US 3916449 A
An implantable Starling-type heart pump which may be adapted for use as a total artificial heart, or as a single ventricle device replacing one side of the heart. A rigid case, mounting blood input and output valves, houses a variable displacement piston pump. A separate spool-type pump control valve assembly directs motive force from a power source which may be gas or other fluid pressure, electro-mechanical or heat energy conversion for alternately initiating piston retraction and extension upon receipt of a signal pulse from the piston pump itself. Blood chamber displacement is a function of pressure and available blood volume.
Claims available in
Description (OCR text may contain errors)
Umted States Patent [191 [1 1 3,9 Davis Nov. 4, 1975  Inventor: Paul Knight Davis, Alemeda, Calif. Artificial lntracorporal Heart, by F, W. Hastings et 73 Assignee; P ifi Roller Die Co Inc" al., Transactions A.S.A.I.O., Vol. 7, 1961, pp.
Hayward, Calif. A Servomechanism to Drive an Artificial Heart In-  Flled' 1974 side the Chest, by K. W. Hiller et a1., Transactions, 2 APPL 525 31 A.S.A.I.O., Vol. 8, 1962, pp. 125-130.
Related Application Data Primary ExaminerRonald L. Frinks  Continuation of Ser. No. 312,668, Dec. 6, 1972,
abandoned. 57 TRAC An implantable Starling-type heart pump which may  U.S. Cl. 3/l.7, 128/205 Rial/733,95, be adapted for use as a total artificial heart or as a ] Int Cl 2 A61F 1/24 single ventricle device replacing one side of the heart.  Fieid S D DIG 3 A rigid case, mounting blood input and output valves, /21 M7689 3 houses a variable displacement piston pump. A separate spool-type pump control valve assembly directs References Cited motive force from a power source which may be gas or other fluid pressure, electro-mechanical or heat en- UNITED STATES PATENTS ergy conversion for alternately initiating piston retrac- 3,182,335 5/1965 Bolie 3/ 1.7 tion and extension upon receipt of a signal pulse from ,6 1970 y the piston pump itself. Blood chamber displacement is 3,568,214 3/1971 Gddschmled a function of pressure and available blood volume. 3,633,217 l/l972 Lance 3,783,453 1/1974 Bolie 3/1 7 18 Claims, 24 Drawin Figures 120 76 22 -4 I 75 77 34 88 l 9 35 8 ,V 86 23 "H Z5 7 I I 6 30 4 H l i & a 4737 '5 85 i 50 5s 53:-5 1 i l :63 I 101- 7 39- 5Z ii i s A 67 t a 60 j US. Patent NOV.4, 1975 Sheet 1 of 15 3,916,449
U.S, Patent Nov. 4, 1975 Sheet20f 15 3,916,449
US Patent Nov. 4, 1975 Sheet3of 15 3,916,449
II I FIE:- -F5- US. Patent Nov.4, 1975 Sheet50f 15 3,916,449
Sheet 6 of 15 US. Patent Nov. 4, 1975 U.S. Patent Nov. 4, 1975 Sheet 7 of 15 3,916,449
US. Patent Nov. 4, 1975 Sheet8of 15 3,916,449
US. Patent Nov. 4, 1975 Sheet 9 of 15 w 185 183 6 W J o a FIG- .13.
U.S. Patent NOV.4, 1975 Sheet 10 of 15 3,916,449
FIE- -14- U.S. Patent Nov.4, 1975 Sheet110f15 3,916,449
U.S. Patent Nov. 4, 1975 Sheet 12 0f15 3,916,449
U.S. Patent Nov. 4, 1975 Sheet 13 of 15 3,916,449
U.S. Patent Nov.4, 1975 Sheet 14 0f 15 3,916,449
FIE--ZCI- FIG- .15].
60 5TKOKE5 PER MIN. """"IZO STRUKES PER MIN.
