The invention relates to a peristaltic pump tube to be peristaltically actuated along part of its length to pump a liquid medium, comprising a piece of tubing surrounding the pump 5 tube with an interspace, and extending past said peristaltically actuated part upstream as well as downstream thereof.

Figs. 1A - lC ^' on the attached drawing, show three different phases of a pump cycle in a schematically shown peristaltic pump with a conventional pump tube 1 for pumping of a liquid. The 0 pump tube 1 rests in a manner known per se on a solid backing 2 and is compressed in order by a number of rollers that are rotatably journalled and evenly distributed around the periphery of a circular disc (not shown) which is journalled rotatable in the direction of arrow A. Only two of the rollers designated 3 5 and 4, respectively, are shown.

In the position shown in Fig. 1A the roller 3 compresses the tube 1 against the backing 2 and, thereby, feeds the liquid present in the pump tube 1 in the direction of arrow B. In the position shown in Fig. 1A the roller 4 has not yet compressed Q the tube 1 against the backing 2. The pressure in the pump tube 1 upstream the roller 3 is supposed to be Pi, which normally corresponds to atmospheric pressure, while the pressure that the feeding roller 3 produces downstream in the pump tube 1, is supposed to be P2. P2 being greater than Pi.

5 In the position shown in Fig. IB both rollers 3 and 4 compress the pump tube 1 against the backing 2.Between the rollers 3 and 4 an occlusion is formed, in which the pressure is Pi, i.e. the same pressure as upstream the roller 4. In order for the peristaltic pump to work correctly it is required that the _, roller 4 compresses the tube 1 against the backing 2 before the compression of the tube 1 by the roller 3 ceases.

In Fig. 1C it is shown when the compression of the tube 1 against the backing 2 by the roller 3 just has ceased, while the roller 4 still compresses the tube 1 against the backing 2. Then, the pump tube 1 is opened under the roller 3 and the pressures in the tube 1 on both sides of the roller 3. are immediately equalized. ^•

Thus, the pressure in the previous occlusion between the rollers 3 and 4 increases immediately from Pi to P2. As indicated in Fig. 1C this pressure-equalization results in an expansion of the pump tube 1 between the rollers 3 and 4, which expansion temporarily changes the flow rate of the liquid so that a pulsation in the flow arises. This pulsation will be greater, the greater the difference is between the pressures P2 and Pi.

Such pulsations in the flow cannot be accepted in e.g. a liquid chromatography system, where a liquid is pumped to a column followed by a flow pulsation sensitive UV-detector. Flow pulsation attenuators are used in such systems to eliminate flow pulsations.

The object of the invention is to brings about a peristaltic pump tube which does not give rise to any disturbing pulsations in the flow.

This is attained by the pump tube according to the invention in that there is a pressure-equalizing connection between said interspace and the inside of the pump tube downstream said peristaltically actuated part.

The invention will be described more in detail below with reference to the drawing, on which

Fig. 2 is a longitudinal section of a first embodiment of a pump tube according to the invention,

Figs. 3A and 3B show cross-sectional views of the tube according to Fig. 2 in a non-compressed state and a compressed state, respectively, and

Figs. 4-8 show five further different embodiments of the pump tube according to the invention.

Fig. 2 shows a longitudinal section of a first embodiment of a pump tube according to the invention in a peristaltic pump shown schematically in the same manner as in Figs. 1A-1C in the form of the backing 2 and the rollers 3 and 4 which in all subsequent embodiments, are supposed to be in the same position as in Fig. IB.

In Fig. 2, the pump tube is designated _> . The pump tube can be of a plastic material based on polymers of fluoridated hydrocarbons, e.g. polytetrafluorethylene, and is intended to be used at pressures up to 10 bars or higher. In the embodiment shown in Fig. 2 the pump tube 5 ends in an outer tube 6 surrounding the pump tube __ . Preferably the outer tube 6 is of the same material as the pump tube 5 _' Downstream the part peristaltically actuated by the rollers 3 and 4, the outer tube 6, thus, extends past the outlet end of the pump tube 5 to an outlet (not shown) . Upstream the part peristaltically actuated by the rollers 3 and 4 the outer tube 6 is, according to the invention, sealingly connected to the outside of the pump tube 5 as schematically indicated by a tubular seal 7 between the outer tube 6 and the pump tube 5•

In that the outer tube 6 surrounds the pump tube 5 with a certain interspace between the tubes as apparent from Fig. 3 , the pressure P2 at the outlet end of the pump tube 5 in the outer tube 6, will be obtained also on the outside of the pump tube 5 between the rollers _ and 4. From Fig. 3B i is apparent that also in a compressed state there are channels between the tubes 5 and 6.

In that the pressures will be the same outside as well as inside the pump tube 5 between the rollers 3 and 4 in the embodiment shown in Fig. 2, the pump tube 5 will not expand in the area between the rollers 3 and 4, when the pressures in the pump tube 5 on either side of the roller 3. sir' ¹ equalized, i.e. when the compression of the tube 5 by the roller 3. ceases. -Thus, no pulsations will appear in the liquid flow even when there is a great difference between the pressures P2 and Pi.

