The invention is particularly applicable to a valve that is extremely sensitive to low cracking pressures and will be described with particular reference thereto; however, the invention could be incorporated in other environments and operable under a variety of pressure conditions.

Prior Check Valves arrangements are not deemed to be sufficiently sensitive to small differential pressures, i.e., cracking pressures, for regulating fluid flow. Specifically, known valve element and biasing arrangements are believed to be insensitive to slight pressure variations on the order of 1/3 (one-third) to 2 (two) psi.CHECK VALVES Use of helical springs to bias a valve element toward a closed position is well known in the art. Unfortunately, helical springs can potentially contaminate the fluid system. Additionally, the biasing force of a helical spring tends to cock the valve element and impose eccentric loads that effect performance of the valve.

Although disc-type springs have been considered in other environments, these springs were not believed to be particularly useful in many situations since the valve structure must be altered to accommodate fluid flow past the disc spring. For example, enlarged, spaced openings were formed in the disc spring to define flow passages therethrough. This, in turn, altered the biasing force and sensitivity of the valve arrangement to low cracking pressures. Alternatively, an imperforate annular disc spring was utilized in which an outer diameter portion was secured to the valve body and an inner diameter portion to the valve element. Since the disc spring was imperforate, it was necessary to define a separate flow passage through the valve element.Check Valves This was not considered particularly desirable since the valve element was, by necessity, of reduced size and, therefore, the surface areas on which the fluid pressure acted were correspondingly reduced. If the valve element was increased in size, the overall valve body and spring also necessitated a change in dimension.

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