U.S. Patent NOV.4, 1975 Sheet 15 of 15 3,916,449
IMPLANTABLE HEART PUMP This is a continuation of application Ser. No. 312,668, filed Dec. 6, 1972 and now abandoned.
BACKGROUND OF THE INVENTION This invention relates to prosthetic devices, and more particularly to a Starling-type heart pump which in alternate forms is utilizable either as a total natural heart replacement or an assist device in conjunction with the natural heart.
Hertofore, various forms of artificial blood pumps have been developed falling into either heart assist device or total artificial heart categories. Heart assist de vices have been developed for supplementing the pumping action of either the left or right ventricles of the heart. However, the left ventricle is more subject to failure, since it ejects blood to the aorta, works against the resistance of the whole circulatory tree and performs several times the work or pumping action of the right ventricle emptying into the less resistant pulmonary sytem.
One of the known heart assist devices is designed to operate in parallel with the left ventricle through connection between the left atrium and the descending aorta, and comprises a rigid tubular housing within which is a flexible tube or bladder having valves at each end. Air pulses introduced between the rigid and flexible tubes intermittently contract and expand the flexible tube for pumping blood within the inner tube. A variation of this in parallel assist device utilizes a diaphragm-operated pumping chamber actuated by air pulses for pumping blood from the left ventricle to the aorta. Another existing form of air pulse driven in parallel assist unit is designed to be connected between the apex of the left ventricle and the descending aorta. US. Pat. No. 3,550,162, to Hoffman et al. discloses a form of assist device of the general type discussed.
A known form of in-series assist device is connected between the ascending and descending parts of the aorta, with the ascending aorta interrupted between the points of connection. In similar fashion to the parallel type devices, it is operated by air pulses and pumps blood within an intermittently expanded and contracted flexible tube. All such assist devices are capable of performing only a part of the workload of the defective side of the heart, will stall in the absence of appreciable blood volume and pressure in the left heart chamber and therefore are incapable of serving as a temporary or permanent replacement for the left or SUMMARY OF THE INVENTION The two principal components of the heart pump of this invention are a variable displacement piston-type 5 blood pumping unit, which in a preferred embodiment right side of the heart when it is rendered incapable of performing a filling or ejecting function. .The devices all suffer common problems of objectionable blood damage, clotting and diaphragm failure.
Total artificial hearts which have been proposed have incorporated both two and four chambers, corresponding to the ventricles and atria of the heart. These total heats have incorporated diaphragm pumps which may be actuated by air or compressed carbon dioxide pulses. One fonn of total heart utilizes oil as a pumping fluid to compress a sac for forcing the blood into the aorta. Problems of blood flow interference, clotting and blood damage are aggravated in total artificial hearts because of the greater number of valves, chambers, material interfaces and passages therein, resulting in greater contact with and abuse of the blood.
is air-driven, and a spool-type control assembly therefor. The pumping unit is adapted for implantation. The control assembly is external and utilizes an air supply, connections and manual emergency control means. The complete heart pump requires, in addition to the two main components, only a source of compressed air and suitable air lines, thus all equipment is readily borne by the user and is transportable.
The pumping unit has a rigid case providing either one or two major blood chambers corresponding to the ventricles of the heart, depending on whether the unit is to replace one or both sides of the natural heart, and each major blood chamber has an associated blood intake valve and a blood outlet valve. A variable displacement blood piston is mounted for reciprocation within each blood chamber for alternately causing blood to be expelled through the outlet valve (systole) and to be received through the inlet valve (diastole). In the form of pumping unit having two major blood chambers initiation of systole or diastole occurs simultaneously in both chambers as in the case of the natural heart. A significant feature of the pumping unit is the inherent sensitivity of the blood pistons to venous pressure and blood volume. As distinguished from prior artificial heart pumps, little or no venous pressure is required for blood chamber filling. Displacement of the blool piston is also affected by displacement of a pressured air driven double acting cylinder that impels the blood piston during systole.
