US20020095972A1 - Low friction piston for gas flow calibration systems - Google Patents
Low friction piston for gas flow calibration systems Download PDFInfo
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- US20020095972A1 US20020095972A1 US09/729,588 US72958800A US2002095972A1 US 20020095972 A1 US20020095972 A1 US 20020095972A1 US 72958800 A US72958800 A US 72958800A US 2002095972 A1 US2002095972 A1 US 2002095972A1
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- piston
- tube
- calibration
- sealing skirt
- low friction
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F25/00—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume
- G01F25/10—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume of flowmeters
- G01F25/11—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume of flowmeters using a seal ball or piston in a test loop
Abstract
A calibration system for a tube prover used in gas flow rate calibration equipment includes a low friction piston which provides an effective seal without the use of mercury. The low friction piston is easily movable in a prover tube of the calibration system in response to gas flow rates, even low flow rates. The piston is constructed of a light weight, low friction fluorinated hydrocarbon material. The piston has first and second seals which provide a positive seal with the inner surface of the prover tube and which maintain the alignment of the piston within the prover tube.
Description
- 1. Field of the Invention
- The present invention relates generally to gas flow rate calibration and in particular to flow rate calibration systems for accurately measuring and establishing gas flow rates for flow meters and similar devices.
- 2. Description of the Prior Art
- Flow rate measurement devices are used in conjunction with many industrial and scientific processes in order to measure, sense, and control gas flow rates. Such devices include flow meters, flow sensors, and flow controllers. To ensure the accuracy of a flow meter or similar device over a given range of flow rates, calibration methods capable of operating over the same range of flow rates must be available and operate accurately.
- A well known method for calibrating flow rate measurement devices is the piston-tube prover method. Generally, in the piston-tube prover method, gas or other fluid is directed through the device to be calibrated which measures the flow rate in the normal manner. The gas exits the device to be calibrated and is directed to the bottom of a precision ground glass tube of a known internal diameter. A piston installed inside the tube rises according to gas flow into the bottom of the tube. After a known time interval, the displacement of the piston is measured and is multiplied by the cross-sectional internal area of the tube to determine the volume of gas that has entered the tube. This volume divided by the time interval (with adjustments for gas temperature and pressure) equals the actual gas flow rate from the flow device. The actual flow rate as measured by the piston displacement can be compared to the flow rate measured by the flow device, and the flow device can be calibrated accordingly.
- The piston-glass tube prover method normally employs a light weight piston with a seal that creates very little friction against the inner surface of the glass tube. Tests have shown that the piston must be able to rise up the glass tube with a pressure differential from the bottom to the top of the piston not in excess of five inches of water in order that very precise gas flow rate measurements may be made. The piston's low friction seal also must be leak proof to maintain high accuracy.
- So far as is known, previous piston provers utilized a mercury, a known hazardous fluid, seal to ensure low friction and zero gas leakage past the seal. For example, the piston-tube provers in U.S. Pat. No. 3,125,879 and U.S. Pat. No. 5,526,674 used a mercury ring seal around the piston. When piston provers were originally designed, mercury was considered to be a less dangerous material, and manufacturers were not aware of potential liability associated with the sale of mercury. However, over time the dangers and liabilities associated with mercury became well known and operator safety became a paramount concern. Various attempts were made by gas calibration equipment manufacturers to limit their liability when selling piston provers with mercury seals. For example, manufacturers provided documentation explaining the dangers of mercury, placed hazardous material labels on the piston provers to alert operators of possible health risks, and added special filters to capture mercury vapors exiting the glass tubes.
- Numerous types of pistons are well known outside of the art of piston provers, but so far as is known none of these pistons were designed for use in a piston-tube prover and none are suitable for such a use. For instance, the piston disclosed in U.S. Pat. No. 3,994,208 used a piston which was unsuitable as a prover. It was designed for a high pressure environment, was constructed of a heavy, stiff material, and relied on a connecting rod to maintain its alignment within a cylinder. The piston had a cylindrical body with a deformable cylindrical flange at one end, and at rest the outside diameter of the flange was less than the inside diameter of the cylinder into which it was installed. In operation, the flange would not deform during the low pressure piston strokes, thus maintaining a relatively large clearance between the piston and the cylinder. During the high pressure strokes, where the pressure on the top of the piston was much greater than the pressure on the bottom of the piston, the flange would deform and press against the cylinder wall to form a tight seal with the cylinder. As a result, the piston maintained a tight seal against the cylinder wall only when the flange was subjected to very high pressure differential across the deformable flange, thereby pressing the flange tightly against the cylinder wall, which was the intended result of the design. However, this flange design was unsuitable for a piston-tube prover because it relied on a high pressure differential to create an effective seal against the cylinder wall, and the seal was only maintained part of the time. Without a high difference in pressure across the flange, the flange would not deform and press against the cylinder wall, and would thus allow gas leakage past the piston. An accurate piston-tube prover for gas flow requires a piston that provides an effective seal even when the pressure difference from the top of the piston to the bottom of the piston is as low as five inches of water or less.
