referring to the figures , in which like reference numerals refer to like elements thereof , fig1 shows a cross - sectional view of a pressure transducer according to the state of the art , such as that presently utilized on the dialysis machine known as gambro ak 100 . the dialysis machine is shown only in the form of a front panel 1 . a luer - coupling 2 of the male - type extends through the front . the coupling is attached to the front 1 by means of a holder 3 . within the dialysis machine , to the left of the front in fig1 the luer - coupling 2 is connected to a pressure transducer 5 by means of a tube 4 containing a blood filter 6 . the pressure transducer 5 is mounted on an electric circuit board which is normally located at a distance from the front 1 . a blood filter 6 is arranged on the tube 4 . the blood filter 6 is a disc filter with a pore - size of about 0 . 2 mm . the membrane of the filter itself is manufactured from a hydrophobic material such as ptfe ( teflon ). in this way the membrane allows air to pass through it but cannot allow fluid , particularly blood , to pass therethrough . the membrane further forms a barrier for particles larger than about 0 . 2 mm , such as bacteria and most viruses . other types of filters can of course be used . the filter can be positioned anywhere on the tube , but is preferably arranged as close to the front 1 as possible , i . e . immediately behind the luer - coupling 2 , as shown in fig1 . the apparatus , of which the pressure is to be measured , is coupled to the luer - coupling 2 by means of a tube 9 which ends in a luer - coupling 7 of the female type . in the embodiment shown in fig1 the luer - coupling 7 is integrated with a blood filter of the disc type 8 . the disc filter is of a known construction , and can be the same filter as the filter 6 within the apparatus . the apparatus in question is connected to the filter 8 by means of the tube 9 . the apparatus can be a drip chamber in a tube - set for the extra - corporeal transport of blood in connection with hemodialysis . the venous pressure is thus measured in the drip chamber . if a simpler tube - set , which has no filter 11 , is used , there is a risk that blood will pass through the luer - coupling 7 to the luer - coupling 2 and further into the inside of the machine into tube 4 and up to the blood filter 6 positioned therein . in order to clean a machine contaminated in this way , the casing of the machine has to be opened and the tube 4 containing the filter 6 replaced , as well as the luer - coupling 2 being replaced where necessary . in order to facilitate such a replacement of the inner blood filter it is , in accordance with the present invention , placed in a separate insert mounted on the front of the machine . such a device is shown in more detail in fig2 . fig2 shows the front 1 of the machine provided with an insert according to the present invention . the insert consists of a cup - shaped container 10 with an outer flange 11 which is sealingly located in a hole 14 in the front 1 . the insert is maintained therein by means of hooks 12 and 13 which grip behind the front 1 when the insert 10 is inserted through a hole 14 in the front . at its bottom , to the left in fig2 the container is provided with an integral horizontal tube 15 which is concentrically positioned in the container 10 . the tube 15 is provided with a through - hole 16 which is connected to a holder 17 for a pressure transducer ( see fig3 ) by means of a projecting stud 18 . the hole 16 is connected with a transverse hole 19 positioned in a tube - coupling 20 . the function of this hole 19 will be explained in more detail below . the orifice of the insert 10 , to the right in fig2 is covered by a cover which is shown in more detail in fig3 . fig3 shows the insert 10 according to a preferred embodiment of the invention . a filter unit 21 is mounted on the tube 15 , the filter unit consisting of a blood filter 22 and thick - walled tube pieces , 23 and 24 , arranged on either side of the filter . the tube piece 23 connects the filter 22 with the tube 15 . the tube piece 24 cooperates with the other end of the blood filter and extends to the right in fig3 up to a cover 25 , which covers the open end of the insert 10 . the cover 25 has a cylindrical portion 26 which extends into the insert 10 and cooperates with the tube piece 24 . the cover 25 is additionally provided with a hole 27 . the hole 27 is positioned just in front of the tube piece 24 so that the outer end of the tube piece is accessible from the outside through the hole . a pressure transducer 28 located in the holder 17 is shown to the left of the insert 10 , as seen in fig3 . the pressure - sensitive surface of the pressure transducer is positioned directly in front of the hole 16 in the tube 15 and against the projecting stud 18 . a seal 29 ensures that the stud 18 is sealed with respect to the pressure transducer 28 . the pressure transducer 28 is electrically connected with a circuit board positioned at a distance from the insert 10 by means of conduits 30 . the conduits and the electrical contacts are well insulated in order to be properly protected . the pressure transducer 28 is of a conventional construction and comprises , for example , a piezoelectric crystal as the active element . the pressure transducer 28 can sense over - pressure as well as under - pressure with respect to the surrounding atmosphere . the insert according to fig3 is intended to cooperate with a drip chamber having a specially shaped head which is provided with an integrated blood filter as well as an outlet connection stub 31 , of which only the connection stub 31 is shown in fig3 . the exact design of the drip chamber head is disclosed in the international patent application no . . . . ( corresponding to swedish patent application no . 