The control assembly is a signal controlled spool-type valving assembly having only two moving parts, which are two spools respectively termed a main spool or main directional spool arid a signal directional spool or reversing spool. The two spools and associated ports and passages control two distinct air circuits, one of which is the working air circuit controlled by the main spool for transmitting-air to drive a reciprocating air cylinder within the pumpingunit and the associated blood piston. In a preferredforrn of control assembly, working pressures are separately regulated during the systolic and diastolic phases, which affects the working rate of the blood piston during its systolic and diastolic functions. In this way the complete pumping cycle may be made to closely approximate the pressure-time signature of the human heart. Working pressure associated with each individual blood chamber of a two chamber pumping unit may also be separately regulated. The other associated circuit is an air pulse signal circuit.
The pumping unit is so constructed that at the points of complete extension or retraction of the air cylinder(s) in the single or double chamber pumping units, an air pulse or signal circuit is opened within the pumping unit, and a pulse of air is returned from the pumping unit through the corectly positioned signal directional spool of the control assembly and directed to a portion of the main spool for displacing it tothe position at which it will direct working air to the air cylinder or cylinders in the pumping unit for causing reverse displacement thereof. The rate of reciprocation of the control spools corresponds to that of the blood pistons and is the heart beat rate. The control assembly is therefore a passive or slave device relative to the pumping unit in that the air pulse or signal depends only upon positioning of elements of the pumping unit itself which, in turn, are sensitive to blood pressure and volume values that control the filling and therefore the ejection volume. A multiple channel conduit is connected between the pumping unit and control assembly for providing the necessary working air, pulse signal air and case venting lines, and conductors for heart function monitoring devices when desired. I
A preferred form of heart pump of this invention includes novel intake and outlet valves, both of which are of a flexible, tricuspid design characterized by extremely low pressure requirements for opening and closing, smooth operation and absence of regurgitation. Mounting of the valves in close proximity to each other is also important in order to sustain adequate flow in the blood chamber. r
The air circuitry in this heart pump provides a sort or cushioned transition at reversal of blood piston displacement. The arrangement of the blood piston within a chamber is such that the circulation of blood within a blood chamber follows a generally circular path from inlet valve to outlet valve. The blood piston is main tained in a sealing relationship with the case of the pumping unit defining the blood-chamber by a novel sealing ring which hasa cross-sectional configuration yielding a rolling action which precludes entrapment of blood between the. sealing ring and surfaces of the blood chamber and blood piston which it contacts. The overall result is reduction of blood stagnation and turbulence and blood abuse. i V
Important objects of the invention are provision of a highly reliable, implantable, Starling-type. heart pump suitable as an assist device for one side of the heart or as a total artificial, heart; and artificial heart pump which lessens damage to the pumped blood relative to that caused by prior devices; a heart .pump that will continue to cycle upon loss of filling volume as a result of heart-.disfunction, but will cease functioning in the event of excessive arterial blockage; and a heart pump and pump system that are readily borne and trans ported by the user and require no auxiliary equipment.
Further objects are to provide an aritificial heart pump in which, relative durations of the systolic andiastolic phases and blood pressures within the pump during such phases closely. approximate the corresponding characteristics of the natural heart; a heart pump having a simple beat rate control; a heart pump incorporating means for accurately monitoring blood output; and a heart pump which can readily be. manually controlled in the event of automatic control function failure.
Additional objects are to provide in a heart pump combination, a pumping unit control having substantially fewer operating parts than heretofore; novel heart valves which operate in a manner less abusive of blood than prior prosthetic valves; and a novel blood sealing ring exhibiting a rolling action which precludes entrapment of blood.
Other objects and advantages of the invention will become apparaent from the following description of preferred embodiments of the invention.
