US3049013A - Pressure control system - Google Patents

Description

Aug. 14, 1962 J. M. BOURGUET ET AL 3,049,013

PRESSURE CONTROL SYSTEM Filed Oct. 20, 1958 4 Sheets-Sheet l INVENTORS.

Jean M.B0urgue1 Roberr D.Drew

" AQQMMZ.

ATTOR Y.

Aug. 14, 1962 Filed 061;. 20, 1958 J. M. BOURGUET ET AL PRESSURE CONTROL SYSTEM 4 Sheets-Sheet 2 52 53 55 57 6l so 7 055K WM r r' FIG.2

Uni-directional g 65 67 Valve J Pressure Differential Process 2 Trunsmiher Chamber Uni-directional 75 Valve 70 Pressure Recording Apporufus INVENTORS.

FIG.3

Jean M.Bourguet Robert D.Drew

ATTORN EY.

1952 J. M. BOURGUET ETAL 3,049,013

PRESSURE CONTROL SYSTEM Filed Oct. 20, 1958 4 Sheets-Sheet I5 45 47 Pressure Differential Transmitter Pressure Recording Apparatus mmm \JKJ

FIG.4

Pressure Differential y 47 Transmitter 4o 48 Uni-directional L J 44 42 Valve 49 Pressure Recording Apparaius Fl (3 5 //v VEA/ TORS. Jean M.B0urguei Robert D.Dr

by QMMQM AT RNEY.

Aug. 14, 1962 J. M. BOURGUET ET AL 3,049,013

PRESSURE CONTROL SYSTEM Filed Oct. 20, 1958 4 Sheets-Sheet 4 Uni-directional 67 Valve GAS PROCESS 66 LIQUID 2 74 Pressure Differential Transmitter 65 I I Uni-directional GAS Valve Recorder and/or Control Apparatus Uni-directional Valve Transmitter or Pressure Booster/ Uni-directional Valve FIG.7

Recorder and/or Control Apparatus IN VENTORS. Jean M.'Bourguet Robert D.Drew

ATTO NEY.

nite rates "lie 3,049,913 PRESSURE EONTROL SYSTEM Jean M. Bourguet, Woodbury, and Robert D. Drew,

Wenonah, N.J., assignors to Socony Mobil Oil (30mpany, Inc, a corporation of New York Filed Oct. 20, 1958, Ser. No. 768,310 7 Claims. (Cl. 73388) This invention relates to instrumentation for direct measurement of the amplitude of the fluctuation of pressure in a process zone as a continuous function and to make control of this amplitude possible. It is particularly applicable to the control of a pneumatic lift used to elevate granular catalyst in a stream of rapidly rising lift gas for recycle in the moving bed hydrocarbon conversion processes.

Various processes, such as cracking, reforming, coking, desulfurization, etc. use a granular contact material or catalyst with the hydrocarbons being brought into contact with the catalyst under pressure and temperature conditions found to permit eflioient conversion of the hydrocarbons to more desirable products. The TCC or Thermofor Catalytic Cracking process is the most widely used moving bed process and recent TCC units have utilized a pneumatic lift for elevation of the granular contact material. This invention will, therefore, be described with respect to its application in the TCC process. It Will, of course, be appreciated that the invention finds application in a variety of processes and is not limited solely to the TCC process.

In the TCC process the catalyst is gravitated as a continuous column from the lift hopper, through an elongated vertical feed leg into an advanced pressure reactor, from the bottom of the reactor downwardly through a kiln and from the bottom of the lciln to a lift pot. The particles are propelled in a rapidly moving stream of lift gas, usually air, from the lift pot through a lift pipe to the elevated lift separator. The particles travel in dispersed form, accelerate rapidly in the lower portion of the lift pipe to a maximum velocity and then gradually drop in velocity to a desired low discharge velocity. The pipe is usually tapered to accomplish the proper velocity control.

