GB2039091A - Pressure booster system for fluids - Google Patents

Abstract

For delivering fluids at high pressure, for example to a liquid chromotography column 240, with a minimum of pulsation and at an accurate flow rate, a pressure booster system includes low pressure injector means 12 (which in the illustrated case comprises first and second cam-actuated pumps 46 and 48) which supplies respective liquids through respective valves 94 and 96 and an accumulator 106 to a high pressure pump 158 the output of which is at the desired high pressure. A detector 140 preferably a variable capacitance in an oscillator circuit, detects the liquid mass in the accumulator 106 and supplies a corresponding signal to control means 242 which regulates the flow rate of the pump 158. The pumps 46, 48 may be phased to deliver sequentially; a further injector 139, under the control of a controller 268, may also serve to supply another fluid stream to the accumulator 106; and where liquid chromotography is concerned a sample injector 270 may be provided for injecting a sample to be analysed into the output from the pump 158. <IMAGE>

Description

SPECIFICATION Pressure booster system for fluids The present invention relates to a pressure booster system for fluids, particularly but not exclusively for use in the field of liquid chromatography where it is necessary to deliver fluids at high pressure with a minimum of pulsation and at an accurate flow rate.

A typical liquid chromatography system employs a packed column to effect separation of solute from a liquid sample. A detector analyzes the outflow from the column to identify particular components in the solute. Many chemical compounds exhibit similar elution character istics and therefore exit the packed column at nearly the same time. Therefore, forcing the liquid sample through the volumn smoothly in a continuous and well defined flow rate is essential to the obtaining of accurate analyses. Prior liquid chromatography systems employ high pressure pumps, of the positive displacement type, to force the liquid sample through the packed volumn. Unfortunately, piston or piston-like pumps inherently produce an output flow having pulsations. High pressure piston pumps depend on proper operation of check valves for precise flow rate delivery.Although the use of dual piston pumps with overlapping cam characteristics has eliminated some of the flow pulsation, elaborate feedback controls are necessary further to reduce pulsations.

In this regard, reference is made to United Stated Specification No. 3917531 (Magnussen) which describes a flow feedback system which employs a flow transducer to vary the speed of a motor driving the pump according to a feedback signal. United States Specification No.

3398689 (Allington) discloses a proportioning system for liquid chromatography applications which utilizes motor velocity feedback as a method of varying the pumping rate of the liquid.

United States Specification No. 3932078 (Ball et al) employs a control means which measures the pressure during the pumping period of one piston and trandforms the same into a pressure standard for a second piston, which is operated by an overlapping cam arrangement.

All of the prior art systems require precision-built high-pressure metering pumps and feedback controls which must adjust for a multitude of corrections as an adjunct to liquid characteristics operating at high pressures. Prior art precision solvent metering pumps are expensive to construct and are markedly less reliable than other components of a liquid chromatographic system.

The present invention provides a pressure booster system for fluids comprising: (a) low pressure injector means for delivering a selected relatively-low-pressure output flow of fluid; (b) accumulating means for accumulating fluid mass from said low pressure injector means, said accumulating means having an output flow; (c) detecting means for detecting a fluid mass in said accumulating means relative to a selected value of fluid mass capable of being confined therein, said detecting means serving to produce a signal representative of the fluid mass in the accumulating means; (d) high pressure pump means for receiving, as its input, the outlet flow of fluid from the accumulating means and for producing a high pressure output flow of fluid; and (e) control means for regulating the flow rate of said high pressure pump means according to the signal received from said detecting means.

The system of the present invention employs a novel and original concept which externalizes in the system hereinafter described.

The system employs injector means which delivers a relatively low pressure output of fluid at a very accurate rate. The injector means operates at very low pressure and thus encounters few of the problems associated with high pressure metering pumps of the same genre. The injector means may take the form of a single pump or a multiplicity of pumps operating in collaboration to pump a single solution or a plurality of solutions.