94 . 02721 - 6 ) filed concurrently herewith , to which reference is made . the drip chamber is attached at the front 1 by means of holding means intended therefor , which are so placed that the stub 31 is positioned directly opposite the insert 10 . when putting the drip chamber into place the stub 31 passes through the hole 27 in the cover 25 into cooperation with the tube piece 24 which seals against the stub 31 . in this way a sealed connection is achieved between the upper part of the drip chamber and the pressure transducer 28 through the blood filter 22 and the blood filter integrated into the drip chamber head . in this way double safety is obtained . if , in spite of this , leakage of blood should occur through the blood filter integrated in the drip chamber head , the blood reaches no further than the blood filter 22 in the insert . when any such leakage is noticed , the cover 25 is removed and the insert 21 can be readily replaced . this is a relatively simple operation and can be carried out without interfering with the machine itself , and without the assistance of service - personnel . when using the insert according to the present invention in connection with a drip chamber , an over - pressure is present in the connection stub 31 and the hole 16 . it is desirable to be able to adjust the level in the drip chamber by regulating the amount of air contained in the drip chamber . this occurs by means of the aforementioned transverse hole 19 and tube coupling 20 ( only the hole 19 being visible in fig3 ). the tube coupling 20 and the hole 19 are connected to a pump , by means of which air can pass through the hole 16 to or from the drip chamber , whereby the level in the drip chamber is adjusted . if this function is not required , the transverse hole 19 ( see fig2 ) can be closed with a cover . alternatively , two embodiments of the insert 10 are made , where the hole 19 is closed in one of them . the latter embodiment can for example be used in connection with a pressure transducer for arterial pressure . the insert 10 according to the present invention can also be adapted for use together with a pressure transducer 5 according to the embodiment in fig1 . in this connection , the holder 17 is replaced by a tube coupling 32 , such as shown in fig4 which by means of an air tube 4 is connected with the pressure transducer 5 . in order to obtain triple safety , the tube coupling 32 can be provided with an integrated blood filter 33 , such as shown in fig4 . this blood filter can , however , normally be omitted . fig4 additionally shows the insert 10 provided with a luer - coupling of the male type 34 corresponding to the coupling 2 in fig1 . once provided with this coupling 34 , the insert 10 can be used for blood tubes or tube - sets according to known technology . the luer - coupling 34 of the male type is fixed to a cover 36 or formed in one piece with the cover 36 on the insert 10 . the cover 36 is fixed to the front 1 and the insert by means of a bayonet coupling 35 . the luer - coupling 34 is thus fixed with respect to the front of the machine . the insert 10 according to the present invention is provided with a blood filter 22 similar to that shown in fig3 . by connection to a luer 7 of the female type according to fig1 the same function as in fig1 is achieved . by using both the filter 22 and filter 33 , an outer blood filter 8 can be omitted in certain applications , if such is desired . it is possible to manufacture the cover 36 , the coupling 34 as well as the blood filter 22 in a single piece , whereby this complete component is replaced in the event of blood leakage . instead of coupling the pressure transducer 28 to a circuit board positioned at a distance by means of conduits 30 , the circuit board can be positioned at the bottom of the insert 10 in connection with the pressure transducer . the invention has been described above with reference to preferred embodiments of the invention . these embodiments can be modified by a skilled man in many ways and such modifications which are obvious for a skilled man are intended to be encompassed within the scope of the invention . the various components described , can be combined in different ways to those shown in the drawings .
removable inserts are disclosed for positioning within a dialysis machine in order to connect a pressure transducer to external apparatus such as a drip chamber . the removable insert comprises a cup - shaped container adapted to be disposed within the dialysis machine with its open end aligned with the front face of the dialysis machine , a cover to cover the open end of the container , the cover including an orifice , a tube extending from the closed end of the cup - shaped container for communication with the pressure transducer , a filter positioned within the container , and a coupler for coupling the tube with the orifice in the cover with the filter interposed therebetween so that the pressure associated with the drip chamber can be monitored by the pressure transducer .