GB2149125A - Flow prover - Google Patents

Abstract

The flow prover for calibrating continuous flowmeters includes a measuring housing 2 comprising a main cylinder 9 having a substantially uniform inside diameter and inlet (6) and downstream (10) sections having inside diameters greater than the main cylinder 9. A displacer 7 movably disposed within the housing 2 has seals 28, 29 which form a fluid barrier while the displacer 7 is disposed within the main cylinder 9. Inlet and downstream section guide means maintain the displacer 7 in axial alignment with the main cylinder 9 while the displacer is disposed within either of these sections 6, 10, assuring smooth exit and entry. The seals 28, 29 are circumferentially compressed when the displacer 7 enters the main cylinder 9 and may be statically or dynamically monitored for integrity without an external pressure source. Means for returning the displacer 7 from the downstream section 10 to the inlet section 6 following a proving cycle and means for detecting the longitudinal disposition of the displacer 7 during a proving cycle are provided. The flow prover also includes an inlet conduit 1, an outlet conduit 11, and a valved bypass conduit 3 fluidly connecting them. The bypass valve 4 is of simple poppet construction, designed to operate at the differential pressure of the flow prover, which is considerably lower than the rated internal pressure of the flow prover. <IMAGE>

Description

SPECIFICATION A compact flow improver This invention pertains to the volumetric measurement of flow and, particularly, a compact flow prover useful in periodically calibrating a continuous flowmeter in a pipeline without interrupting the flow of fluid therethrough.

The compact flow prover of this invention falls generally into that class of flow provers characterized by the measurement of the movement of a piston traveling through a cylinder.

This invention pertains specifically to a compact flow prover having the improved qualities of accuracy, dependability, infrequent and simplified maintenance, simple and light weight construction, low space requirements, and operating flexibility.

One type of device commonly employed for determining the accuracy of a continuous flowmeter is known as a calibrating loop. This device typically comprises a long run of pipe through which a free moving plug or sphere is propelled by the fluid moving therethrough.

By measuring the time that it takes the object to move from one detector switch to another, the rate of fluid flowing through the flow loop can be determined. This type of device is the subject matter of U.S. Patent 2,948, 142 to Zimmerman, U. S. Patent 2,948, 143 to Pruitt, U. S. Patents 3,423, 988 and 3,668, 923 to Grove, and U. S. Patent 3,530, 705 to Lathrop. Calibrating loops generally require a substantial length to maintain a usable accuracy. The high cost of these devices prevents their use in all but the most critical situations.

The use of positive displacement piston-type flowmeters is well documented. Examples of this type of flowmeter which are not particularly suited for calibration purposes include U.S. Patent 1,586,834 to Ormsby, U. S.

Patent 2,652,953 to Gray, U. S. Patent 2,892,346 to Sargent, and U. S. Patent 4,096,747 to Gilson.

An example of a positive displacement piston-type flow prover useful in calibrating flowmeters is seen in U. S. Patent 3,021,703 to Pfrehm which discloses a bidirectional, free-moving piston in a calibration barrel. The movement of the piston is detected by two detector switches which are mechanical in nature, located toward either end of the calibrating barrel. In order to obtain usable accuracy, a considerable run of pipe is required.

For example, if the accuracy of the detector switch is + 0.1 cm, a run of pipe of 13m or more is required to yield desired accuracy of + 0. 02%. In addition, since the detector switch protrudes into the calibrating barrel and the outlet ports are connected to the calibrating barrel, the piston seals will be subject to wear each time they pass the switches and the outlet ports. Because valves must be opened and closed simultaneously, further inaccuracies may be introduced into the measurement and serious disruption of flow may occur.

A device similar to U. S. Patent 3,021,703 is disclosed in U. S. Patent 3,580,045, also to Pfrehm. The device differs from U. S.

Patent 3,021,703 in that the mechanical detector switches are replaced with external proximity switches which detect the passage of a steel band on the piston. The use of a four way spool valve which reduces the complexity of the valving arrangement is also disclosed. However, it is believed that the seals of this valve are subject to wear and leakage and are not amenable to monitoring of seal integrity.

U.S. Patent 3,273, 375 to Howe discloses another type of flow prover comprised of inner and outer tubular members and a free-moving piston located in the inner tubular member.

This arrangement allows for a simpler valving system and eliminates the need for pressure correction. However, the device uses the same external proximity switches discussed above and it is believed that the piston seal life is not greatly improved because the piston must move past outlet ports. In addition, special arresting means are required to stop the movement of the piston at either end of the calibrating barrel. Moreover, it is believed the complicated construction makes assembly and maintenance difficult.