The output of the injector means is fed into means for accumulating fluid mass. Said means may take the form of a fluid container a portion of which is a flexible diaphragm. With such an arrangement, an increase in the volume of fluid within the fluid accumulating means causes outward pressure and moves the diaphragm portion of the container in the same direction, whilst decrease in said volume conversely results in inward movement of the diaphragm and vice versa. The system also includes means for detecting a fluid mass change in the fluid mass accumulating means relative to a reference value of the fluid mass confined therein i.e. volume, density, pressure, and the like.

The output flow from the fluid mass accoumulating means travels to relatively high pressure pump means which in turn boosts the accurately metered inlet flow rate of fluid to a relatively high pressure outlet flow rate of fluid, retaining the accurately metered characteristic of the flow stream. The high pressure pump means is regulated by control means which derives the flow rate adjustments from the detection means which represents the difference between the mass in the fluid mass accumulating means and a reference value. Thus, the fluid mass accumulating means serves as a node in the mechanical and feedback control aspects of the system. The control means may employ an electrical, mechanical, pneumatic, and other known signal transmission media to effect the controlling function.Accordingly, it should be apparent that the pressure booster system for fluids of the invention possesses many advantages not available with the prior known proposals.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a preferred embodiment of injector means forming part of a preferred pressure booster system of the present invention; Figure 2 is an enlarged sectional view taken along the line 2-2 of Fig. 1; Figure 3 is a detached part-sectional view, to a slightly reduced state, taken along line 3-3 of Fig. 1; Figure 4 is a fragmentary part-sectional view illustrating fluid mass accumulating means of the said booster system; Figure 5 is a plan view of the fluid mass accumulating means of Fig. 4; Figure 6 is a part-sectional view of high pressure pump means of the said booster system; Figure 7 is a sectional view taken along line 7-7 of Fig. 6; Figure 8 is an enlarged detail of the right-hand end portion of the high pressure pump means of Fig. 6;; Figure 9 is a detached sectional view taken along line 9-9 of Fig. 8; Figure 10 is a block diagram of the overall pressure booster system; Figure 11 is a block diagram of booster speed control means of the said system; and Figure 12 is a schematic diagram of the electrical circuitry of the pressure booster speed control means.

A preferred embodiment of the fluid pressure booster system of the invention is indicated generally at 10 in Fig. 10. The system 10 includes as one of its elements injector means 12 (Fig. 1) which is employed for delivering a solvent stream. The injector means 12 includes an electric motor 14 which drives through a gear mechanism (not shown) within gear box 16. The motor 14 drives a shaft 18 at a predetermined rotational speed. A coupling 20 connects the shaft 18 to a shaft 22 which turns at the same speed as the shaft 18. A bearing 24, having a flange 26, provides for extension of the shaft 22 to a cam 28. As shown in Fig. 1, the cam 28 contacts cam followers 30 and 32. The shaft 22 extends through a bearing 34 including a flange 36. A cam 38 on the shaft 22 is engaged by cam followers 40 and 42.The shaft 22 is finally supported by a bearing 44 on the terminal end thereof. The functioning of the cam followers 30, 32, 40, and 42 will be explained later.

The injector means 12 includes a first pump 46 and a second pump 48. From Fig. lit will be apparent that the cam 38 operates these pumps 46 and 48.

Fig. 2 depicts the pump 48 in detail, and the components of this pump 48 are virtually identical to the components of the pump 46. Therefore the following description of pump 48 applies correspondingly to the pump 46, shown in Fig. 1.

The pump 48 is activated by the cam follower 32. A washer 52 and an end plate 54 confine between them a return spring 56 which functions to urge the cam follower 32 against the cam 28. The end plate 54 abuts one end of a housing 58 of liquid head portion 60 of the pump 48.

The washer 52, adjacent the annular ring 50, and the end plate 54, offer respective bearing surfaces to the return spring 56. The cam follower 32 contacts a piston 62 such that upon rotation of the cam 28 the piston 62 reciprocates within a piston chamber 64. The cam follower 32 is supported by guide means 66 which include bearings 68 and 70.

