APPARATUS AND PROCESS FOR FLUID FLOW CONTROL

Abstract: An apparatus to meter or control or measure a fluid flow is described. A plurality of parallel flow streets is arranged in such a way that each flow street can digitally pass defined volumes of fluid between two points. This is generally accom­ plished by providing valves in each street which allow sequen­ tially to connect a defined volume chamber in this street to a fluid source, to disconnect that fluid source and to open the street at the other end to the user of the fluid.

Description: This invention relates to an apparatus and a process for metering and controlling fluid flow. More specifically this invention relates to apparatus and process for testing filters. Yet more specifically this invention relates to procedures and apparatus for testing appliances with the aid of a test device which can be added to the system to be tested. Applicant has developed a process for integrity testing a filter which is referred to in the trade as a forward-flow-test process. This process represents a quantitative method for the testing of the functioning of filter elements or complete filter units composed of a plurality of filters. The test process involves subjecting the wetted filter or filters to a pressure below the capillary pressure, i.e. below the pressure necessary to remove the wetting fluid from the largest filter pores. At that pressure the only gas movement through the wetted filter is through diffusion through the wetting fluid in the pores or through leaks. This process is based on measuring the pressure/time behavior of the system to be tested under a set initial pressure. The process and apparatus developed by applicant referred to above constitutes a significant contribution to the art of filter integrity testing. However, for different size users and different kinds of filters different apparatus have to be designed and developed. It would be very desirable to have an apparatus and process available which can be used for a wide variety of applications including filter integrity testing. In particular such apparatus and processes should be useful for a broad range of volumes and flows as well as a broad range of pressures for the user. It is thus one object of this invention to provide an apparatus for metering and/or controlling and/or measuring fluid flow into a user which is applicable to a variety of different users. Another object of this invention is to provide such apparatus or process which can be used by users within a pressure range, volume range and fluid flow range encompassing a factor of 100 or more between the highest and the lowest value for the respective range. It is yet a further object of this invention to provide such apparatus and process which is fully automatic and computer controlled. These and other objects of this invention will become apparent from the following description of preferred embodiments of this invention, the claims as well as the detailed description of the drawing in which Figure 1 shows a schematic arrangement of the apparatus of this invention in a test set-up; Figure 2 shows a block diagram of the pneumatical functions of the apparatus of this invention; Figure 3 shows the principle connections between the computer and the pneumatical units of the apparatus of this invention; Figure 4 shows a flow diagram of the principle steps of the computer control software; EP-A-223 300 describes a gas meter. Binary clack valves are connected in parallel with passage capacities which differ from one another. By opening or closing one of these valves the respective passage is opened or closed. The passage capacity can thereby be adjusted between opened and closed. US-A-3 875 955 describes a digital fluid flow rate measurement or control system. A plurality of individually actuatable value weighted digital bistable valve elements in parallel interconnect a fluid source to a fluid receiver. For measurement, the states of the digital valve elements are controlled to maintain the value of the fluid parameter constant. For control the states of the digital valve elements are controlled to establish a set-point flow rate. US-A-2 627 280 describes a flow control system. There are means for selectively opening and closing one or more of a plurality of orifices of a suitable diameter in a partition and there are means for maintaining a constant predetermined pressure difference between the upstream and the downstream sides of the orifices. The above objects are solved by apparatus and processes as defined in the claims. Preferred embodiments are defined in the dependent claims. Thus in accordance with this invention an apparatus for metering and controlling fluid flow is provided. This apparatus is defined by comprising a plurality of parallel flow streets with each street having associated therewith a different fluid volume. Each street is capable of digitally dispensing its fluid volume. This means that the street is arranged for loading its volume with fluid of a given pressure and thereafter unloading this volume to a user. The actual quantity of fluid dispensed between the fluid volume of an individual street digitally connected to the user is simply given by the gas equation and the initial and final pressure in the fluid volume of the street. The process thus involves the timed connection of a chamber containing fluid under defined pressure, the chamber having defined volume, to the