GB2281080A - System for treating packages of yarn with liquid - Google Patents

Abstract

A system for treating packages of yarn with liquid comprises a treatment vessel (8), a reversing valve housing (2) integral with the vessel (8) and containing a reversing valve (9), a low pressure pump (1) close coupled to the housing (2) and supplying treatment fluid around a unidirectional large bore piping system (3, 3a, 3b) and control means (23, 24) to operate the reversing valve (9) to change the direction of flow of liquid within the treatment vessel (8) from inside to outside of the packages of yarn to outside to inside and vice versa. <IMAGE>

Description

SYSTEM FOR TREATING PACKAGES OF YARN WITH LIQUID The invention relates to a system for treating packages of yarn with liquid.

Yarn employed for textile purposes has traditionally been processed on cylindrical packages wound on permeable tubular cores.

These have been supported on multi-spindle carriers with a central feed orifice in the bottom through which a treatment liquor is distributed to the vertical spindles, and thence radially through the cylindrical packages.

The yarn is dyed by bringing the dyes and process chemicals into physical contact with the fibres being processed by having them in solution or in suspension in water and circulating the liquor through the material being treated by some form of pumping device.

It is also customary to provide some means of reversing the flow of this treatment liquor to attempt to equalise the treatment throughout the entire thickness of the package wall and regular and frequent reversals of flow have been found to be beneficial.

Some manufacturers employ axial flow pumps for circulating the liquor and stop the pump and restart it every few minutes to achieve the frequent reversals necessary for level dyeing. This is difficult and expensive with large horsepower motors. Pumps of this type were often produced by the dyeing machine manufacturer himself, and comprised a series of rotors having sets of rotating radially disposed blades alternating between sets of similar stationary blades. The performance characteristics of such pumps are not suited for treating packages of high density, and they may be unable to develop sufficient head to penetrate fibres such as cotton or cotton/polyester blends, particularly in the form of sewing thread. This inability to develop high pressures meant that this type of pump was also unsuitable for forcing liquor through high resistance pipework.

Such pumps were usually mounted vertically in the bottom of the vessel and leakage from shaft seals rendered electric drive motors vulnerable and required belt drives to be used.

The rotating and stationary members passing each other at high velocity created violent turbulence and shearing forces which tended to break down the delicate dispersion of some very important types of dyestuff.

With the pump located in the heart of the processing vessel it is difficult, if not impossible, to isolate it for use for filling.

draining, or transferring process liquor to or from other vessels and additional means had to be provided. For all of these reasons this type of circulating system has little following in today's marketplace.

The great majority of the world's dyeing machine manufacturers use whatever stainless steel centrifugal pumps are available from local suppliers. Few, if any, such manufacturers have the facilities for making heavy stainless steel castings themselves.

The normal market for such pumps has been the paper and chemical processing industries, which may have to employ extremely complex and tortuous circulating systems, sometimes involving processes which operated continuously, being stopped only for routine maintenance.

These systems required "Volute" type centrifugal pumps in which performance at moderate delivery pressure is sacrificed by shaping the pump casing so as to convert some of the velocity of the liquor leaving the impeller into pressure, to render them capable of operating against high system resistance. The modification to the casing carries the penalty that performance at low head is reduced as is overall efficiency. With pumps of this type readily available from established manufacturers it is not surprising that many dyeing machines have been founded on their use, and indeed, that their adverse effects upon dyeing machine design should have been overlooked and accepted without question, or even mistakenly presented to customers as advantages.

A disadvantage of such high head pumps is that when they are used in machines designed for high temperature operation with flow reversal, the vessel pressure must be increased to withstand the high pressure at increased cost.

As such pumps have delivery ports smaller than their suction ports, it was in the interests of economy that the dyeing machines that grew up around them had circulating systems of the same size as the smaller delivery port. They also used valves and heat exchangers in the piping system with similarly small flow areas, and with correspondingly high total system resistance similar to the chemical processing plants for which the pumps had originally been designed.

Claims by some suppliers that their pumps of this type meet high industry standards for this type of pump are rendered meaningless by the low hydraulic efficiency of such systems.

Even in modern designs of this type by some of the world's largest dyeing machine manufacturers, an overall hydraulic efficiency of only 10r is not uncommon.

The greatest energy loss can take place at the in-line heat exchanger which typically absorbs over 30X of the power supplied to the machine. The reversing valve and the inlet and outlet connections to and from the vessel, together with in-line valves which may have to be used to effect auxiliary functions when filling, draining, or transferring liquor, might consume as much as another 30X. The remaining 30% would include the pipework, valves, carrier etc. that comprise the actual dyeing system.

Circulating the process liquor through the yarn and its physical support system, the dyetubes, spindles and carrier accounts for a very small part of the power applied to the machine, much of which is therefore lost as heat, and a continuous flow of cooling water may be needed to perform a low temperature process.