U.S. Patents 3,492,856 and 4,152,922, both to Francisco, disclose flow provers from which outlet ports on the calibrating barrel are not necessary. These devices utilize a flowthrough piston having a poppet valve in the piston which may be closed during the proving cycle. The poppet valve requires pressuring means such as gas to close the poppet valve at the beginning of the proving cycle.

The pressure required to keep the poppet valve closed during the proving cycle results in a significant pressure drop across the piston. In addition, the mechanical arresting means which are required to stop the piston at the end of the proving cycle cause perturbations in the fluid flow and produce high shock loads in the mechanical components.

U. S. Patent 3,492, 856 uses external proximity switches located on the calibration barrel and retrieves the piston at the end of the proving cycle by means of a cable and drum.

U. S. Patent 4,152,922 discloses a piston retracting means comprised of a rod connected to a measuring piston which has at its other end a retracting piston located in a hydraulic cylinder. The movement of the measuring piston is detected by proximity switches which detect the movement of the retracting piston in the hydraulic cylinder. In this prover, the measuring piston seals may be damaged by the presence of entrained solids such as grit or sand which may be in the measured fluid and become trapped be tween the calibrating barrel and the piston seals. If this prover is operated in a horizontal position, the situation is aggravated since the solid particles will tend settle along the bottom of the cylinder.

A further problem associated with the flow provers heretofore mentioned is that horizontal operation results in reduced piston seal life along the bottom of the piston because of the weight of the piston.

It is a feature of this invention to provide a compact flow prover which does not have the disadvantages associated with the devices heretofore known. A further feature is to provide a compact flow prover with improved accuracy and dependability, reduced space and weight requirements, simplified construction and maintenance, and operating flexibility. These and other features will be apparent to those skilled in the art in the following description of the invention.

The compact flow prover of this invention determines the rate of flow by measuring the time in which a displacer traveling through a cylinder displaces a known volume of fluid.

The compact flow prover of this invention comprises a measuring housing, a displacer moveably disposed along the axis of the measuring housing, and means for detecting the longitudinal disposition of the displacer in the measuring housing. The housing defines three distinct sections including a hollow main cylinder with inlet and downstream sections attached at either end. The main cylinder has a substantially uniform inside diameter. The displacer is provided with seals along its periphery which forms a fluid barrier while the displacer is disposed within the main cylinder.

The cross-sectional area in the inlet and downstream sections is larger than that of the main cylinder so that fluid may flow past the displacer when it is disposed within either of these sections. Guide means are provided in the inlet and downstream sections of the housing for maintaining the displacer in axial alignment with the main cylinder when it is disposed within either of these sections.

Means are provided for encouraging the displacer to enter the main cylinder from the inlet section at the start of a proving cycle.

Means are also provided for returning the displacer from the downstream section to the inlet section at the end of a proving cycle.

Operation of the compact flow prover of this invention is simple. With the displacer held in the inlet section by the return means, flow of the fluid to be measured is initiated into the inlet section and through the main cylinder and downstream section. After the return means are released, the encouraging means, and the flow of fluid through the inlet section cause the displacer to move toward the main cylinder. The inlet section guide means ensure a smooth entry of the displacer into the main cylinder by maintaining the displacer in axial alignment with the main cylinder. Once it enters the main cylinder, the displacer is propelled therethrough by the flow of the measured fluid.

As the displacer moves through the main cylinder, the time required for it to move a predetermined longitudinal distance corresponding to a known volume is measured and may be used to calculate the rate of fluid flow. The downstream section guide means maintain the displacer in axial alignment with the main cylinder as it exits therefrom and enters the downstream section. The flow of fluid through the housing is terminated or bypassed and the return means are used to bring the displacer from the downstream section. through the main cylinder and into its launch position in the inlet section. The compact flow prover is then ready to begin another proving cycle.

An advantage of the compact flow prover of this invention is that the flow of fluid past the displacer while it is disposed within the inlet and downstream sections provides a cleansing of the displacer seals which tends to remove any solid material which may be deposited therein. This cleansing extends the useful life of the displacer seals. Another advantage is that fluid flows through the entire cross-section of the main cylinder along its entire length so that no dead spots develop which would tend to allow suspended particles to settle, especially when the prover is operated in the horizontal position. Still another advantage is that the displacer may be of light weight construction resulting in less wear on the displacer seals in the interior surface of the main cylinder. The single barrel construction also facilitates assembly and maintenance accessibility.

