Method for monitoring and controlling liquid flow rate

Abstract: To control rate of liquid flow, particularly dyebath turnover utilising a reverse valve (9), liquid is circulated in a circulating system using a pump motor set comprising a centrifugal pump (1) driven by an electric motor, which pump motor set has a relationship between motor current and liquid flow rate which is both substantially linear and significantly inclined, the rate of liquid flow being determined from the motor current consumed.

Description: The invention relates to a method and apparatus for monitoring and controlling rate of bath turnover and has particular though not exclusive application to apparatus for dyeing yarn packages. In the preparation of yarn for the manufacture of textile products, the yarn may be prepared for dyeing by winding it on to a perforated cylindrical core or dye tube formed as a cylindrical bobbin, such a wound bobbin being referred to as a package. A plurality of packages can be stacked on a plurality of slightly smaller diameter perforated tubes, or possibly cruciform or triangular extrusions, called spindles, mounted vertically on a circular manifold or carrier. The carrier after loading with dye tubes and packages can be lowered into a cylindrical vessel known as a kier. The kier is equipped with a pump, a heat exchanger and a reversing valve and may be closed and pressurised. Dyeliquor is then circulated through the packages in both of opposite directions to effect dyeing under pressure and at high temperature. If liquor were to be made to flow in one direction only then there would be a tendency for dyeing to be uneven since fibres contacted first by dyeliquor are treated with the most concentrated or least exhausted dyeliquor. If the dye is permitted to "strike" on the inside of the package only it may take a long time for the concentration level to equalize in the mass of the fibre. It will eventually do this by a process called "migration" by which dye in the more concentrated regions tends to move back into the dyeliquor as the concentration of the dyeliquor decreases and thus moves into fibres which have absorbed lower amounts of dye. As the temperature is the driving force by which many dyestuffs are absorbed into the molecular structure of fibre, raising the temperature on one-way flow, while accelerating the dyeing process, may also increase initial unevenness. It will also increase the need to migrate to a level basis again later. Thus while dye concentration can eventually become completely even by reliance on migration, the time required for such equilibrium to be reached is many times greater than the time required for a mere application phase and it is clearly advantageous to take steps to reduce the need for migration by providing conditions to encourage the dye to strike as evenly as possible. Periodic flow reversal is an accepted technique to minimise the unevenness and optimum evenness can be obtained by relating both frequency of flow reversal and rate of temperature rise to rate of dyebath turnover. United States patent no 3,635,056 discloses a liquor circulating device in a dyeing machine comprising a switching valve provided within the casing to change the direction of flow and to control the flow rate of liquor fed by means of the pump. Generally speaking if the flow is reversed as soon as the entire dyebath has passed through the yarn once in one direction at constant temperature and then once in the other direction the difference in depth of shade across the package wall will be more or less as low as possible in the "strike phase". If, as is usual, the process requires that the temperature be increased, then for maximum uniformity of dye application, the amount of the increase needs to be in relation to bath turnover rather than to time. The physical characteristics of the yarn and consequently the resistance to flow of the package itself may change as temperature is increased, thus altering its resistance to flow, so that the rate of flow may not be the same in both directions and the expression "litres per minute" may be a less meaningful measure of the actual work done on the yarn than "bath turnovers per minute". The package characteristics may change also as flow rate is increased, with a tendency for some packages to "blow" on inside out flow. This does not always mean that the package is physically destroyed, but that deformation of the package or separation of fibres may take place in some areas and not in others, resulting in unequal treatment in different places in the package, particularly at the top or bottom of the spindle or at package spaces, thereby resulting in unlevel application. On outside to in flow the spaces in the interstices of the yarn can be almost closed by excessive pressure such that flow is virtually stopped. Also any deviation from a tolerance acceptable to the dyer needs to be instantly brought to his notice so that a malfunction of a mechanical component