the liquid injection device in one embodiment ( fig1 a ) is constituted essentially by a piece of tubing , a reservoir 1 , a pump system 2 , an intermediate chamber 3 of variable volume , a regulation system 4 which may include the wheels of a peristaltic pump , and a non - return valve 7 . a disconnection system 6 is situated upstream from the non - return valve 7 , between said valve and the regulation system . pressure sensors 5 and 8 are situated downstream and upstream from the non - return valve . in the absence of injection , i . e . when the pump is deactivated , constant pressure exists between the non - return valve and the second regulation system . the constant pressure is lower than the opening pressure of the non - return valve . if the non - return valve is defective , backflow of liquid towards the pump is prevented by the flow of liquid associated with the pressure that exists in the intermediate segment , with this pressure in the intermediate segment being due to the presence of the peristaltic cassette which , in the absence of injection , is very effective at occluding the tubing . the opening pressure of the occlusion system constituted by the wheels of the peristaltic cassette is greater than 8 bars , whereas the opening pressure of the first occlusion system is equal to 0 . 5 bars . the present invention is naturally not limited solely to the example described above , with all configurations of the description also being included . thus , and preferably , the first occlusion system , or the regulation system , or both of them , are of the automatic clamp type . it is also possible to use a fourth occlusion device , preferably located downstream from the disconnection system , which device is activated in the event of an alarm being triggered . the device of the present invention can also include a pressure sensor measuring the pressure of the liquid in a length of tubing situated upstream from the intermediate segment . with reference to fig2 a , a preferred disconnection system 6 comprises an upstream piece 10 having an intermediate chamber 12 of adjustable volume , and a downstream piece 14 provided with the non - return valve 7 and capable of co - operating in reversible manner with the upstream piece 10 so as to form a sealed link . the upstream piece 10 is constituted by a hollow tubular body 15 that is open at both ends , defining an inside volume that is split into two by an open internal radial wall 16 placed between an injection chamber 18 and the intermediate chamber 12 of adjustable volume , constituting a decompression chamber as explained below . the intermediate chamber 12 contains a pre - split resilient septum 20 whose diameter is substantially equal to the inside diameter of the intermediate chamber 12 so as to form a piston that is movable in translation . the downstream piece 14 comprises a hollow circularly - symmetrical body 22 that is extended at its two open ends by respective hollow rods . the body 22 surrounds an inside volume which is split in two by an open radial wall 24 placed between a first chamber 26 in which the non - return valve 7 is formed , and a second chamber 28 facing towards the patient . the hollow rod 30 adjacent to the first chamber 26 has a free end whose shape includes a frustoconical portion , and it is designed to be placed inside the intermediate chamber 12 by passing through the septum 20 and the opening of the wall 16 . the hollow rod 30 has an outer annular collar 32 that comes into abutment against the septum 20 so as to drive it in translation inside the intermediate chamber 12 ( fig2 b ), the septum 20 coming into abutment against the wall 16 when the rod 30 is pushed home fully into the piece 10 , the tubular body 15 then coming into abutment against the body 22 ( fig2 c ). locking means are also provided between the pieces 10 and 14 , e . g . in the form of a resilient locking tab situated outside the body 15 and having a free end that snap - fastens against a shoulder or a groove in the outside surface of the body 22 . such a tab 34 is shown in fig2 b in association with a shoulder that faces in the opposite direction to the hollow rod 30 when the bodies 15 and 22 are in abutment . a non - return valve 7 shown is formed by a plug 38 that is capable of being compressed ( collapsing ) radially enabling it to be bypassed by the liquid when the pressure of the liquid upstream from the plug 38 is greater than or equal to the opening pressure of the non - return valve 7 . this type of plug is preferably as described in u . s . pat . no . 4 , 929 , 230 , i . e . a plug made of resilient material of longitudinal section that can be seen in fig2 a to 21 and 2 ′ a , 2 ′ b , and even more clearly in fig3 . the plug 38 has a first end directed towards the second chamber 28 with sealing means 46 that co - operate with the inside surface of the second chamber 28 , a second end directed towards the hollow rod 30 , at least one frustoconical surface portion 40 between the sealing means and the second end , and a cavity 42 extending inside said plug said first end and over a depth that is greater than the distance between the sealing means and the free edge of the first end . this plug 38 also has a retractable wall 44 between at least a portion of said frustoconical surface 40 and said cavity 42 , said retractable wall 44 extending at least from the end of said cavity 42 as far as first end and retracting into said cavity 42 when the radial resultant of the pressure exerted on said frustoconical surface 40 by said liquid is greater than the sum of the radial compression strength of the retractable wall 44 plus the internal pressure of the cavity 42 . this type of plug 38 can also be placed in the tubing as a second occlusion system 4 . in a preferred embodiment , the opening pressure of the non - return valve 7 is greater than its closing pressure . by way of example , the plug 38 can be shaped so that it is compressed , thereby opening the valve 7 , starting from a pressure of 1 . 