GB2070449A

GB2070449A - Homogeniser

Info

Publication number: GB2070449A
Application number: GB8105666A
Authority: GB
Original assignee: Vickers Ltd
Current assignee: Vickers Ltd
Priority date: 1980-02-28
Filing date: 1981-02-23
Publication date: 1981-09-09

Abstract

An homogeniser for liquids such as milk comprises a conduit (14, 16, 18, 20, 40) through which the liquid to be homogenised is passed. The conduit includes an annular seat (22) having a bore (24) through which the liquid flows and also a member (30) which is displaceable along the conduit. A non-resiliently supported abutment (32) is provided to restrain the member (30) in a position along the conduit where it co-operates with the seat (22) so that the liquid flowing through the bore (24) is subjected to a homogenising action as it passes between the seat (22) and the member (30). The abutment (32) is moveable along the conduit by a screw assembly (42) to control the rate of liquid flow. <IMAGE>

Description

SPECIFICATION Improvements in or relating to homogenisers This invention relates to homogenisers and more particularly but not exclusively is concerned with homogenisers for homogenising milk or the like prior to analysis.

In our United Kingdom Patent Application No. 8006749 there is described a liquid-analyser comprising a sample cell and a sampling device for introducing a sample into the cell. The sampling device comprises a piston and a cylinder, the cylinder being closed at one end by a wall to define with an end face of the piston a sample chamber, the cylinder also defining with the piston a flushing chamber located on the opposite side of piston seal means to the sample chamber. Means are provided for effecting relative movement of the piston and cylinder to allow relative reciprocation of the piston between two positions in the cylinder to fill and to empty said sample chamber, respectively. The sample chamber has a valve-controlled inlet and a valve-controlled outlet, the inlet being connected to a sample probe and the outlet being connected to the sample cell via a homogeniser.

It is often necessary to analyse liquids such as milk to determine, for example, the fat, protein, lactose and total solids content for quality control and other recording purposes. That analysis can be performed using infra-red techniques.

The use of the word "milk" in this specification is intended to include other dairy products susceptible to analysis by such techniques.

One of the problems associated with analysing milk is that the fat content of milk is concentrated into globules which typically have a size distribution of 0.1 to 30 microns, with a peak at about 5 microns. The variation in size is such that the scatter of the infra-red radiation by the globules is not functionally dependent upon the concentration of fat. Consequently, the scatter cannot be calibrated out on the analysing apparatus.

This problem has been overcome by subjecting milk samples to an homogenisation process immediately prior to analysis. Homogenisation can be achieved using ultrasonic techniques. Such techniques result in a typical globule-size distribution of 0.1 to 2 microns having a peak at 0.5 microns.

Ultrasonic homogenisation, however, only allows a relatively slow analysis-cycle rate to be used. Typicaliy, the rate is 100 cycles/hour with a maximum of about 120 cycles/hour. At higher cycle rates, the ultrasonic energy that has to be imparted to a sample (in a reduced exposure time for achieving the same degree of homogenisation) produces too much heat in the sample, excess heat interferring with the subsequent analysis of the sample.

Mechanical homogenisers have also been used.

Such homogenisers consist of an annular seat defining an entry passage for milk at high pressure and a ball which is loaded against the seat by a pre-loaded compression spring or the equivalent thereof. The homogenisation of the globules is believed to be achieved by a shearing action which occurs as milk flows past the seat and the ball, the ball having been forced from the seat against the spring loading by the pressure of the milk. The seats of such homogenisers tend to wear rapidly. Additionally, the globule size distribution varies. It has been found that such homogenisers only achieve an average degree of homogenisation similar to that achieved by using ultrasonic techniques although higher flow rates are possible.

Brief Summary of the Invention It is an object of the invention to provide a mechanical homogeniser which is less subject to one or more of the above-mentioned disadvantages.

