Backflush filter system for downhole pumps

A well rod pump having a filter system to remove particulate material from the fluids produced from the well and an automatic back flush system using pumped fluid to flush particulate material from the filter system in response to increased pressure differential across the filter system, including a rod moved by a piston to open the valves of the pump, and a time delay connected to continue to hold the valves open for a period sufficient to allow back flushed particles to settle in the well. Well treatment chemicals may be injected into the well with the back flushing fluid.

BACKGROUND OF THE INVENTION 
The present invention relates to the field of pumping of oil well fluids 
from a downhole location in an oil well to the surface adjacent the well. 
More particularly, the invention relates to the protection of the pump 
from well bore solids that can abrade or jam the pump. More particularly 
still, the invention relates to the filtration of solids from the well 
bore fluid by filter media prior to the entry of the fluids into the pump, 
and the downhole cleaning of the filter media to limit the need to remove 
the pump and filter from the well bore to replace or clean the filter 
after the filter has restrained amounts of the solid particulates 
sufficient to reduce its capacity. 
Downhole pumps are placed in well bores to pump well fluids from a location 
within the well bore upward to the surface. Such pumps provide the energy 
to lift the well fluid where the natural well pressure is too low to force 
the well fluid to the surface. One major consideration in the cost of 
producing oil from low production wells is the cost of lifting the well 
fluid to the surface. The lifting cost is a function of original equipment 
cost and the cost to run, and maintain or replace the equipment, and the 
cost to service the well and equipment. Pumping costs are a major 
contributor to production costs, and marginally producing wells are 
commonly abandoned because the overall cost of pumping, including 
equipment maintenance, is too high in comparison to the value of any oil 
produced from the well. This is particularly true where the well is 
pumping from a formation which gives up produced fluid with a high 
abrasive particulate content. These abrasives tend to migrate with the 
well fluid into the pump, and contribute to high pump wear and 
maintenance. As a result of the presence of these particulates, rapid 
abrasive damage can occur on the precision pump surfaces, particularly on 
the critical interface of the plunger with the barrel. Additionally, many 
other pump components, such as critical valves, abrade in the presence of 
the particulates, which leads to inadequate pump performance. As a result 
of this wear and damage, the pump must be pulled out of the well to be 
repaired or replaced. Removal and reinsertion of the pump may take several 
hours, or several days, at significant cost to the well operator. The more 
abrasive the well fluid, the more often the pump must be pulled for 
servicing and repair. 
U.S. Pat. No. 4,969,518, Schmitt, et al., fully incorporated herein by 
reference, discloses a significant improvement in pump structure that 
permits a significant increase in pump downhole time, i.e., the length of 
time the pump remains in the hole pumping, before it must be removed for 
service. This improvement is provided by a filter member having tortuous 
paths therein that decrease in size from the well side to the pump side of 
the filter. Additionally, the filter includes a trip member that allows 
fluid to bypass the filter if the filter should become clogged while still 
in service. This filter provides substantial protection to the pump, and 
permits the pump to remain in the well bore for longer periods without 
service or replacement, and thus lowers the cost of pump maintenance, 
repair or replacement. 
Despite the technological advance of the invention described in U.S. Pat. 
No. 4,969,518, there was still a need to pull the pump after the filter 
media capacity is reduced by becoming clogged, or loaded. For example, on 
a well in Wyoming with a history of requiring pump repair every 7 days, 
the filter media of the '518 patent increased the pump downhole time to 
214 days. However, despite the tremendous decrease in lift cost associated 
with such an increase in downhole time, the pump still has to be removed 
for filter replacement and pump inspection/service. 
The invention of my copending application Ser. No. 08/100,612, filed Jul. 
30, 1993, now U.S. Pat. No. 5,413,721, the disclosure of which is 
incorporated herein by reference, provided a significant improvement over 
the '518 invention. That invention provided a downhole cleaner which, in 
cooperation with the pump, forces well bore particulates outwardly from 
the filter upon a preselected reduction in filter efficiency exhibited by 
a preselected pressure differential across the filter media of the filter, 
which cleans the filter in place in the well bore and permits continued 
use of the filter and pump without the need to pull the pump to clean or 
replace the filter. 