The fault does not lie with the pump manufacturers, who are fully conscious of the factors involved in system design, for example a DURCO pump manual states "Friction loss is inversely proportional to the fifth power of the pipe diameter ratio". This means that a small increase in area can make up for a less than perfect shape in the passageway. Doubling the cross sectional diameter of an existing system reduces the friction losses to about 3% whereas streamlining such a system while retaining the same pipe diameter can only very slightly reduce the power requirement, and the use of small diameter pipes and components in the circulating system, while saving money and thereby profiting the manufacturer, increases the cost of both electricity and cooling water to the user of the machine.

Reversing valves in dyeing machine have traditionally been of the least expensive rotating ell type in which the total volume of flowing liquor is bypassed back to the pump in the reversal or part-open condition, resulting in maximum motor current consumption when least work is being done on the load. This is not desirable at any time, but particularly if the reversing valve is used to control the rate of flow through the load throughout the entire dyecycle, as for example, when processing a part load.

Side thrust developed in the unit by the high velocity liquor tended to force the valve sideways and the cast stainless steel components tended to rub against each other and "Gall", which roughed up the mating surfaces and could cause it to seize up completely.

In the dyeing of warp beams, the practice has been established for many years, of providing a throttle valve at the pump discharge, and closing it before moving the reversing valve, thus stopping all flow, and removing this side thrust from the reversing valve, then changing the position of the reversing valve, and opening the throttle valve either to a preset position or to a predetermined pressure differential, over a period of as much as 45 seconds, so as very gently to resume flow in the opposite direction.

Warp beams comprises cotton fibres laid side by side which form a very solid mass, difficult to penetrate, which becomes tighter and more dense as the fibre absorbs moisture and swells. This means that it requires higher pressure to penetrate it than any other textile package. At the same time it possesses very little strength in the lateral direction as the fibres are easily forced apart, thus "Blowing" the beam, and creating a channel through which liquor escapes and pressure is lost.

The fibres adjacent to the channel are stretched and the physical integrity of the beam can only be restored by stopping the process and rewinding the beam.

From the technical point of view the procedure is sound since closing the throttle valve and stopping the flow reduces both the motor current and the Net Positive Suction Head (NPSH) requirement to a minimum and thus reduces the tendency to generate foam. Changing the reversing valve position with the flow stopped overcomes the inherent defect in a "by-pass" reversing valve that allows circulation rate, motor current and NPSH to rise to maximum.

The need to process at high temperature requires the pump suction connection to be pressurized to a pressure not less than the sum of the vapour pressure corresponding to the required temperature plus the NPSH for the particular pump at the flowrate in use. In practice it is desirable that the actual pressure at the pump suction should be slightly greater than this to provide a margin of safety.

The penalty for failing to provide sufficient pressure is cavitation and reduction in pump performance with a corresponding reduction in dyeing efficiency, with the possibility of unlevel dyeings.

A more subtle penalty, which may not produce a detectable reduction in pump discharge pressure, is incipient cavitation, in which vapour bubbles, sometimes of microscopic size, are formed at the entrance to the impeller and in vortices behind the impeller blades.

With clean water, these tiny bubbles may collapse as they pass into higher pressure regions. However, most dyeing processes involve soaps, detergents and other chemicals which can render the bubbles more permanent. They then manifest themselves as foam and pass into other regions of the machine, and particularly into the interstices of the yarn, where they may impair the free access of dyeliquor to the yarn and can cause spotty dyeings.

Stopping the flow while reversing minimises this tendency and for all these reasons is sound practice. Bypassing the flow increases the tendency.

However, in conventional piping systems this very desirable procedure requires a full system sized throttle valve at the pump discharge connection, and an automatic operator with the necessary instrumentation to effect the sequence of operations.

The same effect can be obtained by separating the reversing valve ports to provide a wide land between them so that the valve becomes a "Throttling" type, rather than a "By-pass" type so that during reversal, flow is automatically reduced to zero and motor current to minimum. However, as this may further increase the diameter of the housing in which the ell rotates, this could exacerbate the acknowledged problems of the ell type valve.

The rotating ell may have appeared as a logical way of reversing flow to early designers, but it provides an undesirably sharp change of direction and to be effective it requires a large diameter, accurately machined housing. Liberal clearance, with an attendant loss of performance, may have to be provided to avoid galling under deflection.

According to the invention a system for treating packages of yarn with liquid comprises a treatment vessel, a reversing valve housing integral al with the treatment vessel, a low pressure pump and a large flow section pipe system so connecting the pump and the reversing valve housing as to form a unidirectional flow circuit for the liquid.

Advantageously the low pressure pump is a collection ring centrifugal pump.