- U.S. Pat. No. 5,884,550 disclosed a piston for an internal combustion engine or compressor. The piston of this patent included a single cantilevered seal around its circumference which was designed to replace a traditional piston ring. The seal had a slightly larger diameter than the piston body (approximately 0.001 to 0.003 inches), and the seal had a uniform thickness from base to tip. To create a tighter seal, the seal was manufactured with a higher coefficient of thermal expansion and/or lower mechanical modulus than the rest of the piston. During operation, the high pressure from the engine or compressor exerted force on the seal causing it to press against and maintain contact with the cylinder. As a result, the piston relied on high pressure to create an effective seal against the cylinder wall. The integrity of the seal was created by forcing the seal against the side of the cylinder wall. The pressure differential across the seal was high enough to overcome any friction between the seal and the wall. Also, the piston was constructed of carbon or carbon composite to reduce weight and improve heat dissipation. Such a material would not be capable of flexing and conforming closely to the wall of the cylinder without high pressure the seal against the wall. If any non-uniformities existed in the cylinder wall, the piston would catch and possibly get stuck in the cylinder absent a large pressure differential to push the piston through the cylinder. Finally, the piston relied on a single seal and a connecting rod to maintain the alignment of the piston within the cylinder. The piston was not “free floating,” but was instead guided through the cylinder wall by the connecting rod.
- The present invention provides a tube prover flow calibration system. The flow calibration system according to the present invention includes at least one calibration tube which has an inner surface and an inner diameter. A piston with an outer end, an inner end and an outside diameter is disposed within the calibration tube. The piston itself forms a seal with the inner surface of the cylindrical tube and includes at least one flexible sealing skirt. Such a sealing skirt is located toward the outer end of the piston and maintains continuous contact with the inner surface of the tube. A processor computes gas flow rate based upon measurements of the movement of the piston within the tube and other factors.
- The present invention also provides a low friction piston-glass tube prover assembly. The assembly according to the present invention includes a calibration tube which has an inner surface. A piston with an outer end and an outside diameter is disposed within the calibration tube and forms a seal with the inner surface of the calibration tube. The piston also includes at least one flexible sealing skirt which is in contact with the inner surface of the calibration tube.
- The present invention further provides a low friction piston for calibrating a gas flow meter. The piston according to the present invention includes a piston body. The piston body moves longitudinally within the calibration tube in response to a gas flow in the calibration system. The piston body is also made from a resilient material and includes at least one sealing skirt which extends outwardly from the piston body. The sealing skirt contacts the inner surface of the calibration tube and seals the calibration tube against leakage of the gas flow past the piston body in the calibration tube.
- FIG. 1 is a simplified diagram of a flow rate calibration system of the type employing precision-bored cylinders with the piston of the present invention;
- FIG. 2 is an isometric view of a piston according to the present invention;
- FIG. 3 is a top view of the piston of FIG. 2;
- FIG. 4 is a cross sectional view of the piston along4-4 of FIG. 3; and
- FIG. 5 is a cut-away isometric view of the piston within a glass cylinder.
