US2951450A - Fluid pump - Google Patents

Description

J. c. FISHER 2,951,450

FLUID PUMP Sept. 6, 1960 2 Sheets-Sheet 1 Filed April 17, 1956 INVENTOR. OHN c. FISHER ATTORNEYS Sept. 6, 1960 .1. c. FISHER 2,951,450

FLUID PUMP Filed April 17, 1956 2 Sheets-Sheet 2 INVENTOR. JOHN C. FISHER ATTORNEYS FLUID PUMP John C. Fisher, 45 Sparks St., Cambridge, Mass.

Filed Apr. 17, 1956, Ser. No. 578,777

9 Claims. (Cl. 103223) This invention relates to an improved pump particularly suitable for use in transmitting corrosive fluids, toxic or inflammable fluids and fluids containing abrasive materials in suspension, and other fluids which cannot be satisfactorily handled by conventional pumps.

Displacement, rotary and centrifugal type pumps not only embody one or more impellers and other moving parts with which the liquid being pumped comes in contact, but also a power-transmitting element driven from an external source. When such pumps are used to transmit corrosive liquids, solvents, etc. the moving parts and other surfaces coming in contact with the liquid must either be made from a relatively costly, corrosive-resistant material, or they must be provided with a protective coating which after a relatively short period of use is apt to Wear or become stripped, thus introducing contamination into the liquid being pumped. Moreover, since such pumps are driven from an external source it is necessary to use packing glands or the like seals which must be periodically replaced in order to guard against leakage. Consequently both the initial and maintenance costs of such pumps are relatively high.

The principal objects of the present invention are to provide a pump which has completely sealed fluid carrying members so that no leakage is possible, such as might occur with conventional centrifugal, vane, piston or rotary pumps; to provide a pump having the aforementioned advantages but which embodies a positive displacement action, as distinguished from a non-positive displacement type such as disclosed in my copending application Serial No. 553,015, filed December 14, 1955; and to provide a simple, effective and reliable means of eliminating from the output of any type of fluid pump the pulsations of pressure and discharge which are inherent in output of many conventional pumps, and also of the pumps described herein.

More specific objects are to provide a pump capable of handling a fluid containing solid or abrasive particles, such as encountered in a coolant system for machine tools, to provide a pump which can safely handle toxic materials such as radio-active substances and highly inflammable or explosive fluids, etc., where leakage must be avoided, and to provide a pump the output of which may be varied without using a valve or the like.

Further objects will be apparent from a consideration of the following description and the accompanying drawings, wherein:

Fig. l is a sectional elevation of a pumping system constructed in accordance with the present invention;

Fig. 2 is a section on the line 2-2 of Fig. 1;

Fig. 3 is a section on the line 3-3 of Fig. l; and

Fig. 4 is a schematic view of a modified form of the invention.

In accordance with the present invention I provide a pumping system comprising a pumping means operative to discharge into an external circuit, a pulsating unidirectional fluid flow and simultaneously draw in from an Patented Sept. 6, 1950 intake or a return line a unidirectional fluid flow, and a pressure-smoothing device connected with the discharge and inlet lines and operative to eliminate the pressure peaks from the pulsating fluid flow so as to obtain a relatively smooth or even pressure wave. The pumping means may comprise any conventional type of pump operative to discharge a unidirectional pulsating fluid flow into a discharge line, or it may comprise a pump of the type shown in my aforesaid copending application operating in association with a fluid rectifier, but where a positive displacement action is desired the pumping means prefenably comprise a pair of compressible chambers such as cooperating bellows, arranged so that when one is compressed the other is expanded.

Where, as is preferred, bellows are employed they should be identical and one end of each is completely closed and the otherend of each is formed with an output opening so that as the bellows are operated there is induced an alternating or oscillating fluid flow through their respective output openings. These output openings are connected to a fluid rectifier, such as shown in my copending application, so that the resultant flow is changed from an alteranting to a pulsating, unidirectional flow which is acted on by the smoothing device to eliminate the pressure peaks from the pulsating flow.

