Fluid handling – Line condition change responsive valves – Direct response valves
Patent
1992-08-07
1994-04-26
Nilson, Robert G.
Fluid handling
Line condition change responsive valves
Direct response valves
F16K 1514
Patent
active
053057953
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a nonreturn valve, in particular for use in connection with medical infusion appliances, comprising a housing with a central chamber into which open an inlet channel and an outlet channel, which channels may be separated by a sealing membrane provided with a flow passage, wherein the membrane has a marginal part clamped in the housing, a central sealing part and a thinner annular wall that links both parts.
Such a nonreturn valve is described in the EP-A-02 47 824. This valve is not suited for slight pressure differences between its inflow side and its outflow side, i.e. the valve does not ensure a reliable opening and closing when the pressure differences are slight. In order to operate at all with small pressure differences, the initial tension of the clamped-in membrane in this valve must only be very small. However, this condition can be maintained only with great difficulty and especially because of the tight manufacturing tolerances that have to be adhered to in the manufacture of these valves, even small deviations lead to relatively large drawbacks. However, small manufacturing tolerances result in higher manufacturing costs. Also the opening force for the membrane is relatively high, which inter alia can be traced back to the construction and the shape and the clamping position of the membrane.
Nonreturn valves such as these are used in medical technology, e.g. in the so-called parallel infusion technique in which, for example by means of an infusion pump or a syringe, medicines in very small quantities are added via a secondary connection to an infusion solution which is administered to a patient through an infusion bottle by drip feeding. Care must be taken in this case to prevent the medicine from the infusion pump to flow back into the drip-feed, which danger exists when the flow of the infusion solution to the patient is inadvertently blocked, perhaps temporarily. The nonreturn valves in question for this reason are so constructed that during the normal operation they link the two systems together in the inflow direction to the patient, but separate them in the opposite direction.
The demands made on a nonreturn valve of this type are therefore very high. It must be ensured for example that the nonreturn valve opens at a pressure of as low as 0.01 bar, which is produced by gravity, in order to allow the unrestricted inflow of infusion solution, and on the other hand it has to withstand a closure pressure of approximately 6 bar which can occur during a fault in the pump system. The said opening sensitivity must also be present immediately after the effect of the full closure pressure. It must also be able to reliably shut down conveying rates of 0.1 ml/h, as this is normally the lowest conveying rate used in the injection pumps.
A further nonreturn valve proposed for the application mentioned is the subject of EP-A-01 82 045 which shows such a nonreturn valve with a sealing disc which in the rest position is held against the inlet opening by a central two-point support and which through the infusion pressure of the gravity system is displaced in a bow-like manner, so that the infusion solution can flow around the sealing disc. A similar solution is described in the DE-U-87 17 726. Finally in the DE-C-26 05 348 is shown a nonreturn valve which operates by a valve disc floating upwards when there is an overpressure in the pump system.
Tests have shown that, in common with all the said nonreturn valves, at least one of the said requirements cannot be met by them. Test results are published in an article of the journal "Biomedizinische Technik", volume 35, issue No. 3/1990, which article raises further requirements to be addressed to such nonreturn valves. Of special emphasis in this case is the throughflow preventing flow resistance caused by the nonreturn valve which leads to a reduction in the throughflow which, for the purpose of precisely controlling the throughflow, should be kept as low as possible.
The object of the invention therefore is to improve a nonreturn val
REFERENCES:
patent: 3270771 (1966-09-01), Morgan
patent: 3354902 (1967-11-01), Obermair
patent: 3827456 (1974-08-01), Sheppard
patent: 4593720 (1986-06-01), Bergandy
patent: 4776839 (1988-10-01), Doumenis
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