- Referring first to FIG. 1, a flow
rate calibration system 30 according to the present invention is shown. Thesystem 30 generally includes afluid source 120 such as a pump or compressor which supplies a fluid to a gasflow measuring device 130 to be calibrated. If desired, thedevice 130 to be calibrated might be the pump or the compressor itself. The present invention is not limited to the calibration of any particular type ofgas flow device 130. The present invention is instead useful in calibrating any sort of machine, gage, or apparatus, the operation of which requires accuracy in flow measurement, control or the like. Furthermore, the present invention contemplates that various types of fluid flows may be measured, including water, air, various inert gases, and even hazardous, caustic or toxic fluids and vapors. The fluid flow, schematically indicated by arrow Q, leaves thedevice 130 to be calibrated and flows through tubes or conduits into the low friction piston-glasstube prover assembly 35 of the present invention. Avalve 140 may be included as indicated upstream of thedevice 130 to control the flow Q through thecalibration system 30. - As gas flows into the
assembly 35,piston 10 moves upward longitudinally withintube 20. Thepiston 10 moves upward because the flow Q is introduced from the bottom oftube 20, below thepiston 10. It should be noted that the top 12 of thepiston 10 corresponds to an outer end with respect to the gas flow being measured. In other words, the top orouter end 12 does not generally contact the gas flow being measured because it is facing out or away from the volume of gas being measured. Similarly, the bottom 11 of thepiston 10 corresponds to an inner end with respect to the gas being measured. The bottom orinner end 11 contacts the gas flow being measured because it faces inward, toward the gas flow Q. As such, when the terms top, bottom or the like are used, they can be understood as corresponding to outer or inner ends respectively. The present invention contemplates that, if desired, the vertical alignment of the piston may be altered such that the inner orbottom end 11 is actually vertically above, or on the same level or elevation with, the outer ortop end 12. - Still referring to FIG. 1,
displacement measurement device 110 preferably determines the distance thatpiston 10 travels during a given time period. Thedisplacement measurement device 110 may be any conventional device capable of measuring the distance thatpiston 10 travels. It is preferable that thedisplacement measurement device 110 measure piston displacement without physically contacting thepiston 10, such as by ultrasonic waves, laser light, or any similar means. The product of the distance that thepiston 10 travels and the inside circular cross-sectional area of thetube 20 generally equals the volume of gas that has entered the tube. Dividing this volume of gas by the time it took for thepiston 10 to travel the measured distance generally gives the gas flow rate. Anabsolute pressure gauge 150 and agas temperature sensor 160, each of the conventional type, are provided to sense the pressure and temperature of gas acting on thepiston 10. The pressure and temperature readings obtained may be famished electronically or manually to aprocessor 100 for flow rate computations, as will be set forth. This flow rate can be compared to the flow rate measured by thedevice 130 to be calibrated, and conventional calibration methods may be applied. Alternatively, somesystems 30 measure the instantaneous velocity of thepiston 10 rather than its overall displacement. Multiplying the instantaneous velocity by the inside cross-sectional area of thetube 20 produces the instantaneous flow rate Q. Various other conventional measurements and calculations can be made as are well known in the art. The present invention is not limited to any particular calibration scheme or set of measurements, but can be used in conjunction with various known measurements and analyses. - As shown in FIG. 1,
processor 100 receives information fromdisplacement measurement device 110.Processor 100 can be any conventional device suited to receive information or data and perform mathematical or logical operations using that data. For example, a conventional personal computer programmed with an appropriate algorithm could be used, or a specially designed processor could be employed. In a more crude system, numerical information could be gathered manually or with a hand held numerical sampling device and mathematical operations could be performed in a free standing processor or even by hand. - In a preferred embodiment, the
processor 100 is integrated into the flowrate calibration system 30, so that when thepiston 10 moves, that movement is detected bymeasurement device 110 automatically, and theprocessor 100 automatically determines the flow rate. Measurements of gas temperature fromsensor 160 and pressure fromgauge 150 permit theprocessor 100 to automatically remove any effect of gas temperature or pressure variations on flow rate measurements. If desired, theprocessor 100 is not integrated with the flowrate calibration system 30, but instead receives the data from themeasurement device 10 in a batch, after the measurements are taken. For example, measurements may be recorded manually, even by hand, and entered into theprocessor 100 by keystrokes on a keyboard. It is contemplated that themeasurement device 110 may record displacement, velocity, or any other quantity which can be used in conjunction with other known or measured quantities to determine flow rate. - Referring now to FIGS. 2, 3 and4, a