user, whereby through the chamber volume, chamber pressure, user pressure and timing of the connections a defined mass flow is provided to the user without a measurement of the flow. This digital fluid supply is provided from a plurality of streets containing chambers of defined but vastly differing volumes, thereby achieving a very broad variation in applications. More specifically in accordance with a preferred embodiment the apparatus of this invention comprises the following elements: a. A first connector unit for the connection with a pressure controllable source of fluid. This connector serves for a connection of the individual streets to a source of fluid of defined pressure. The fluid volumes are filled through this connector from the fluid source with a defined quantity of fluid, which quantity can be calculated through the gas equation from the volume and the pressure of the fluid source. b. A plurality of n fluid flow streets. Each of these streets comprises in serial flow connection. aa. An inlet valve being in fluid communication with one side of the connector; bb. A chamber of defined volume, said chamber having a chamber inlet and a chamber outlet, said chamber inlet being connected to the other side of said inlet valve; cc. An outlet valve connected with one side of the chamber outlet. The volume sizes of the chambers of these n streets form a series from a smallest to a largest volume. Preferably each larger volume is significantly larger than the next smaller volume. In accordance with particularly preferred embodiments the volume sizes of this series are a geometrical series. Yet both preferred is an arrangement in which each higher volume is ten times as large as the immediately preceding smaller volume. The preferred range of volumes is presently 0.01 to 1000 ml. yet more preferably the chambers have a volume size of 0.02 ml, 0.2 ml, 2 ml, 20 ml and, optionally 200 ml. In yet other terms, the preferred arrangement of the streets is such that the volume sizes of the individual chambers are defined by the following equations: Vol 0 = z Vol 1 = z * f Vol 2 = z * f² Vol 3 = z * f³ . . . Vol n = z * f n In this equations Vol m means the volume of the m-th chamber. The value z constitutes the volume of the smallest chamber (Vol 0), the counting beginning with 0 in this preferred embodiment, f constitutes the factor by which the volumes increase through the streets. This factor f in the preferred embodiment is 10. Generally f will be in a range of 2 to 20. c. A second connector unit for connection with a user of fluid. This connector is in fluid communication with the other side of the outlet valves. d. A plurality of 2 * n actuating means for operating one of the n inlet valves or respectively on of the n outlet valves upon the receipt of a corresponding actuating signal at the input thereof. These actuating means are adapted and arranged to either open the street completely, i.e. open both the inlet and the outlet valve of the respective street, or open the street for digital fluid dispensing, i.e. carry out a cycle of fluid dispensing opening the inlet valve with the outlet valve closed so that the respective chamber of the street is being filled with fluid at the pressure of the fluid source; thereafter closing the inlet valve, thereafter opening the outlet valve for dispensing the fluid from the chamber to the user. e. A computer control unit is operatively connected to the inputs of the actuating means. The computer is arranged and programmed to provide signals to the actuating means for opening and closing the respective valves in a predetermined and controlled fashion. Preferably this control is such that initially streets are selected by the computer depending upon the speed of pressure build-up at the user so that the user is provided with fluid at the given pressure of the fluid source; thereafter streets are selected to digitally provide the user with slugs or shots of fluid from the respective chamber of a selective street such as to subject the user to a predetermined pressure/time characteristic. This pressure/time characteristic preferably is such that a constant pressure is maintained at the user. In accordance with a further embodiment of this invention a process for passing fluid is provided. In accordance with this process fluid is passed from the inlet of a manipulator to an outlet thereof in accordance with a further defined procedure. The manipulator is a multi path unit or a multi street unit as further defined herein. The process is characterized by first passing the fluid through the path or street with the chamber having the smallest volume. This street is preferably also the street with the highest flow resistance. The process involves an automatic determination of the pressure/time behavior of the user being supplied with fluid through this street. The pressure/time behavior can then be such that the pressure rise at the user is too low. Then the consumption of the fluid by the user is apparently too slow. In accordance with this process of the invention the flow is then switched to another street having a higher volume and generally and preferably a lower flow resistance. This measuring and switching is repeated, until the pressure/time behavior of the user is in a desired range. In this operation the streets are used not in a digital fluid providing manner but in a straight flow arrangement. The further embodiment of this invention involves the