The critical features of catalyst velocity control in the lift have been developed and are described now in the patent literature. It is sufficient for this application to state that there is a minimum pressure drop across the lift for any given set of conditions which produces minimum attrition and that this point can be found by reducing the total air to the lift until the pressure drop across the lift reaches a minimum and commences to increase with further gas reduction. While these facts are well known now, it is difficult to continuously maintain a pneumatic lift in operation at the point of minimum attrition because of slight changes in gas flow, temperature, pressure, etc. which occur in the process. The lift tends to drift from the point of minimum attrition and any movement from this point results in undesirable increase in attrition. Unfortunately, this drift is diflicult to recognize and unnecessary catalyst dam-age occurs long before the shift can be recognized.

This invention is based on the observation that the fluctuation of a main variable, such as the pressure in a pneumatic lift pipe, is often a better indication of the stability of the operating conditions than the main variable itself. When upsets are beginning to take place, the fluctuation of the main variable often increases before the absolute value of the variable starts to change appreciably. Also, the ratio of fluctuation of the main variable to the value of the main variable is often so small that it does not even appear on the recorder or indicators used to measure the main variable. This is decidedly unfortunate since the detection of the fluctuation of the main variable, such as, for instance, the fluctuation of pressure in a pneumatic lift, would give a warning in case of an approaching upset in lift conditions and hence correction could be made before any real damage took place. Detection through the main variable, such as the pressure in the lift pipe, is possible but often too slow to give a warning and the upset in operating conditions is so advanced when detected by observation of the main variable that damage has been done to the process and a loss has already been suffered. As an example, in a pneumatic lift operation elevating granular catalyst in a TCC system, an increase of the pressure in the lift pipe of 25 percent means that the operation has gone into an undesirable surging condition. The corresponding increase of the fluctuation in pressure is 5 0 percent and hence it is seen that the pressure fluctuation is a far more sensitive indicator than the pressure itself.

The object of this invention is to provide a method and means of suppressing a main pressure variable in a process while keeping only the fluctuation of the pressure for record on a zero-centered instrument.

A further object of this invention is to provide a method and means of suppressing a pressure variable in a process while keeping only the fluctuation of the pressure for record on a zero-shifted instrument.

A further object of this invention is to provide a method and means of measuring the average amplitude of fluctuation of pressure in a process to permit this average amplitude to be used for control purposes.

These and other objects will become obvious from the following detailed description of the invention to be read in conjunction with the attached figures.

FIGURE 1 is a diagrammatic representation of a TCC system with the apparatus of the invention incorporated for lift control purposes.

FIGURE 2 is a vertical sectional view showing valve control means developed as a part of this invention.

FIGURE 3 is a diagrammatic showing of apparatus arranged in accordance with the invention to indicate average pressure amplitude.

FIGURE 4 is a diagrammatic showing of apparatus arranged in accordance with the invention to indicate pressure fluctuation on a zero-centered instrument.

FIGURE 5 is a diagrammatic showing of apparatus arranged in accordance with the invention to indicate pressure fluctuation on a zero-shifted scale.

FIGURE 6 is a diagrammatic showing of apparatus arranged in accordance with the invention to indicate pressure fluctuation of a processing liquid which. has a fluctuating pressure during operation of the process.

FIGURE 7 is a diagrammatic showing of apparatus arranged in accordance with the invention to indicate pressure fluctuation in readable magnitude when the pressure fluctuation in the process is too feeble to be used directly.

In one important aspect, the invention involves communicating a first and second pressure indicating zone with a process zone to permit fluid to transfer from each zone to the other and sufliciently restricting the transfer of fluid between the first and second indicating zone to develop between the two zones a pressure differential which is directly related to the pressure fluctuation in the process zone so that this pressure differential can be read directly and used to effect control of the operation of the process. The invention will now be described in detail first by a discussion of the T CC process where the invention is used to control the operation of the pneumatic lift at maximum efliciency operation with minimum attrition.