low friction piston 10 according to the present invention is shown. Thepiston 10 is preferably cylindrical in shape with a circular cross section as shown in FIG. 3 and generally has acylindrical piston body 50 and at least one sealingskirt 60. It should be recognized that other cross sectional shapes could be used for thepiston 10, so long as the shape of thepiston 10 conforms to the shape of thecalibration tube 20 to provide a seal as hereinafter described. For example, it may be useful in some applications to make the piston oblong or other shape in cross-section. The sealingskirt 60 is preferably formed integrally with thepiston body 50. In practice, thepiston 10 of the present invention may be manufactured by machining on a lathe or other similar tool, preferably from a single piece of material. However, it is contemplated that the piston may be made from multiple pieces to be assembled, if design or manufacture requirements so dictate. - The material used for the
piston body 50 and the sealingskirt piston 10 of the present invention. Fluorinated hydrocarbons are light weight and allow the piston to rise under very low pressure differentials. Furthermore, fluorinated hydrocarbons are resilient as well as strong so as to provide an excellent low friction seal with theinner surface 40 of thecalibration tube 20. It should be understood that other light weight, low friction materials might also be used, and that the present invention is not limited to the use of any particular material, so long as the characteristics herein described are present. - As best seen in FIGS.2-4, the
piston 10 has apiston body 50 having aninner end 11, and anouter end 12. An inner weight cutout ormaterial relief pocket 70 is formed extending inwardly into thepiston body 50 from theinner end 11 of thepiston body 50 adjacent acylindrical side wall 80 to a lower wall orbase 90. Similarly, an outer weight cutout ormaterial relief pocket 71 is formed extending inwardly into thepiston body 50 from theouter end 12 of thepiston body 50 adjacent acylindrical side wall 81 to a lower wall orbase 91. Typically, each of the cutouts orpockets piston body 50. - The
piston body 50 has a nominal outer diameter D measured at acylindrical side wall 15. The diameter D is determined by the size of thetube 20 in which thepiston 10 is to be used. The length L of thepiston body 50 is typically preferably about 1.6 times the diameter D. The cutouts orpockets piston body 50 has an outercylindrical wall 16 adjacent thecutout 70 and an outercylindrical wall 17 adjacent thecutout 71. It is preferred that the thickness or radial width of each of thecylindrical walls piston bodies 50 according to the present invention. - Flow
rate calibration systems 30 according to the present invention are generally adapted for use in calibrating flow rates with piston-glasstube prover assemblies 35 havingcalibration tubes 20 having inner diameters (I.D.) ranging from about 0.5″ inner diameter to about 3.0″ inner diameter. Above about 3.0″ diameter, the cost of precision ground glass tubes becomes high. Beyond this size, devices known in the art as bell provers are available to calibrate gas flow measuring devices. - The following table sets forth example dimensions for
pistons 10 according to the present invention:Calibration Tube I.D. 0.50″ 1.0″ 3.0″ Piston Diameter (Φp) O.D. 0.506″ 1.006″ 3.006″ Skirt seal diameter > inside .006″ .006″ .006″ diameter of tube by: Piston Length (L) 0.8″ 1.6″ 4.8″ Depth of Cutout 0.2″ 0.4″ 1.2″ Cutout I.D. 0.25″ 0.5″ 2.5″ Skirt Thickness Adjacent Cutout 0.25″ 0.25″ 0.25″ - Extending downwardly and outwardly from the
side wall 15 of thepiston body 50 is at least one sealingskirt 60 extending around the entire circumference of thepiston body 50 for sealing contact with theinner surface tube 20.Skirt 60 has a first thickness t1 at its base orinner portion 61 where it connects to thepiston body 50, and has a second thickness t2 at its end orouter portion 62 furthest from thepiston body 50. Preferably, the first thickness t1 is greater than the second thickness t2 so that theskirt 60 is tapered outwardly from the piston body. According to the present invention, theskirt seal 60 comes to a verythin edge 62 that could be described as feather thin or sharp. It is preferred to keep theouter edge 62 ofskirt 60 be kept thin and sharp to minimize contact area with thetube 20 and consequently undesirable minimize seal friction. Because of the dimensions of thepiston body 50 and theskirt 60, however, there is adequate sealing pressure against thetube 20. - In the embodiment shown, the
piston 10 includes asecond sealing skirt 60′ for reasons which are described below. During manufacture, in order for a cutting tool to reach the inner portion ofskirt 60, a reduceddiameter portion 63 is preferably machined first with a flat 65 extending inwardly from the skirt. In this manner, the cutting tool can be moved beneath theskirt 60 and theskirt 60 can be machined to very close tolerances for reasons described below. In a similar fashion, when thesecond skirt 60′ is included, then a second reduceddiameter portion 64 is also preferably included. If desired, the sealing skirts 60, 60′ may be included without the inclusion of the reduceddiameter portions piston 10. - The sealing skirts60, 60′ are shown in FIG. 4 as having the
