U.S. patent number 3,921,435 [Application Number 05/406,043] was granted by the patent office on 1975-11-25 for apparatus for detecting valve failure in a reciprocating pump.
This patent grant is currently assigned to Exxon Production Research Company. Invention is credited to Willis W. Howard.
United States Patent |
3,921,435 |
Howard |
November 25, 1975 |
Apparatus for detecting valve failure in a reciprocating pump
Abstract
A system for detecting early failure of valves employed in
reciprocating pump includes a temperature sensing element
positioned on each valve or on the pump in the immediate vicinity
of each valve, and means responsive to the sensing element for
indicating temperature. An increase in the temperature of one valve
over the temperature of the other valves provides an indication of
valve failure.
Inventors: |
Howard; Willis W. (Houston,
TX) |
Assignee: |
Exxon Production Research
Company (Houston, TX)
|
Family
ID: |
26263847 |
Appl.
No.: |
05/406,043 |
Filed: |
October 12, 1973 |
Current U.S.
Class: |
374/5; 73/168;
73/40; 374/E13.001; 374/E1.005 |
Current CPC
Class: |
F04B
53/10 (20130101); F04B 49/10 (20130101); G01M
3/002 (20130101); G01K 1/026 (20130101); G01K
13/00 (20130101); G01M 3/184 (20130101) |
Current International
Class: |
G01M
13/00 (20060101); G01M 3/18 (20060101); G01M
3/00 (20060101); F04B 53/10 (20060101); F04B
49/10 (20060101); G01M 3/16 (20060101); G01K
13/00 (20060101); G01K 1/02 (20060101); G01K
1/00 (20060101); G01M 003/40 () |
Field of
Search: |
;73/40,49.7,49.2,168 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Queisser; Richard C.
Assistant Examiner: Rasco; Marcus S.
Attorney, Agent or Firm: Graham; Robert L.
Claims
I claim:
1. Apparatus for detecting leakage of fluid past a valve of a
reciprocating pump having at least two suction valve cages and at
least two discharge valve cages mounted externally of the pump body
which comprises:
a. a plurality of temperature sensing elements, one for each pump
valve cage;
b. means for mounting a temperature sensing element on the outer
surface of each valve cage;
c. means responsive to said temperature sensing element for
indicating the temperature of each valve cage; and
d. means for comparing the temperature of each of said valve cages
with the temperature of at least one other of said valve cages.
2. Apparatus as defined in claim 1 wherein said temperature sensing
element is an electric device capable of providing an electric
output indicative of temperature.
3. Apparatus as defined in claim 2 wherein said electric device is
a resistance thermometer and said means for indicating the
temperature includes an instrument electrically connected to said
resistance thermometer and means for visually indicating or
recording the output of said resistance thermometer.
4. Apparatus as defined in claim 2 wherein the means for mounting
said electric device on said pump valve cage includes magnetic
insulating material adapted to magnetically attach each electric
device to its associated valve cage and to insulate said
thermometer from external effects.
5. Apparatus as defined in claim 2 wherein said means for comparing
said temperatures includes a temperature recorder electrically
connected to said instrument for automatically plotting temperature
of each thermometer as a function of time.
6. Apparatus as defined in claim 1 wherein the means for comparing
the temperature of each valve cage includes means for comparing the
temperature of each suction valve with the temperature of at least
one other suction valve cage, and for comparing the temperature of
each discharge valve cage with the temperature of at least one
other discharge valve cage.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to and apparatus for detecting valve failure
in reciprocating pumps.
2. Description of the Prior Art
Reciprocating pumps are useful in the field of high pressure, high
volume operations such as those found in oil well drilling
operations, water flooding operations, and oil well stimulation.
Such pumps normally employ a piston or plunger reciprocated through
a pumping cycle which includes a suction stroke and a discharge
(power) stroke. During each pumping cycle, liquid is drawn through
the pump suction valve into the pump cylinder on the suction stroke
and forced through the pump discharge valve at an elevated pressure
on the power stroke. For the pump to function properly, each valve
must maintain a fluid-tight seal. The reciprocating action of the
pump imposes severe operating conditions on the valves which
greatly shortens their effective lives. They are subjected to
cyclic shock loads, high differential pressures, and abrasive or
corrosive nature of the liquid being pumped. Because of the
tendency of valves to fail repeatedly under these severe operating
conditions, most pumps are designed to permit replacement of valves
or valve parts. The valves are normally mounted in the pump body at
convenient locations accessible through cover plates. Other designs
include external valve pods or replaceable valve cages.