In this invention, however, in some installations it was necessary or 
desirable to stop the sucker rod pump after the filter was cleaned for 
long enough to make sure that particles forced from the filter had time to 
settle to the bottom of the well bore and thereby avoid starting flow of 
well bore fluids which still contained a high proportion of particulate 
matter. This required the presence of an operator at the surface to turn 
the pump off and on or the use of special surface equipment to 
automatically delay the initiation of pumping operations. 
SUMMARY OF THE INVENTION 
The present invention integrates a back flush filter system with a rod pump 
to form a new rod pump system which automatically flushes particulate 
material from the filter, at the same time holding open both the standing 
valve and the travelling valve, and automatically holding them open for a 
long enough time to insure that high pressure fluid in the production 
tubing can clean the filter. After flushing the particulate material from 
the filter, the pumping system continues a pre-calculated dwell sequence 
that allows the discharged particles to settle into the rat hole. When the 
dwell timing mechanism senses the completed cycle, it automatically 
returns to normal pumping operation.

DESCRIPTION OF THE EMBODIMENTS 
FIG. 1 illustrates a conventional pumping jack 22 with a polish rod 24 
suspended from the pumping jack and extending downwardly through a 
wellhead 20 and well tubing 18 within the casing 16 of an oil well. The 
polish rod is connected to a string of sucker rods 28 which in turn is 
connected to a sucker rod sub 30. The sucker rod sub reciprocates a 
plunger rod 32 within the barrel 40 of a sucker rod pump to induce well 
fluids to flow upwardly through the barrel and the tubing to be produced 
through the wellhead 20 at the surface of the ground. The pump is 
supported in the tubing by a hold-down unit 14, and an automatically 
operated filter cleaning unit 10 is supported below the hold-down unit. 
As will be later described, the barrel of the pump contains a reciprocable 
pump plunger, standing and traveling valves, a reference cell, and a 
trigger sub for operating the reference cell to mechanically open the 
traveling valve. 
Below the pump barrel is a filter section 50 for filtering well fluids that 
are produced through the pump and below the filter section 50 is engine 
section 60 which provides power for operating the reverse flush operation. 
Connected below the engine section is a sensor valve assembly 70 which 
responds to differential pressure to cause the reverse flushing operation. 
A sensor valve filter 80 attached to the lower end of the sensor valve 
completes the assembly. 
Reference is now made to FIGS. 2A to 2F for a detailed description of one 
embodiment of the system of this invention. 
As seen in FIG. 2A, the sensor valve filter 80 consists of one or more 
annular permeable members having perforations through which well fluid may 
flow but which will filter out a major portion of particulate material 
which may be carried with the well fluid. The sensor valve filter is 
threadingly connected to a coupling 71 which forms the lower end of the 
sensor valve assembly 70. The coupling is threadingly connected to a 
tubular housing member 90 which contains the sensor valve assembly 70 and 
the engine section 60. The upper end of the coupling 71 has an axial 
passageway 72 and a cup shaped counterbore 73 which is proportioned to 
receive an annular valve seat 74. A tubular sensor valve assembly housing 
76 is mounted concentrically on the coupling and extends upwardly 
therefrom to a valve head 77. The housing 76 is substantially 
concentrically disposed within housing member 90, leaving an annular space 
76a between them. Fluid communication is provided between the annular 
space 76a and the interior of coupling 71 by ports 71a in the upper wall 
of the coupling. A spool valve 75 is longitudinally slidably received 
within the housing 76 and includes at its lower end a ball valve 78 which 
is retained in sealing engagement with the valve seat 74 by means of a 
compression spring 79 which extends between a shoulder on the spool valve 
and the lower end of the valve head 77. The ball valve is sealably 
retained within a counterbore in the lower end of the spool valve, the 
seal being provided by any suitable means as for example, an O-ring. The 
spool valve is provided with one or more radial openings 79a and the 
sensor valve housing 76 also has one or more corresponding radial openings 
81. The spool valve has a length which is less than the distance between 
the end of the coupling 71 and the lower end of the valve head 77, the 
difference in distance being substantially equal to the longitudinal 
distance between the centers of the spool valve radial openings and the 
valve housing radial openings, so that when the spool valve moves to the 
upper end of its allowed movement the radial openings are aligned. 