outer edge 62 of theskirts outer end 12 ofpiston body 50. The distance is typically comparable to the depth of thecutouts outer edge 62 of each of the sealing skirts 60, 60′ is slightly larger than the outer diameter D, preferably about 0.003″. With theskirts inner wall tube 20 is provided for pressure drops encountered (usually 5″ water or less) in gas flow calibration. Further, as has been noted, sealing is obtained with minimal friction at the thin outer edges 62. - It is preferred that the
piston 10 be light weight. As shown in FIGS. 2, 3, and 4 one way of reducing the weight of thepiston 10 is to machine arecess 70 in theinner end 11 of thepiston 10. In addition to or in substitution for therecess 70, asimilar recess 71 can be machined in theouter end 12 ofpiston 10. In order to further decrease the weight of thepiston 10, the reduced diameter recesses 63, 64 could be machined deeper or longer. Generally, there is at least onereduced diameter portion diameter portions diameter portion skirt - Referring now to FIG. 5, the operation of the
piston 10 within thetube 20 is illustrated in greater detail. The flow Q of fluid from the device 130 (FIG. 1) to be calibrated is shown as entering thetube 20 at theinlet 21. The fluid flow Q applies a pressure P1 to theinner end 11 ofpiston 10. Another fluid, generally air from the atmosphere or some other fluid that is purposely introduced into the outer end 22 oftube 20 applies a second pressure P2 to theouter end 12 of thepiston 10. When the first pressure P1 is sufficiently greater than the second pressure P2 thepiston 10 rises vertically withintube 20. This occurs when the difference in pressure is sufficient to overcome any friction between thepiston 10 and theinner wall 40 of thetube 20, as well as the weight of thepiston 10. - In order that an accurate measurement of the fluid flow Q be made, it is preferable that the
piston 10 be very reactive to the flow Q. In other words, as soon as the flow Q enters thetube 20, the piston should begin to rise, and thepiston 10 should rise a distance that is in proportion to the amount of fluid that has entered thetube 20. Thepiston 10 should not remain motionless in thetube 20 while pressure builds beneath it, but instead should begin moving when comparatively little pressure has built up beneath it. It is therefore most preferable that thepiston 10 be light weight, that none of the fluid flow Q leaks or gets past thepiston 10, and that there be very low friction between the sealingskirt 60 and theinner wall 40 of thetube 20. - If, for example, there were a large amount of friction between the
inner surface 40 oftube 20 and the sealingskirt 60 ofpiston 10, then the fluid flow Q would compress and pressure P1 would increase, butpiston 10 may not move. As a result, the piston displacement would be less than it would have been absent friction. Consequently, the volume of fluid measured by the piston displacement would be less than the volume of fluid that flowed out of thedevice 130 to be calibrated. The results would be similar if thepiston 10 were too heavy or if the seal betweenskirt 60 and theinner wall 40 oftube 20 were to leak. - In a preferred embodiment, by using a
lightweight piston 10 made of a resilient material with aflexible sealing skirt 60, within atube 20 having precision groundinner surface 40, the present invention has been able to very accurately measure the fluid flow Q. The sealingskirt 60 is preferably machined to be adequately thin so that it can flex to accommodate any irregularities on theinner surface 40 of thetube 20. In this manner, none of the fluid flow Q can leak or get past thepiston 10. Furthermore, the thin construction of the sealingskirt 60 generally applies very little force against theinner wall 40 oftube 20, thereby lowering the coefficient of friction between theinner wall 40 and the sealingskirt 60. In a preferred embodiment, thepiston 10 is manufactured from a fluorinated hydrocarbon known to exert very small frictional forces. Thepiston 10 is preferably machined to very close tolerances so that the actual diameter of the sealing skirts 60, 60′ does not vary from the design diameter by more than achievable machining tolerances. With the present invention, it has been found that by using the piston of the present invention machined to such precision, the seal between the sealingskirt piston 10 and thetube 20 can be reduced. It has also been found that the interface between the sealingskirt - The
piston 10 preferably has two sealing skirts, afirst sealing skirt 60 located toward theouter end 12 of thepiston 10, and asecond sealing skirt 60′ located toward theinner end 11 of thepiston 10. If desired, more sealing skirts of similar configuration could be added depending upon design requirements. It has been found that using two sealingskirts piston 10 from becoming misaligned and catching or “cocking” in thetube 20, i.e. thepiston 10 stays in very close alignment with theinner wall 40 of thetube 20. If thepiston 10 were to misalign in the tube, then the seal afforded about thepiston 10 would be lost. This would result in an inaccurate measurement as described above. - In another preferred embodiment, the lower or