Preferably a heating coil is provided in the treatment vessel instead of an in-line heat exchanger. By close coupling the pump to the reversing valve which is also within the vessel a significant proportion of the piping system losses can be eliminated.

Advantageously such a system provides an unrestricted path from the load to the pump suction connection such that the flow area is never less than the area of the pump suction connection and an unrestricted path from the pump discharge connection to the load such that the flow area is never less than the area at the pump discharge connection.

The direction of flow through the load can preferably be reversed in such a manner that the discharge area is progressively reduced to zero by rotating the valve in either direction, with the porting so arranged that the suction area remains at all times greater than the discharge area, whereby the machine may be operated continuously in any such throttled condition without damage to the pump or any of the other undesirable effects from cavitation.

Both the pump delivery and the pump suction connections can advantageously be closed off in the "No-flow" position by further rotation of the valve so that the pump is made available for auxiliary filling and emptying functions, by means of external connections, without requiring large shut-off valves in the main circulating system.

The number of obstructions or changes of section of passageways through which the liquor flows can be reduced to a minimum, and the area of those that cannot be eliminated can be increased to a maximum thereby reducing the cost of circulating liquor.

Other restrictions to liquor flow can be eliminated by removing all in-line valves from the system. Such valves are commonly of the vane or "Butterfly" type, and still offer considerable resistance when open. If the reversing valve can be made to provide the total shut-off function for which other valves in the external pipework have normally been used, there will be a consequent reduction in the cost of the machine by the elimination of both the in-line valves and their automatic operators.

Housing the valve entirely inside the treatment vessel reduces the resistance to flow by the reversing valve. since the area through which liquor has to flow can be greatly increased and the power required to circulate it can be reduced.

Also, it naturally follows that if a lower pressure pump of high efficiency can be used, a given performance can be provided in a vessel of lower pressure rating by a motor of lesser horsepower.

With the system losses thus reduced to a fraction of their traditional level, the need for the pump to provide a high discharge pressure no longer exists, and the design feature which provided it can be dispensed with, with a consequent reduction in shear, turbulence and NPSH, resulting in a cleaner and more efficient pump design as the flowing liquor more accurately follows the shape of the impeller blades and passes smoothly into a truly annular collector ring.

Preferably, the reversing valve is of the swash plate type.

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 according to the invention; Figure 2 is a cut-away perspective view of a reversing valve of the system of Figure 1 in an 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 schematic plan view of a piping arrangement for the system of Figure 1; Figure 5 is a sectional view taken in the direction of arrows V-V of Figure 4 with the reversing valve in a position for inside-to-outside flow; Figure 6 is a view similar to Figure 5 with the valve rotated 1800 into a position for outside-to-inside flow;; Figure 7 is a view similar to Figure 5 with the reversing valve rotated to a 900 position for no flow; Figure 8 is a view similar to Figure 5 with the reversing valve rotated to a 2700 position for no flow; and Figure 9 is a view similar to Figure 5 with the valve rotated to a 292.50 position for return to a stock tank.

Referring to the drawings and firstly to Figure 1, a system for treating packages of yarn with liquid comprises a pump which as shown is 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, 3o 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, 3a to the reversing valve housing 2 and back to the pump 7 via a pipe 3hl 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 the position 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 3k back to the pump 7.

The position of the valve 9 to give the flow described with respect to Figure 3 is that shown in Figure 5. 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 suction connection 7 of the pump 1.

If the valve 9 is rotated through 1800 to the position of Figure 6, fluid flowing into the housing 2 through the flange 5 is, as shown in Figure 2, 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. Figures 2 and 6 thus show entirely opposite flow through the load to that of Figures 3 and 5.

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 loosing 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 a high pressure pump is no longer required and the collector ring centrifugal pump 1 shown can provide ample pressure. Such a pump can have a characteristic curve much better suited to the requirements of the widest range of yarn packages and can generate less turbulence or shear in the sensitive dye liquor. By means of the arrangement described. an increase in operating efficiency, and a reduction in power, time and water required to process a given load of yarn can be obtained and the machine can be easier to manufacture, operate and maintain.

Figure 7 shows the valve 9 in a 900 position, that to say midway between the position of Figure 5 and the position of Figure 6. As the valve is moved from full flow in one direction through the 900 position of Figure 7, at which there is zero flow, to full flow in the other direction, the current of the motor driving the collector ring-type centrifugal pump 1 also falls to a minimum at the position of zero flow when the main line connections between the valve and the pump are both closed.

Once it is established that there is the ability completely to cut off circulation in the main circulating system without having to use cut-off valves, it is possible to provide suitable connections so as to use existing passageways to perform tasks that would otherwise require additional external valves and pipework.