Referring now to FIGURE 1, a diagrammatic showing of a TCC system, a reactor 10 is shown in superimposed position with a kiln 11 of annular cross-section through which is located a vertically extending pneumatic lift pipe 12. At the base of the lift pipe is located a lift pot 13 and associated gas apparatus for elevating the catalyst in dilute phase form through the lift pipe 12 to a separator 14. The gas and catalyst separate in the separator 14, the gas being discharged to the atmosphere through the pipe 15, the catalyst settling to the base of the separator 14 to form a compact gravity flowing mass. Catalyst is withdrawn from the bottom of separator 14 through an elongated gravity feed leg 16 into the reactor 14} which is maintained under advanced pressure and temperature. A seal gas such as steam or flue gas is introduced into the lower section of the gravity feed leg through a conduit 17 controlled by the valve 18 by means of a suitable feed pot 19. This gas is introduced at slightly higher than reactor pressure so that some gas will flow downwardly with the catalyst into the reactor to prevent the escape of reactants from the reactor. The remainder of the seal gas flows upwardly through the seal leg countercurrently with the catalyst and escapes to the atmosphere through the vent pipe 20. Suitably prepared hydrocarbon reactants are introduced into the reactor through the conduit 21 and travel concurrently with the catalyst and through the void spaces in the bed to the lower section of the vessel. The conditions are maintained so that a substantial amount of the reactants are cracked in the presence of the catalyst to provide an increased amount of high octane motor fuel. The reaction products are withdrawn from the catalyst through the conduit 22 and pass through suitable processing apparatus not shown. During the cracking reaction a carbonaceous deposit is formed on the catalyst and the spent catalyst is Withdrawn continuously from the bottom of the reaction vessel 10 through the multiplicity of conduits 23 and transferred to the top of the kiln 11. Air is introduced into the gravitating bed of catalyst in the kiln 11 through the conduit 24. A portion of the air travels upwardly through the bed to burn a portion of the contaminant on the catalyst, the flue gas being discharged to the atmosphere through the conduit 25 located near the top of the Vessel. The remainder of the air travels downwardly through the catalyst bed to complete the combustion of the contaminant, the flue gas being discharged to the atmosphere through the conduit 26. The regenerated and reheated catalyst is withdrawn from the bottom of the kiln through the conduits 29 and introduced into the lift pot 13. It is seen that the catalyst travels as a continuous compact gravitating stream from the hopper 14 downwardly through the various vessels to the lift pot 13. The speed of gravitation of the catalyst is controlled by the rate of removal of catalyst from the lift pot 13 through the lift pipe.

A blower 30 is used to provide air under a modest pressure of, for example, 5 to 10 p.s.i.g. or less to the lift. The air travels to the conduit 31, the flow being measured by the meter 32. This air stream is then split into a secondary'stream 33, which is introduced into the catalyst bed around the lower end of the lift pipe and is used to control the flow of catalyst into the lift pipe. The remainder of the lift gas is passed through the conduit 34 which projects upwardly into the bottom of the lift pipe and introduces this air stream into the lift pipe without passing through any substantial thickness of catalyst bed in the lift pot 13. By this expedient the total flow of air can be controlled independent of the flow of catalyst. The flow measuring instrument 32 is connected to controller 35 which operates automatic valve 36 in line 34 to maintain the total flow rate of air to the lift substantially constant. A controller 37 is connected to the top of the lift pot 13 by the conduit 38 and the controller operates an automatic valve 39 so as to maintain the pressure in the upper portion of the lift pot substantially constant, thereby maintaining substantially constant catalyst flow.

It has been discovered that for minimum attrition in the pneumatic lift the velocity conditions of the catalyst must be carefully controlled. A rapid acceleration is desirable in the lower portion of the lift up to a maximum critical velocity, at which point the catalyst must then be gradually reduced in upward velocity to a critical discharge velocity. Slight changes in velocity pattern of the catalyst in the lift will cause substantial change in efliciency of operation of the lift and damage to the catalyst or attrition rate. These facts have been discussed fully and completely disclosed in Patent Number 2,819,121 issued January 7, 1958. The patent teaches that for control of a lift of this type so as to provide minimum attrition in the lift, the gas flow through the lift must be controlled to maintain a pressure fluctuation in the upper portion of the lift at a fixed ratio of the pressure fluctuation at the bottom of the lift. This invention provides a method and means for automatically reading or controlling the lift as a result of such reading of the pressure fluctuation in the upper portion of the pneumatic lift. While the invention was made to solve this specific problem, it of course has broader application and can be used in many other circumstances where a measure of pressure fluctuation is a valuable indicator.