Reciprocating pumps designed for high pressure, high volume
operation normally are high-speed multiplex plunger pumps having
three, five, or more throws or units. Such pumps include a suction
valve and discharge valve for each unit. A triplex pump, for
example, includes three suction valves and three discharge valves
interconnected by a common suction line and a common discharge
line.
The failure of any one of these valves has normally been detected
by a marked decrease in pumping rate or pumping pressure. It will
be apparent that for a valve leakage to appreciably affect the
output pressure or rate, the leakage or backflow through the faulty
valve must be quite high. This means that the flow area past the
valve must be large indicating that the valve or valve seat has
been severely eroded. Such damage normally requires replacement of
both the valve seat and valve which is not only expensive but
frequently is time consuming because of the difficulty in pulling
the valve seat.
Another problem associated with valve failure in multiplex pumps is
that of identifying the faulty valve. The decrease in pumping
pressure or rate indicates valve failure but provides no
identification of the faulty valve. It is not uncommon for the
operator to replace two or more valves before locating the damaged
valve.
SUMMARY OF THE PRESENT INVENTION
The present invention provides a simple and effective system for
detecting and indicating valve failure in reciprocating pumps. A
particularly attractive feature of the system is that it is capable
of detecting and identifying incipient valve failure before the
valve parts have become severely damaged.
The invention relies on detecting an increase in the temperature of
the valve of the pump in the immediate vicinity of the valve.
During the early stages of valve leakage -- that is, before the
flow area past the valve has been enlarged sufficiently to affect
pump rate or pressure -- the heat of friction generated by the
backflow of fluid past the leaking valve is greater than the rate
at which the heat can be dissipated through the metal surrounding
the valve. By monitoring the temperature of the valve or of the
pump in the immediate vicinity of such valve and comparing that
temperature with a normal operating temperature of the pump, valve
failure can be detected almost as soon as the valve begins leaking.
Experience has shown that the temperature increase occurs before
other failure characteristics, e.g. decrease in rate or pressure,
minifest themselves.
In a preferred embodiment, of the invention the system includes a
temperature measuring step performed on each of the pump valves
followed by the step of comparing such temperatures with one
another. Since coincidental failure of two or more valves is
unlikely, the valves which seal provide the normal operating
temperature. A leaking valve will show a marked increase in
temperature over the other valves.
Although the temperature of the suction valves can be measured and
compared with temperature of the discharge valves to provide an
indication of valve leakage, it is preferred that the suction
valves be compared with suction valves and the discharge valves
with discharge valves. Tests have shown that there is a slight
difference in the normal operating temperature of each type of
valve.
The temperature comparison step is preferably performed by plotting
the temperature of the various valves. Any substantial upward
deviation of the plot is indicative of a valve failure.
Also contemplated by the present invention is the step of plotting
the differential temperature. The amount of temperature increase or
differential required to indicate valve failure will depend upon
several factors including the sensitivity of the equipment
employed, the frequency at which the measurements are compared, and
the type of fluid being pumped. For a given system, the normal
temperature deviation can be determined through observing the
thermal behavior of the valves under normal operating conditions.
Any departure outside the limits of the normal deviation provides
indication of possible leakage. For most systems a deviation
increase of about 5.degree.F above the normal operating temperature
will provide a positive indication of valve failure.
The apparatus for detecting valve failure in a reciprocating pump
includes a temperature sensor mounted on each valve or on the pump
in the immediate vicinity of the valve, means for determining the
normal operating temperature of the pump under substantially the
same pumping conditions, and means for comparing the temperature of
each valve with the normal operating temperature. In a preferred
embodiment of the apparatus, the temperature sensing device may
include an electric temperature-sensing element, such as a
resistance thermometer (thermistor) or thermocouple, mounted
externally of the pump in the immediate vicinity of each valve. The
means for comparing the temperatures may include for comparing the
measured temperatures of a particular valve with a normal
temperature or with the temperatures of the other valves on the
same pump. Although the comparision may be by a visual indication,
a plot or record is preferred since it provides a permanent record,
permits determination of normal temperature deviation, and
facilitates detection of temperature deviation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view of a fluid end of a plunger pump
(shown mostly in longitudinal cross-section) provided with
temperature sensing elements.