2 bars for the liquid in the hollow rod 30 , the retractable wall 44 returning to its initial shape and thus closing the valve 7 when the pressure of the liquid in the hollow rod is equal to or less than 0 . 8 bars . prior to any injection ( fig2 a and 2b ) the pieces 10 and 14 of the connection system 6 are empty of liquid , i . e . they have atmospheric pressure ( pa ) within them . in general , throughout the description below , when said atmospheric pressure pa is not mentioned , it should be assumed that it is to be added to the liquid pressure mentioned . after the pieces 10 and 14 have been connected together , the injection device is primed ( fig2 c ) by sending liquid at a pressure greater than 1 . 2 bars ( p & gt ; 1 . 2 ) into the injection chamber 18 . this liquid passes along the hollow rod 30 , the septum 20 closing the intermediate chamber 12 in sealed manner , which chamber presents substantially zero volume in communication with the injection chamber 18 . because of this pressure of 1 . 2 bars which is greater than the opening pressure of the valve 7 , the valve is opened and the liquid can pass through the first chamber 26 and leave the second chamber 28 in communication with the outside ( pa ). the following step ( fig2 d ) consists in stopping the delivery of liquid under pressure , the injection chamber 18 then being filled with a liquid at a pressure of about 0 . 8 bars ( p0 . 8 ) causing the valve 7 to close by virtue of the retractable wall 44 returning to its initial position . once the valve 7 has closed , the injection device is connected to the patient so that the patient &# 39 ; s venous pressure which is close to 0 . 2 bars ( p0 . 2 ) corresponds substantially to the pressure of the liquid in the second chamber 28 . during injection ( fig2 e ), the pressure of the liquid in the disconnection system 6 is greater than 1 . 2 bars ( p8 ), thereby holding the valve 7 open . once injection is over ( fig2 f ) the situation of the disconnection system 6 is identical to its situation ( fig2 d ) preceding the injection step ( fig2 e ). when the patient is disconnected ( fig2 g ) from the injection device , the valve 7 remains closed , since the pressure of the liquid in the second chamber 28 is substantially zero ( ignoring atmospheric pressure ) and the pressure of the liquid in the injection chamber 18 is substantially of the order of 0 . 8 bars . thus , when the pieces 10 and 14 of the disconnection system 6 are moved apart ( fig2 h ), as the hollow rod 30 is withdrawn and the collar 32 moves away from the wall 16 , the septum 20 also moves away from the wall 16 since the liquid pressure in the injection chamber 18 is greater than the pressure inside the second chamber 28 . the volume of the chambers 12 and 18 is designed to enable the septum 20 to move far enough away from the wall 16 to enable the pressure in the chambers 12 and 18 to drop to the level of atmospheric pressure so that the two pieces 10 and 14 can be separated ( fig2 ) without any risk of liquid flowing out from the second chamber 28 or from the hollow rod 30 . it will be understood that the internal volume of said upstream piece 18 is shaped so as to make it possible to obtain liquid pressure in the disconnection system 6 which is less than or equal to atmospheric pressure prior to said upstream and downstream pieces 10 and 14 being separated fully . because of this disconnection system , the plug 38 prevents the liquid that has filled the second chamber 28 and that has been in communication with the tubing connected to the patient from flowing back upstream . in addition , any outflow of liquid is avoided when the pieces 10 and 14 are disconnected . when the injection device is used on a new patient , a new downstream piece 14 ′ is used which is connected to the upstream piece 10 that has already been used on a preceding patient ( fig2 ′ a and 2 ′ b ). the subsequent steps in performing injection are identical to the steps illustrated by fig2 c to 21 as already described .
the invention relates to a device for injecting liquid , comprising a piece of tubing on which there is situated at least a first liquid occlusion system . according to the invention , a regulation system is situated upstream from the first occlusion system , the two systems defining an intermediate segment in which the pressure , in the absence of injection , is greater than the pressure that exists downstream from the first occlusion system so as to direct any leak of liquid from the first occlusion system downstream . the invention is applicable to a pump used for injecting contrast liquid for medical imaging .