The pressure smoothing device comprises cooperating chambers constructed and arranged so that when one is expanded, the other is compressed. Each of these chambers is provided with a single port and a relatively rigid duct connects the port of one chamber with the discharge line and a second duct connects the other port with the intake or return line leading to the pumping means. The cooperating chambers may comprise a relatively rigid enclosure divided by a flexible diaphragm so as to define the cooperating chambers, the diaphragm being such as to respond to fluid pressure so as to expand or enlarge one chamber which receives a fluid surge from one line and simultaneously compress the associated chamber so as to force fluid through its port into the other line; or such cooperating chambers may comprise a pair of bellows, each having but a single opening, one communicating with the discharge line and the other communicating with the intake line.

Where the pressure smoothing device is thus connected in the system the steady average component of the output pressure difierence causes the chamber connected with the low pressure or intake line to be compressed (i.e. decrease its internal volume) and the other chamber to expand (i.e. increase its internal volume) so as to admit a quantity of fluid from the discharge line, and the resultant of all the alternating components of the output pressure difference produces a purely alternating motion about this average displaced position. Consequently the peaks of the pulsating fluid flow are, in effect, flattened out so as to fill in the troughs, as hereinafter more fully explained.

The various parts of the system may be made from any suitable corrosion-resistant metal, a chemically inert plastic such as a polyamide (nylon), polyethylene, halogenated polyethylene (Teflon), polyvinylidene chloride (Saran), a suitable polyester or an epoxy resin, provided they possess the desired degree of rigidity, strength and fatigue resistance. In any case the particular material selected will depend upon the type of fluid on which the pump is to operate, and these same considerations are applicable to the external circuit and parts associated therewith.

Where bellows or the like compressible chambers constitute the pump, any suitable means may be employed to a 3 this end one or more electrodynamic vibrators or the like may be used, or the mechanical equivalent such as a crank, or other type of reciprocating motor.

Referring to Figs. 1 to 3, the embodiment shown there in comprises essentially a positive displacement pump unit P connected with a fluid rectifier R having discharge and intake lines connected with the pressure smoothing device S. The pump P comprises a pair of spaced circular plates land 2 which may be supported in any suitable manner and rigidly connected by a plurality of circumferentially spaced rods 4. The plates 1 and 2 are provided with four pairs of circumferentially spaced aligned openings which receive bushings 5 and 6 and these bushings slidably support four guide rods 8; The inner ends of these guide rods are rigidly secured to a driving flange 18 and their opposite ends are secured to a terminal ring 12.

Midway between the driving flange and terminal ring is a circular crosshead'15 which is pinned or otherwise suitably secured to each of the guide rods. Each face of the crosshead is formed with a centrally disposed circular recess and these recesses receive the inner closed ends of a pair of identical coaxially disposed bellows l6 and 18 which, as above noted, may be of Teflon, corrosion-resistant metal or other suit-able material. An adhesive or other suitable means anchors the closed ends of the bellows in the circular recesses of the crosshead so that one of the bellows is expanded and the other is contracted in response to movement of the crosshead. The opposite or open ends of the bellows are formed with circular gasket flanges 20 and 22 which contact the plates 1 and 2, respectively. Cap screws 24 and 25, extending through the plates 1 and 2 into compression rings 26 and 28, clamp the flanges against the plates so as to provide a fluid-tight joint.

The change of internal volume for a given linear displacement of each bellows should be approximately equal on both compression and elongation of the bellows, and the two bellows units should be nearly identical to one another in this respect. If the volume-vs.-displacement characteristic of each bellows is not truly linear, then the stroke of the bellows relative to its normal length must be made small enough so that a reasonable approximation to such a linear characteristic is obtained. For a given stroke, this can be achieved by using a suitably large number of convolutions in the bellows, so that the per-unit displacement of each convolution is small.

Each plate 1 and 2 is provided with a port or opening registering with the opening in the bellows and these openings receive output ducts 3t and 3 2. Circumposed about the bellows and guide rods are helical springs 34 and 36, the ends of the spring 34 being seated in grooves formed in the plate 1 and the adjacent face of the crosshead 15 and those of the spring 36 being similarly seated in grooves on the opposite face of the crosshead and adjacent face of the plate 2. The effective stiffness of the combination of the bellows, and the effective moving mass of these bellows, springs and crosshead are prop0r tioned so that the natural frequency of this moving system is equal or nearly equal to the frequency of the reciprocating motion which is imparted to the system by the actuating means presently to be described.