Radial openings 82 are provided in the upper end of the coupling to provide 
a fluid path from the interior of the coupling into an annulus 83 between 
the tubular housing member 90 and the sensor valve housing 76. 
The engine section 60 is slidably received within the housing 90 above the 
sensor valve assembly 70. The engine section consists of axially extending 
elements comprising a piston 85, a cage 86 connected to the piston, a 
metering orifice seat 87, received within the lower end of the cage, and 
an annular seat retaining plug 88, having a cavity 88a therein, attached 
to the lower end of the cage 86 and securing the metering orifice seat in 
place. The metering orifice seat is provided with an orifice 89 
therethrough to conduct fluid between the interior of the cage 86 and the 
bore of the seat retaining plug 88. As seen in FIG. 2B, an upper cage 91 
is threadingly connected to the upper end of piston 85 and is provided 
with radial openings 92 to provide fluid communication with a cavity 93 
which is between the engine section 60 and the filter section 50. An 
actuator rod 32 extends upwardly from the upper cage 91 through the filter 
section 50. The filter section is mounted on a coupling 31 which is 
threadedly engaged with the upper end of engine housing member 90. At its 
lower end the connector 31 is provided with a rod guide 29 which has 
openings 30 therethrough for fluid communication between the cavity 93 and 
the interior of the inner perforated tube 33 of the filter section 50. The 
collar 35 is preferably provided with an O-ring 37 or other suitable seal 
to sealingly engage the rod 32 to prevent fluid flow through the collar 
between the interior of the filter section and the space above the collar. 
The filter section comprises an inner perforated tube 33 threadedly engaged 
at its lower end with a connector 31 which is in turn threadedly connected 
to the tubular housing 90. At its upper end the inner tube 33 is connected 
to a collar 35 which slidably engages the actuator rod 32 which extends 
axially of the collar. An imperforate shroud 34 surrounds and is spaced 
away from the inner perforated tube, and is also connected at its upper 
end to the collar 35. The shroud extends downwardly from the collar 35, 
terminating above the connection of the inner perforated tube 33 to the 
coupling 31, but below the lowest extent of the apertures in the inner 
perforated tube, thereby allowing fluid communication between the exterior 
of the shroud and the exterior of the inner tube. One or more permeable 
filter elements 36 surround and are spaced away from the shroud 34, the 
filter elements being connected at their lower end to a coupling 38 and at 
their upper end to another coupling 38a (See FIG. 3C) which is spaced 
upwardly above coupling 35 to allow fluid communication between the 
annulus intermediate the filter elements 36 and the shroud 34 and the 
interior of the coupling 38a. 
The coupling 38a is connected to a pump hold-down assembly 14 which 
comprises a plurality of upwardly facing cup seals 40 for sealingly 
engaging the bore of the tubing in which the pumping system is installed 
and holding the pumping system in place. A mandrel 95 is provided on which 
the cup seals are mounted between rings 96, 97 and locknut 98, the mandrel 
being threadingly engaged with locknut 98 and with a coupling 99 which is 
connected to coupling 38a. 
The upper end of the mandrel 95 is threadingly engaged with a standing 
valve housing 100 and retains a standing valve seat 101 against an annular 
shoulder 102 within the standing valve housing. The standing valve 103 
seats on the seat 101. A trigger sub 104 is longitudinally slidably 
received within the pump barrel 40 above the standing valve and has a 
downwardly facing cup shaped cavity 105 proportioned to receive the 
standing valve ball when the valve is opened. The trigger sub is also 
provided with two guide elements 106 which slidingly engage the 
surrounding housing and which are provided with longitudinal grooves 107 
to allow fluid passage longitudinally around the trigger sub. The upper 
end of the trigger sub has a flat hammer face 108, as seen in FIG. 2D. 