In a specific implementation of the compact flow prover of this invention, fluid is introduced into the inlet section of the measuring housing by means of an inlet conduit. The fluid leaves the measuring housing through an outlet conduit in communication with the downstream section of the measuring housing. Means for bypassing the measuring housing is provided which includes a valved bypass conduit fluidly connected to the inlet and outlet conduits. In a preferred implementation, an improved bypass valve is provided which has a simpler construction and operation than bypass valves heretofore known.

Since the. bypass valve does not have to anticipate differential pressure across the valve equal to the rated internal pressure of the flow prover, the valve can have a simple poppet construction rated for considerably lower pressure, thus offering an economical advantage over conventional valves. The improved bypass valve provided also has the advantage of enabling monitoring of its seal integrity without an external pressure source which is required to monitor the seals of known bypass valves.

In another implementation, the displacer return means comprise a hydraulic cylinder and piston. The hydraulic cylinder is connected to the displacer by a rod or shaft extending through the housing in axial alignment with the main cylinder. Following the proving cycle, the displacer is returned to its launching position by introducing a hydraulic fluid under pressure into the hydraulic cylinder. The inlet section guide means comprise the rod connecting the displacer to the hydraulic piston and a journal bearing located in the wall of the housing which slidably engages the rod. The rod may be of relatively small diameter and low weight.

Another implementation provides an encouraging means comprising a compression spring in the inlet section of the housing. The spring encourages the displacer to enter the main cylinder when the return means is released, thus eliminating the need for a pressurized gas or hydraulic fluid to encourage the displacer at the beginning of the proving cycle.

Another implementation provides a downstream section guide means comprising a displacer pilot extending from the downstream face of the displacer and an axial sleeve bearing located in the downstream section.

The axial sleeve bearing and the pilot are in axial alignment with the main cylinder and the sleeve slidably engages the pilot as it enters the downstream section. These downstream section guide means maintain the displacer in axial alignment while it is disposed within the downstream section, allowing for a smooth exit and entry of the displacer between the main cylidner and the downstream section.

In another implementation, the detecting means comprise a rod connected to the displacer, a journal bearing located in the wall of the housing slidably engaging the rod, a detector flag positioned at the other end of the rod, and a plurality of detector switches which detect the passage of the detector flag and simultaneously provide a signal. Since the detector flag and detector switches are located outside the housing, extremely precise optical detector switches or magnetic detector switches may be used. Another advantage of external placement of the detecting means is that maintenance and calibration of the compact flow prover are greatly facilitated. Still another advantage is that the detecting means may be made insensitive to temperature variations of the flowing fluid, eliminating the need for correction of the distance between the detector switches due to thermal expansion.

In another implementation, the main cylinder is chamfered at either end and the displacer is provided with a plurality of compressible seals. As the displacer enters the main cylinder, the seals are circumferentially compressed. The fluid trapped in the annular space formed between the seals is also compressed. If the seals are functioning properly, the pressure of the fluid trapped between the seals will be higher than the fluid in the main cylinder and this pressure differential will not dissipate until the displacer exits the main cylinder. Thus, by comparing the pressure in the annular space with the line pressure, the integrity of the displacer seals may be verified. Means are provided for verifying the integrity of the displacer seals statically and while the displacer is in the proving mode.

Thus, the integrity of the displacer seals may be verified without removing the prover from operation. Since the integrity of the prover seals is quickly ascertained, error introduced by leakage of fluid past the seals is easily eliminated.

In another implementation, the compact flow prover is operated in a vertical position and is provided with pliable, spring loaded displacer seals. This specific implementation is capable of handling very dirty fluids such as crude oil.

In another implementation, the compact flow prover is operated in a horizontal position and is provided with less pliable displacer seals which are capable of supporting the weight of the displacer. This specific implementation provides a seal which is capable of handling low lubricity fluids.

Optionally, means are provided for monitoring the integrity of the seals of the detector rod and displacer rod.

A control system is optionally provided to simplify the proving sequence. The use of permissive actions minimizes and identifies problems with the prover. For example, the displacer cannot be launched unless it is in the fully retracted position and the bypass valve closed with positive seal integrity. When the displacer is at the end of its stroke, the bypass valve will open after a predetermined time delay. Once the valve is opened, the displacer is permitted to return. The bypass valve cannot close until the displacer is in its launch position.

The compact flow prover may be used to calibrate a continuous flowmeter connected in series with the flow prover. The accuracy of the continuous flowmeter is determined by comparing electrical pulses therefrom with high frequency electrical pulses generated by the flow proving system as the displacer moves a predetermined distance within the main cylinder. The volume of fluid displaced thereby may be corrected for temperature and pressure expansion of the cylinder.

Figure 1 is a side sectional view of the compact flow prover in the launch position.