From Fig. 2 it will be seen that the piston 62 extends through a bushing 72 held in place by the end plate 54. Bearing means 74, within the bushing 72, supports and guides the piston 62 independently of the cam follower 32. This bearing means 74 may be of carbon such that that piston 62 is lubricated thereby. Seal means 76, which may comprise an element 78 of cuplike configuration, effectively seals the piston chamber 64 against leakage. The liquid head portion 60 includes an inlet 80 and an outlet 82. The inlet 80 and the outlet 82 do not have the check valves normally associated with liquid chromatographic systems. Fastening means 88 holds the housing 58 to the end plate 54, thus holding the bushing means 72 and the seal means 76 in place. It should be noted that the first pump 46 has an outlet line 90 (Fig. 1) and an inlet line (not shown).

The shaft 22 operates, via the cam 38, valve means indicated generally by the numeral 92 which valve means 92 includes a first valve 94 and a second valve 96. The cam followers 40 and 42 are associated with these valves 94 and 96 respectively. Fig. 3 illustrates the second valve 96 which is substantially identical to the first valve 94. These valves 94 and 96 are depicted as double, two-way slider valves similar to those manufactured and marketed under model number 201-00 by Altex Scientific, Inc. By way of example, the second valve 96 functions such that fluids ultimately delivered by the second pump 48 originate in a fluid reservoir (not shown) and enter an inlet tube 98, as indicated by directional arrow 100 in Fig.

3. The cam follower 42 operates the second valve 96 such that fluids pass through housing 102 of said second valve 96 to an inlet tube 84 connecting to the inlet 80 of the liquid head 60. The fluid flows through the inlet 80 to the piston chamber 64 from which the piston 62 discharges the fluid through the outlet 82. Since the slider mechanism of the second valve 96 is well known in the art, the specific functioning thereof will not be described in greater detail.

In a similar manner, fluid emerging from the outlet 82 of the liquid head 60 passes through an outlet line 86 and through valve housing 102 to an exit line 104 (directional arrow 108) which leads to fluid mass accumulating means in the form of an accumulator 106, Fig. 4. The backstroke of the piston 62 of the second pump 48 coincides with the movement of fluid through the inlet tube 98 of the second valve 96 and the inlet tune 84 of the liquid head 60.

Seriatim, the flow of fluid through the exit line 104 of the second valve 96 and the outlet line 86 of the liquid head 60 coincides with the forward chamber-emptying stroke of the piston 62.

Returning to Fig. 1, it will be seen that the cam followers 42 and 44 actuate slider mechanisms 110 and 11 2 of the valves 94 and 96 respectively. Return springs 114 and 11 6 of these slider mechanisms 110 and 112 bear on respective supports 118 and 120 to urge cam followers 40 and 42 into contact with the cam 38.

It will be understood that the cam 38 operates the valves 94 and 96 such that the first valve 94 discharges to the accumulator 106 while the second valve 96 sucks fluid from the fluid reservoir, and vice versa. Thus, the accumulator 106 receives a steady flow of relatively low pressure but very-accurately-metered fluid from the injector means 12.

The accumulator 106 (Fig. 4) receives the fluid delivered by the injector means 12 and the valve means 92 through an inlet port 11 5 which connects to the exit line 104 of the valve 96 and a corresponding exit line (not shown) of the valve 94. The accumulator 106 includes a housing 117. A conduit 119 conducts fluid from the valve means 92 to a mixing chamber 121.

A magnetic stirring impeller 122 in the chamber 121 thoroughly mixes the fluids from the injector means 12 and further injector means 139 (discussed hereinafter) with the use of a dipole stirrer 124. Fluids entering the inlet port 115 pass into a connected chamber 126 located above the chamber 121 (Fig. 4). The chamber 126 is divided into a system fluid section 128 and a capacitance section 130 by a diaphragm 132. Fluid being pumped by the injector means 12 impinges on the diaphragm 132 before entering an exit conduit 134 and an exit port 136. In general, the stirring impeller 122 may be constructed of non-reactive material such as Teflon, Kel-F, and the like.

Referring to Fig. 10, the further injector means 139 (shown schematically) serves to deliver another fluid stream to an inlet port 138 of the accumulator 106. The injector means 139 is similar in construction to the injector means 12.

The desired solvent composition or gradient is determined by the relative flow rates of fluid from the injector means 12 and 139. Thus, the fluid mass accumulator 106 could, if desired, be arranged to accept a multiplicity of fluid streams for a multiplicity of injector means. The mixing chamber 121 permits the blending of the fluid outputs of the injector means 12 and 139, which, in the case of a liquid chromatography gradient, would consist of distinct solvent streams.