inner sealing skirt 60′ actually does not act as a seal at all, but instead allows the fluid flow Q to pass. In that particular embodiment, the effective operation of thepiston 10 depends upon the integrity of the upper or outer sealingskirt 60. The advantage of having theinner sealing skirt 60′ allow fluid to pass is that theinner sealing skirt 60′ still provides mechanical stability to thepiston 10 and prevents thepiston 10 from misaligning or catching in thetube 20. At the same time, theouter sealing skirt 60 “pulls” thepiston 10 upward or outward, rather than theinner sealing skirt 60′ pushing thepiston 10. This prevents cocking and jamming even further. In an embodiment where theinner seal 60′ is meant to allow the fluid flow Q to pass by the sealingskirt 60′, the sealingskirt 60′ may be notched or scored, as with a utility knife or razor blade. In this manner, fluid can pass sealingskirt 60′, but the sealingskirt 60′ nevertheless provides mechanical stability to thepiston 10. - Forces on a body due to pressure can be calculated by taking the product of pressure and the surface area over which the pressure acts. If one is mainly concerned with forces acting along a single axis, i.e. up and down within
tube 20, then the surface area that matters can be described as the projection of a three dimensional surface onto a two dimensional plane. For example, as best shown in FIGS. 3 and 4, the surface area over which any pressure on either theouter end 12 orinner end 11 would act can be described by the formula πφp 2/4, where π is the well known mathematical constant and φp is the diameter of the piston. When installed inside the calibration tube, the diameter of the piston φp is preferably equal to the inside diameter of the calibration tube φT. This is because prior to installation into thetube 20, thepiston 10 has outside diameter φP which is greater than the inside diameter φT of thecalibration tube 20. - In one embodiment, the diameter φT of the
tube 20 is about 0.006″ less than the diameter φp of the piston. In this manner, when thepiston 10 is installed into thetube 20, there is an interference fit between thepiston 10 and thetube 20 and the sealingskirt tube 20. As shown in FIG. 5, various forces act upon thepiston 10, including a force due to the pressure P1 acting over the area just described, a force due to pressure P2 acting over the same area, forces due to friction, and forces due to the weight of the piston itself. Thepiston 10 of the present invention is capable of moving within the tube even when the difference in pressure or pressure differential between P1 and P2 is about 5.0″ water, the standard conditions under which gas flow is calibrated. - If desired, the piston may be able to travel within the calibration tube when the pressure differential is less than about 2.5″ water. Alternatively, the net force due to pressure acting on the piston can be described as the product of the pressure differential (P1-P2) and the cross sectional area of the calibration tube (πφT 2 /4).
- The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, and components, as well as in the details of the illustrated construction may be made without departing from the spirit of the invention.
Claims (35)
1. A low friction piston for sealing an inner surface of a gas flow calibration tube in a flow calibration system comprising:
a piston body being movable longitudinally in the calibration tube in response to a gas flow in the calibration system, the piston body being formed of a resilient material; and
at least one sealing skirt extending from a portion of the piston body to contact the inner surface of the calibration tube and seal against leakage of the gas flow past the piston body in the calibration tube.
2. The low friction piston of claim 1 , further comprising a second sealing skirt integrally formed with and extending from a portion of the piston body to contact the inner surface of the calibration tube and seal against leakage of the gas past the piston body in the calibration tube.
3. The low friction piston of claim 2 , wherein the second sealing skirt is adapted to allow the gas flow to pass by the second sealing skirt.
4. The low friction piston of claim 2 , wherein the inner surface of the tube includes an inner diameter and the outer diameter of the tip of the second sealing skirt is adapted to be greater than the inner diameter.
5. The low friction piston of claim 1 , further comprising a second sealing skirt integrally formed with and extending from a portion of the piston body to contact the inner surface of the calibration tube provide proper alignment of the piston body in the calibration tube.
6. The low friction piston of claim 1 , wherein the sealing skirt is formed integrally with the piston body.
7. The low friction piston of claim 1 , wherein the resilient material of the piston body is a synthetic resin material.
8. The low friction piston of claim 1 , wherein the resilient material of the piston body is fluorinated hydrocarbon.
9. The low friction piston of claim 1 , wherein the at least one sealing skirt is adapted to be in dry contact with the inner surface of the calibration tube.
10. The low friction piston of claim 1 , wherein the piston body is adapted to contact the inner surface of the calibration tube with an interference fit.
11. The low friction piston of claim 1 , wherein the inner surface of the tube has an inner diameter and the at least one sealing skirt has an outer diameter and the outer diameter of the sealing skirt is adapted to be greater than the inner diameter of the tube.
12. The low friction piston of claim 1 , wherein the at least one sealing skirt has a first thickness adjacent the piston body and has a second thickness adjacent the inner surface of the calibration tube, and the first thickness is greater than the second thickness.
13. The low friction piston of claim 1 , wherein the piston body includes a weight reducing cavity formed in an outer end of the piston body.