Figure 4 shows that the pipe 3 includes a return-to-stock tank connection 16, a by-pass connection 17 which is also connected by a pipe 18 to the central duct 12 and has a vacuum extract connection 19 and that the pipe 3h includes a fill-from-stock tank connection 20, a water fill connection 21 and a drain connection 22. A motor 23 and gear arrangement 24 for driving the valve 9 is also shown.

The design of reversing valve 9 provides excellent access to the actual working bore in which the valve rotates both from the point of view of manufacture and inspection and also facilitates removal and replacement of the valve when replacing the bearings which are advantageously formed of material sold under the Registered Trade Mark Teflon.

In the angular position of the valve 9 shown in Figure 7, the vessel 8 can be filled from a stock tank via the connection 21. A fill by-pass passage and valve of the same size is provided from the pump discharge connection into the inside flow line. With the vessel 8 vented to atmosphere and the valve open, the machine can be filled through the packages. displacing air from the yarn as it fills. This reduces the tendency for air to be trapped in interstices of the yarn.

where it could remain as small bubbles and result in undyed spots. so that the yarn is wetted out as part of the filling process, but it would also be possible to run the pump 1 while filling to speed up the process.

With the valve 9 in the same position it is also possible to fill the machine from a stock tank by way of the connection 20. The same arrangement would be used as above except that a level sensor would indicate when the reversing valve 9 had been covered with liquid and the pump 1 would then be started. Again the liquid would be driven through the load to wet it out as part of the filling process. When the stock tank had been emptied, a sensor would close the fill valve and the normal reversing sequence could be started.

In all cases incoming water passes through the pump 1 and then through the load on inside-to-outside flow, the pressure to drive the air from the load is provided in the first case, by the water supply and in the second case, by the pump 1.

Vacuum may be used to fill the machine from the stock tank by connecting a vacuum source to the top of the vessel and opening the stock tank valve. In both the 900 position of Figure 7 and the 2700 of Figure 8, the valve 9 is closed and liquid cannot circulate in the main system. To return the liquid in the main system to the stock tank via the connection 16 shown in Figure 4, the valve 9 is rotated to the 292.50 position shown in Figure 9. By offsetting the discharge port in the valve, the pump suction connection 7 can be connected to the bottom of the machine and the pump discharge connection 4 can be connected to the connection 16 to the stock tank.Although the suction port in the valve is not fully open in this operation, sufficient area is available for liquid to be drawn from the bottom of the vessel and pumped to the stock tank until a suitable sensor stops the pump and closes the stock tank valve. However replacing a symmetrical valve with an off-set valve complicates the operation unless there is a substantial demand for the facility to return liquid to the stock tank and it may be better to utilise a symmetrical valve.

A vacuum extract cycle can be performed as a repeating series of short vacuum pulls with the valve 9 in the position of Figure 7, letting the vacuum pump pull down to its maximum vacuum, then opening the vacuum valve and letting vacuum act on the load and allowing it to settle to an agreed level before closing the valve and letting it recover again before repeating the cycle.

Although the system for treating packages of yarn with liquid shown is a vertically oriented system it is only an example of one advantageous system and many other configurations are possible including horizontally oriented systems.

Claims (10)

1. A system for treating packages of yarn with liquid comprising a treatment vessel, a reversing valve housing integral al with the treatment vessel, a low pressure pump and a large flow section pipe system so connecting the pump and the reversing valve housing as to form a unidirectional flow circuit for the liquid.

2. A system according to claim 1, in which the low pressure pump is a collection ring centrifugal pump.

3. A system according to claim 1 or claim 2, in which a heating coil is provided in the treatment vessel instead of an in-line heat exchanger.

4. A system according to claims 1 to 3, in which the pump is close coupled to the reversing valve which is within the treatment vessel.

5. A system according to any one of claim 1 to 4, providing an unrestricted path from the load to a suction connection of the pump such that the flow area is never less than the area of the pump suction connection and an unrestricted path from a discharge connection of the pump to the load such that the flow area is never less than the area at the pump discharge connection.

6. A system according to claim 5, in which the direction of flow through the load can be reversed in such a manner that the discharge area is progressively reduced to zero by rotating the valve in either direction, with the porting so arranged that the suction area remains at all times greater than the discharge area, whereby the machine may be operated continuously in any such throttled condition without damage to the pump or any of the other undesirable effects from cavitation.

7. A system according to claim 5 or claim 6, in which both the pump delivery and the pump suction connections can be closed off in the "No-flow" position by further rotation of the valve so that the pump is made available for auxiliary filling and emptying functions, by means of external connections, without requiring large shut-off valves in the main circulating system.

8. A system according to any one of claims 1 to 7, which has no in-line valves and in which the reversing valve can provide a total shut-off function.

9. A system according to any one of claim 1 to 8, in which the reversing valve is of the swash plate type.

10. A system for treating packages of yarn with liquid substantially as hereinbefore described and illustrated with reference to the accompanying drawings.