The hammer face 108 is positioned to engage the lower end of a push rod 109 
upon upward movement of the trigger sub 104. The push rod 109 is centrally 
disposed within a reference cell 110 which is suspended from a pump 
plunger cage 111, and is the lowest element in the reciprocable pump 
plunger suspended from the sucker rod string 28. 
Reference cell 110 is received within the pump barrel 40 and comprises a 
tubular housing 112 having a diameter less than the inside diameter of the 
barrel to form an annular space 113 therebetween for passage of well 
fluid. The housing 112 is closed at the lower end by a bottom plug 114 and 
at the upper end by an upper plug 115. Each plug has a central bore 116 
dimensioned to fit closely around the push rod 109. O-rings 117 between 
the rod and the bore provide a fluid-fight seal to prevent fluids from 
leaking into or out of the reference cell. The upper plug includes an 
upwardly extending tubular portion 115a which is threadedly engaged with 
the pump plunger cage 111 to provide support for the reference cell. Ports 
115b in the tubular portion allow fluid flow from the annulus surrounding 
it to the plunger cage. The reference cell is filled with a viscous fluid 
whose viscosity is substantially unaffected by temperature variations 
within the usual range of temperatures encountered in oil and gas wells. 
Within the reference cell, two metering spools 118, 119 are mounted on the 
push rod 109. Spool 118 is held in a fixed position on rod 109 by 
retaining tings 120, which may be conventional snap tings. Spool 119 is 
slidably positioned on the rod, and is resiliently biased upwardly into 
engagement with spool 118 by a spring 121 which is supported on another 
retaining ting 120 and a washer 122. Axial ports 123 allow fluid flow 
through spool 118, and smaller axial metering ports 124 allow fluid flow 
through spool 119. Spool 118 sealingly and slidingly engages, by means of 
seals 125, which may be O-rings, the inside wall of the housing 112, and 
also sealingly engages, by means of seal 126, which may be an O-ring, the 
rod 109. Spool 119 slidingly engages both the interior of housing 112 and 
the rod 109, but need not be sealed with respect to either. A compression 
spring 127, which may be a coil spring, extends from the upper plug 115 to 
the spool 118, biassing the spool downwardly. A stop 128 extends 
downwardly from the upper plug. 
Pump plunger cage 111 may be a conventional plunger pump cage freely 
movable within the barrel 40 and having a ball seat 129, held in place by 
the upper end of the tubular extension 115a of the upper plug 115, and a 
ball valve 130, forming a conventional travelling valve, which in closed 
position inhibits flow of fluid from above the travelling valve to below 
it. Pump plunger 131 is threadedly connected to the upper end of the cage 
111 and comprises a conventional pump plunger which sealingly engages the 
inside diameter of the barrel 40. As seen in FIG. 2E, the upper end of the 
pump plunger is connected to a transition sub 132 which connects the pump 
plunger to the plunger rod 32. The transition sub is provided with ports 
133 which allow flow of fluid between the bore of the pump plunger and the 
bore of the barrel 40 above the pump plunger. As shown in FIG. 2F, the 
plunger rod is connected to the sucker rod sub 30. 
Operation 
The operation of the pumping jack 20 causes reciprocation of the polish rod 
22, which in turn reciprocates the pump plunger 131. The pump plunger is 
connected to the reference cell 110, so it is reciprocated as well. As the 
pump plunger moves downwardly within the barrel 40, well fluids in the 
barrel lift the ball valves 130 and 103 off their respective seats. As the 
pump plunger moves upwardly, the ball valves are seated, and fluid above 
the travelling valve 130 is lifted up the length of the stroke of the pump 
plunger, thereby producing well fluids at the well head 24, while at the 
same time allowing additional well fluid to flow into the barrel from the 
filter section 50, by means of the openings in the permeable falter 
elements 36 and the annulus between the filter elements and the shroud 34, 
passing upwardly around the collar 35 and through the packoff mandrel 95. 