14. The low friction piston of claim 1 , wherein the piston body includes a weight reducing cavity formed in an inner end of the piston body.
15. The low friction piston of claim 1 , wherein the piston body has an outside diameter and at least one reduced diameter portion, and the reduced diameter portion has a diameter which is less than the outside diameter of the piston body.
16. A low friction piston-glass tube prover assembly for use in a gas flow calibration system comprising:
a calibration tube having an inner surface;
a piston with a outer end and an outside diameter, the piston being disposed within the calibration tube in sealing communication with the inner surface of the calibration tube; and
at least one flexible sealing skirt disposed on the piston in contact with the inner surface of the calibration tube.
17. The low friction piston-glass tube prover assembly of claim 16 , wherein the at least one flexible sealing skirt is formed integrally with the piston and contacts the inner surface of the calibration tube.
18. The low friction piston-glass tube prover assembly of claim 16 , further comprising a second sealing skirt formed integrally with the piston and contacting the inner surface of the calibration tube.
19. The low friction piston-glass tube prover assembly of claim 18 , wherein the second sealing skirt is adapted to allow the gas flow to pass between the second sealing skirt and the inner surface of the calibration tube.
20. The low friction piston-glass tube prover assembly of claim 18 , wherein the second flexible sealing skirt has an inner portion connected to the piston, and an outer portion in contact with the inner surface of the tube, and the inner portion is thicker than the outer portion.
21. The low friction piston-glass tube prover assembly of claim 18 , wherein the inner surface of the calibration tube has an inner diameter, and the second sealing skirt has an outer diameter and the outer diameter of the second sealing skirt is greater than the inner diameter of the calibration tube.
22. The low friction piston-glass tube prover assembly of claim 16 , wherein the at least one flexible sealing skirt has an inner portion connected to the piston, and an outer portion in contact with the inner surface of the tube, and the inner portion is thicker than the outer portion.
23. The low friction piston-glass tube prover assembly of claim 16 , wherein the piston is in dry contact with the inner surface of the calibration tube.
24. The low friction piston-glass tube prover assembly of claim 16 , wherein the sealing skirt contacts the inner surface of the calibration tube in an interference fit.
25. The low friction piston-glass tube prover assembly of claim 16 , wherein the inner surface of the calibration tube has an inner diameter, and the sealing skirt has an outer diameter and the outer diameter of the sealing skirt is greater than the inner diameter of the calibration tube.
26. A tube prover flow calibration system comprising:
at least one calibration tube, having an inner surface and an inner diameter;
at least one piston having an outer end, an inner end and an outside diameter disposed within the at least one calibration tube in sealing communication with the inner surface of the cylindrical tube;
at least one flexible sealing skirt located toward the outer end of the at least one piston for maintaining continuous contact with the inner surface of the tube; and
a processor for computing gas flow rate based upon sensed movement of the piston within the tube.
27. The calibration system of claim 26 , wherein the at least one flexible sealing skirt is formed integrally with the piston and contacts the inner surface of the calibration tube.
28. The calibration system of claim 26 , further comprising a second sealing skirt formed integrally with the piston and contacting the inner surface of the calibration tube.
29. The calibration system of claim 28 , wherein the second sealing skirt is adapted to allow the gas flow to pass between the second sealing skirt and the inner surface of the calibration tube.
30. The calibration system of claim 28 , wherein the second flexible sealing skirt has an inner portion connected to the piston, and an outer portion in contact with the inner surface of the tube, and the inner portion is thicker than the outer portion.
31. The calibration system of claim 28 , wherein the inner surface of the calibration tube has an inner diameter, and the second sealing skirt has an outer diameter and the outer diameter of the sealing skirt is greater than the inner diameter of the calibration tube.
32. The calibration system of claim 26 , wherein the at least one flexible sealing skirt has an inner portion connected to the piston, and an outer portion in contact with the inner surface of the tube, and the inner portion is thicker than the outer portion.
33. The calibration system of claim 26 , wherein the piston is in dry contact with the inner surface of the calibration tube.
34. The calibration system of claim 26 , wherein the sealing skirt contacts the inner surface of the calibration tube in an interference fit.
35. The calibration system of claim 26 , wherein the inner surface of the calibration tube has an inner diameter, and the sealing skirt has an outer diameter and the outer diameter of the sealing skirt is greater than the inner diameter of the calibration tube.