DESCRIPTION OF THE FIGURES porating a double-chamber pumping unit, showing its.
connection with an air source and with associated portions of the blood circulation system;
FIG. 2 is an end elevational view of the pumping unit of FIG. 1, with parts broken away;
FIG. 3 is an enlarged vertical cross-sectional view of the pumping unit shown in FIG. 1, taken substantially along line 3-3 thereof; I
FIG. 4 is an enlarged vertical cross-sectional view of the pumping unit of FIG. 1, taken along a plane disposed from theplane of FIG. 3 and along line 4-4 in FIG. 3.
FIG. 5 is an enlarged horizontal cross-sectional view of the pumping unit of FIG. 1 showing the blood pistons thereof in the fully retracted position;
FIG. 6 is an exploded fragmentary view showing a portion of the blood piston sealing ring in the pumping unit of FIG. 1, with associated parts;
FIG. 7 is a fragmentary cross-sectional view of the air cylinders and associated parts of the pumping unit of FIG. 1;
FIG. 8 is a fragmentary view of a signal jet tube assembly in the'air signal circuit of the heart pump of FIG. .1;
FIG. 9 is a partially cross-sectional, partially schematic view showing the pumping unit of FIG. 1 and a form of control assembly therefor, with the parts positioned at the completion of the filling or diastolic phase of the pumping cycle;
FIG. 10 is a view similar to FIG. 9, but. showing the positions of parts at completion of the blood ejection or systolic phase of the pumping cycle;
FIGS. 1 1a and 1 1b are partial cross-sectional views of the pumping unit of FIG. 1 during the diastole phase, taken along the sameplane as FIG. 10, showing two stall conditions; 1
FIG. 12 is a partially cross-sectional, partially schematic view of the pumping unit of FIG. 1 with a moodified form of dual pressure control assembly;
FIG; 13 is an exploded view of control assembly componentsand associated parts of the heart pump of FIG.
FIG. 14 is an isometric view of the air circuitry in the control assembly of FIG. 1;
FIG. 15 is an enlarged top plan view, with parts broken away, of the control assembly of FIG. 1;
FIG. 16 is an end view, with parts broken away, of the control assembly shown in FIG. 15;
FIG. 17 is a partially cross-sectional, partially schematic view of a form of single-chamber pumping unit and control assembly therefor, showing the positions of parts at the end of the diastolic phase;
FIG. 18 is similar to FIG. 17, but shows the positions of parts at the end of the systolic phase;
FIG. 19 is a fragmentary view of a preferred form of inlet valve for the pumping unit of FIG. 1;
FIG. 20 is a fragmentary view of a preferred form of outlet valve for the pumping unit of FIG. 1;
FIG. 21 is a graph showing the relationship between venous pressure and blood filling volume exhibited by the pumping unit of this invention, when operating at 60 and beats per minute;
FIG. 22 is a fragmentary view of a modified form of blood piston sealing ring; and
FIG. 23 is aschematic view of a modified form of control assembly utilizing three different operating pressures and associated parts of a double-chamber pumping unit of this invention.
DESCRIPTION OF PREFERRED EMBODIMENTS Double-Chamber Pumping Unit v Pumping unit 11 (FIGS. 1 and 3) comprises a rigid case formed of a pair of similar, generally hemispherical, rigid case members 17 and 18, each having squaretoothed annular edge portions 19 and 22 respectively which are in interfitting relation. Each case member also has formed therein two parallel open-ended tubular protrusions 23, 24, 25 and 26 providing two ports for each case member. The case is preferably fabricated from an inert plastic material, such as polycarbonate plastic, which will be suitable for implantation and will withstand autoclave sterilization.
FIG. 1 schematically illustrates portions of the human circulatory system directly communicating with the valves of the heart, specifically, the veina cava 27, pulmonary artery 28, lungs 29, pulmonary veins 32 and aorta 33. Tubular ports 24 and 26 respectively are provided for surgical connection with the pulmonary artery 28 and the ascending portion of the aorta 33. Ports 23 and 25 respectively are adapted for surgical connection with the natural right atrium associated with the vena cava 27 and the natural left atrium associated with the pulmonary veins 32, for introduction or ejection of blood through valves to be described.