can be detected and corrected before sub-standard products are produced, instead of, as happens all too frequently, such correction being effected as a result of an inquest after sub-standard products are produced. The sensitivity and speed of response of flow rate control devices are of major importance. It was once standard practice to set flow rate by means of a throttle valve which was normally in a wide open position; to set reversal times by means of a mechanical timer; and in the same way to set temperature on a clockwork pen type recording instrument with a circular chart. To give a simplified example, if the temperature is to be raised from say 80°C to 140°C in 30 minutes, or 2°C per minute, at a bath turnover rate of 3 per minute, the most level application of dyestuff will result from the carefully controlled increase of 0.66°C per bath turnover. Different dyestuffs strike in different temperature ranges and different combinations of dyestuffs will add complications to this simple example. For optimum results different rates of temperature increase may be required in different temperature ranges during the dye application period. It is not only to maintain an existing standard, but also to establish and fully exploit the potential of the apparatus on the widest range of packages, that the rate of dyebath turnover should be monitored and accurately controlled. Accurate measurement of flow rate in close coupled circulating systems such as packing dyeing machines is however not easy, partly because of the inevitable turbulence and eddy currents that are invariably present and also because of the variations in temperature that are inherent in the process. Also, the higher the velocity in the circulating system the further do the flow characteristics depart from the ideal laminar condition required for accurate flow measurement, and the more difficult it becomes to measure the work done on the yarn. The work done by the pump can be determined from the current which the drive motor which drives it consumes but in the majority of pumps used in dyeing machines this does not bear a linear relationship to liquor circulation. It is conventional practice to use volute type pumps in which the pump casing is so shaped as to modify the pump curve by converting velocity into pressure at a chosen part of its range and it is not uncommon for the current curve to rise to a maximum and then to fall off again. If there are two different flow rates at which the same current is consumed it is obviously unsuitable for control purposes. According to the invention a method of monitoring rate of liquid flow in a circulating system for treating packages of yarn with liquid, comprises circulating the liquid using a pump/motor set comprising a centrifugal pump driven by an electric motor to circulate the liquid, which pump/motor set has a relationship between motor current and liquid flow rate which is both substantially linear and significantly inclined wherein the pump incorporates a pump casing with a collector ring having minimum resistance to flow and of ample volume to collect the unmodified flow of liquor directly from the pump impeller, and a reverse valve wherein, the flow is throttled rather than bypassed as it is closed to reverse the flow direction, such that the entire volume of the liquid passes through the packages of yarn and none of it bypasses back to the pump, and determining the rate of liquid flow from the motor current consumed. Thus the pump is designed to have a power curve straight enough to provide an accurate direct measurement of rate of flow. The rate of flow may be rate of dyebath turnover, and control means compatible with existing computer technology can be used in association with the pump thereby rendering conventional flow measuring devices obsolete. Preferably the angular displacement of the reverse valve can be continuously adjusted for flow control purposes in response to motor current readings. Such a pump is described in our patent specification GB-2 266 750 and can have a power curve which bears a close relation to actual flow rate such that it is ideal for monitoring for control purposes. Thus with suitable pump design the flow rate of liquor through the pump can be brought under accurate control. The throttle type reverse valve, which is the subject of our patent no. GB-2 281 080 is highly suitable for this purpose. Advantageously system resistance is reduced to enable a high flow, low head collector ring pump with a steep, straight power curve to be used. The invention is diagrammatically illustrated by way of example in the accompanying drawings in which:- Figure 1 is a diagrammatic perspective view of a system for treating packages of yarn with liquid; Figure 2 is a cut-away perspective view of a reversing valve of the system of Figure 1 in a out-to-in position; Figure 3 is a cut-away view of the valve of Figure 2 in an in-to-out position and including a container for yarn to be treated; Figure 