Referring now to FIGURE 4, 4 19 represents a vessel in which a pressure fluctuation is taking place. Vessel 4% may be a portion of the lift pipe 12 of FIGURE 1. Attached to the vessel 4th by means of a conduit 41 is a chamber 42. The connection at between vessel and 42 is arranged so that the pressure in chamber 42 follows quite faithfully the pressure in the vessel .10. A second chamber 43 is attached to the chamber i2 by means of a conduit 44. In the conduit 44 is a flow restricting device 45 so that there is restricted communication between the chambers 4-2 and 4-3. For any given pressure fluctuation this flow restriction can be adjusted so that chamber 43 will reach a pressure intermediate between the maximum pressure obtained in chamber 42 and the minimum pressure obtained in chamber 4 2, and furthermore this flow restriction can be so adjusted that the pressure in chamber 43 remain substantially constant. Chamber 42 is connected by means of conduit 46 to a pressure differential transmitter 47, and chamber 4-3 is connected by conduit 48 to the same pressure di'lferential transmitter. Thereby the pressure difference between chambers 42 and 43 can be read directly and transmitted by connection 49 to a pressure recording apparatus 5 3?. It is seen that by this expedient a full-scale direct reading zero-centered indication of the pressure differential occurring in vessel 46 is provided. Hence, even though the pressure fluctuation in the vessel 40 may be only a very small portion of the absolute pressure in the vessel, it can be measured as a full-scale reading by the apparatus of this invention.

FIGURE 5 shows a modification of the apparatus in which the fluctuation is recorded as a full-scale reading on a pressure recording apparatus but with the zero of the instrument displaced from its center position. The apparatus arrangement is very similar to the apparatus of FIGURE 4 and hence identical numbers have been used for identical pieces of apparatus. In the apparatus combination of FIGURE 5, however, in place of the flow restricting device 45, a unidirectional valve 51 is used. Suitable unidirectional valves adapted to operate on very slight pressure differential were not found in the market and hence the apparatus combination of FIGURE 2 was designed for this purpose. Referring now to FIGURE 2, the conduit 52 connects to the chamber 42 and has in it a jet 53 designed to control the flow rate of the air from the chamber 42 to the chamber 43. A valve plate 54 hinged at one end 55 is adapted to close over the end of the conduit 52. A spring 56 is located between the plate 54 and a fixed bracket 57 so as to provide bias toward the closed position. A connecting rod 58 is attached to the valve 54 and extends through the body 59 of the valve. A cap 60 is threaded on the end of the connecting rod 58 and designed to put variable tension on spring 61. By this arrangement a fine adjustment of the closing pressure on the valve plate 54 can be maintained. By appropriate adjustment of the valve springs, gas will flow from chamber 42 to :3 when the pressure in the chamber 42 is sufficient to open the valve, but when the pressure in the chamber 42 drops, the valve will close preventing the flow of gas from the chamber 43 to the chamber 42. By appropriate adjustment the pressure in the chamber 43 can be adjusted to substantially the maximum pressure occurring in the chamber 48. In processes of this type unusual pressure fluctuations occur from time to time and in order to prevent chamber 43 from indicating only unusually high pressure fluctuations, a bleed orifice 62 is located in the pipe 52 and an adjustable needle valve 63 is provided so that only a very small bleed stream of gas is permitted to transfer back from the chamber 43 to the chamber 42. This will permit the chamber 43 to com pensate for unusual pressure fluctuations and will permit the chamber 63 to indicate generally the maximum pressure occurring in the chamber 4! As seen, therefore, on the pressure recording apparatus 64, the zero of the indicator has been shifted by this apparatus combination to one side of the meter so that the pressure fluctuation can be read full scale on a zero-shifted instrument.