According to the instant invention there is provided an homogeniser for liquids which comprises: (i) a housing through which a conduit extends, the conduit having a first end constituting an inlet for liquid to be homogenised and a second end constituting an outlet for homogenised liquid; (ii) an annular seat provided in the conduit and defining a bore through which the liquid flows when passing from said first end to said second end; (iii) a member located within the conduit between the seat and said second end and mounted so as to be displaceable along the conduit; and (iv) a means of restraining the member in a position along the conduit where part of the member co-operates with said seat whereby liquid flowing through the bore passes between the seat and the member and is thereby subjected to a homogenising action, the restraining means being in the form of a non-compressible abutment mounted for movement along the conduit by means of a screw in threaded engagement with the housing thereby to control the rate of flow of liquid between the seat and the member.

In a preferred embodiment the abutment is in the form of a plunger mounted for displacement within, and in sealed relationship with respect to, the conduit. In this case it is preferred for the plunger to have a first end which abuts against the member and a second end opposite to the first end, the control of the rate of flow of liquid past the seat and the member being effected by the screw acting on the second end of the plunger.

The member is preferably a ball.

Preferably, the relative sizes of the bore of the annular seat, in the region of the seat adjacent to the member, and of that part of the member which co-operates with the seat are selected to maximise the degree of homogenisation that can be achieved. In the case where the bore is circular it has been found that, as the inner diameter of the bore is reduced from being substantially equal to the diameter of said part of the member, the degree of homogenisation achieved reaches a peak. Advantageously, the diameter of the bore is about 80 to 90% of the diameter of said part.

It is also preferred for the bore of the annular seat to taper at a small angle (e.g. about 1.50) so that its diameter is less in the region adjacent to the member than in the region nearer to the inlet of the conduit. In this regard, it has been found that the degree of homogenisation achieved reaches a peak as the degree of taper is increased from zero, i.e. from a bore having a cylindrical surface, and, consequently, the degree of taper is selected accordingly.

In an embodiment, the annular seat is in the form of a separate component which is located in the passage adjacent said first end of the conduit.

In this case that end of the annular seat opposite to that end which co-operates with the member has an O-ring seal which, in use of the homogeniser, is compressed between the seat and a sampling device or other component to which the homogeniser is secured and which, in use, supplies liquid to the homogeniser inlet.

Brief Description of the Drawing For a better understanding of the invention and to show how the same may be carried out, reference will now be made, by way of example, to the accompanying drawing which shows a crosssection through a homogeniser in accordance with the instant invention.

Detailed Description The homogeniser is indicated generally by reference numeral 10. It has a housing 12 and a conduit through the housing 12. The conduit includes a passage 14 having sections 16, 18 and 20, sections 16 and 20 being of substantially the same diameter, which diameter is greater than the diameter of section 18.

A separate component in the form of an annular seat 22 is located at a first end of the conduit in section 16 and abuts a shoulder formed by the change in diameter of the sections 16 and 18 of the passage 14. The seat 22 defines a circular bore 24 which serves as an inlet, into the conduit, for liquid to be homogenised. The seat 22 is channel-shaped in section and an O-ring seal 26 is located in the channel to seal the seat 22 with respect to passage section 1 6.

The bore 24 of the seat 22 converges towards that end which abuts the shoulder between sections 16 and 18. The surface of the bore of the seat 22 is at an angle of 1.50 to a true cylindrical surface and the diameter of the bore at the end abutting the shoulder is 4.0 millimetres (mm).

A resilient sealing member in the form of an 0ring seal engages the free end of the seat 22 and holds it in position against the shoulder as will be more fully explained below.

A member in the form of a ball 30 is located in the passage section 18. The ball 30 has a diameter of 4.75 mm and is displaceable along passage section 1 8 so that it can co-operate with the seat 22 to homogenise liquid passing through the bore 24. The ball 30 is located in position by a non-compressible abutment in the form of a plunger 32 slidable in the passage section 1 8. The plunger 32 has a first end provided with a recess 34 to centralise the ball 30. The plunger has an 0ring seal 36 to seal it with respect to the passage section 1 8.