The outer face of the drive flange is integral with spaced cars 38 which carry a wrist pin 40 that pivotally connects one end of a connecting rod 42 to the drive flange. The other end of the connecting rod is pivotally connected by a crank pin 44 to a counterbalanced crank 45 mounted on crankshaft 46 which is rotated or oscillated by any suitable mechanism (not shown) effective to impart oscillatory movement to the flange 10, guide rods 8 and crosshead 15.

As the crosshead 15 executes its motion, which is approximately sinusoidal in its time-variation, bellows 16 is alternatively subjected to increases and decreases in its internal volume, while bellows 18 is simultaneously subjected to equal and opposite changes of volume. Thus, each bellows alternately admits extra fluid on its expansion stroke and then discharges this fluid on its compression stroke, both the entrance and exit of fluid taking place through the open port or duct to which the bellows is connected. It will be noted that there is no internal flow from one bellows to the other. Hence, in the conduits 30 and 32 there is a purely reciprocating flow of fluid, which is rectified by means of the fluid rectifier R.

The fluid rectifier comprises a cylindrical block or body 48 having four longitudinally extending venturi- like passages 51, 52, 53 and 54-, the upper ends of the passages 52 and 53 being connected by a passage 57, and the upper ends of the passages 51 and 54 being connected by a passage 58. The lower ends of the passages 51 and 52 are connected by a passage 60 and the lower ends of the passages 53 and 54 are likewise connected by a passage 61. The passages 51 and 52 are provided with ball checks 63 and 64 and each has a retainer pin, the arrangement being such that inward flow from the passage 60 is prevented, but outward flow to the passage 60 is permitted. The passages 53 and 54 are also provided with ball checks 65 and 66 and associated retainer pins, the arrangement being such that inward flow from the passage 61 is permitted, but outward flow to the passage 61 is prevented. The duct 30 is connected by a line 68 with passage 58 and the duct 32 is connected by a line 70 with passage 57. The passage 60 is connected to the discharge line 72 and the passage 61 is connected with an intake 0 return line 74.

With this particular type of rectifier a pressure surge transmitted from the compressed bellows 16 to passage 58 forces fluid outwardly through output passage 51 and simultaneously there will be a reverse surge created by the expansion of bellows 18 which draws fluid in through input passage 53 and passage 57. When the movements of the bellows are reversed a pressure surge transmitted from bellows 18 to the passage 57 forces fluid outwardly through output passage 52 and simultaneously the reverse surge created by the expansion of bellows 16 draws fluid inwardly through input passage 54, thus producing a full wave rectification.

Hence, fluid alternatingly surges outwardly through passages 57 and 58 into discharge line 72 simultaneously with fluid alterna tingly surging inwardly from intake 74 through passages 53 and 54. Since the volume of fluid transmitted in response to each surge is relatively small, being less than the volume of the inlet and connecting passages, the path of flow is from the intake 74, connecting passage 61, then through inlet passages 53 and 54, along connecting passages 57 and 58, through outlet passages '51 and 52 to the connecting passage 60 and then to discharge line 72, there being no unidirectional flow of fluid from bellows 16 to bellows 18 through the crosshead.

The discharge and intake lines 72 and 74 are connected with the pressure-smoothing device S which comprises a rigid cylindrical housing 76 having rigid end plates 78 and 80 secured thereto by cap screws extending through gaskets to provide a fluid tight chamber. The ends of four symmetrically disposed parallel guide rods 82 are secured to the end plates, and a circular crosshead 84, formed on each face with annular bosses 85 and 86 which carry guide bearings 88, is slidably supported on the rods 82. The marginal portions of the crosshead 84 are provided with a plurality of spaced openings 90 to permit fluid within the chamber readily to flow from one side of the crosshead to the other. The fluid within the housing 76 is preferably a low vapor pressure, low kinematic viscosity, stable liquid which may be introduced into the housing by removing one or more cap screws and replacing them after the housing has been filled.

Each face of the crosshead 84 is formed with a centrally disposed circular recess and these recesses receive the closed inner ends of a pair-of identical coaxially disposed bellows 92 and 94 which may be of the same construction and material as the bellows 16 and 18 of the pump. An adhesive or other suitable means secures the ends of the bellows 92 and 94 within the recesses so that as one is expanded the other is contracted in response to a pressure surge. The opposite or open ends of the bellows are formed with circular gasket flanges 95 and 96 which contact the end plates 78 and 80, respectively. Cap screws 98 and 99, extending through the plates 78 and 80 into compression rings 101 and 102 clamp the flanges against the plates so as to provide fluid tight joints.