A circular plate member 30 (FIGS. 3 and 4), which may also be formed of an inert plastic material, is located within the pump case with its periphery in contact with the interior surface'of edge portions 19 and 22. Member 30 has a peripheral flange portion 34 and is secured to case edge portion 19 (FIGS. 4 and 5) and 22 (FIGS. 3 and 5) by a series of screws 35. The central portion of member 30 has a cylindrical shape projecting in both directions axially of member 30 i (FIGS. 3 and 7) which provides a stationary cylinder rod 36 of a double acting cylinder assembly. Respectively fixed to the ends of rod 36 in case members 17 and 1.8 by screws 39 are circular pistons 42 and 43, and a central bore 38 extends fully through pistons 42 and 43 and rod 36. An O-ring 60 is seated around the periphery of each piston 42 and 43.
Slidingly received within bore 38 is a rod 52 (FIGS. 3
and 7) that is slightly shorter than rod 36. Rod 52 has a central bore 53 extending from its end within case member 17 but terminating short of its opposite end. A second rod 54 is received within the bore 53, and at the outer end of rod 52 there is fixed, by a screw 57, the flat face 50 of an air cylinder 55 having its cylindrical wall 51 seated around O-ring on piston 42. The open end of cylinder 55 is threaded around the periphery of a ring 46 which is slidingly fitted around rod 36 in sealing relation thereto by an O-ring 48. When cylinder face 50 is in contact with piston 42, ring 46 contacts a shoulder 56 of plate member 30. Cylinder 55 with ring 46 slides relative to rod 36 and piston 42 and carries rod 52 with it. Rod 54, received within bore 53 of rod 52 has fixed to it by a screw 63 a flat faced air cylinder 59 having a cylindrical wall 61, threaded around a ring 47. Rod 54 with cylinder 59 thereon, slides within rod 52 relative to rod-36 nd piston43. O-rings 60 and 48are respectively seated: in piston 43 and ring 47.
The inner surface of case member 17 immediately adjacent edge portion 19 (FIG. 6) is formed with a stepped section providing a threaded portion 64 and a flat portion 65 terminating in a rectangular groove 66. This section of case member 17 provides seating for elements of an assembly for mounting a hollow piston 67 (FIGS. 2,3 and 6), which overlies air cylinder 55, and as will be described, reciprocates for pumping blood present in the chamber defined between the piston and case wall. The leading end of piston 67 is partially tapered forwardly to a flat face (FIG. 3). The interior defines a cylindrical chamber 81 (FIG. 6) having an annular shoulder 82 inside its face 80. When cylinder 55 (FIG. 3) is within piston 67 with face 50 contacting shoulder 82 of the piston, there is clearance space between the opposed surfaces of the piston and air cylinder for purposes to be described.
The annular open end of piston 67 is formed with an annular groove 68 (FIG. 6) of L-shaped cross-section, and piston 67 is sealingly attached to case member 17 by a resilient sealing ring, which may be formed of silicone rubber material, and which, when in an uncompressed condition has a cross-section as shown in FIG. 6, including a T-shaped portion 72, a C-shaped portion 73 and a pair of opposed L-shaped portions 74.,Ring .69 is attached to case member 17 (FIGS. 3 and 7) by the T-shaped portion 72 inserted in slot 66 and is retained therein by a retaining ring 75 received within the case portion 65 and having a notched end for mating with the portion 72. An annular retaining-nut 76 is threaded into the threaded case portion 65, and resilient sealing ring 77 is compressed between nut 76' and flange portion 34 of plate member 30.