The passage section 20 is screw threaded to receive the threaded stem of an adjustable screw 42. The plunger 32 has a second end opposite to the first end and the adjusting screw acts on the second end so that the first end of the plunger abuts against the ball 30 and urges it against the seat 22.

An annular space 38 is defined between the opposing end faces of the seat 22 and the plunger 32, the ball 30 and the part of the passage section 1 8 surrounding the ball 30. This annular space 38 receives liquid homogenised by the seat 22 and the ball 30. The conduit through the housing also includes a passage 40 which connects the annular space 38 to the exterior of the housing 12 to provide a second end which serves as an outlet for homogenised liquid. The passage 40 can be screw threaded as shown for receiving a sample line connector (not shown).

The housing 12 and the seat 22, the plunger 32 and the flow-adjusting screw 42 are all made of stainless steel. The bail is made of synthetic sapphire. The diameters for the seat 22 and the ball 30 and the angle for the taper of the bore have been selected to maximise the degree of homogenisation that the homogeniser 10 can achieve.

The homogeniser 10 is typically used in an infra-red milk analyser. The homogeniser 10 is secured by bolts, extending through three equallyspaced bores 44, to a component in the form of a milk sampling device (shown schematically only by chain dotted lines) which delivers milk under high pressure into the bore 24. An annular rubber gasket 46 is positioned on a central annular boss 48 on the housing 12. Once the homogeniser 10 is secured to the sampling device, the O-ring seal 28 is compressed to substantially half its thickness and holds the seat 22 in abutment with the shoulder between passage sections 1 6 and 1 8. It is believed that the seal 28 acts as a stiff suspension for the seat 22. The flow-adjusting screw 42 acts against the plunger 32 via a resilient intermediary in the form of an insert 50 of resilient material such as rubber.

The sampling device is preferably of the type described in the aforementioned United Kingdom Patent Application No. 8006749.

A typical milk analysis cycle consists of four samples; two samples are passed to waste to flush a filter clean; and two samples are passed to a sample cell for analysis.

Using the homogeniser 10 just described, cycle rates of up to 260 cycles/hour have been achieved. The cycle time is 1 3.8 seconds, each sample taking approximately 2 seconds to process and there being a delay of approximately 5 seconds before the start of the next cycle.

The desired milk flow rate is set in the homogeniser 10 as follows:- a) the flow-adjusting screw 42 is turned to move the plunger 32 towards the seat 22 thereby loading the ball 30 against the seat 22 to stop milk flow; b) the flow-adjusting screw 42 is then turned in the opposite sense to relieve the load on the ball 30; c) as the load on the ball 30 is relieved, the milk which is typically at a pressure of 40 MN/m2, starts to flow; and d) the flow-adjusting screw 42 is continued to be turned until the desired flow rate is achieved.

In the particular application described, the ball 30 is used as a non-return valve for the sampling device.

Additionally, the homogeniser 10, in optimising the diameters of the seat 22 and the ball 30, in optimising the taper angle for the bore of the seat 22 and in optimising the degree of compression of the O-ring seal 28 achieves a degree of homogenisation better than the prior-used ultrasonic homogenisers.

It has also been found that the seat 22 is subjected to very little wear as compared to priorused mechanical homogenisers. Additionally, the homogeniser 10 has been found to give more consistent homogenisation than those prior-used homogenisers. It is believed that this is because the homogeniser 10 does not have a compression spring or its equivalent to maintain the ball in cooperation with the seat. Hence the ball-to-seat separation is constant for any given setting of the flow-adjusting screw whereas the spring or equivalent in the prior homogenisers allows variation in ball-to-seat separation under the influence of the pressurised milk.

Modifications can be made within the scope of the invention.

For example, the O-ring seal 28 or the resilient insert 50 may be omitted from the construction. In either instance, however, the degree of homogenisation is not as good as when both are present. The removal of the O-ring seal 28 had a greater effect than the removal of the insert 50.