The plates 78 and 80 are formed with ports or openings registering with the openings in the bellows and these ports receive ducts 104 and 105 which are connected by Ts 106 and 108 to the intake and discharge lines 74 and 72, respectively. Circumposed about the bellows, inwardly of the guide rods, are helical springs 110 and 112, the adjacent ends of which abut the bosses 85 and 86 with their opposite ends seated in grooves formed on the inner faces of the plates 78 and 80. The effective combined stiffness of the helical springs and the bellows is proportioned relative to the effective moving mass of the bellows, springs and crosshead so that the natural frequency of this moving system in the absence of any damping force is equal or nearly equal to twice the basic frequency of the pumping unit. As hereinafter explained, this tuning of the moving system makes the magnitude of the pressure pulsation of twice the pump fre quency wholly dependent upon the internal damping force, if any, of the smoothing device, and not upon the characteristics of the pump or the nature of the external fluid circuit. The motion of the crosshead now becomes predominantly a double-frequency motion about an average position such that the static force of the combined stiffness just balances the average pressure difference across the external fluid circuit. Hence, in ducts 104 and 105 there is a purely alternating flow of fluid which is predominantly a sinusoidal flow of twice the pump frequency.

The discharge line 72 may be connected to one or more distributing lines or any type of apparatus through which a steady, non-pulsating, unidirectional fluid flow is desired, and likewise the return or intake line 74 may be connected to such apparatus, a reservoir or other means for supplying a fluid flow to the rectifier R.

Principle of operation In order more fully to appreciate the principles and mode of operation of the above-described system we may assume that the motion of the crosshead is sinusoidal in its time-variation, then the discharge (i. e. the fluid volume per unit time emerging from the pump) will be a series of identical, consecutive half-sinusoids in the fluid conduits which connect the rectifier assembly to the external fluid circuit. Such a waveform of fluid discharge is undesirable in many applications of this pump, and it is necessary in such cases to remove the pulsations from the external flow.

The pulsating discharge from the bellows pump P may be identically represented as the sum of the following components, which at each instant of time add algebracial- 1y .to yield the actual-instantaneous value of the discharge:

(1) A constant average value, which is the desired part of the discharge;

.(2) A sinusoidal discharge of twice the frequency of the motion of the crosshead of the pump;

(3) A sinusoidal discharge of 4 times the frequency of the motion of the crosshead, and

(4-) An infinite series of simple harmonic discharge .waves, each of higher frequency andsmaller amplitude than the preceding one, with frequencies which are even multiples of the fundamental frequency of the crosshead. T

'6 1fthe desired average value of the discharge be de noted by the symbol Q, then this Fourier series representation of the rectified sinusoid of instantaneous discharge 9 may be written mathematically as t=time n:2,4,6,8... It will be evident from inspection of this equation that the major elements of the pulsation in the discharge are the sinusoidal components of twice the basic frequency and 4 times the basic frequency, which is denoted by f in the equation. The amplitudes of the second, 4th and 6th harmonics, relative to the average value are, respectively, 0.6667, 0.13333, and 0.05714. Hence, if we elimimate the 2nd and 4th harmonics from the total discharge, we have a substantially uniform flow. Of course, if we wish a very smooth output, we must eliminate all harmonic components up through the 20th, for which the relative amplitude is 0.005012, an entirely negligible quantity for practical purposes.

It is thus possible to obtain virtually perfect elimination of any one harmonic component of the discharge represented by the above equation, and hence, by reiteration of this means, to eliminate any desired number of the harmonic components of the discharge. This unit, of course, is passive, in that it has no external prime mover, but is set into motion of a reciprocating nature by virtue of the pulsations in the pressure diiference between its open ports.

It will be noted that the particular unit above described differs from the assembly used for pumping in only two significant ways:

(1) It is entirely enclosed in a leakproof container of some suitable metal or plastic material, which is filled with a chemically inert, incompressible liquid in such a way that there are no voids in the space outside the bellows units but within the container.

(2) The relative magnitudes of the effective moving mass and the net effective stiffness of the springs and bellows units are such that the natural frequency of the moving system is equal to or nearly equal to the frequency of the lowest harmonic component of this discharge, or twice the frequency of the pumping unit.