FIG. 2 is an enlarged, longitudinal sectional view of a mounting
assembly for attaching a temperature sensing element to a pump.
FIG. 3 is a schematic wiring diagram showing circuitry and
instrumentation for monitoring the temperatures of the pump
valves.
FIG. 4 is a plot illustrating the type of record obtainable with
the system of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Although the present invention can be used with most any type of
reciprocating pump, it finds particular advantageous application in
high pressure plunger pumps. For purposes of illustration, the
present invention will be described in connection with such a pump.
As illustrated in FIG. 1, the fluid end of the plunger pump is of
sectionalized construction comprising a cylinder body 10, a
crossbore body 11, a suction valve assembly 12, and a discharge
valve assembly 13. These components are connected together by
coupling assemblies, each illustrated as 14. The coupling
assemblies 14 each include a segmented collar and an internal seal
ring for sealing the joint between the parts joined.
The suction and discharge valves are mounted in valve cages which
are positioned externally of the pump body. The externally mounted
valve cages facilitate valve replacement. Each valve cage includes
housing members 18 and 19 joined by coupling assembly 20. In
assembled condition the housing member 18 and 19 define an internal
chamber which contains the valve parts. As best seen in FIG. 1, the
suction valve includes disc valve 21, valve seat 22, retainer 23
and spring 24 assembled in the conventional manner. The discharge
valve assembly 13 also includes these parts arranged to permit flow
from the crossbore body 11 to the discharge line.
The operation of the pump involves reciprocating the plunger
through a suction stroke and a power stroke. On the suction stroke,
the plunger 16 moves from the broken line position to the solid
line position of FIG. 1, drawing fluid through the suction valve 12
into the pump; on the power stroke the plunger, moving in the
reverse direction, forces fluid out the discharge valve 13 at an
elevated pressure.
In multiplex plunger pumps, the total pump assembly may be provided
with two, three, five, or more throws or units. In such a pump, a
common suction line connects to each of the suction valves and a
common discharge line connects to each discharge valve. The pumps
are normally constructed to operate in timed relation so that the
output pressure is relatively constant.
The disc valves 21 for plunger pumps are normally constructed of
forged steel or alloy and may be provided with leather or plastic
facings or, as illustrated, may be provided with metal facings.
These valves 21 are normally of the flat disc or of the conical
type (also known as skirt or wing valves). The seats 22 may be
forged, heat-treated stainless steel. As evident from FIG. 1, the
contact area between the valve 21 and valve seat 22 is small
relative to the total area subjected to the internal pressure. This
results in extremely high bearing or contact pressures. The high
stresses and cyclic and impact loading on these parts normally
cause the disc valve 21 to fail earlier and more frequently than
other valve parts. If this failure can be detected early, the valve
can be repaired merely by replacing member 21 before erosion damage
to other valve parts or valve housing occurs.
The detection system of the present invention will be described
with reference to a triplex pump, schematically illustrated in FIG.
3. Each of the pumping units similar to the one described
previously and shown in FIG. 1 are connected to a common power end
(not shown). For purposes of illustration the pumping units are
identified by the references A, B, and C; and the pump components,
e.g. crossbore body 11 and suction discharge valves 12 and 13, are
identified by the same reference numerals shown in FIG. 1. It
should be emphasized, however, that the detection system of the
present invention may be used in monoblock constructions or other
pump designs.
The detection system includes a temperature sensing element
positioned in the immediate vicinity of a valve or valve housing of
the pump and means responsive to the sensing element for
determining the temperature of the element.