An homogeniser in which the bore of the seat 22 was not tapered was tested, both the O-ring seal 28 and the insert 50 having been omitted. Using that homogeniser, only a degree of homogenisation similar to that obtainable using an ultrasonic homogeniser was achieved. The insert 50 may be replaced by an equivalent resilient intermediary carried by the plunger.

Further modifications include using a seat having a cylindrical bore and not optimising the diameter relationship of the seal and the ball.

However, in such a case the degree of homogenisation achieved will not be as good as that achieved using the homogeniser 10.

Still further modifications include, for example, replacing ball 30 by a member having an alternative profile for co-operating with the seat, for example conical; making the plunger 32 and flow-adjusting screw 42 as an integral component; making the seat screw-threaded so that it can be screwed into the passage section 1 6; or integrally forming the seat with the housing.

If a pressure gauge can be used with the analyser, the flow rate through the homogeniser 10 can be set using a different method to that described above. In this method the analyser is actuated to cause the sampling device to feed a series of samples through the homogeniser 10.

The pressure at which the samples are fed is monitored. The flow-adjusting screw 42 is turned to move the plunger 32 towards the seat 22 thereby loading the ball 30 against the seat 22 to restrict milk flow. The screw is turned until the pressure gauge shows that milk is being forced through the homogeniser 10 at the required pressure.

While a number of possible modifications have been mentioned above, the homogeniser 10 described with reference to the drawing is the preferred form of homogeniser since, in that homogeniser, various features have been optimised to achieve an improved degree of homogenisation combined with a relatively high analysis cycle rate.

It will be appreciated that, although the homogeniser has been described as homogenising milk, the homogeniser is usable to treat other substances having for example an oil or fat content and which require homogenisation for analytical or other purposes.

Claims

1. An homogeniser for liquids comprises:- (i) a housing through which a conduit extends, the conduit having a first end constituting an inlet for liquid to be homogenised and a second end constituting an outlet for homogenised liquid; (ii) an annular seat provided in the conduit and defining a bore through which the liquid flows when passing from said first end to said second end; (iii) a member located within the conduit between the seat and said second end and mounted so as to be displaceable along the conduit; and (iv) a means of restraining the member in a position along the conduit where a part of the member co-operates with said seat whereby liquid flowing through the bore passes between the seat and the member and is thereby subjected to a homogenising action, the restraining means being in the form of a non-compressible abutment mounted for movement along the conduit by means of a screw in threaded engagement with the housing thereby to control the rate of flow of liquid between the seat and the member.

2. An homogeniser as claimed in Claim 1 wherein said abutment is in the form of a plunger displaceable along, and in sealing relationship with respect to, the conduit.

3. An homogeniser as claimed in Claim 2 wherein the plunger has first and second opposite ends and is displaceable along the conduit by means of said screw acting on its second end so that its first end abuts against and restrains the member in said position.

4. An homogeniser as claimed in Claim 3, wherein the screw acts on said second end via a resilient intermediary.

5. An homogeniser as claimed in any one of the preceding claims wherein said member is a ball.

6. An homogeniser as claimed in any one of the preceding claims wherein the bore is a circular bore and the diameter of the bore in the region adjacent to the member is substantially less than the diameter of said part of the member which cooperates with the seat.

7. An homogeniser as claimed in Claim 6 wherein the diameter of the bore is about 80 to 90% of the diameter of said part of the member which co-operates with the seat.

8. An homogeniser as claimed in any one of the preceding claims wherein the bore is circular and it is tapered such that its diameter is less in the region adjacent to the member than in the region nearer to the inlet of said conduit.

9. An homogeniser as claimed in Claim 8 wherein the bore tapers at an angle of about 1.5 .

10. An homogeniser as claimed in Claim 1 substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

11. An homogeniser as claimed in any one of the preceding claims and secured to a component for supplying liquid to said inlet, a resilient sealing member being located between said component and the seat to hold the seat in co-operating relationship with said member.

12. An homogeniser as claimed in Claim 11 wherein the component is a milk sampling device.