Figure 2 is a side sectional view of the compact flow prover in the proving cycle.

Figure 3 is a side sectional view of the compact flow prover at the end of the proving cycle.

Figure 4 is a side sectional view of the compact flow prover in the displacer return mode.

Figure 5 is an expanded view of an implementation of the bypass valve.

Figure 6 5 an end view of the invention of Figures 1-4 along the lines 6-6.

Figure 7 is an expanded view of an implementation of the downstream section guide means.

Figure 8 is an expanded view of the displacer in the main cylinder.

Figure 9 is a sectional view of an implementation of the displacer as seen in Figure 8 along the lines 9-9.

Figure 10 is a sectional view of a specific implementation of the displacer seals.

Figure 11 is a sectional view of another specific implementation of the displacer seals.

Figure 1 2 is a side sectional view of the volume compensator.

Figure 1 3 is a block diagram of typical hydraulics.

Figure 1 4 shows a block diagram of a specific implementation of control circuitry which may be provided.

Specific implementations of various operating modes of the compact flow prover of this invention are shown in Figures 1-4. The compact flow prover shown includes inlet conduit 1 and outlet conduit 11 in fluid communication with housing 2, and bypass conduit 3.

Bypass valve 4 is located in bypass conduit 3 and is operated by bypass valve actuator 5.

Housing 2 includes inlet section 6, main cylinder 9, and downstream section 10, all in axial alignment. Inlet section 6 is in fluid communication with inlet conduit 1 and main cylinder 9. Downstream section 10 is in fluid communication with main cylinder 9 and outlet conduit 11. The inside diameter of main cylinder 9 is substantially uniform. The cross sectional areas of inlet section 6 and downstream section 10 are larger than the cross sectional area of main cylinder 9.

Displacer 7 is shown movably disposed within housing 2. Displacer seals 28, 29 are positioned on the periphery of displacer 7.

Shaft 8 is connected to the center of the 0 upstream face of displacer 7. Shaft 8 extends through journal bearing 1 5 in inlet section 6 and is connected to hydraulic piston 1 6 which is slidably disposed in hydraulic cylinder 1 7.

Detector rod 1 9 is connected to displacer 7 and extends from inlet section 6 through journal bearing 20. At its other end, the detector rod 1 9 is provided with detector fag 21. Detector unit 22 is provided with precision detectors 23, 24 and 25 to detect the passage of detector flag 21. The detectors can be optical detectors such as photomicrosensors, Model EE-SH3M, available from OM RON. Magnetic detectors would also be acceptable if detector flag 21 is appropriately modified. Alternatively, a linear transducer may be used.

The downstream section guide means are comprised of displacer pilot 13, extending from the center of the downstream face of displacer 7, and axial sleeve bearing 1 4, located in downstream section 10 and in axial alignment with displacer pilot 1 3.

Compression spring 1 2 is located in axial alignment around shaft 8 in inlet section 6 to aid in encouraging displacer 7 to enter main cylinder 9 during the launch mode.

In the specific implementation shown in Figure 5 bypass valve 4 is of a simple poppet design and is positioned in bypass conduit 3.

Poppet 60 is shaped as a conical frustum and is connected to actuator stem 63. Poppet 60 is shown abutting valve seat 68 positioned between upstream flange 61 and downstream flange 62. Poppet 60 is provided with seals 64 and 65. Annular space 66 between seals 64 and 65 is in fluid communication with channel 67 formed in valve seat 68. Channel 67 may be connected to a pressure element (not shown).

Figure 6 shows an end view of the compact flow prover of Figures 1-4 as seen along the lines of 6-6. The figure shows shaft 8 slidably engaged by journal bearing 1 5 and detector rod 1 9 slidably engaged by journal bearing 20. Inlet conduit 1 is bifurcated to allow fluid to enter inlet section 6 through fluid inlet ports 26 and 27. This arrangement allows fluid to enter inlet section 6 in a substantially longitudinal direction, reducing or eliminating radial and angular forces on displacer 7 and permitting shaft 8 to have a reduced diameter and weight. Monitoring means (not shown) may be provided for monitoring the integrity of the seals (not shown) in journal bearings 1 5 and 20.

Figure 7 shows an implementation of the downstream section guide means. Displacer pilot 1 3 is secured to displacer 7 by means of nut 69. Displacer pilot 1 3 and shaft 8 may be of unitary construction. Displacer pilot 1 3 is shown slidably engaged by bushing 70 in axial sleeve bearing 1 4. Axial sleeve bearing 14 and displacer pilot 1 3 are in axial alignment with main cylinder 9. Axial sleeve bearing 14 is provided with channel 71 to allow fluid to escape from axial sleeve bearing 1 4 as displacer pilot 1 3 enters. This displacement of fluid from axial sleeve bearing 14 provides a gentle arresting mechanism to slow the movement of displacer 7 as it enters downstream section 10.