'When this assembly is connected in shunt across the output and return conduits from the fluid rectifier, the steady average component of the output pressure difference will cause the crosshead 84 to be displaced toward the bellows 92 which is connected to the low-pressure (return) conduit. The resultant of all the alternating components of the output pressure difference will cause the crosshead to execute -a purely alternating motion about this average displaced position. As. the crosshead moves in this fashion, the forces which are exerted upon it from without itself arethe following:

A. The resultant of the internal fluid pressures transmitted through the closed ends of the bellows units;

B. The resultant of the forces exerted through the closed bellows ends due to the inherent stiffness of the bellows units themselves;

C. The resultant of the forces due to the springs;

D. The resultant of the liquid pressure exerted by the liquid which fills the container.

Where, as here shown, the annular space between the rim of the crosshead 84 and the housing wall is large and the outer portion of the crosshead-is provided with several openings 90, then the filler liquid can move freely around and through the crosshead, and force D can be made as small as desired.

According to Newtons law, the net acceleration of the moving crosshead is equal-to the sum of forces A, B, C and D, divided by the effective mass of the moving system. Now the acceleration of the crosshead is a reciprocating one consisting of a Fourier series of harvolume of the other bellows.

monic accelerations, and at twice the basic frequency of the pump, this component of acceleration is just provided for by the sum of forces B and C. Hence, for this double-frequency acceleration, force A must be equal and opposite to force D, since the unit is in mechanical resonance at twice the basic frequency. Therefore, by making the damping force due to the filler liquid as small as desired, I can correspondingly reduce the alternating Component of pressure dilference between the discharge conduit and the intake conduit of the pump, at the frequency of mechanical resonance of this pulsation-smoothing unit. Thus, I have a means of eliminating to any desired degree the pressure pulsation of any given frequency, by tuning the smoothing device S to resonance at this frequency, and by making the effective internal damping of the smoothing unit as small as necessary.

Since this smoothing device has been assumed to be resonant at twice the basic frequency, the pressure pulsation of this frequency is virtually eliminated from the output pressure of the pump, and as a result, the double-frequency component of the discharge from the pump must also disappear from the flow in the external fluid circuit. This component of the discharge is now flowing, in effect, through the pressure-smoothing unit and thus bypassing the external fluid circuit. In reality there is no true flow through the smoothing device, since there is no connection internally between the high-pressure bellows and the low-pressure bellows, but because of the incompressible liquid which just fills the space outside the bellows units but inside the container, any increase in the internal volume of one bellows must exactly equal the corresponding decrease in the internal Therefore, the net effect observed from the external fluid circuit is the same as if the double-frequency alternating component of discharge were flowing without impedance through the bellows device and thus bypassing the external circuit.

It should be noted in passing that the motion of the crosshead 84 in the smoothing device will bepredominantly a double-frequency simple harmonic motion, since it responds most to this frequency of its own resonance, and its peak-to-peak excursion is limited to that which is required just to bypass the Znd-harmonic discharge component in the output of the pump as shown by the above equation. Thus, there is no possibility of the occurrence of dangerous amplitudes of motion within the device.

By connecting across the output conduits of the pump another smoothing device like the one just described, but tuned to a mechanical resonance at four times the basic frequency, we can eliminate from the output the 4thharmonic components of pressure and discharge. In similar fashion, we may eliminate any or all of the higher harmonics of pressure and discharge, by adding more units in parallel, each tuned to resonance at the frequency which it is to eliminate.

It should be noted in this connection that the size of the bellows units in each successive smoothing device can be smaller than in the preceding device. Thus, in this situation, the change of volume per stroke required for the Znd-harmonic smoothing device is 0.4244 times that of the pumping device, the change per'stroke of the 4th-'harmonic unit is 0.08486 times that of the pumping device, etc.

To summarize, the important and novel features of the pressuresmoothing device of this invention are:

(1) There are'no check valves of any lcind within the unit.

(2) There is no internal passageway between one bellows and the other.

(3) The moving system is tuned to mechanical resonance at the frequency of pressure and/ or flow pulsation which it is desired to eliminate from the output of the (4) The bellows-and-crosshead assembly is completely enclosed in a leakproof enclosure, and the space outside the bellows units but inside the container is completely filled with an incompressible liquid having a low temperature-coeflicient of expansion, so that (a) the internal pressure acting on the bellows units is transmitted to the outer container rather than being home by the bellows alone, and (b) the change of volume of one bellows is always constrained to be exactly equal and opposite to the change of volume of the other bellows, when the crosshead moves.

