and level of the compressor
and its driver at the proper elevation and (2) minimize vibration and prevent its trans-
mission to adjacent building structures and machinery. There are five steps to accom-
plish the first objective:
1. The safe weight-bearing capacity of the soil must not be exceeded at any
point on the foundation base.
2. The load to the soil must be distributed over the entire area.
3. The size and proportion of the foundation block must be such that the
resultant vertical load due to the compressor, block, and any unbalanced
force falls within the base area.
4. The foundation must have sufficient mass and weight-bearing area to pre-
vent its sliding on the soil due to unbalanced forces.
5. Foundation temperature must be uniform to prevent warping.

Bulk is not usually the complete solution to foundation problems. A certain weight
sometimes is necessary, but soil area usually is of more value than foundation mass.

Determining if two or more compressors should have separate or single foundations
depends on the compressor type. A combined foundation is recommended for recipro-
cating units, since the forces from one unit usually will partially balance out the
forces from the others. In addition, the greater mass and surface area in contact with
the ground damps foundation movement and provides greater stability.

Soil quality may vary seasonally, and such conditions must be carefully considered in
the foundation design. No foundation should rest partially on bedrock and partially on
soil; it should rest entirely on one or the other. If placed on the ground, make sure that
part of the foundation does not rest on soil that has been disturbed. In addition, pilings
may be necessary to ensure stability.

Piping Piping should easily fit the compressor connections without needing to
spring or twist it to fit. It must be supported independently of the compressor and
anchored, as necessary, to limit vibration and to prevent expansion strains. Improp-
erly installed piping may distort or pull the compressor’s cylinders or casing out of
alignment.

Air Inlet The intake pipe on an air compressor should be as short and direct as pos-
sible. If the total run of the inlet piping is unavoidably long, the diameter should be
increased. The pipe size should be greater than the compressor’s air-inlet connection.