For control purposes it is highly desirable to have the fluctuation of pressure indicated as a substantially constant value between maximum and minimum limits. The apparatus combination of FIGURE 3 is adapted to provide this result. The process chamber 65 is connected to a conduit 66. A conduit 67 is connected to a detecting chamber 63 and has in it a unidirectional valve 69 so that fluid is permitted to flow only from the process chamber into the detecting chamber 68. Another conduit 79 is connected to the conduit 66 and also to a detecting chamber 72.. In the conduit 76? is located a unidirectional valve 72 arranged to permit fluid to flow only from the detecting chamber 71 to the process chamber 65. By this arrangement the maximum pressure occurring in the process chamber will be maintained in the detecting chamber 63 whereas the minimum pressure occurring in the process chamber 65 will be maintained in the detecting chamber 711. It will be understood, of course, that the conduits 67 and 70 could be connected directly to the process chamber as long as their connection was sufficiently close to each other. A bleed line 73 with valve 74 therein is provided to maintain a very slight flow of gas between chambers 68 and 71. It is apparent that without such a bleed, chamber 68 would maintain a pressure equal to the highest pressure which had occurred in the process at some earlier time, and likewise chamber 71 would maintain a pressure equal to the lowest pressure which had occurred in the process at an earlier time. The device would then not be indicating the current maximum and minimum pressures, and would, in effect, be inoperative. The slight flow of fluid between chambers 68 and 71, and through bleed line 73 and valve 74-, will relieve these high and low pressures to a level where the present pressure levels existing in the process will determine the pressures in chambers 68 and 71 by passing through unidirectional flow control means 69 and 72. This flow can be made so small that it will normally have no substantial effect upon the pressure differential maintained between the first detecting chamber and the second detecting chamber. The first detecting chamber is connected to a pressure differential transmitter 7 5 by means of connection 76 and the second detecting chamber is connected to the pressure differential transmitter 75 by means of connection 77. This substantially constant pressure differential, being a measure of the amplitude of pressure fluctuation in the process chamber 65, can thereby be transmitted directly to a pressure recording apparatus 78 providing a substantially uniform reading. Alternatively, this pressure differential can be used to operate known apparatus for adjusting conditions in the process chamber to maintain the pressure differential substantially constant. This apparatus combination is particularly useful in the con- 5 trol of pneumatic lifts such as is indicated in Patent Number 2,819,124 which issued January 7, 1958.

Referring to FIGURE 6, there is shown an apparatus combination similar to that disclosed on FIGURE 3 but adapted for use particularly with a process liquid. Similar elements have been given similar numbers for simpliflcation of description.

It is seen on FIGURE 6 that liquid is transferred from the process chamber 65 to the first detecting chamber 68 when the pressure reaches the maximum in the chamber 65, and liquid is transferred from the second detecting chamber 71 when the pressure in the process chamber 65 reaches its minimum value. A diaphragm 79 is located across the first detecting chamber 68 to separate the chamber into a liquid compartment and a gas compartment. Similarly, a diaphragm Si is located across the second detecting chamber to also separate this chamber into a liquid compartment and a gas compartment. By this arrangement the pressure is transmitted from an incompressible fluid to a compressible fluid and the pressure is then transmitted through the compressible fluid to the differential transmitter 75. This pressure ditferential can then be used to operate a recorder or a control apparatus in a manner similar to that described with respect to FIGURE 3.

FIGURE 7 shows a somewhat similar arrangement to that disclosed with respect to FIGURES 3 and 6 but provides additionally means for increasing the pressure differential indication so as to facilitate the use of pressure differential for control purposes. The same numbers have been used to identify the same parts as used in FIGURES 3 and 6. While this embodiment is obviously very similar to that disclosed with respect to FIGURE 3, there is located in the conduit 66 a transmitter or pressure booster 81. This pressure booster has the ability to increase the pressure indication it receives from the process chamber 65 a fixed number of times. By this expedient the pressure maintained in the first and second detecting chambers is substantially increased and the differential maintained between these chambers is also increased. This is necessary in many instances because pressure recording or control apparatus operates more efficiently under substantial pressure. The transmitter or pressure booster 81 will not be described here in detail as it is commercially available in a variety of forms. Pneumatic transmitters for this application would normally have an output signal ranging from a minimum of 3 p.s.i.g. when the input signal was at its own minimum, to a maximum output of 15 p.s.i.g when the input signal was at its own maximum. The input range of the transmitter must be sufliciently large so that the process conditions are at all times within that range. A typical pneumatic transmitter for this use in connection with the monitoring of TCC lift pipe pressure fluctuation has an output range of 3 to 15 p.s.i.g. when the input signal varied from O to l p.s.ig. for full range An example of a commercially available transmitter of this type would be a Taylor Model No. 206RF2.