(5 Dampen-ing force may be introduced into the unit, if for any purpose this should be desirable, by obstructing, to a greater or lesser degree, the flow of the filler liquid around and through the crosshead as it moves. The residual harmonic pressure pulsation in the output of the pump is determined by the amount of damping thus introduced.

Note, in connection with item 4, above, that the highpressure bellowsmust expand slightly because of its internal pressure. This expansion ceases when the effective inward pressure due to the stresses in the bellows wall itself and the outside pressure of the now-compressed filler liquid just balance the internal pressure acting on the bellows. lows must contract slightly (i.e. decrease its internal volume), until the excess pressure acting on its outer surface is just balanced by the stresses in its own wall and the internal pressure of the fluid within this bellows. If the bellows units are reasonably rigid themselves, then these changes of volume just described are small. Further changes of volume are due entirely to the displacements of the crosshead, and since the filler liquid is virtually incompressible and is enclosed in a leakproof, rigid housing, any such change in the internal volume of one bellows must be exactly equal and opposite to that of the other bellows. This is a necessary feature of the device, for if the instantaneous flow rate at the intake conduit of the fluid rectifier is not equal to the instantaneous flow rate at the discharge conduit of the rectifier, cavitation may occur within the body of the rectifier or within the pump unit itself.

It follows from the foregoing that oscillating the crosshead 15 produces a purely alternating flow in the lines 68 and 70, as indicated by the symbols; that this alternating flow is transformed by the rectifier into a pulsating, unidirectional flow in the discharge line 72, as indicated by the symbols; that the pulsating, unidirectional flow in discharge line 72 is eifective to produce a purely alternating fluid flow in ducts 104 and 105 of the smoothing device S, which is predominantly a sinusoidal flow of twice the pump frequency; and the alternating flow in ducts 104 and 105 is effective to produce an essen-' tially steady flow in the discharge line 72 on the downstream side of its connection with the duct 105, since the dominant component of pulsation, namely, the second harmonic, is virtually suppressed, and simultaneously there is produced a pulsating unidirectional flow in duct 104 on the upstream end of its connection with duct 104. If it is desired, as many units of this type as necessary may be added in parallel to the 2nd-harmonic smoothing device, each of the other smoothing devices being tuned to one of the harmonic frequencies which are normally present in the discharge of the pump. These frequencies, in this case, are the following multiples of the basic pump frequency: 2nd, 4th, 6th, 8th, 10th, etc.

It is clear that a smoothing device of the type just described can be used to eliminate the pulsations from the discharge of any type of fluid pump operating under steady conditions, since any such discharge can be resolved into a constant average value plus a Fourier series of harmonic variations. It is also clear, that, if 2 harmonic variations in pressure or flow lie close enough to one another on the frequency scale, then a single smoothing device which is tuned to some appropriate frequency of resonance intermediate to the 2 frequencies which At the same time, the low-pressure bel- I must be removed, can be used to suppress both these harmonic components of the discharge.

The aforementioned principles are applicable to various other types of systems embodying two or more conduits in which there is an oscillating fluid 'flow. Inthe system shown in Fig. 4 there are three identical pumping units P1, P2, and P3 connected with a rectifying unit R and a pressure smoothing device S is connected across the discharge and return lines leading to and from an apparatus or system A the operation of which requires a relatively smooth and continuous unidirectional fluid flow.

Each of the pumping units is identical to the pumping unit P above described and the same reference charac: :ters are applied to the same parts. These three pumping units are radially disposed about a-common drive shaft 46a and circumferentially spaced 120 apart. The shaft 46a carries a crank 45a which is connected to the driving flanges of the pumping units by rods 110, 111 and 112, as in the embodiment of Fig. 1.

The output ducts 30 of the pumping units are interconnected by lines 114, 115 and 116 and the output ducts 32 are connected with conduits 120, 121 and 122 whichlead to the rectifying unit R. The rectifying unit -R' comprises output passages 124, 125, 126 and input passages 124, 125', 126'. The passages 124 and 124' are connected at one end to each other and to the conduit 120 and at their other ends are connected to the intake and discharge lines 145 and 135 through one-way check valves 140 and 130 respectively. As apparent "from Fig. 4, the passages 125 and 125 and the pairs of vpassages 125, 125' and 126, 126 are likewise interconnected and connected to the conduits 121 and 122 respectively and further are likewise connected through check valves 131, 14-1 and 132, 142 to the intake line 145 and discharge line 135.