Figure 8 shows an enlarged view of displacer 7 in main cylinder 9. Main cylinder 9 is shown chamfered at either end to facilitate the smooth entry of displacer 7. For example, a 4" chamfer of 5 cm gives suitable results with a 32.385 cm inside diameter cylinder. The interior surface of main cylinder 9 is preferably plated with a corrosion resistant material and honed smooth. The main cylinder 9 must have a substantially uniform inside diameter to provide accurate measurement and provide long displacer seal life. For example, it has been found that a32.385 cm + 0.001 inside diameter cylinder, with a 0.1 mm hard chrome plate and a 1 2 RMS or better finish, gives suitable results.The particular diameter and length of the cylinder are chosen based on the flow rates to be measured and the accuracy required.

Displacer 7 is comprised of conical portion 72 and ring portion 73. Seals 28 and 29 are prevented from slipping off displacer 7 by retaining rings 36. Annular space 32 formed between seals 28 and 29 is in fluid communication with channel 58. Volume compensator 37 is provided in fluid communication with channel 58 to prevent excessive pressure in annular space 32.

Figure 9 shows a view of the displacer seen in Figure 8 along the lines 9-9.

Figure 10 shows an expanded view of displacer seals 28 and 29. Displacer seals 28 and 29 are comprised of resilient outer layer 34 and metallic energizer 35. The material of outer layer 34 may be any material typically used for seals such as polytetrafluoroetheylene or polybutylene and is selected based on the chemical resistance of the material to the fluid being measured, the lubricity of the fluid, and horizontal or vertical orientation of the compact flow prover in operation. The material of energizer 35 is preferably a metallic alloy. The seals are prevented from slipping off of displacer 7 by retaining rings 36 and held in place by bands 33 which may be made of steel or aluminum. Base portion 34 of seals 28 and 29 extends beyond rings 36. Lip 74 is pressed outward by metallic energizer 35.

Figure 11 shows an alternate implementation of displacer seals 28' and 29'. Base portion 34' is shown not extending beyond rings 36. However, lip 74' is pressed out beyond rings 36 by metallic energizer 35'.

Figure 1 2 shows a side sectional view of volume compensator 37. Volume compensator 37 is comprised of housing 38, inner element 39, outer element 41, compression spring 40, and seal 42. Inner element 39 is slidably engaged by seal 42. The chamber formed between inner element 39 and outer element 41 is in fluid communication with the fluid surrounding volume compensator 37.

Figure 1 3 shows a block diagram of typical hydraulics used with the specific implementations. This system is comprised of hydraulic pump 43 driven by motor 47, lift selector valve 48 operated by lift actuators 49, and reservoir 44. The supply and return of hydraulic fluid to hydraulic cylinder 1 7 is controlled by displacer release solenoid 45 and displacer return solenoid 46. Similarly, bypass valve actuator 5 may be controlled by means of bypass close solenoid 50 and bypass open solenoid 51. The hydraulic system is protected from overpressure by means of relief valve 52.

Figure 14 shows a block diagram of a specific implementation of control circuitry which may be used to control the compact flow prover of this invention. This circuitry is comprised of control box 53, prover controller 56, and printer 75. Control box 53 is electrically connected to detector 23, any seal monitoring means which are provided, prover controller 56, and the hydraulic system. Prover controller 56 is electronically connected to detectors 23 and 24, continuous flow meter 57 and printer 75.

The operation of this specific implementation of the compact flow prover of this invention is best described by reference to Figures 1-4. The flow of fluid through the compact flow prover in the launching mode is shown by solid arrows in Figure 1. The fluid enters inlet conduit 1 and flows into housing 2. Fluid is prevented from flowing through bypass conduit 3 during the proving cycle by closing bypass valve 4 by means of bypass valve actuator 5. Fluid enters inlet section 6 of housing 2, flows through main cylinder 9, and exits housing 2 through outlet conduit 11.

The proving cycle is commenced by allowing hydraulic fluid to drain from hydraulic cylinder 1 7 as discussed below. Displacer 7 is encouraged to enter main cylinder 9 by compression spring 1 2 and the flow of fluid through inlet section 6. As displacer 7 enters main cylinder 9, fluid is displaced from main cylinder 9 into downstream section 10 and out of housing 2 through outlet conduit 11 as shown in Figure 2. Detectors 24 and 25 provide signals as detector flag 22 passes therethrough. The rate of flow is determined by measuring the time between signals.