In the preferred embodiment, the temperature sensing element is an
electrical device such as a resistance thermometer (e.g.
thermistor) or a thermocouple. As schematically shown in FIG. 3,
thermistors are provided on each of the six valves of the triplex
pump. Thermistors are well known temperature sensing devices which
operate on the electrical resistance principle. Thermistors 27 and
30 are on the suction and discharge valve assemblies of unit A,
thermistors 28 and 31 on the suction and discharge valve assemblies
of unit B, and thermistors 29 and 32 on the suction and discharge
valve assemblies of unit C.
The thermistors are electrically connected to instrumentation which
provides an indication of the temperature of each. The thermistors
can be provided with separate temperature gage or recorder. The
instrumentation in this embodiment includes a recorder 35 and a
temperature meter 36, with multiplexer or scanning device 37. Each
thermistor is connected to a channel output of the scanner 37. As
illustrated, thermistors 27, 28, 29, 30, 31, and 32 are connected,
respectively, to channel contacts 38, 39, 40, 41, 42, and 43.
In order for the comparison to be more accurate, thermistors 27-29
are connected in sequence to the first three channels, 38, 39, and
40, and thermistors 30-32 are connected in sequence to the second
three channels, 41, 42, and 43. The empty channels of the scanner
37 may be connected to other temperature sensing elements, as for
example on a second pump.
The scanner rotor 44 is indexed or stepped from one contact to the
next in counterclockwise sequence. The residence or dwell time at
each contact can ve varied depending on the construction of the
instrument. Individual leads interconnect the channel contacts and
the thermistors, and wire 45 electrically connects the rotor 44 to
instrumentation 46 for converting the output of each thermistor to
a value which is indicative of temperature. A suitable instrument
46 is a Wheatstone bridge arrangement in which the thermistor
constitutes one leg of the bridge. The bridge output may be
delivered to a galvanometer or other temperature indicating
instrument 36 and also to recorder 35. Power may be supplied to the
instrument in the form of standard alternating current in which
case the instrument may be equipped with a rectifier for converting
to DC current. The return path from each thermistor connects to
ground wire.
Since the system of the present invention relies on measuring the
temperature generated by frictional flow, it will be realized that
each sensing element should be positioned as close to its
associated valve disc 21 as possible. It has been found convenient
in the pump construction provided with external valves, to position
the sensing element on the external surface of the valve cage. As
illustrated in FIG. 1, thermistor 27 is mounted on the downstream
side of the suction valve 12 and thermistor 30 is mounted on the
downstream side of discharge valve 13. It is preferred that the
sensing elements, e.g. thermistors, be in physical contact with the
metal valve cage and be provided with insulation material to reduce
ambient effects. FIG. 2 illustrates one arrangement for mounting
the sensing device, e.g. thermistor 27, to the valve cage. The
thermistor 27 is embedded in a magnetic composition material which
not only provides an insulation but also serves to maintain the
thermistor 27 in contact with the metal cage. As illustrated, the
magnetic material is arranged in layers, with the lower layer 50
having a hole formed therein conforming to the outer diameter of
the thermistor 27 and the inner two layer 48 and 49 provided with a
slot for the lead wire. The top layer 47 covers the thermistor 27.
The layers 47-50 are cemented or glued together and are preformed
to the surface curvature of the valve cage. The lead from each
thermistor may be a shielded single conductor, the shield providing
the return path to the instrumentation.
Under pumping conditions, the temperature of each of the valve
cages is continually monitored by the scanner 37 and is compared
with a normal operating temperature under substantially the same
pumping condition. The normal operating temperature may be
determined by monitoring all of the valve cage temperatures. Since
coincidental failure of two valves is unlikely, a temperature of
one of the valve cages substantially greater than the temperature
of the other valve cages will indicate valve failure. The amount of
deviation from the normal required to indicate valve failure will
vary depending upon several factors, including the type of pump,
the pumping rate, and the type of liquid being pumped. As a
practical matter, the operator probably will monitor the
temperatures and carefully observe the direction of deviation of a
particular valve cage. With experience, the deviation
characteristics which provide an indication of valve failure for a
particular pump can be ascertained.
Although the normal deviation is dependent upon the accuracy of the
instrument, experience has shown that using the instrument of the
type described above the deviation which provides an indication of
valve failure is about 5.degree.F.