use of the multi street manipulator in a digital fluid flow arrangement. In this process a source of fluid of defined pressure is connected to the individual streets. A connection between a user of the fluid and the outlet valves of the streets is also provided. The fluid is then passed to the user from one of the streets by a cyclic and digital fluid flow operation. In other words, the user is connected to the fluid volume trapped in the street, but not to the fluid source directly. The cyclic operation preferably is opening the input valve of the street to fill the respective volume with the fluid of a given pressure; closing the input valve or respectively disconnecting the fluid source from the chamber; thereafter connecting the chamber containing the fluid of the defined pressure with the user; the latter is preferably and simply done by opening the outlet valve of the street. It is, however, also within scope of this invention to use for instance a rotating chamber valve which in one position is connected to the fluid source and in the other position is connected to the user. Preferably such a chamber valve having only one valve body would in a third position provide a direct connection between the source fluid and the user. When employing this type of valve the first embodiment of the process would be carried out with the valve in the connecting position while the digital fluid providing process would be carried out by switching the valve back and forth between the other two positions mentioned. Figure 1 shows schematically an arrangement of the apparatus 1 of this invention as employed in an integrity testing set-up in connection with a filter housing 2. Test gas is supplied from a test gas source 3 via an inlet conduit 4 to the apparatus 1 for metering and controlling fluid flow. A vent line 5 is connected to the apparatus and the fluid as controlled by the apparatus 1 is supplied via conduit 6 to the filterhousing 2. Within the filter housing 2 a filter (not shown) is arranged which divides the interior of housing into two portions. The test fluid from conduit 6 can flow from one portion of the housing through to the other portion only via the filter or filters to be tested. In the actual test procedure these filters are employed in a wetted stage. In Figure 2 the apparatus 1 of this invention is shown in more detail. The arrangement of the individual units will be described in the following in conjunction with the operation of a filter integrity testing procedure. The apparatus 1 of this invention in this preferred embodiment is comprised of essentially two units. The first unit 10 can be viewed as the source of test fluid of constant pressure. This unit also serves for the flow control at the given pressure. The second unit 30 constitutes the unit for digital flow control and comprises a plurality of paths 31, 32 . . .39. Preferably the number of paths is 2 to 10, more particularly 3 to 8. In a specific example 4 paths have been successfully employed. The apparatus 1 of this invention is preferably arranged for fully automatic computer controlled operation. Each computer input is schematically represented by a reference numeral CI while each computer output is represented by a reference numeral CO. It is of course to be understood that the usual converting units are employed which allow either the conversion of the measured signal into a signal which can be received by a digital computer, such units generally involving an analog to digital convertor, and units to convert the digital information from a computer into signals which then actuate valves or switches or the like, such apparatus may involve digital to analog converters. The pressure of the fluid from the fluid source 3 in conduit 4 is determined by the pressure sensor DA1. The computer receives a corresponding signal via the computer input signal CI1. In order to maintain the pressure of the fluid at a constant value a throttle valve V1 is employed downstream of the location of the pressure detector DA1. The throttle valve V1 is operated by a computer generated signal coming from the computer output CO1. The vented test fluid is passed to vent conduit 5. The arrangement is such that there is constantly a significant stream of test fluid, usually air, vented through line 5 so that a good control and amendments of a constant pressure in the system is feasible. The pressure control fluid from the vent valve V1 is passed via conduit 7 to a flow control unit 40. This flow control unit comprises two parallel passages 41 and 42. The passage 41 is controlled by a valve V2. The passage 42 is controlled by a valve V3 and by a controllable flow resistor or throttle D1. Signals from computer outputs CO2, CO3 and CO4 from the computer control the operation of valve V2, valve V3 and throttle D1 respectively. Both passages 41 and 42 lead to a buffer chamber VO1. This buffer chamber VO1 typically and preferably has a volume in the range of 50 to 5.000 ml. The buffer chamber serves to provide a sufficient supply of the fluid to be passed onto the user 2, in this case the filter housing. The buffer volume also has the function to prevent otherwise occurring wave formation or oscillations in the fluid stream. A pressure sensor DA2 in the connecting line 8 between unit 10 and unit 30 determines the pressure of the fluid in this line and supplies a corresponding signal to the computer input CI2. The multi-path unit 30 comprises a plurality of paths 31, 32 ... 