Fig. 4 also depicts detecting means 140 for detecting a fluid mass in the accumulator 106.

The diaphragm 132 has, as one of its elements, a conductive portion 142 which is electrically connected to earth. The diaphragm 132 is held between the housing 117 and a member 144 by fastening means 146. The detecting means 140 includes a capacitance electrode 148 which is fixed to the under surface of a printed circuit board 150. Circuit components 152 and 154 and a connector 156 are mounted on the top of the printed circuit board 150 (Fig. 5). Full details of the electrical components of the system 10 will be described later. Impingement of system fluid on the flexible diaphragm 132 creates a variable capacitance between the conductive portion 142 and the capacitance electrode 148. Thus, changes in the mass of fluid present in the accumulator106 is detected by the detecting means 140.Thus, in the illustrated preferred embodiment, the amount of the fluid mass is transduced into a capacitance value.

However, it should be noted that an optical or a mechanical mechanism could be used to perform the same function.

Fluids passing through accumulator 106 enter high pressure pump means 158 illustrated in Figs. 6 to 9. As shown, in the preferred embodiment the high pressure pump means 158 is a piston-driven diaphragm pump. However, other types of high pressure pumps, such as a solenoid-driven diaphragm pump, a dual-piston pump, or the like may be employed to boost the pressure of the fluid arriving from the accumulator 106. For example, the fluid pressure may be boosted from a slightly positive absolute value to over 700 kilograms per square centimeter. The pump means 158 includes a housing 160 having an enclosure 162, which defines a chamber 164. The chamber 164 holds lubricating fluid which is depicted in Figs. 6 and 8 as an oil bath 166.

A variable-speed motor M-10 (Fig. 12) rotates a shaft 168 at a rate determined by control means 242. The shaft 168 is supported by a bearing 1 70 before it extends through an opening 172 in the enclosure 162. A seal 174 prevents escape of oil from the chamber 164 while permitting the shaft 168 to rotate. The inner end of the shaft 168 is supported by a needle bearing 174 located within the chamber 164. A cam 176 is fixed to the shaft 168 by fastening means 178. Thus, the cam 176 rotates with the shaft 168. A cam follower 180 rollingly abuts the edge of the cam 176, and is fastened to a cam follower shaft 182 by fastening means 184.

The shaft 182 extends through bearing means 186 and contacts a piston 188. The enclosure 162 is shaped to provide a shelf 189 (Fig. 7) which is engaged by a guide roller 192 which serves to prevent turning of the cam follower shaft 182 about its axis.

The high pressure pump means 158 has, as a component thereof, a liquid head 190 which is bolted onto the enclosure 162 by bolt means 194. Turning to Fig. 8, a filler plug 196, having a vent screen 198, occupies a replenishment port 200. Thus, the level of the oil bath 166 may easily be maintained. The piston 188 moves, within a guide member 202, in reciprocal fashion. A port 204 ensures that a chamber 206, in which the piston 188 reciprocates, always contains oil. The stroke of the piston 188 is such that its forward pumping stroke extends beyond the port 204 to seal the same (as indicated in phantom lines) while the backstroke of the piston 188 opens the port 204. The guide member 202 is held in place by a plate or end wall 208 which is constructed as part of the enclosure 162.