4 is a sectional view through a centrifugal pump; Figure 5 shows a plot of pressure against flow in a dyeing vessel for various pumps; Figure 6 shows a plot of power against flow rate for a pump suitable for use in a method according to the invention; and Figure 7 shows similar plots to that of Figure 6 but for pumps generally unsuitable for use in a method according to the invention. Referring to the drawings and firstly to Figures 1 and 2, a system for treating packages of yarn with liquid comprises a collector ring-type centrifugal pump 1 to be rotated by a prime mover, not shown, a reversing valve in a housing 2, a large diameter pipe 3 connecting an output connection 4 of the pump 1 to an input connection 5 of the reversing valve housing 2, a large diameter pipe 3 b , connecting an output flange 6 of the reversing valve housing 2 to an input connection 7 of the pump 1 and a treatment vessel 8 (figure 3) mounted on the reversing valve housing 2. Fluid is circulated unidirectionally as indicated by arrows in Figure 1 from the pump 1 through the pipe 3, 3 a to the reversing valve housing 2 and back to the pump I via a pipe 3 b , that is to say the pump 1 is not reversible. The angular position of a reversing valve 9 in the reversing valve housing 2 determines the direction in which the fluid flows through spools of yarn 10 mounted on holders 11 in the vessel 8. Thus with the valve 9 in one position as shown in Figure 3, fluid entering the connection 5 of the reversing valve body 2 flows upwardly through a central vertical duct 12 into the holders 11 passes from inside to outside, that is to say radially outwardly of the spools of yarn 10, and falls down in the vessel 8 to pass through a perforated support 13 to flow through a peripheral channel 14 of the reversing valve housing 2 to leave the reversing valve housing through the flange 6 to flow through the pipe 3 b back to the connection 7 of the pump 1. The housing 2 can be of considerably smaller diameter than that required for a rotating ell while at the same time providing a large area for flow without sudden change of direction of fluid in the valve housing itself. Liquid enters the unit at one end through the flange 5, is directed upwards through the load and after passing through the load returns downwards via the large spaces 14 and out through the flange 6 to the input connection 7 of the pump 1. If the valve 9 is rotated through 180° to the position of Figure 2, fluid flowing into the housing 2 through the flange 5 is deflected downwardly by the valve 9 to flow upwardly through the spaces 14, outwardly through the perforated support 13, radially inwardly through the spools of yarn 10 to the spindles 11 and downwardly therefrom into the central duct 12 to flow outwardly through the flange 6. The two valve positions thus give entirely opposite flow through the load. The valve 9 is cylindrical and can be provided with wide bearings on both sides of the port openings both to act as seals in themselves and to reduce leakage by supporting the valve 9 at what could otherwise be rubbing surfaces thereby permitting closer clearances to be employed rather than the conventional small diameter shaft bearings at some distance from the mating ports as in the ell-type valve. A higher overall mechanical efficiency can thus be obtained without losing any of the versatility that has previously been provided by extra in-line valves in the circulating system. The total system resistance to fluid flow can thus be greatly reduced to the extent that there is no requirement for a high pressure pump and the collector ring centrifugal pump 1 shown can provide ample pressure. Such a pump is shown in greater detail in Figure 4. A pump shaft 21 has a keyway 22, whereby it can be coupled to be driven by drive means such as an electric motor, and extends through a bearing stand 23 in which bearings 24 and 25 are provided. It further extends through a simple pump casting 26 which is secured by bolts 27 to the bearing stand 23 and which mounts shaft seals 28. An impeller 29 is keyed to the other end of the shaft to that having the keyway 22 therein and has arcuate radially extending passages 30 into which, in operation of the pump, fluid flows from an axial fluid inlet 31, the fluid being thrown radially outwardly of the impeller by the high speed rotation thereof. A collector ring 32 is provided around the radially outer edge of the impeller 29. The collector ring 32 is provided as two annular trough-shaped members of pressed stainless steel sheet, that is to say a rear member 32 a and a forward member 32 b welded together by a peripheral weld. The rear member 32 a is welded to a simple cast ring 33 secured by bolts 34 to the pump casting 26. The forward member 32 b is secured by a weld 35 to the axial inlet 31. Reinforcing webs extend around the members 32 a and 32 b and at the underside mount support feet 37. There is a radial outlet connection (not shown) from the collector ring 