"Positive Displacement Reciprocating Pump Fundamentals - Power And Direct Acting Types" By Herbert H. Tackett, Jr., James A. Cripe, Gary Dyson Page 5

ADVERTISEMENT

Table of Contents
POSITIVE DISPLACEMENT RECIPROCATING PUMP FUNDAMENTALS—
49
POWER AND DIRECT ACTING TYPES
to 25 micron and in concentrations not to exceed 1 percent by
to exceed 40 percent by volume. This design does not have the
volume. Suitable for application pump speeds up to API-674
same speed limitation requirement as the ball valve design.
(1995) and Hydraulic Institute speed limitations.
Stuffing Box Designs and Applications
As the name indicates this valve is a ball, Figure 13, which is
often guided by an exterior cage as it opens and closes. The
Reciprocating pumps use various methods of packing as their
seating surface of the valve is spherical while the valve seat is
sealing methodology. For packing to be reliable it must always be
normally beveled. This forms a radial “line contact” between the
in contact with a lubricant such as the pumped product or an
valve and valve seat to create a tight seal.
external flush. Because of this lubricating effect the packing in a
reciprocating machine will always leak to some extent. This
leakage is essential in ensuring long packing life.
The pump vendor’s experience is crucial in determining the most
appropriate packing option for the service. This experience should
be used to ensure both long packing life and low leakage rates.
Choosing the correct stuffing box configuration for the fluid being
pumped, its operating conditions, and any Environmental
Protection Agency (EPA) or regulatory requirements are essential to
both emissions’ control and reliability. The most common stuffing
box designs available, with their advantages or disadvantages, are
described below. This serves as a guide when considering the design
options for an application. The pump vendor should assist in
finalizing the design configuration.
This simple design, Figure 15, allows flexibility for various seal
types. Packing may be square, “V” ring, or nonadjustable designs.
The majority of the lubricant migrates into pumped fluid. This con-
figuration can be used on a broad range of fluids. It is particularly
suitable for those fluids that exhibit poor lubricity.
Figure 13. Ball Type Valve.
Largely used in small chemical injection metering pumps, the
design is also well suited for slurry and sludge services. This
design can tolerate solids up to 250 micron in concentrations not
to exceed 40 percent by volume. Use of this design does have a
negative aspect; dependant upon stroke length and pump
product, pump speed should not exceed 50 to 55 percent of
API-674 (1995) limits because of the weight of the ball.
This elastomeric valve type, Figure 14, is best suited for
slurry services (drilling mud, bauxite, borax, and coal). The
design consists of an elastomer fastened to valve head and has
stems extending at both ends to guide it as it opens and closes.
The seating surfaces between the valve and valve seat are
beveled. The elastomer insert conforms around trapped solids to
Figure 15. Standard Lubricated Stuffing Box.
create a tight seal when the valve returns to the valve seat.
Figure 16 illustrates a simple box design that allows flexibility
for various seal types and performs more reliably than a standard
lubricated stuffing box in the majority of cases. This design
allows lubricant to be fed under the last ring of packing. This
area is where the lubrication is most needed to resist the sliding
wear. With this configuration very little lubricant migrates into
the pumped fluid and the design is suitable for the use of low
pressure drip type lubricators. Packing may be square, “V” ring,
or nonadjustable designs.
Figure 14. Elastomeric Type Valve.
Design variation using this principle is available for pressures
between 750 psig (52 barg) and 5000 psig (345 barg). This
design can tolerate solids up to 250 micron in concentrations not
Figure 16. Alternate Lubricated Stuffing Box.

ADVERTISEMENT

00 votes

Related Articles

Related forms

Related Categories

Parent category: Business