The pressure smoothing device S comprises a pair of opposed cylinders 150 and 151 having their open ends formed with flanges between which is clamped a flexible diaphragm 154 which defines apair of expansible chambers 155 and 156 arranged so that when one expands the other contracts. The opposite ends of the chambers are connected by lines 160 and 161 tothe discharge-and return lines 135 and 145, respectively, which lead to and from the apparatus or system A.

In operation the oscillations imparted to the crossheads of the pumping units producean alternating flow in the conduits 114, 1 and 116 and also in the output lines 120, 121 and 122, but the'c'heck valves 130, 13 1 and 132 of the rectifying unit permit'only a unidirectional, pulsating flow in the discharge line 135. Like wise the check valves 140, '14-1 and 142 permit only a unidirectional flow in thereturn line v145. As a result the main body of fluid being circulated does not flow into the internal circuit including the pumping umts and associated lines, but rather is circulated through the rectifying unit R. Since the smoothing device S is connected across the discharge and return lines, it is effective to smooth out the pulsations in the discharge line and produce corresponding pulsations in the return line on the down stream side of its connection therewith, as above explained.

The diaphragm 154 may be of any suitable corrosionresisting metal or other material of known resilience and stifiness and the mass within the chambers 155 and 156 is primarily determined by the dimensions of the chambers and the liquid density. Although the diaphragm 154 is operative throughout a Wide range of frequencies of the pumping units, yet for the most efflcient operation the pumping units are operated at a substantially constant speed or frequency and a diaphragm 154 is selected that has a natural frequency of six times the normal operating frequency of the pumping units.

It will be noted that in both of the embodiments herein shown the entire pumping apparatus including the pumping unitsyfluid rectifiers and smoothing unitprovides'ra completely enclosed system which may be 'made from any suitable material 'inertto the fluid being pumped, and that there are no moving parts such as impellers, drive shafts, or the like which come into direct contact with the fluid. Hence, the apparatus may not only be used to pump fluids containing abrasive particles such as encountered in the coolant fluid used with machine tools,

pose of illustration and that various changes and modifications may be made without departing irom the spirit and scope of the invention as set forth in the appended claims.

I claim:

1. In apparatus of the class described, a pump having a fluid flow opening and operative to provide an oscillating fluid flow through said opening, an intake line for supplying fluid, a discharge line for carrying discharged fluid, rectifying means connected to the intake and discharge lines and to said opening to provide unidirectional fluid flow in said intake line and to provide unidirectional pulsating fluid flow in said discharge line in re sponse to operationof the pump, pulse smoothing means for smoothing out pulsations in fluid flow in said discharge line including a pair of compressible chambers arranged so that when one chamber is expanded the other chamber will becompressed, and means connecting one of the chambers in flow communication with the intake line and the other of the chambers in flow communication with the discharge line.

2. In apparatus of the class described, a fluid pump including an expansible chamber having a fluid flow opening, and means for alternately expanding and compressing the chamber to draw in and discharge fluid to and from the chamber through said opening; an intake line for supplying fluid; a discharge line for carrying discharged fluid; rectifying means to provide unidirectional fluid flow in said intake line and unidirectional pulsating fluid flow in said discharge line in response to operation of the pump, the rectifying means including an input passage and an output passage connected at one end of each to each other and .to said opening, the other ends of the input and output passages being connected respectively to the intake and discharge lines, and check means in each of the input and output passages; and pulse smoothing means for smoothing pulsations in fluid flow in said discharge line and for introducing pulsations in fluid flow in said intake line including a pair of compressible chambers connected to each other so that when one chamber is expanded the other will be compressed and vice versa, and means connecting one of said pair of chambers in fluid flow communication with said intake line and the other chamber of said pair of chambers m fluid flow communication with said discharge line.

3. Apparatus of the class described comprising pumping and rectifying means having discharge and intake lines and operative to discharge a pulsating unidirectional flllld flow through the discharge line and draw in a unidirectional fluid flow through the inlet line, and pressure smoothing means comprising an enclosed chamber containing a liquid, two bellows within said chamber and arranged so that when one is expanded the other is compressed, each of said bellows having a port, a duct connecting one port with the discharge line and a second duct connecting the other port with said intake line.