Description of Reduction to Practice The method and equipment described herein were used to control a pneumatic lift elevating granular catalyst by means of an air stream. This lift had the following characteristics:

The apparatus was operated at optimum conditions for minimum attrition, and also at conditions of too high and too low lift air rates, both of which give excessive catalyst attrition. The following characteristics of operation for the apparatus of this invention were obtained:

Lift Air Rate, Percent of 110 High 100 Opti- 95 Surg- Optimum. Velocity. mum. ing.

Pressure, 82 Ft. Elevation in {6.4 HzO 10.5 HZO 13.5 H20.

Lift Pipe, H20 and p.s.i.g. 0.23 0.38 0.49.

Percent Change from Opti- 40 30.

mum.

Pressure Fluctuatioiii, 8% Ft. 2.2 H10. 4.4 1320.-.. 6.7 H 0.

Elevation in Li t ipe, 4 H20 and Sig. 0.08 0.16 0.2..

Percent Change from Opt1- 50.

mum.

Pressure Maintained in Low 7.9.

Pressure Chamber, p.s.1. g.

Pressure Maintained in Bligh 10.1.

Pressure Chamber, p.s.1.g.

Pressure Difierence Between 2.2.

High and Low Pressure Chambers, p.s.i.g. Times Real Fluctuation 11 9.5 9.2.

It can readily be seen that the pressure fluctuation is more sensitive to slight changes in the operation than is the pressure itself, and that the fluctuating pressure, after passing through a pressure booster, was converted into separate high and low pressures which were proportional to the fluctuation itself with a boosting rate of 10 fold. The separate high and low pressures have successfully been used in conjunction with a differential pressure transmitter and other known apparatus, such as described in US. Patent No. 2,819,121, for adjusting the lift air rate to maintain optimum conditions.

The invention has been disclosed hereinabove for use and control of a pneumatic lift and with respect to the figures provided with this application. It is understood that the invention will have broader utility, and alternate uses of the invention are therefore contemplated. The only limitations intended are those found in the attached claims.

We claim:

1. Apparatus for measuring the amplitude of pressure fluctuation in a chamber which comprises a first detecting vessel, a second detecting vessel, a conduit connected between the first and second vessel, conduit means connecting at least one of the detecting vessels with said chamber, means located in the conduit between said first and second detecting vessels adapted to maintain a substantially constant pressure in at least one of the detecting vessels, bleed means associated with each constant pressure vessel adapted to prevent pressure lock while substantially preventing pressure change in said constant pressure vessel for a period longer than that required for a complete wave length of the fluctuating pressures and a differential pressure indicating means attached to both the first and second detecting vessels, adapted to indicate the pressure difi'erential between the first detecting vessel and the second detecting vessel.

2. Apparatus for measuring the amplitude of pressure fluctuation in a chamber which comprises in combination: a first detecting vessel, a second detecting vessel, communicating conduit means between said first and second detecting vessels, a first unidirectional fiow control means in said communicating conduit means, adapted to allow fluid to enter the first detecting vessel while substantially preventing the backward flow of fluid from said first detecting vessel, a second unidirectional flow control means in said communicating conduit means adapted to allow fluid to leave the second detecting vessel while substantially preventing the backward flow of fluid into said second detecting vessel, conduit means communicating the chamber with the communicating conduit means at a location intermediate the first and second unidirectional flow control means, a differential pressure transmitter attached to the first and second detecting vessels, adapted to determine the pressure difference between the first and second detecting vessels, and a recorder attached to said differential pressure transmitter, adapted to record the pressure differential between the first and second detect- 3 ing vessels whereby the amplitude of the pressure fluctuation in the chamber is obtained.