39 connecting conduit 8 and conduit 9, thus providing for a fluid connection in a controlled fashion between the user 2 and the source of pressure controlled fluid. The buffer volume or buffer chamber VO1 can be viewed as the source of this pressure control fluid. Conduits 8 and 9 constitute an inlet connector and an outlet connector for the respective ends of the parallel flow paths 31, 32 ... 39. Each of the paths has an inlet and outlet valve function - in case of path 31 the inlet valve function is represented by valve V5 and the outlet valve function is represented by valve V6 - and a fluid volume between the two valves - in the case of path 31 this volume is VO2 - so that each of the volumes between the valve functions can be filled with the fluid of defined pressure from the buffer chamber VO1 and thereafter can be connected to the user 2. In the case of the last path 39 represented in Figure 2, the inlet valve function is given by valve Vx, the outlet valve function by valve Vy and the chamber of given volume between the two valve functions is represented by the volume VOx. A third pressure sensor DA3 is operatively connected to conduit 9 and a signal corresponding to the pressure determined by this pressure sensor DA3 is supplied to the computer via the computer input CI3. The connection between the outlet connector line 9 connecting all the parallel outlets of the plurality of paths 31, 32 ... 39 and the inlet conduit to the user (in this particular case filter housing 2), is made via a vent valve V4 controlled by computer generated signals from the computer outlet CO5. The vent valve, if operating under venting conditions, releases fluid into vent line 5. This vent valve V4 serves to vent the user 2 in a normal operating cycle at the end of such a cycle and can also serve as a safety valve in case the pressure in line 9 should inadvertently rise above a set value. In the test procedure the filter housing 2 is connected to conduit 6 and the fluid source 3 is connected to conduit 4. Certain inputs are made to the computer as will be described in conjunction with Figures 3 and 4. The operation of the test procedure, which is fully automatically controlled by the computer, first opens valve V1 completely while the pressure in line 4 is measured by DA1 and a corresponding signal is received by the computer from computer input CI1. Valves V2 and V3 are also fully opened thereby filling the buffer chamber VO1 with test fluid. The path 31 with the highest flow resistance and the smallest volume VO2 is initially provided by opening valves V5 and V6 to supply test fluid via conduit 9 to conduit 6 and ultimately to the filterhousing 2. Valve V4 at this stage is fully opened, i.e. no fluid is being vented. This is the normal operation position of vent valve V4 which, as pointed out, is only used as a safety valve and for venting the user 2 at the end of a test cycle. The rise of the pressure in conduit 9 which corresponds to the rise of the pressure at the user 2 is determined via the pressure sensor DA3 and the respective information is provided to the computer via the computer input CI3. The computer determines the time/pressure behavior at this point. If the pressure increase at line 9 is too low, then the computer generates a signal to close both valves V5 and V6 and switches to the next higher path 32 by opening the respective valves. Each path 31, 32 ... 39 has its inlet valve and its outlet valve controlled automatically via a connection to a respective computer output so that the inlet valve and the outlet valve of each path can be operated independently. Thus for path 31 or path 39 respectively inlet valve V5 is controlled from computer outlet CO50, inlet valve Vx for path 39 is controlled from computer output COx and correspondingly outlet valve V6 of path 31 is controlled from computer outlet CO60 while outlet valve Vy is controlled from computer outlet COy. After switching to the path 32 with the next lower flow resistance and the next higher volume, the pressure/time behavior in line 9 is again determined by the computer and the switching to the next path is continued until the pressure/time behavior in the line is as desired. Then the flow of test fluid to the user 2 is continued until a pressure in conduit 9 and thus at the user 2 has been reached which is close to the test pressure, e.g. about 90% of the test pressure has been reached. Thereafter the flow of test fluid to the user 2 is reduced. This is accomplished by automatically closing valve V2 through a signal from computer output CO2 and operating the throttle D1 controlled by computer output CO4 so that the pressure rise, i.e. the pressure/time behavior is as desired, namely significantly slower than prior to closing valve V2. Once the pressure sensor DA3 indicates that the test pressure has been reached in line 9 and thus at the user 2 the computer generates a signal to close also valve V3. No more fluid is supplied to the user 2 and the pressure decay, the time/pressure behavior of the user 2, is determined via the pressure sensor DA3 and the values are registered in the computer from the computer input CI3. Based on this pressure decay information and additional information initially provided to the computer, the computer selects one of the paths 31, 32 ... 