As well fluids flow into filter section 50, sand and other solid particles 
carried with the well fluids are restrained by the falter elements 36, 
with the particulate material either adhering to the exterior of the 
filter elements or being caught within pores. In time, with continued 
loading of particulate materials, the filter elements will begin to plug 
up and restrict flow of well fluids, creating a pressure differential 
across the filter elements during upward strokes of the plunger, so that 
the pressure of the well fluids within the pumping system is significantly 
less than the pressure of the well fluids in the well tubing surrounding 
the pumping system. 
The well fluid within the falter section is in communication with the 
interior of the engine section 60 and the interior of the sensor valve 
assembly 70, through the orifice 89, so that a reduction of the pressure 
in the falter section also reduces the pressure holding the ball valve 78 
on its seat 74, causing a pressure differential across the ball valve 
which tends to lift it off the seat. When the force of this pressure 
differential exceeds the load of the spring 79 the ball valve is lifted 
off the seat, allowing tubing pressure, i.e. the pressure of the well 
fluid surrounding the sensor valve assembly, to be applied against the 
lower end of the spool valve 75. The area then exposed to tubing pressure 
is much greater, preferably five to ten times greater, than the area of 
the ball exposed to tubing pressure when it is seated. Thus the 
differential pressure is great enough to move the spool valve 75 upwardly 
until it engages the lower end of valve head 77. This movement brings 
radial openings 79a into alignment with radial openings 81. Well fluid may 
then flow from the tubing bore through the filter 80, the ports 71a, the 
annular space 76a, the sensor valve ports 79a and 81, the interior of the 
sensor valve and the cavity 88a in the seat retaining plug 88. The purpose 
of the orifice 89 is to relieve pressure surges from below the piston, so 
the orifice is small enough that there is a substantial pressure 
differential across the metering orifice seat, applying an upward force 
against the seat retaining plug 88 sufficient to move the engine piston 85 
upwardly and thereby move the actuating rod 32 upwardly to engage the 
valve ball 103 of the standing valve and lift it off the valve seat 101. 
The actuating rod 32 continues upwardly to engage the top of the cavity 
105 in the trigger sub 104, and then lifts the trigger sub upwardly until 
its upper end 108 is in a position to engage the push rod 109 on the next 
downward stroke of the pump plunger, moving the push rod upwardly with 
respect to the plunger until the upper end 108 of the trigger sub engages 
the lower plug 114 of the reference cell, so that the load of the pump 
plunger is exerted against the trigger sub. The upward movement will also 
cause the upper end of push rod 109 to move upwardly within the reference 
cell 110 to engage ball valve 130 of the travelling valve. The push rod 
109 continues to move upwardly, carrying the metering spools 118, 119 
upwardly through the viscous fluid within the tubular housing 112. Spool 
119 will separate from spool 118 during this upward movement, against the 
force of spring 121, allowing the viscous fluid to flow comparatively 
freely downwardly through the larger ports 123 in the upper spool 118, 
until the upper spool engages the stop 128. The travelling valve is 
therefore opened and held open, allowing well fluid in the barrel above 
the plunger pump to flow downwardly through the annulus around the 
reference cell 110, past the trigger sub 104, through open standing valve 
seat 101 to the filter section 50 and through the outer permeable filter 
elements 36 to dislodge particulate material. The particulate material 
then falls to the bottom of the well. 
When the metering spools in the reference cell are at the limit of their 
upward travel, the spring 121 closes spool 119 against spool 118, so that 
the viscous fluid can flow upwardly past the metering spools only through 
the smaller axial metering ports 124 in spool 119. Spring 127 biases the 
metering spools downwardly, and the force of downwardly flowing well fluid 
on push rod 109 also urges the metering spools downwardly. Such downward 
movement is restricted by the metering spools, and the flow of the viscous 
fluid through the metering ports acts to determine the time that the push 
rod bears against valve ball 130 and holds the ball off seat 129. This 
timing is a function of the viscosity of the fluid within the reference 
cell 110 and the size of the metering ports, as well as the weight of the 
push rod and the head of well fluid above the reference cell. Well fluid 
will continue to flow downwardly until the push rod 109 is retracted so 
that the travelling valve 130 can close. This back flushing of the filter 
elements may continue for only a few seconds, or for one or more cycles of 
the pump, depending upon the designed characteristics of reference cell 
elements, such as the size of the ports in the metering spool 119, to 
insure that the particulate material washed from the filter elements falls 
downwardly well below the filter section before the pump begins pumping 
again, to avoid picking up the same particulate material. 