This plate 208 also provides a surface 210 for the bearing support of spring members 212 and 214. The spring member 212 ensures contact of the cam follower 180 on shaft 182 against the cam 176. For this purpose, the cam follower shaft 182 includes a fixed collar 216. The spring member 212 urges the cam follower shaft 182 away from the surface 210 of the plate 208. Similarly, the piston 188 includes a collar 218 fixed to the piston 188 by a ring member 220. It will be apparent that the spring member 214 urges the piston 188 into continual contact with end 222 of the cam follower shaft 182. The piston chamber 206 terminates, at one end thereof, in a relatively rigid member 224, porous to the oil being pumped by the piston 188. Adjacent the porous member 224 is a relatively-flexible diaphragm or membrane 226 which is impervious to the oil pumped.This flexible diaphragm 226 forms one side wall of a fluid chamber 228 within the liquid head 190. A diaphragm return spring 230 (Fig. 9) is held in place within the chamber 228. The liquid head 190 includes an inlet 232 and an outlet 234. The inlet 232 accepts fluid leaving the exit port 136 of the accumulator 1 06. It should be noted that the inlet 232 and the outlet 234 include respective check valves which ensure the flow of fluid as indicated by the directional arrows in Fig. 8. Fluid entering the inlet 232 flows to a passage 236 and consequently into the fluid chamber 228. At this point, the movement of the diaphragm 226, actuated by the pumping action of the piston 188, constricts the volume of the fluid chamber 228 and forces the fluid into passage 238. The fluid then passes from the passage 238, through the outlet 234, to a desired delivery terminal.In the case of a liquid chromatography system, the outlet flow from the outlet 234 enters a packed column 240, shown schematically in Fig. 10. In the case of check valve failure, the porous member 224 supports the diaphragm 226 against rupture.

In Fig. 10, the system 10 is shown schematically. The injector means 12, composed of the first and second pumps 46 and 48, and the first and second valves 94 and 96, and/or the further, similarly constructed, injector means 139, deliver fluid to the fluid mass accumulator 106. The combined fluid streams travel to the high pressure pump means 158 and a column 240 disposed thereafter. The detecting means 140 senses the fluid mass in the accumulator 106 and produces a signal representing the detected fluid mass which is then sent to the control means 242. The control means 242 compares this signal with a reference signal and in turn produces an error signal which regulates the flow rate of the high pressure pump means 158. This regulation of the high pressure pump means 158 contributes to maintenance of the mass of fluid contained in the accumulator 106 at a reference value.In the embodiment shown in the drawings, the flow rate of the high pressure pump means 158 is controlled by the magnitude of the voltage reaching the motor shaft 168. Thus, the flow rate of fluid leaving the high pressure pump means 158 equals the flow rate of fluid being delivered by the injector means 12 and/or any other injector means. A controller 268 may determine the composition and/or gradient of solvents delivered by any multiplicity of the injector means. A sample injection means 270 combines the sample to be analysed with the solvent stream leaving the high pressure pump means 158.

Fig. 11 depicts schematically a particular embodiment of the control means 242. As heretofore described, the fluid mass signal from the detecting means 140 is received by the control means 242 and is converted into a signal which regulates the flow rate of the high pressure pump means 158. The control means 242 includes an oscillator 244 which generates a frequency signal 252 which is inversely proportional to the capacitance between the capacitance electrode 148 and the conductive portion 142 of the diaphragm 132. The frequency signal 252 is transformed into a voltage signal by a frequency to voltage converter 246. The resulting voltage signal 254 is received by a summing amplifier 248.A reference voltage generator 250 also sends a voltage signal 256, representative of a reference mass value for the fluid mass accumulator 106, to the summing amplifier 248 which in turn sends a voltage signal 258 which controls the speed of the motor of the high pressure pump means 1 58. It should be noted that such motor may be a simple D.C. motor. Thus, an increase in the pumping rate of the injector means 12 increases the fluid mass in the fluid mass accumulator 106. The detecting means 140 detects such an increase and signals the same to the control means 242 which then increases the pumping rate of the high pressure pump means158. The increased flow rate from the high pressure pump means 158 tends to decrease the mass of fluid in the fluid mass accumulator 106.The null circuit described hereinbefore, with the control means 242, essentially renders the high pressure pump means 158 as a slave to the injector means 12, and/or 139.

Fig. 12 illustrates an embodiment of an electrical circuit which performs the nulling function associated with the detecting means 140 and the control means 242. The following table is a complication of values of the components shown in Fig. 12: TABLE 1 FIG. 12 CIRCUIT ELEMENTS R-10 200 K.ohm VC-10 Range 10-100 p.f.

