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.

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.

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.