32. Since the collector ring 32 is formed of stainless steel, it can have a very smooth interior which provides minimal resistance to flow of liquid around the collector 32 from the positions at which the liquid leaves the radially outer edge of the impeller 29 until it passes out through the radial outlet. From Figure 5 it can be seen that the resistance to flow of a conventional system robs the user of the most useful part of the pump performance and also how a well designed system can provide an improved performance while bringing down all the pressures in the system and eliminating the need for a high pressure volute type pump. Designing the pump so that the pump casing is a collector ring with minimum resistance to flow, of ample volume to collect the unmodified flow of liquor directly from the pump impeller can ensure that the power curve bears a close relationship to the actual flow rate such that it is ideal for monitoring for control purposes. As can be seen in Figure 6 an ideal power curve can provide for an increase in flow of 50 cubic metres per hour to require almost exactly an extra 1.5kW (2 horsepower) at any position on the curve. Accurate control requires a relatively steep curve and while there are pumps with such steep curves there are none in the low head high flow rate range, a straight curve is of no use if it is substantially horizontal since there is no inclination to indicate change for control purposes. In the pump shown in Figure 7, particularly that which starts at the lower position at the left hand side the same horsepower is consumed at two different flow rates for example 90 kW (120 horsepower) at both 504 m 3 /hr (2220gpm) and 874 m 3 /hr (3850gpm) such that the curve could not be used for control purposes above about 363m 3 /hr (1600gpm). A man skilled in the art will readily be able to design control apparatus to sense the level of motor current consumed and the time for which it was consumed thereby to calculate the rate of liquid flow in a circulating system and to reverse the flow when a required quantity of liquid had flowed.

Claims: A method of monitoring rate of liquid flow in a circulating system for treating packages of yarn (10) with liquid, comprising circulating the liquid using a pump/motor set comprising a centrifugal pump (1) driven by an electric motor to circulate the liquid, which pump/motor set has a relationship between motor current and liquid flow rate which is both substantially linear and significantly inclined, wherein the pump (1) incorporates, a pump casing with a collector ring (32) having minimum resistance to flow and of ample volume to collect the unmodified flow of liquor directly from the pump impeller (29), and a reverse valve (9) wherein flow is throttled rather than bypassed as it is closed to reverse the flow direction, such that the entire volume of the liquid passes through the packages of yarn (10) and none of it bypasses back to the pump (1), and determining the rate of liquid flow from the motor current consumed. A method according to claim 1 wherein the liquid flow to be controlled is dyebath turnover. A method according to claim 2 wherein angular displacement of the reverse valve (9) is continuously adjusted for flow control purposes in response to motor current readings. A method according to Claim 1, 2 or 3, wherein the reverse valve (9) is located in a housing (2), a large diameter pipe (3, 3a) connecting an output connection (4) of the pump (1) to an input connection (5) of the housing (2) and a large diameter pipe (3b) connecting an output flange (6) of the housing (2) to an input connection (7) of the pump (1) A method according to Claim 4, wherein liquid is circulated unidirectionally from the pump (1) through the pipe (3, 3a) to the housing (2) and back to the pump (1) via the pipe (3b). A method according to any one of Claims 1-5 , wherein angular position of the reverse valve (9) in the housing (2) determines the direction in which liquid flows through the yarn packages (10). A method according to Claim 6, wherein with the valve (9) in one position, fluid entering the body (2) flows upwardly through a central vertical duct (12) into holders (11), passes radially outwardly of the packages of yarn (10), and falls down in vessel (8) to pass through a perforated support (13) to flow through a peripheral channel (14) of housing (2) to leave the housing to flow through pipe (3b) back to pump (1), and wherein if the valve is rotated through 180°, fluid flowing into the housing (2) is deflected upwardly by the valve (9) to flow upwardly through channel (14), outwardly through the perforated support (13), radially inwardly through the packages of yarn (10) and downwardly into the central duct (12) to flow to the pump (1).

Inventors: CLIFFORD FRANK GRAHAM, TSUI WILLIAM, CLIFFORD, FRANK GRAHAM, TSUI, WILLIAM
Applicants: FALMER INVESTMENT LTD, FALMER INVESTMENTS LIMITED
Application year: 1997
Main classification: D06B5
IPC codes: D06B23, D06B5