4. Apparatus of the class described comprising pumping and rectifying means having discharge and intake lines and operative to discharge a pulsating unidirectional fluid flow through the discharge line and draw in a unidirectional fluid flow through the inlet line, and pressure smoothing means comprising an enclosed chamber containing a liquid, two coaxially disposed bellows with closed adjacent ends within said chamber, said bellows being arranged so that when one is expanded the other is compressed, the opposite end of each bellows having a port, a duct connecting one port with the discharge line and a second duct connecting the other port with said intake line.

5. Apparatus of the class described, comprising two bellows, each having a single opening at one end, a conduit connected with each opening, means for compressing one of said bellows and simultaneously expanding the other so as to cause an oscillating fluid flow in the conduits, a fluid rectifier having a discharge passage connected at one end with one conduit, a second discharge passage connected at one end with the other conduit, a return passage connected at one end with the first conduit, a second return passage connected at one end with a second conduit, a discharge duct connecting the opposite ends of the discharge passages, a return duct connecting the opposite ends of the return passages, a discharge line connected with the discharge duct, an intake line connected with the return duct, and check means in said passages conjointly operative in response to an oscillatory flow in said conduits to discharge a pulsating unidirectional fluid flow through said discharge line and draw in a unidirectional flow through said intake "line, two compressible chambers arranged so that when one is expanded the other is compressed, each of said chambers having an opening, a duct connecting one opening with said discharge line, and a second duct connecting the other opening with said intake line so as to smooth out the pulsations in the fluid flow in said discharge line and introduce corresponding pulsations in the fluid flow in said intake line.

6. Apparatus as set forth in claim 5, wherein balanced springs act on said bellows so as to oppose oscillating movement thereof, the resultant stiffness of said springs being such that the natural frequency of said bellows conforms to the frequency of said pulsating flow.

7. Apparatus as set forth in claim 5, wherein a pair of coaxially disposed balanced helical springs act on said bellows so as to oppose oscillating movement thereof, resultant stiflness of said springs being such that the natural frequency of said bellows conforms to the frequency of said pulsating flow.

8. Apparatus of the class described, comprising a driving shaft, three pumping units radially disposed about said shaft and circumferentially spaced 120 apart, each of said pumping units having an output line, means connecting said drive shaft and pumping units so that an alternating fluid flow takes place in the output lines in response to rotary movement of said shaft, a fluid rectifier having a discharge line and an intake line, said rectifier having a branch line connected with each output opening, a duct connecting one opening with said discharge line and a second duct connecting the other opening with the intake line.

9. Apparatus of the class described, comprising at least one pair of expansible chambers, each chamber having a single output opening, means for compressing one of said chambers and simultaneously expanding the other so as to cause an oscillating fluid flow through each of said openings, a conduit connected with each opening, a fluid rectifier having discharge passages and return passages connected with the conduits, the discharge passages having check means permitting an outward flow and the return passages having check means permitting an inward flow, an intake line connected with the return passages and a discharge line connected with the discharge passages the parts being operative to discharge a pulsating unidirectional fluid flow through said discharge line and draw in a unidirectional flow through said intake line, and pulse smoothing means including two compressible chambers arranged so that when one is expanded the other is compressed, each of said chambers having an opening, a duct connecting one opening with said discharge line, and a second duct connecting the other opening with said intake line so as to smooth out the pulsations in the fluid flow in said discharge line and introduce corresponding pulsations in the fluid flow in said intake line.

References Cited in the file of this patent UNITED STATES PATENTS 2,316,278 Orshansky Apr. 13, 1943 2,348,538 Hagen May 9, 1944 2,430,723 Lupfer Nov. 11, 1947 2,764,999 Stanbury Oct. 2, 1956 2,780,065 Spannhake Feb. 5, 1957 2,811,931 Everett Nov. 5, 1957 FOREIGN PATENTS 4,270 Netherlands Dec. 1, 19.19 360,628 Germany Oct. 5, 1922 425,500 Great Britain Mar. 15, 1935 605,039 Great Britain July 14, 1948 695,556 Great Britain Aug. 12, 1953 1,100,067 France ..1 Mar. 30, 1955

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