Downward movement of push rod 109 is restricted so long as it is being 
engaged by the trigger sub 104. However, when the back washing of the 
permeable elements 36 is begun, the fluid pressure of the well fluid 
within the pump is applied to cause fluid flow also around the shroud 34 
in the filter section 50, and through the perforated tube 33, down through 
the engine section 60. This eliminates the pressure differential holding 
the engine piston up. Pressure differential across the sensor valve 
assembly 70 will also be eliminated, so the spring 79 can push the ball 
valve 78 to closed position, ready for the next actuation cycle when the 
permeable elements of the filter section are loaded again. With no 
pressure differential to hold it up, the weight of the piston 85 will 
cause it to tend to move downwardly. However, the rate of downward 
movement is controlled by the size of orifice 89, through which fluid 
below the piston must flow to allow the piston to move downwardly. The 
rate of movement may therefore be designed in by means of the size of the 
orifice. Downward movement of the piston will retract actuator rod 32 so 
that it will no longer resist downward movement of push rod 109, and will 
allow standing valve ball 103 to seat. The sensor valve and the orifice 89 
are dimensioned so that the downward movement of the piston and the 
resetting of the sensor valve occur after the backwash cycle is completed. 
It is important that when a backwash cycle is initiated, the upward force 
on the spool valve 75 is in excess of that required to hold the valve 
fully actuated, even with pressure differential fluctuations resulting 
from well fluid entering the spool valve, so that the force is sufficient 
to lift the engine piston 85. The fluid entering the spool valve reduces 
the pressure differential almost as soon as it is applied, and must 
increase in pressure enough to force the piston 85 upwardly. It has been 
determined that a ratio of the opening force to the force required to hold 
the spool valve in fully opened position is preferably five or ten to one. 
Thus, if the differential pressure is 100 psi, and a ratio of five to one 
is used, the spool valve will not return to its closed position until the 
pressure differential drops to 20 psi. Neglecting fluid frictional losses, 
80% of the differential pressure is therefore available to do the work of 
actuating the engine piston while still maintaining the spool valve in 
open position. It can be readily seen that the higher the ratio of the 
sensor valve, the higher the operating efficiency and percentage of energy 
delivered from the well bore is available to actuate the engine piston. 
As previously noted, the viscous fluid used in the reference cell 110 is 
substantially viscosity stable at normal well operating pressures at 
temperatures typically ranging from 50.degree. to 300.degree. F. Such 
stability is an important factor in proper functioning of the reference 
cell. A synthesized silicone based oil, such as Dow Corning 200 Fluid @ 
500 CS, produced by Dow Coming Company, has been found to be satisfactory 
for this purpose. Other fluids may be used as the application may warrant, 
provided they achieve the necessary viscosity stability. 
FIG. 3 shows an alternative structure for the metering orifice 89 shown in 
the engine section in FIG. 2A. In this embodiment metering orifice seat 87 
is replaced by a ball valve seat 187 having one or more bypass orifices, 
such as orifices 188. A ball check valve 189 rests on the seat, and cage 
190 is biassed downwardly against the ball by a spring 191 which engages a 
flange 192 of the cage. The ball check valve and spring pressure are sized 
to hold the valve closed under the force required to actuate the engine 
piston, but to allow the valve to open when a pressure surge is incurred. 
An upper extension 193 of the cage guides it to maintain the cage wings 
194 in proper contact with the ball. This structure functions to relieve 
pressure surges on the sensor valve assembly which may occur when the 
trigger sub strikes the reference cell. Such a pressure surge could result 
in premature closing of the sensor valve. 