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
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US09/729,588 US6427517B1 (en) | 2000-12-04 | 2000-12-04 | Low friction piston for gas flow calibration systems |
PCT/US2001/012974 WO2002046707A1 (en) | 2000-12-04 | 2001-04-19 | Low friction piston for gas flow calibration systems |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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US09/729,588 US6427517B1 (en) | 2000-12-04 | 2000-12-04 | Low friction piston for gas flow calibration systems |
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US20020095972A1 true US20020095972A1 (en) | 2002-07-25 |
US6427517B1 US6427517B1 (en) | 2002-08-06 |
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US09/729,588 Expired - Lifetime US6427517B1 (en) | 2000-12-04 | 2000-12-04 | Low friction piston for gas flow calibration systems |
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US (1) | US6427517B1 (en) |
WO (1) | WO2002046707A1 (en) |
Cited By (2)
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CN104198020A (en) * | 2014-09-12 | 2014-12-10 | 武汉大学 | Flow calibrator based on static weighing method |
CN112729685A (en) * | 2020-11-30 | 2021-04-30 | 上海典圆测试设备有限公司 | Calibration device for DET piston air leakage measuring instrument |
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US6602060B2 (en) * | 1998-12-11 | 2003-08-05 | Ovation Products Corporation | Compressor employing piston-ring check valves |
US20040140626A1 (en) * | 2003-01-16 | 2004-07-22 | Hall Matthew C. | Sealing device |
US7096565B2 (en) * | 2003-06-19 | 2006-08-29 | Powerwave Technologies, Inc. | Flanged inner conductor coaxial resonators |
WO2006012092A2 (en) * | 2004-06-29 | 2006-02-02 | The United States Of America, As Represented By The Secretary, Department Of Health And Human Services | Safer attenuated virus vaccines with missing or diminished latency of infection |
DE602005023625D1 (en) * | 2004-07-30 | 2010-10-28 | Gl Tool And Mfg Co Inc | VALVE |
WO2011008973A2 (en) * | 2009-07-15 | 2011-01-20 | The Intellisis Corporation | Constant memory implementation of a phase-model neural network |
US20130068095A1 (en) | 2010-05-26 | 2013-03-21 | Ge Healthcare Bio-Sciences Ab | Piston head with sealing arrangement |
US8857401B2 (en) | 2011-03-08 | 2014-10-14 | Rohan Gunning | Low drag piston |
RU2623985C2 (en) * | 2012-09-06 | 2017-06-29 | Бревилл Пти Лимитед | Waffle iron |
WO2021086419A1 (en) * | 2019-10-28 | 2021-05-06 | Tsi Incorporated | Flow references |
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US3125879A (en) | 1964-03-24 | Flow rate calibration | ||
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US3120118A (en) * | 1961-01-23 | 1964-02-04 | Service Pipe Line Company | Fluid meter calibrator |
US3270549A (en) * | 1964-08-14 | 1966-09-06 | William R Martin | Fluid meter calibrating device |
US3580045A (en) * | 1968-07-16 | 1971-05-25 | Exxon Research Engineering Co | Meter prover |
GB1420754A (en) * | 1972-05-08 | 1976-01-14 | Secretary Industry Brit | Flowmeter calibration or proving apparatus |
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GB2244337A (en) * | 1990-05-24 | 1991-11-27 | Keith Andrew Marley | Measuring fluid flow |
US5526674A (en) | 1992-04-30 | 1996-06-18 | Sierra Instruments, Inc. | Method and apparatus for improved flow rate measurement and calibration |
DE19523215B4 (en) | 1995-06-27 | 2004-09-16 | Luk Lamellen Und Kupplungsbau Beteiligungs Kg | Formation of a piston for a master cylinder |
US5884550A (en) | 1996-03-13 | 1999-03-23 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Integral ring carbon-carbon piston |
JP3955127B2 (en) * | 1997-05-19 | 2007-08-08 | 学 根本 | helmet |
-
2000
- 2000-12-04 US US09/729,588 patent/US6427517B1/en not_active Expired - Lifetime
-
2001
- 2001-04-19 WO PCT/US2001/012974 patent/WO2002046707A1/en active Search and Examination
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN104198020A (en) * | 2014-09-12 | 2014-12-10 | 武汉大学 | Flow calibrator based on static weighing method |
CN112729685A (en) * | 2020-11-30 | 2021-04-30 | 上海典圆测试设备有限公司 | Calibration device for DET piston air leakage measuring instrument |
Also Published As
Publication number | Publication date |
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US6427517B1 (en) | 2002-08-06 |
WO2002046707A1 (en) | 2002-06-13 |
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