In Fig. 4 a second embodiment of the pump tube according to the invention for obtaining the same pressure on the outside of the peristaltically actuated part of the pump tube as inside the pump tube downstream this part is shown.

In the embodiment shown in Fig. 4, a jacket 8 surrounds the pump tube which is designated 9 and extends to an outlet (not shown) . By means of schematically indicated tubular seals 10 and 11, the jacket 8 is sealingly connected with the outside of the pump tube 9 upstream as well as downstream the part which is peristaltically actuated by the rollers 3 and 4.

To obtain the same pressure P2 on the outside of the peristaltically actuated part of the pump tube 9 as inside the ._ pump tube 9 downstream the peristaltically actuated part, at least one hole 12 is present in the pump tube 9. which hole 12 downstream the peristaltically actuated part, connects the inside of the pump tube 9 with the interspace between the pump tube 9 and the jacket 8.

A dead volume in which the pump medium is cumulated, is obtained in the embodiment shown in Fig. 2 as well as in the embodiment shown in Fig. 4 between the pump tube _. and 9 _» respectively, and the outer tube 6 and the jacket 8, respectively. In many cases, this dead volume can be accepted, e.g. when the pump is only used to pump one and the same liquid. However, when different liquids are pumped, this dead volume can cause contamination

problems. To eliminate these problems, some embodiments of the pump tube according to the invention will be described below, which embodiments do not have any dead volume.

Fig. 5 shows a third embodiment of the pump tube according to the invention. The pump tube which is designated 5 as in Fig. 2, ends also in this case in an outer tube 13 surrounding the pump tube 5- However, in the embodiment shown, the outer tube 13 is permanently closed downstream the outlet end of the pump tube 5. and is, upstream the part peristaltically actuated by the rollers 3 and 4, sealingly connected with the outside of the pump tube 5 as schematically indicated by a tubular seal 14.

To obtain the same pressure on the outside of the peristaltically actuated part as inside the pump tube 5 downstream that part, the outer tube 13 is, upstream the peristaltically actuated part, connected to an outlet via a hole 15 in the wall of the outer tube 13.

Thus, in operation, the liquid from the outlet end of the pump tube 5 will be pumped into the interspace between the pump tube 5 and the outer tube 13 to the outlet via the hole 15.

Fig. 6 shows a variation of the embodiment shown in Fig. 5- In the embodiment shown in Fig. 6 the hole 15 in the closed outer tube 13 surrounding the pump tube 5 is connected to an outlet via the interspace between the outer tube 13 and a third tube 16 which surrounds the outer tube 13 and which, preferably, is of the same material as the pump tube 5 and the outer tube 13.

Upstream the part of the pump tube 5 peristaltically actuated by the rollers 3 and 4, the third tube 16 is sealingly connected with the outside of the pump tube 5 via a tubular seal 17• Thus, in the embodiment shown in Fig. 6 the liquid will be pumped to the outlet from the outlet end of the pump tube 5 via ,on the one hand, the interspace between the pump tube 5 and the outer tube 13, and, on the other hand, the interspace between the

outer tube 13 and the third tube 16 surrounding the outer tube 13-

Both in Fig. and Fig. 6 the outer tube 13 is shown permanently closed downstream the outlet end of the pump tube __ , e.g. by 5 means of a plug (not shown) .

In e.g. the embodiment shown in Fig. 5. the outer tube does not necessarily have to be permanently closed.

Fig. 7 shows an embodiment where the outer tube designated 18, is non-permanently closed by means of a schematically indicated

Id safety valve 19 which by means of e.g. a spring 20 can be adapted to open at a predetermined pressure in the outer tube 18. Also in this case, the outer tube 18 is sealingly connected with the outside of the pump tube 5 via the seal 14 upstream the part peristaltically actuated by the rollers 3 and 4. As in the

15 embodiment according to Fig. 5 the hole 15 in the outer tube 18 is connected to the outlet upstream the part of the pump tube 5 peristaltically actuated by the rollers 3 and 4.

Fig. 8 shows a fifth embodiment similar to the one shown in Fig. 4. Also in this case a jacket 8 surrounds the pump tube which is

20 designated 21. The jacket 8 is sealingly connected with the outside of the pump tube 21 upstream as well as downstream the part peristaltically actuated by the rollers 3 and 4 by means of the tubular seals 10 and 11, respectively. According to the invention the interspace formed between the jacket 8 and the

25 pum tube 21 in this embodiment, is filled with a liquid, e.g. of the same type as the one that is being pumped. To transfer the pressure inside the pump tube 21 downstream the part peristaltically actuated by the rollers 3 and 4 to the outside of this peristaltically actuated part of the pump tube 21, a

30 pressure-transferring membrane 22 is provided in the wall of the pump tube 21. This membrane can be made up of e.g. a section having a thinner wall thickness. Thus, also in this case, no

pulsations in the flow will appear, as no expansion of the pump tube 21 will take place in the region between the rollers 3 and 4 when the compression of the pump tube 21 by the roller 3 . ceases.