FIG. 4 provides an alternative structure for the inner perforated tube 33 
and the shroud 34. The perforated tube 33 is replaced by a tube 133 which 
extends upwardly from rod guide 29 and terminates below rod guide 35A. 
Tube 133 has a cup-shaped cover 137 slidably mounted on its upper end, the 
cover being provided with radial ports 138 through which fluid may flow 
when the cover is in its upper position. Seal 141, which may be an O-ring, 
provides sealing engagement of the cover with the actuator rod 32. When 
there is sufficient differential fluid pressure below the cover within the 
tube, the cover slides upwardly the distance allowed by pins 139 which 
slide in slots 140 in the upper extension, so that the ports 138 are above 
the top of the upper extension. When there is no such differential 
pressure, as during normal operation of the pump, this alternative design 
will prevent dirt or sand from falling into the engine piston. 
The apparatus and method of this invention may also be used in conjunction 
with well treatment with chemicals, providing automatic injection of 
chemicals. A chemical container 134, as shown in FIG. 1, may be connected 
to the well head 24 with a hose 135 from the container inserted so that 
the vacuum generated in the well head will pull chemicals from the 
container each time the filter is back washed, to inject the chemicals 
into the well. 
In the preferred embodiment, permeable filter elements 36 are precision, 
stainless wire wrapped, perforated tubes which, through subsequent 
processing and metallurgical fusing creates a rugged highly permeable 
precision tubular membrane. This precision membrane possesses many 
desirable qualities for the application including low well fluid passage 
pressure drop across a broad range of viscosities encountered in petroleum 
production wells. This filter membrane also performs efficiently with 
regard to its release of the built up particulates upon back flush 
cycling. The commercially available embodiment of this preferred filter 
media membrane is sold by Stren Company of Houston, Texas under its 
trademarks "PumpCard" and "HiFlo Precision Stainless Steel Cartridge 
System." These cartridges presently are in use in PumpCard.TM. tools sold 
by the aforementioned Stren Company in successful service to the petroleum 
production industry. They are presently being serviced, when they become 
loaded and require retrieval from the well for cleaning, by washing them 
off, commonly with a pressure washer water spray at the pump repair shop. 
This precision stainless cartridge type may be preferably used with or 
without an outer perforated protective sleeve placed over the precision 
membrane. These cartridges are generally available in filtration ratings 
of 25 and 50 microns, and may be additionally manufactured at a broad 
range of micron ratings, as may be desirably employed for the range of 
well fluid conditions to be pumped. The permeable filter elements 36 could 
also be media bodies having small tortuous passages therethrough having a 
nominal size of about 0.0004 inches, which narrow as they pass through the 
elements 36 from the outside to the inside. Another product which can be 
used is a casting of acrylic fibers impregnated with phenolic resin, with 
the passages formed therein formed randomly therein during casting. One 
suitable product is sold by Cuno, Inc. of Meridian, Conn. and identified 
by the registered trademark "Micro-Klean." The permeable filter elements 
36 may include grooves cut therein to increase the number of passages 
extending through filter portion 40. Other filtering media, including 
screening, may be used. Tubular screens of the "V-Wire" and other profile 
wire types as sold by Johnson Filtration Systems, Inc. of St. Paul, Minn., 
and other brands may be used as may be desirable under certain conditions. 
Perforated tube 33 may be made of the same material as the permeable 
filter elements 36, and typically is of finer micron rating to exclude 
particulates from entering the engine cavity. 
The overall pump configuration described is classified, under American 
Petroleum Institute specifications for rod pumps entitled "API 11 AX", as 
an "RHBE insert" type of pump. However, the invention is also applicable 
to other rod pumps of typical designations such as RWBC, tubing pumps and 
the like. In addition, the concept of the invention is also applicable to 
other types of pumps. 
Several embodiments of the invention are shown and described, but the 
invention also includes all variations within the scope of the appended 
claims, and equivalents thereof.