The detection system of the present invention was tested on a
triplex pump of the following description: Plunger size, inches 3.5
Plunger stroke, inches 18 Operating, rpm 140 Crossbore flow
passages, diameter, inches 1.6 Valve size, inches 2.0 Valve type,
skirted disc Valve material steel with plastic facing
A thermistor probe manufactured by Yellow Springs Instrument
Company and sold under the trade designation YSI Series 400, probe
number 409, described as "attachable surface temperature" was
selected as the thermistor probe for each of the valves of the
triplex pump. The probes were mounted in magnetic stripping
material which was purchased from Bickley Equipment Company of
Houston, Texas. This particular arrangement was quite convenient in
that it permitted the probes to be mounted on the pump without
modifying the pump in any way and it also permitted removing or
relocating the probes if necessary. The lead wire was type 9770
manufactured by Beldon. the scanner and bridge circuits were
provided by a YSI Model 47 "Scanning TeleThermometer" manufactured
and sold by Yellow Springs Instrument Company, Inc. Of Yellow
Springs, Ohio. This instrument provided a meter calibrated in
degrees F. from 60.degree. to 200.degree.F. The indexing mechanism
was operated electrically and provided settings of 20 seconds,
11/2minutes, or five minutes for each of the eleven channels. This
instrument operates on standard 110 volt power. In the initial test
of the equipment, a recorder was not used. The temperatures were
visually observed from the meter during the sequencing of the
scanner. However in order to describe the thermal behavior of the
pump valves under various conditions, reference is made to the plot
of FIG. 4. This plot represents a strip chart recorder driven at 5
inches per minute. The ordinate of the plot is scaled in .degree.F
and the abscissa in time (minutes). The .DELTA.t represents the
dwell time of the rotor at each channel which, as indicated above,
may be varied. Initially, the instrument will provide an
identification channel which in the YSI Model 47 instrument is
calibrated at 60.degree.F. The record of the identification
temperature is shown at 51 on the plot. During initial operation,
the pump valves will probably be in good working condition so that
variations in temperature thereof will be within the normal
expected deviation which is a function of the accuracy of the
instruments. As the rotor 44 indexes through channels 38-43 the
temperature of each thermistor will be recorded. Thus, the lines
indicated 52-57 represent one cycle through channels 38-43, with a
dwell time .DELTA. t at each setting. The rotor 44 may continue or
may reset to repeat the cycle. During the first cycle through the
channels, the normal variation of temperature between the
thermistors is indicated by .DELTA.T.sub.1. The normal variation as
mentioned above will depend upon the accuracy of the instruments,
but it should be within about 5.degree.F.
To illustrate the effects of changes in ambient conditions or
changes in the temperature of the liquid being pumped, another
cycle is indicated at a time subsequent to the first cycle. These
temperature ranges are represented by numerals 61-66, and again
represent the temperature of the thermistors 27-32 at the new
pumping conditions. Here again the normal variation in temperature
is within the expected range of .DELTA.T.sub.1. It will be
appreciated that experience will determine the value of the normal
deviation or distribution and will determine the limits. If the
temperature of any thermistor does not deviate from this normal
value, the operator can be reasonably certain the valves are
functioning properly. A valve failure will produce a record similar
to that shown in the third cycle which is at a time subsequent to
the second cycle. As illustrated, the values 67-70 and 72 of the
thermistors mounted on the valves of units A and C are within the
normal data distribution range (.DELTA.T.sub.1) indicating that
these valves are functioning properly. However, the temperature
value 71 of channel 42 has increased well above the normal
deviation indicating that the discharge valve of the second unit,
B, has failed. The value of .DELTA.T.sub.2 was about
10.degree.F.
It should be realized that the temperature increase of a faulty
valve will not, under most conditions, increase markedly from one
cycle to the next, but will show only a slight deviation. However,
the trend will always be upward, whereas in a properly functioning
valve, the deviation will fluctuate; that is, the temperature will
increase and decrease within the normal distribution range.
Modifications of the improved apparatus include use of other types
of thermometers or mounting means. Thermocouples positioned on the
surface of the pump or in suitable thermowells in the pump
represent one alternative embodiment. Other alternatives will be
apparent to those skilled in the art.
* * * * *