Figure 3 shows dispiacer 7 at rest in downstream section 10 after the proving cycle is completed.

Displacer 7 is returned to the launching position by opening bypass valve 4 and applying pressure to hydraulic cylinder 1 7. Fluid displaced by the movement of displacer 7 enters housing 2 through outlet conduit 11 and exits through inlet conduit 1 as shown in Figure 4.

Positioning outlet conduit 11 on the side of downstream section 10 is preferred for several reasons. As displacer 7 exits main cylinder 9, displacer pilot 1 3 engages axial sleeve bearing 1 4 to keep displacer 7 in axial alignment with main cylinder 9. Displacement of the fluid from downstream section 10 and axial sleeve beaming 1 4 serves as a natural arresting mechanism to stop the movement of displacer 7, eliminating the need for any special arresting means. Also, it is impossible for displacer 7 to block the flow of fluid from downstream section 10 after displacer 7 enters downstream section 10 since fluid exits therefrom in a radial direction.A more significant advantage is that suspended solids, such as sand or grit, which may be present in the fluid will be less likely to adhere to displacer seals 28 and 29 because of the cleansing action by the flowing fluid.

Shaft 8 and journal bearing 1 5 function as an inlet guide means while displacer 7 is disposed within inlet section 6. It can be readily appreciated, however, that other guide means and other displacer return means are possible.

The bifurcated arrangement of inlet conduit 1 shown in Figure 6 is preferred because fluid is introduced into inlet section 6 in a substantially longitudinal direction, thereby reducing or eliminating radial and angular forces on displacer 7 and permitting shaft 8 to have a reduced diameter and weight. The reduced weight of shaft 8 results in lengthened seal life when the compact flow prover is positioned horizontally. The reduced diameter of shaft 8 results in a lower pressure drop across displacer 7 while it is disposed within main cylinder 9. It is readily appreciated that other arrangements of inlet conduit 1, such as three, four or more ports, are possible.

It is also desirable to have a minimal pressure drop in the fluid flowing past displacer 7 while it is disposed within inlet section 6. The diameter of inlet section 6 should therefore be substantially larger than the diameter of displacer 7. The conical shape of displacer 7 aids in reducing the pressure drop by reducing turbulence in the fluid flowing therepast. It can be readily appreciated, however, that other displacer shapes are possible.

As displacer 7 enters main cylinder 9, displacer seals 28 and 29 are compressed as they contact chamfers 30 or 31. This circumferential compression of displacer seals 28 and 29 causes the pressure to increase in annular space 32, resulting in a seal which does not require conventional external block and bleed pressuring. A more significant advantage is that there is only a low pressure drop across displacer 7 as it moves through main cylinder 9 because the seals cause only minimal friction as they slide against the interior surface of main cylinder 9.

Depending on the type of fluid to be measured, the compact flow prover may be operated in either a horizontal or a vertical orientation. Figure 10 shows displacer seals which are suitable for use in a compact flow prover operated horizontally. As displacer 7 slides through main cylinder 9, gravitational forces acting on the weight of displacer 7 will tend to pull it toward the bottom of main cylinder 9. If the seals could not support the weight of the displacer, metal to metal contact would occur with the disastrous consequences of damaging the finish of main cylinder 9. Thus, seals 28 and 29 are provided with a base portion 34 which extends beyond rings 36.

To ensure long life of seals 28 and 29, it is preferred that they are made from a more rigid seal material, such as for example polytetrafluoroetheyiene. The use of a more rigid seal material allows the seals to be used with a fluid having a low lubricity. On the other hand, the use of a more rigid seal material is not recommended for use with fluids having a high content of suspended solids as particulate matter will be more likely to remain embedded in the seals.

For operation of the compact flow prover in the vertical position, seals 28' and 29' shown in Figure 11 are suitable. Since seals 28' and 29' do not have to support the weight of displacer 7, only lips 74' need to contact the interior surface of main cylinder 9. Seals 28' and 29' may be made of a more resilient material such as VITON. Solids entrained in the fluid measured are less likely to remain embedded in seals 28' and 29' and are more likely to be removed by the flow of fluid past the seals while displacer 7 is disposed within either inlet section 6 or downstream section 10. Hence, seals 28' and 29' are suitable for use with a dirty fluid such as crude oil.

However, the softer seal material will cause a higher friction to develop and its use with fluids having low lubricity is not recommended.