On the piston 67 itself, one of. the I -shaped portions 74 of sealing ring 69 is seated within the L-shaped groove 68 and the other portion 74 is compressed thereagainst by a retaining ring 78 having an L-shaped groove 79. Retaining ring 78 is screwed to piston 67 by a series of screws 90. It is seen (FIGS. 3 and 6) that with the described assembly, portion 73 of sealing ring 69 will effect a rolling motion relative tothe cylindrical surface 83 of piston 67 and the opposed surfaces of case member 17, ring 75 and nut 76, during reciprocation of piston 67, and such rolling action precludes entrapment of blood between such surfaces. A piston 85, (FIG. 3) similar to and mounted in the same fashion as piston 67 faces the opposite direction therefrom within case member 18. Mounting means for piston 85 includes sealing ring 86, retaining ring 87, retaining nut 88, sealing ring 89 and retaining ring 92.
A blood chamber (FIG. 3) is defined between blood piston 67 and case member 17, and a similar blood chamber 101 is associated with piston 85. The chamber surfaces are treated with Dacron fibers to support and retain live fetal cells or natural tissue growth. Blood is drawn into chambers 100, 101 upon retraction of pistons 67 and 85, and expelled upon extension of the pistons. Port tube 23, associated with piston 67, and port tube 25, associated with piston 85, are respectively provided for surgical connection with the right atrium associated with veina cava 27 (FIG. I) and the left atrium associated with pulmonary veins 32 and for mounting'blood inlet valves. preferred form of inlet valve (FIG. 19) utilized to replace the tricuspid and'rnitral valves of the natural heart, is a flexible, normally open three-leafed valve, which may be molded of a silicone rubber material. Valve 120 includes a collar portion 121 for seating and vulvanizing into the outer end of a port tube 23, 25 (FIG. 3). Integral with the collar portion 121 are three similar leaves 130 (FIG. 19) each molded along a generally semicircular line of attachment with the collar portion,'opening in the direc tion of flow into the pumping unit and spanning onethird the distance around collar portion 121. The leaf inner end 140 can best be described as resembling in shape the pointed bottom end of a shield. A dart shaped reinforcing portion 141 is molded onto the inner face of leaf 130 at the center point of inner end 140 thereof. Relative to the interior of the valve, leaf 130 is mildly convex adjacent its line of attachment to collar portion 121 and mildly concave adjacent dart shaped portion 141. In the normally open condition inner ends 140 of the three leaves together define an inwardly opening triangular mouth. The mouth is enlarged by flexing of leaves 130 during introduction of blood to the pumping unit (diastole) and is closed to flow of blood during expulsion (systole). Dart shaped portions 141 contribute to effective closure and sealing of leaves 130 during systole.
Each outlet valve 170 (FIG. 20) used is a threeleafed normally closed valve, which includes a collar portion 171 for seating in port tubes 24 and 26. Three similar leaves 180 are molded to collar portion 171 along a generally semicircular line of attachment spanning one third the distance around collar portion 171 and opening away from pumping unit 11 so that the leaves open outwardly thereof. Relative to the interior of the valve the leaves are convex, and the outer end portion 181 of each leaf (FIG. 20) includes two straight equal legs defining a 120 angle. In the closed condition, as during diastole, the end portions 181 of leaves 180 are in sealing contact to prevent reverse flow of blood. During systole or outflow the flexible leaves separate to provide a three-pointed outward opening mouth for passage 'of blood. Also, during outflow, the leaves exhibit an outwardly directed bulging effect which is of importance as the leaves thus impel blood which otherwise might undesirably remain at the outer surfaces of the valves.