R-12 10 K.ohm R-14 100 K.ohm C-10 620 p. farads R-16 8.2 K.ohm C-12 0.02 micro farads R-18 100 K.ohm C-14 0.02 micro farads R-20 82 K.ohm C-16 0.001 micro farads R-22 10 K.ohm C-18 0.01 micro farads R-24 39 K.ohm C-20 15 micro farads R-26 22 K.ohm C-22 0.1 micro farads R-28 30 K.ohm C-24 100 micro farads R-30 10 K.ohm C-26 2.2 micro farads R-32 3.9 K.ohm R-32 3.9 K.ohm R-34 200 K.ohm R-36 47 K.ohm R-38 2.2 K.ohm R-40 4.7 K.ohm R-42 1 K.ohm R-44 68 K.ohm R-46 470 K.ohm R-48 1.5 K.ohm R-50 0.3 K.ohm R-52 56 K.ohm Z-10 RCA CA-3130 Z-12 National Semi-conductor LM2907N Z- 14 1/4 National Semi-conductor LM 339N Z-16 1/4 National Semi-conductor LM 339N Z-18 1/4 National Semi-conductor LM 339N 0-10 MPS 6531 CR-10 IN914 0-12 MPS 3638A CR-12 IN914 0-14 MPS 3638A CR-14 IN914 Q-16 2N 5189 CR-16 IN914 0-18 RCA 40375 CR-18 IN914 0-20 2N 6386 CR-20 IN914 CR-22 MR850 CR-24 ME850 L-10 300 Micro-henry M-10 Printed Motors, Inc. Model U-9 VC-10 or detecting means 140 serves as a summing node sensor. As shown in Fig. 12, VC-10 is a variable capacitor which is a part of the oscillator 244 formed by amplifier Z-10 and resistors R-10, R-12, and R-14. The output frequency signal 252 is a square wave signal which may have frequency from 1 to 10 kilohertz. The frequency signal 252 is received by integrated circuit Z-12 which includes a charge pump 260. The integrated circuit Z-12 serves as a portion of the frequency to voltage converter 246, which has frequency-doubling characteristics.Capacitors C-12 and C-14, and r,;-sistors 8-141 and R-18 form a two-pole low-pass filter. The signal 254 feeds into integrated circuit Z-14. C-10 determines the size of the charge emitted form the charge pump 260 with each axis crossing of the frequency signal 252. R-22 biases the output transistor in the operational amplifier in Z-12. R-16, R-20, and C-26 determine the voltage gain of the operational amplifier portion of Z-12. R-16 and C-26 form a zero which increases the gain of the operational amplifier of Z-12. R-20 aids in this stabilization of the feedback loop.Passive components C-16, R-28, and R-30, R-24, R-26, and CR-10 combine with Z-16, to produce a triangular wave signal 262 with the D.C. offset voltage signal 256, the output of the reference voltage generator 250. Z-14 compares the voltage signal 254 and signals 262 and 256 to produce the pulse width modulated signal 258 directly proportional to the voltage signal 254. Thus, Z-14 serves as the summing amplifier 248.

Q-10, Q-12, Q-14, and Q-16 drive Q-18 synchronously "on" and "off" at a very fast rate. R-38-serves as a pull-up resistor for Z-14 while C-20 filters the power supplied thereto.

R-40 functions to limit the peak current through Q-10. Q-10 and Q-12 turn on and off in complementary sequence. The pulse-width modulated signal 258, which is quite high and positive, pushes current through CR-12, C-22, R-42, R-44, Q-14, and to the base of Q-16.

Q-14 bypasses to ground, through CR-16, any excess current received from Q-10. The current through R-44, which is not bypassed, passes to the base of Q-16 and turns it on. The limiting action of Q-14 prevents Q-16 from being over-driven when the system is initially turned on. Thus, Q-16 can be turned off more quickly. After charge up of C-22, R-42 limits the drive current through Q-10 such that 0-14 does not bypass measurable current to ground after the charge up period of C-22. The collector of 0-18 reaches a low value after a short time from the beginning of the turn-on sequence.When the pulse width modulated signal goes to a low value, Q-12 turns "on" and 0-10 turns "off" allowing the voltage at the emitter of Q-12 to go to a low value. C-22 supplies a negative bias to remove large currents very rapidly from the bases of Q-16 and Q-18 through CR-20. Consequently, 0-16 and 0-18 are turned off very rapidly permitting the voltage on the collectors thereof to go to a high value. This "onoff", high/low sequence takes place at a relatively high frequency, thus eliminating the need of a large heat sink to dissipate heat from 0-18.

