Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

Chemical Pumps Metallic and Nonmetaliic 319
Bolting
As threaded studs will impose tension in the composite case during assembly,
it is preferable to use through bolting. This leaves the casing in
compression rather than in tension. When through bolting cannot be
used, the bolts or studs are fastened into stainless steel or alloy inserts
and are molded into the piece. The inserts are gnarled and grooved on the
outside diameter to prevent twisting or pulling within the piece when
torque is applied to the fastener. The inserts are usually a class 3 fit on the
inside diameter for the fasteners. A blind end insert is used to give a positive
stop for tiie studs. When inserts are used, it is best to mold them
within the piece rather than post insert them. When they are molded in
the piece they should be located at least Vs in. below the finished surface
so that when machining is being done, the cutting tool does not have an
interrupt cut against the insert resulting in weakening of the mounting of
the insert. When inserts are used, care has to be taken by the designer
that there is proper flow of the composite material to avoid a path for
leakage during hydrostatic testing.
Gaskets
With nonmetallic pumps, most main gaskets are O-rings, These can be
either round or square cross sectional O-rings. O-rings result in less bolt
loading on the main bolts. If gasket surface requires final machining,
then it is recommended that the surfaces be coated with the base resin to
prevent wicking of the pump fluid through the exposed ends of the glass
reinforcement resulting in leakage of the gasket.
Sack-up Support for Bolting
To reduce the bolt head or nut loading, it is recommended that when
washers are used their diameter should be at least three times the diameter
of the bolt. Casing covers usually have inserts for the gland studs as
well as inserts for jacking bolts to aid in the disassembly of casing covers.
Inserts require optimum strength to absorb radial and axial forces
and must be compatible with the atmospheric conditions and in many
cases with the liquid being pumped.
Stuffing Box Area
If the glands are made of a composite material, they must be capable of
withstanding the torque that is applied without creeping. Depending
whether an inside or outside seal is used, the gland may need additional