In a preferred implementation of the invention, the integrity of displacer seals 28 and 29 is verified by monitoring the pressure in annular space 32. If there is no decrease in pressure as displacer 7 moves from one end of main cylinder 9 to the other, the dynamic integrity of displacer seals 28 and 29 is verified. A pressure element, such as a trans ducer, can be located internally sending a signal electronically through wiring in either detector rod 1 9 or displacer shaft 8. The preferred method is fluidly connecting annular space 32 with an externally located pressure element (not shown) by means of channel 58 connecting annular space 32 with conduit 59 formed in detector rod 1 9.

The static method of determining seal integ rity involves positioning displacer 7 within main cylinder 9 with bypass valve 4 in the open position. The pressure in annular space 32 may thus be observed for a longer period of time using the static method. This method may be preferred at times since minimum duration of the proving cycle can be as low as 1/3 second or less.

In larger embodiments of the invention which are used for higher flow rates, the diameter of main cylinder 9 and displacer 7 may be substantial. The volume of fluid com pressed in annular space 32 may be therefore quite large, exceeding several cubic centi meters or more. Hence, the pressure in annu lar space 32 would become excessive without some modification. For this situation, a vol ume compensator 37 as shown in Figure 1 2 may be provided to allow for expansion of the fluid volume. As the fluid in annular space 32 is compressed, inner element 39 compresses compression spring 40 against outer element 41. Fluid between inner element 39 and outer element 41 is expelled from volume compensator 37 while seal 42 forms a fluid barrier which prevents the fluid compressed in annular space 32 from escaping into main cylinder 9.

In the launch and proving modes, displacer release solenoid 45 shown in Figure 1 3 is opened and hydraulic fluid allowed to drain into reservoir 44 as it is displaced from hydraulic cylinder 1 7 by hydraulic piston 16.

Displacer 7 is returned to its launch position by closing displacer release solenoid 45, opening displacer return solenoid 46 and filling hydraulic cylinder 1 7 with fluid from reservoir 44 by hydraulic pump 43.

Hydraulic pump 43 is driven by motor 47.

The rate of hydraulic fluid pumped is determined by lift selector valve 48 which is operated by lift actuators 49. The hydraulic system is preferably used to also control bypass valve 4 by means of bypass close solenoid 50, bypass open solenoid 51 and bypass valve actuator 5.

The internals of control box 53 shown in Figure 1 4 are arranged to allow certain permissive actions. Thus, displacer 7 can be prevented from being launched unless a signal from bypass valve 4 indicates closed and a signal from bypass valve seal monitor 54 indicates that the pressure in bypass valve seal 55 is higher than line pressure. Detector 23 can also be required to indicate that displacer 7 is in launch position before closing bypass valve 4.

As displacer 7 travels through main cylinder 9, detector flag 21 will pass through detector 24 which provides a signal to prover controller 56. Upon receiving this signal, prover controller 56 internally generates a series of high frequency electrical pulses which are counted until detector flag 21 passes through detector 25. For even greater accuracy, the prover controller determines fractional pulses using the duai chronometry method which is well recognized in the industry, although other well known methods, such as the four counter method or the phase lock loop method, will work equally well.

The volume of fluid displaced is determined from the distance between detectors 24 and 25 and the diameter of main cylinder 9, corrected for pressure and temperature expansion. In a preferred implementation, the detectors will be mounted on a shaft made of a material with a low thermal expansion coefficient, such as Invar, so that no temperature or pressure correction will be required for the distance between detectors 24 and 25, the measured length. From the elapsed time and the volume so determined, the flow rate can be calculated. The flow rate is then compared with the output generated by continuous flow meter 57.

It is also preferred that seal monitoring means for displacer 7, hydraulic shaft 8 and detector rod 1 9 provide a signal verifying seal integrity or indicating possible error in the measurement caused by the escape of fluid past any of these seals. If desired, the prover controller 56 may be equipped with a printer 58 to provide a hard copy of data and calculations.

While I have described above the specific implementations of my invention, many other variations will occur to those skilled in the art.

It is intended that all such variations which fall within the scope of the appended claims be embraced thereby.

Claims (9)

1. A compact flow prover, comprising: (a) a fluid inlet conduit; (b) a housing comprising: (i) a main cylinder having a substantially uniform inside diameter and inlet and downstream ends; (ii) an inlet section having an inside diameter greater than the inside diameter of said main cylinder, said inlet section being in fluid communication with said inlet conduit and said inlet end of said main cylinder; and (iii) a downstream section having an inside diameter greater than the inside diameter of said main cylinder, said downstream section being in fluid communication with said downstream end of said main cylinder; (c) an outlet conduit being in fluid communication with said downstream section; (d) a displacer movably disposed within said housing, said dispiacer having an upstream face, a downstream face, and displacer seal means for forming a fluid barrier between said inlet and downstream ends while said displacer is disposed within said main cylinder; (e) inlet guide means for limiting radial movement of said displacer while said displacer is disposed within said inlet section; (f) downstream guide means for limiting radial movement of said displacer while said displacer is disposed within said downstream section;; (g) means for detecting longitudinal disposition of said displacer in said housing at predetermined positions; (h) means for returning said displacer from said downstream section to said inlet section; (i) a bypass conduit being in fluid communication with said inlet conduit and said outlet conduit; and (j) a valve positioned in said bypass conduit which can be opened for placing said prover in a displacer return mode or closed for placing said prover in a proving mode.