The schematic also shows means for current limiting 0-18 using current sensing resistor R-50 and Z-18 and its associated circuitry. Z-18 compares a reference voltage derived from R-32, R-34, and R-36, and the signal voltage developed across C-18. Such a signal voltage averages the voltage drop across the current sensing resistor R-50 with a dual time constant originating from R-46, R-48, and CR-18.For instance, when the voltage drop across R-50 is less than the voltage across C-18, CR-18 is reversed biased so that R-46 and R-48 determine the time constant associated with C-18. When the signal voltage exceeds the reference voltage in comparator Z-18, the output of comparator Z-18 overrides the pulse width modulated signal from Z-14, thereby shutting down the driver section of the circuit. R-36 drops the reference voltage to a low level which guarantees that the driver section will remain in an off condition for a set time period. When the signal from C-18 is discharged below the lowered reference signal.

Z-14 is again ready to reactivate the driver section of the circuit. The "on-off" action of this current limiting occurs at a predetermined frequency.

L-10 and C-24 combine to produce a low pass filter which reacts slowly to voltage changes from the driver section of the circuit. By this means the pulse width modulated signal is converted to a D.C. signal supplied to M-10 which is a D.C. motor driving the high pressure pump means 158. R-52, 0-20 and CR-24 form a dynamic brake which prevents overspeeding of M-10.In other words, when CR-24 is forward biased, Q-20 is off and the L-10, CR-22 low-pass filter controls M-10. However, if the D.C. voltage generated by the motor M-10 exceeds the D.C. current supplied across C-24, CR-24 will reverse bias and 0-20 goes "on". This short circuits and therefore brakes M-10. Diode CR-22 clamps the voltage on the collectors of Q-16 and 0-18 to a thirty-five volt source 264, when 0-18 is in the "off" condition.

Returning to Fig. 1, it will be seen that the electric motor 14 provides the motive force for the injector means 12. The motor 14 may be a stepping motor such as a Copal, SP45. Control means 266 determines the selected speed of the motor 14 and therefore the selected pumping rate of the injector means 12. The control means 266 may consist of a drive module such as Copal DM 402X linked to a PG-01 pulse generator. The drive module and pulse generator may be controlled by a simple variable resistor or "pot" having about a 500 K.ohm rating. Thus, the user may set the pot to control the speed of the stepping motor 14. Such control may be programmed automatically.

In operation, the user sets the speed of the stepping motor 14 via the control 266. Thus, a pumping rate for the injector means 12 is selected and may correspond to a pressure value necessary to push fluid through the liquid chromatography volumn 240. The motor 14 turns the shaft 18 which in turn causes the first and second pumps 46 and 48 to deliver a carefully metered low-pressure fluid, in conjunction with the first and second valves 94 and 96, to the fluid mass accumulator 106. The fluid passes through the accumulator 106 also serves as a node for a feedback system which controls the speed of the motor M-1 0 which is the motive means for the high pressure pump means 1 58. The detecting means 140 and the control means 242 comprise a null circuit which results in the proper pumping rate for the high pressure pump means 158. The resulting output therefrom passes to the liquid chromatography column 240.

While in the foregoing specification an embodiment of the invention has been set forth in considerable detail for the purpose of making a complete disclosure of the invention,-it will be apparent to those of ordinary skill in the art that numerous changes may be made in such detail without departing from the scope of the invention, as defined by the following claims.

Claims (13)

1. A pressure booster system for fluids comprising: (a) low pressure injector means for delivering a selected relatively-low-pressure output flow of fluid; (b) accumulating means for accumulating fluid mass from said low pressure injector means, said accumulating means having an output flow; (c) detecting means for detecting a fluid mass in said accumulating means relative to a selected value of fluid mass capable of being confined therein, said detecting means serving to produce a signal representative of the fluid mass in the accumulating means; (d) high pressure pump mena s for receiving, as its input, the outlet flow of fluid from the accumulating means and for producing a high pressure output flow of fluid; and (e) control means for regulating the flow rate of said high pressure pump means according to the signal received from said detecting means.