3. Apparatus for measuring the amplitude of pressure fluctuation in a chamber which comprises in combination: a first detecting vessel, a second detecting vessel, conduit means connected between the first and second vessel, a directional flow control means located in said conduit means, adapted to permit flow of fluid from the first to the second detecting vessel while substantially preventing flow of fluid from the second to the first vessel, a flow restricting device in said conduit means, located between the first detecting vessel and the directional flow control means, adapted to substantially inhibit sudden pressure changes in the flow control means, a connecting conduit between the chamber and the first detecting vessel, and a diiferential pressure indicating means attached to both the first and second detecting vessels, adapted to indicate the pressure differential between the first detecting vessel and the second detecting vessel.

4. Apparatus for measuring the amplitude of pressure fluctuation in a chamber which comprises in combination: a first detecting vessel, a second detecting vessel, conduit means connected between the first and second vessel, flow restricting means located in said conduit means, a conduit connecting the first detecting vessel with the chamber, and a differential pressure indicating means attached to the first and second detecting vessels, so as to determine the pressure diflerential between said vessels, the flow restricting means being adjusted to maintain the pressure in the second detecting vessel substantially constant intermediate the maximum and minimum pressure present in the chamber, for a period of time greater than the time required for a complete wave length of the fluctuating pressure.

5. Apparatus for measuring the amplitude of pressure fluctuation in a liquid under pressure in a chamber which comprises in combination: a first detecting vessel, a second detecting vessel, conduit means connected between the first and second vessel, a first unidirectional valve located in said conduit means adjacent said first detecting vessel, adapted to prevent escape of liquid from said first detecting vessel, a second unidirectional valve located in said conduit means adjacent said second detecting vessel, adapted to prevent liquid from entering said second detecting vessel, a connecting conduit between said chamber and said conduit means, attached to said conduit means between the first and second unidirectional valve, bleed means associated With said first and second vessel, adapted to prevent pressure lock in said vessels, a first diaphragm located across the interior of the first detecting vessel, adapted to provide a liquidfree gas indicating region, a second diaphragm located across the interior of the second detecting vessel, adapted to provide a liquid-free gas indicating region, conduit means communicating the liquid-free gas indicating re gions of the first and second detecting vessels with a pressure differential measuring device, whereby the amplitude of the pressure fluctuation of the liquid in the chamber is thereby determined.

6. In a process in which a fluid pressure is developed in a confined zone and the pressure fluctuates periodically from a maximum to a minimum value, the improved method of measuring the amplitude of the pressure fluctuation comprising transferring fluid between the confined zone and a first indicator Zone, transferring fluid from the first indicator zone to a second indicator zone when the pressure in the first indicator zone rises to a predetermined value greater than the pressure in the second indicator zone, at a flow rate suflicient to maintain in the second indicator zone a pressure intermediate the maximum and minimum pressure developed in the confined zone, restricting the flow of fluid from the first indicator zone to the second indicator zone to a value low enough to substantially suppress pressure fluctuation in the second indicator zone, bleeding fluid continuously from the second indicator zone to the first indicator zone at a low enough flow rate to prevent any substantial reduction of pressure in the second indicator zone, so as to compensate for irregular or unusual pressure fluctuations, and measuring the pressure differential between the first indicator zone and the second indicator zone, Whereby the amplitude of pressure fluctuation is obtained directly on a zero-shifted measurement.

7. In a process in which a fluid pressure is developed in a confined zone and the pressure fluctuates periodically from a maximum to a minimum value, the improved method of measuring the amplitude of the pressure fluctuation comprising transferring fluid from the confined zone to a first indicator zone When the pressure in the confined zone rises and preventing the return of said fluid from said first indicator zone when the pressure in the confined zone falls, transferring fluid from a second indicator zone to the confined zone when the pressure in the confined zone falls and preventing the return of fluid to said second indicator zone when the pressure in the confined zone rises, transferring continuously a small bleed stream of fluid from the first indicator zone to the second indicator zone, so as to correct for unusual pressure fluctuations in the confined zone, and determining the dilferential in pressure between the first and second indicator zones to obtain a continuous indication of the magnitude of pressure fluctuation in the confined zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,005,773 De Florez June 25, 1935 2,378,227 Lee June 12, 1945 2,445,335 Philorick et a1. July 20, 1948

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