39, which when digitally operated will accomplish a compensation for the pressure decay by a number of cycles per time unit, which number is within a preset range. In other words, the computer selects automatically that one of the paths 31, 32 ... 39 for which under a given pressure differential between the respective chamber VO2 ... VOx when switched z times per minute into connection with the user 2 provides a compensation for the pressure loss registered via the computer input CI3, with the proviso that this number z be within a defined range. Preferably this range of digital fluid supplies through the respective path is in the range of 2 to 20, more preferably in the range of 6 to 10 per minute The initial selection by the computer of a given path may or may not accomplish the desired purpose. If this selection accomplishes the desired purpose and a defined number of digital gas supplies compensates exactly the pressure drop, for example, 1 digital gas supply of the respective path every 8.7 seconds, then this value is registered in the computer and further processed, displayed, etc. If, on the other hand, the goal by this initial selection by the computer of a path is not achieved then the operation continues as follows. At the given pressure differential between the buffer volume VO1 and the test pressure at the user 2 the smallest volume VO2 is supplied and the pressure/time behavior of the fluid in line 9, i.e. in the user 2, is determined. If this pressure/time behavior if still one of decaying pressure, then the path with the next higher volume is selected; again the pressure/time behavior in line 9 is determined; and again a switch to the path of next higher volume is accomplished, if the pressure is still falling. Then, once a path has been found for which the compensation for the pressure decay is accomplished and for which the number of cycles required are within the desired range, the operation is continued in that path, the value or values are registered for the process, etc. If the switching to the next path results in a pressure increase when the number cycles is at the lower limit of the desired range of cycles per unit time, then the computer either automatically switches back to the previous path with the next smaller chamber volume and increases the set pressure for the buffer chamber VO1, or it remains in that path and reduces the set pressure for the buffer chamber VO1. Correspondingly, if the path in which the digital fluid supply is being carried out at the upper limit of cycles per time unit still does not quite compensate for the pressure decay, e.g. it would require 13 switches or digital fluid supplies per minute rather than 6 to 10, then an increase in the pressure set point for the buffer chamber VO1 is automatically provided by the computer. Ultimately, the apparatus 1 operates so that the test pressure at the user 2 is maintained by digitally operating the fluid supply through the respective path and at a given pressure differential between the pressure of the buffer chamber VO1 and the user 2. These values then allow the computer to precisely determine and display the integrity and quality of the respective filter being tested. Thus in this specific example of filter integrity testing the computer selects in an iteration procedure a path with a given chamber volume, a pressure differential between the buffer chamber VO1 and the user 2 and a number of cycles or digital fluid supplies within the given range of cycles per time unit so that the pressure at the user 2 is maintained right at the test pressure. Typically the test pressure does not change more than 2 mbar during this steady state operation. Figure 3 schematically shows the computer CO as employed in the preferred embodiment of this invention. The computer has a first processor PRO1 and a second processor PRO2 which are connected by means of a datalink line DL. The first processor PRO1 essentially operates valves V1, V2 and V3 controlled by the pressure signal from the pressure sensor DA2, i.e., among other things, to maintain a set pressure in the buffer volume VO1. the second processor PRO2 receives the signal corresponding to the pressure in the pressure sensor DA1 via the input CI1 and the signal corresponding to the pressure in the pressure sensor DA3 via the input CI3. This processor operates the valves V4 via the output CO5 as well as the 2 * n valves V5, V6 ... Vx, Vy of the n paths 31, 32 ... 39 via the outputs CO50, CO6O ... COx, COy. This processor PRO2 is also operatively connected to a LCD display 101, to a key board 102 and to a printer 103. The principle steps of the automatic operation of the filter integrity test procedure are shown in the flow diagram of Figure 4. The first step ST1 consists in the adjustment of the test pressure. The value for this test pressure has been input to the computer before. In this stepST1 the valve V1 with valves V2 and V3 opened is adjusted so that the pressure at the sensors DA2 corresponds to preset pressure differential below the test pressure. In the next step ST2 the appropriate digital filling volumes are determined. This step in other words determines the initial path 31, 32 ... 39 which is to be used in the beginning of the pressure compensation operation with digital supply of a gas volume VO2 ... VOx. Details are given in the attached software program. In the third step ST3 the operating pressure for the buffer chamber VO1 is provided to the background processor PRO1 and in a cyclic operation the valve V1 is adjusted via the computer output CO1 so that the pressure in the buffer chamber VO1 is maintained at a constant value, namely a given amount above the test pressure. In the fourth step ST4 the system pressure limits for refilling to the user are fixed. In the fifth step ST5 the computer automatically sets the parameter for filling the user 2 with a computed fill volume and DELTA p. In the sixth step ST6 the actual flow is measured. In the seventh step ST7 the test time is determined. If this test time has not exceeded a preset value of e. g. 600 seconds, than the system returns into the program to resume step ST2. If the test time has not been exceeded than the system is vented in step ST8. Typical and therefore preferred ranges for individual process parameters, which also apply to the apparatus to this invention, are shown in the following:

Claims: A process for passing fluid from a source (3) of fluid through a controller (1) to a fluid user (2), in particular a filter testing unit, said controller comprising a plurality of parallel flow paths (31, 32.....39) each including a respective chamber (VO x ), the chamber of each path having a different volume from those of chambers of other paths, wherein one of said paths is used for fluid passage, said process being characterized by a) determining the pressure/time behavior of the user (2) and thereupon selecting one of said paths for said fluid passage, b) passing fluid through said selected one path to said user in a digital manner by alternatingly aa) opening an inlet of said selected path connected to said source (3) to fill same with fluid, an outlet of said path connected to said user being closed, bb) closing said inlet and opening the outlet of said selected path, thereby supplying a fluid volume as a fluid pulse to the user. A process in accordance with claim 1, further comprising, c) determining the pressure/time behavior of said user in step (a) by automatically measuring a pressure decay in said user; d) compensating the pressure decay by providing a fluid volume from the chamber of said selected path to said user by cycles according to step (b) to maintain the number of such cycles necessary per time unit to compensate the pressure drop speed within a predetermined range; e) repeating steps (c) and (d). A process in accordance with claim 1 or 2, wherein the number of cycles per minute is in a range of 4 to 12, more particularly 6 to 10 cycles per minute. A process in accordance with claim 1 or 2, wherein the volume sizes of the chambers (VO x ) of said paths form a series of volumes sizes from a smallest to a largest volume, in particular wherein each larger volume is significantly larger than the next smaller volume. A process in accordance with claim 4, comprising prior to step (a), the steps of passing fluid through the flow path with the chamber of smallest volume; automatically determining the pressure/time behavior of the user; if said pressure/time behavior is indicating too fast a consumption of fluid by the user, automatically switching to passing said fluid through the path with the chamber of next higher volume; repeating the above steps until the pressure/time behavior of the user is in a desired range. A process in accordance with one of the preceding claims comprising controlling the pressure of the source (3) of fluid at a value that equals a pressure set point, in particular wherein said pressure set point is 0.1 to 5 bar, more specifically 0.2 to 2 bar above the user-pressure. A process in accordance with claim 6, comprising carrying out one or both of the following steps if the pressure decay at said user is such that for the given pressure set point and for the operating flow path, the operation is outside of the desired ranges: a) changing the pressure set point for the supplied pressure fluid; b) switching to a new target path; with the proviso that the number of cycles required per time unit to compensate for the pressure drop with fluid at the given pressure set point and for the target path is within the desired or given ranges. A process in accordance with one of the preceding claims, wherein the fluid is a gas, preferably air, nitrogen, carbon dioxide, a noble gas or ammonia. A process in accordance with one of claims 1 - 4, in which the fluid user comprises a filter unit (2) comprising a filterhousing with a housing inlet, one or more pre-wetted filters arranged therein to divide the interior of the housing into two areas so that fluid can flow from one area to the other only through said filter(s), one of the areas being in fluid communication with the housing inlet, the other being in communication with the housing outlet, in which process said housing inlet is put into fluid communication with each of said outlet valves, and, prior to step (a): fluid is initially supplied until a first pressure has been attained in said user, which is near the test pressure; the fluid flow from the fluid supplier to the user is throttled such as to reduce the pressure increase per unit of time in the user until the test pressure has been established in the user housing inlet chamber; the connection between the fluid connection between the flow and the source of fluid is switched off. An apparatus for metering and controlling fluid flow comprising a plurality of parallel flow paths (31, 32......39) each including a respective chamber (VO x ), the chamber of each path having a different volume from those of the chambers of other paths, characterized in