Cylinder 55, with ring 46 and cylinder 59 with ring 47 reciprocate in opposite directions relative to rod 36 as double-acting cylinders, and their reciprocation is synchronized so that both simultaneously initiate an extension or retraction stroke. Appropriate passages and porting for synchronization include through bore 93 (FIG. 7) extending through rod 36 and pistons 42 and 43 in parallel with bore 38. Another passage 94 extends in parallel on the opposite side of bore 38, but is closed at both ends and communicates with a passage 99 leading to an area between piston 42 and ring 46, and also with a passage 102 leading to an area between piston 43 and ring 47. FIGS. 3, and 7 show cylinders 55 and 59 and spools or rods 52 and 54, in the completely retracted position. Inner spool 54 includes a reduced diameter portion 95 (FIG. 7) located to span the midpoint of bore 38 when spool 54 is retracted. Outer spool 52 includes a series of three reduced diameter portions 96, 97 and 98. When spools 52 and 54 are retracted, portion 96 is at the midpoint of bore 38, portion 97 is spaced toward cylinder 59 but overlies portion 95 of inner spool 54, and portion 98 is midway between portion 97 and the free end of the spool. A passage 103 extends between passage 94 and bore 38 in 8 rod 36 and communicates with spool portion 97 when rod 52 is retracted. A passage 104 extends between bores 38 and 93.
Blood output from a blood chamber 100, 101 is readily and accurately measured by utilizing a small bar magnet 283 (FIG. 9) embedded within the associated blood piston 67, with an end flush with the piston inner edge surface, and a sensor 284 mounted in alignment therewith on the opposed surface of central plate member 30. Sensor 284 is a Hall magnetic effect transducer which provides a varying electrical output when subjected to a varying magnetic field. The amplitude of variation in electrical output is a direct function of the variation in strength of the magnetic field. As has been described, the output of the pumping unit depends on blood piston dislacement, and correspondingly, the amplitude of the change in electrical output from the transducer depends on the distance between its blood piston and stationary central plate member 30. An electrical connection 285 within an additional channel of conduit 13 is provided between transducer 284 and an external electrical recording device of conventional construction. For example, the transducer can be connected to an oscillograph which will record a plot of the electrical output variation during travel of the blood piston, i.e., a plot of blood piston displacement. Such plot readily is calibrated and translated so that blood output volume per stroke can directly be represented on the oscillograph graphs.
As seen in FIGS. 1 and 13 conduit 13 for introducing pressured air to pumping unit 11 is a flexible ribbon having multiple air channels. Conduit 13 is preferably formed of extruded silicone rubber and at the end which connects with pumping unit 11 receives multiple rigid tubes 105, 106 and 108, and T-tubes 107 and 113 (FIGS. 4 and 13) which communicate with the interior of the pumping unit. Conduit 13 extends through the case, through flange portion 34 of plate member 30 and an opening 109 therein. The rigid tubes are clamped in the end of conduit 13 by a pair of clamp plates (FIGS. 4 and 3) within the opening 109. Tubes 105, 106 and 108 respectively communicate with passage 93, bore 38 and passage 94, and T-tubes 107 and 113 terminate within clamps 115 and communicate with opening 109. The opposite end of conduit 13 is adapted to be connected to a control assembly for pumping unit 11 such as control assembly 12 (FIGS. 1, 13, 15, 16), the main component of which is a spool valve assembly, e.g., 117 (FIGS. 1, 9, 10 and 14), 201 (FIG. 12) or 230 (FIG. 23).
Control Assembly A preferred form of control assembly 12 incorporating spool valve assembly 117 (FIGS. 1, 9, 10 and 14) has an associated housing 160 (FIGS. 1 and 16) for an air pressure gage 174 (FIG. 16). Valve assembly 117 (FIGS. 13 and 15) includes a valve body 119 for seating a main spool 122 having a circular piston 123 on one end and a similar piston 124 on the opposite end, and for seating a reversing spool 125 having a single piston 126 at one end. A port plate 127 is mounted on the top surface of valve body 199, a cap 128 is at the side adjacent to piston 123 of main spool 122 and a cap 129 is at the opposite side.
The control end of conduit 13 receives rigid tubes 105a, 106a, 107a, 108a and 113a (FIG. 13) respectively in the same channels as tubes 105, 106, 107, 108
. and 113. Each such tube communicates with a port in