2. A pressure booster system as claimed in claim 1 in which the accumulating means comprises a fluid container having an inlet, an outlet, and a flexible diaphragm forming a portion of said container.

3. A pressure booster system as claimed in claim 2 in which the detecting means comprises means for detecting the position of the flexible diaphragm.

4. A pressure booster system as claimed in claim 3 in which said means for detecting the position of the flexible diaphragm comprises transducer means for transducing the detected position of the flexible diaphragm into said signal representing said fluid mass in the accumulating means.

5. A pressure booster system as claimed in claim 4 in which the means for detecting the position of the flexible diaphragm comprises an electrically-conductive portion movable with said flexible diaphragm, a capacitance electrode spaced a selected distance from said electrically conductive portion of the flexible diaphragm, and means for measuring capacitance generated between said capacitance electrode and said electrically conductive portion of said flexible diaphragm and for generating a signal representative of said capacitance.

6. A pressure booster system as claimed in claim 5 in which the control means for regulating the flow rate of the high pressure pump means comprises: (a) an oscillator which receives the capacitance signal from said means for measuring capacitance and generating a signal representative thereof and which produces an output frequency signal representative of the capacitance between said capacitance electrode and said electrically conductive portion of said flexible diaphragm; (b) means for converting said output frequency signal to a voltage signal; and (c) summing amplifier means for comparing said voltage signal with a reference voltage signal and for producing a voltage from said comparison for motivating the high pressure pump means.

7. A pressure booster system as claimed in any preceding claim in which the high pressure pump means comprises: (a) a piston reciprocable within a first chamber adapted for containing a first fluid; (b) motive means for reciprocating said piston; (c) a flexible membrane forming a wall of said first chamber and also forming a wall of a second chamber adapted for containing a second fluid, said flexible diaphragm being movable with the stroke of said piston; (d) valve means for permitting the filling and emptying of said second chamber, coordinated with the movement of said flexible membrane; (e) spring means for returning said flexible membrane in a direction opposite to the movement of said piston urging said first fluid against said flexible membrane; and (f) a relatively rigid member interposed said piston and said flexible membrane said relatively rigid member being porous to said first fluid.

8. A pressure booster system as claimed in claim 7 in which said high pressure pump additionally comprises: (a) a cam rotatable by said motive means; (b) cam follower reciprocable by said cam, said cam follower bearing on said piston and imparting reciprocal motion thereto; (c) first spring means urging said cam follower into contact with said cam; and (d) second spring means urging said piston into contact with said cam follower.

9. A pressure booster system as claimed in claim 8 in which said cam follower is an elongate member and said high pressure pump means additionally comprises means for preventing axial rotation of said cam follower.

10. A pressure booster system as claimed in any preceding claim in which the low pressure injector means comprises: (a) a shaft; (b) motive means for turning said shaft at a selected rotational speed; (c) first reciprocal pump means operated by a first cam fixed to said shaft; (d) second reciprocal pump means operated by said first cam fixed to said shaft; (e) a fluid reservoir; (f) first valve means operated by a second cam fixed to said shaft, said first valve means permitting flow of fluid from said fluid reservoir to said first reciprocal pump means during the intake stroke of said first reciprocal pump means, and permitting discharge of the fluid being pumped from said first reciprocal pump means; and (g) second valve means operable by said second cam fixed to said shaft, said second valve means permitting flow of fluid from said fluid reservoir to said second reciprocal pump means during the intake stroke of said second reciprocal pump means, and permitting discharge of the fluid being pumped from said first reciprocal pump means.

11. A pressure booster system as claimed in claim 10 in which said first and second cams of said injector means are positioned on said shaft such that said first and second reciprocal pump means of said injector means are coordinated to pump fluid during separate time intervals.

12. A pressure booster system as claimed in any preceding claim in which said low pressure injector means is first injector means for delivering a selected relatively low pressure output flow of a first fluid and said system further comprises at least a second injector means for delivering a selected relatively low pressure output flow of a second fluid, and said means for accumulating fluid mass accumulates fluid mass from said first and second injector means.

13. A pressure booster system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.