that each flow path (31, 32....39) is provided with an inlet valve (V x ) connecting said path with a fluid source (3) and with an outlet valve (V y ) connecting said path with a fluid user (2), and said apparatus comprises means for determining the pressure/time behavior of the user (2) and thereupon selecting one of said paths for said fluid passage, and means for controlling said valves in a selected path in order to pass fluid to the fluid user in a digital manner by alternately aa) opening an inlet valve of said selected path connected to said source (3) to fill same with fluid, an outlet valve of said path connected to said user being closed, bb) closing said inlet valve and opening the outlet valve of said selected path, thereby supplying a fluid volume as a fluid pulse to the user. An apparatus in accordance with claim 10, comprising a) a first connector unit (8, 10) for connection with a pressure controllable source (3) of fluid; b) each said chamber having a chamber inlet and a chamber outlet, said chamber inlet being arranged for a fluid flow connection with said first connector (8), in particular, wherein said chamber is otherwise closed; with the proviso that the volume sizes of the chambers (VO x ) of the path form a series of volume sizes from a smallest to a largest volume, in particular wherein each larger volume is significantly larger than the next smaller volume; c) a second connector (6, 9) unit for connection with a user (2) of fluid, said connector being in fluid communication with the outlet of each of said chambers; d) a plurality of actuating means adapted and arranged to independently operate each path such as to connect the individual chamber (VO x ) to the first connector (8) and/or to the second connector (9); e) a computer control unit (36) operatively connected to said actuating means (V x , V y ) for providing actuating signals to said actuating means for carrying out the respective connections and disconnections of said chambers. An apparatus in accordance with claim 11, wherein there are 2 * n actuating means each having an input and a manipulating output, said actuating means being adapted and arranged to operate and connected with its manipulating output to one of said n inlet valves or respectively n outlet valves upon the receipt of an actuating signal at the input thereof; and said computer control unit is operatively connected to said input's offset actuating means for providing actuating signals to the inputs of said actuating means. An apparatus in accordance with claim 12 or 13, further characterized by the following features: a) said actuating means are adapted to switch the corresponding valve (V x or V y ) upon receipt of the actuating signal from the open status to the closed status; b) a source-pressure-sensor (DA2) having its pressure sensing area in or near said first connector unit (8) and thus in fluid communication to the source of fluid (3) when connected and having its signal output (CI2) adapted for direct or indirect control connection to said source of fluid such as to provide fluid of controlled pressure from said source at said first connector independently of the flow rate; c) a user-pressure-sensor (DA3) having its pressure sensing areas in or near said second connector unit (9) and thus in fluid communication to the user and having its signal output (CI3) adapted for direct or indirect control connection to said computer such as to provide information on the pressure of the user when connected therewith; d) the pressure sensors (DA2, DA3) are adapted to operate under pressures up to 10000 mbar, in particular up to a pressure in the range of 50 to 6000 mbar; e) a pressure supply unit (10) having an inlet end for connection with a supplier (3) of pressurized fluid and an outlet end connected to said first connector (8), said pressure supply unit being adapted for providing fluid from said supplier at a constant pressure to its outlet end, and comprising one or more of the following elements: aa) a source-vent-valve (5) connected with its control input to a pressure-sensor arranged to sense the pressure of the fluid supplied by said supplier to said pressure controller; bb) a buffer chamber (VO1) just upstream of and in connection with said first connector (8); cc) said source-pressure-sensor (DA2) being arranged to sense the pressure in the area of the buffer chamber and first connector; dd) said buffer chamber (VO1) having two inlets, the first inlet thereof connected via an on-off valve (V2) and the second inlet thereof connected via an on-off valve (V3) in line with an adjustable throttle (D1) to said vent-valve; f) a user-vent-valve (V4) arranged between said second connector and the fluid user (2); g) each pressure sensor generates a signal at its signal-output which is correlated to the pressure it senses, and the signal outputs are connected to the computer and also all operating mechanisms of the valves are connected to said computer; h) each flow path is arranged and adapted to also provide a flow resistance to said fluid which is significantly different from that of the volume-wise preceding and following path; preferably the flow resistance of the path of the higher chamber volume being lower than the flow resistance of the path of the lower chamber volume and vice versa.

Inventors: RANDHAHN, HORST W. DR.
Applicants: PALL CORPORATION
Application year: 1987
Main classification: G01F11
IPC codes: G01F11, B01D65