2. A compact flow prover according to claim 1, further comprising: (k) means for monitoring integrity of said displacer seal means while said displacer is in said main cylinder.

3. A compact flow prover according to claim 1, wherein said inlet guide means comprises: (i) a shaft axially connected to said upstream face of said displacer, said shaft being of sufficient length to extend beyond said inlet section while said displacer is disposed within said downstream section: and (ii) a journal bearing in said inlet section, said bearing in axial alignment with and slidably engaging said shaft.

4. A compact flow prover according to claim 3, wherein said displacer return means comprises: (i) a hydraulic cylinder axially aligned with said shaft having a substantially uniform inside diameter; (ii) a hydraulic piston axially connected to said shaft, said hydraulic piston movably disposed within said hydraulic cylinder; and (iii) a hydraulic source for causing said displacer to return by pressuring said Cylinder with said source.

5. A compact flow prover according to claim 4, further comprising: (1) piston launch means for encouraging said displacer to enter said main cylinder from said inlet section while a fluid is flowing therethrough.

6. A compact flow prover according to claim 5, wherein said launch means comprises a spring located in said inlet section, said spring being axially aligned with said shaft.

7. A compact flow prover according to claim 1, wherein said downstream guide means comprises: (i) a displacer pilot axially extending from said downstream face of said displacer; and (ii) an axial sleeve in said downstream section, said sleeve axially aligned with said displacer pilot.

8. A compact flow prover, comprising: (a) a fluid inlet conduit; (b) a housing comprising: (i) a main cylinder having a substantially uniform inside diameter with chamfered inlet and downstream ends; (ii) an inlet section having an inside diameter greater than the inside diameter of said main cylinder, said inlet section being in fluid communication with said inlet conduit and the inlet end of said main cylinder such as to allow fluid flow therethrough in a substantially longitudinal direction; and (iii) a downstream section having an inside diameter greater than the inside diameter of said main cylinder, said downstream section being in fluid communication with the downstream end of said main cylinder; (c) an outlet conduit being in fluid communication with said downstream section such as to allow fluid flow therefrom in a substantially radial direction; (d) a displacer movably disposed within said housing, said displacer having an upstream face, a downstream face, and displacer seal means for forming a fluid barrier between said inlet and downstream ends while said displacer is disposed within said main cylinder; (e) inlet guide means for limiting radial movement of said displacer while said displacer is disposed within said inlet section, said inlet guide means comprising:: (i) a shaft axially connected to the upstream face of said displacer, said shaft being of sufficient length to extend beyond said inlet section while said displacer is disposed within said downstream section; and (ii) a journal bearing in said inlet section, said bearing in axial alignment with and slidably engaging said shaft; (f) downstream guide means for limiting radial movement of said displacer while said displacer is disposed within said downstream section, said downstream guide means comprising: (i) a displacer pilot axially extending from the downstream face of said displacer; and (ii) an axial sleeve located in said downstream section, said sleeve axially aligned with said displacer pilot; (g) means for detecting longitudinal disposition of said displacer in said housing at predetermined positions; (h) means for returning said displacer from said downstream section to said inlet section, said return means comprising: (i) a hydraulic cylinder axially aligned with said shaft having a substantially uniform inside diameter; (ii) a hydraulic piston axially connected to said shaft, said hydraulic piston movably disposed within said hydraulic cylinder; and (iii) a hydraulic source for causing said piston to return by pressuring said hydraulic cylinder with said source; (i) a bypass conduit being in fluid communication with said inlet conduit and said outlet conduit; (j) a valve positioned in said bypass conduit which can be opened for placing said prover in a displacer return mode or closed for placing said prover in a proving mode,; (k) means for monitoring integrity of said displacer seal means while said displacer is in said main, cylinder; and (I) piston launch means for encouraging said displacer to enter said main cylinder from said inlet section while a fluid is flowing therethrough.

9. A compact flow prover substantially as described with reference to, and as shown in, the accompanying drawings.