Controlled volume liquid meter defining improved plunger means

Claim 1

In a controller for a controlled volume liquid meter defining aperture means for receiving a cassette which includes a variable volume liquid metering chamber having a flexible membrane wall, an inlet port adjacent one end of said chamber, an outlet port adjacent the other end of said chamber, the inlet and outlet ports defining paths of liquid flow therethrough which are transverse to the direction of liquid flow in said chamber, said controller defining a pair of plunger members, and means for alternatingly pressing the plunger members against said membrane wall to alternatingly open and close said inlet and outlet ports, the improvement comprising, in combination: said plunger members being carried by a leaf spring member which is deflectable in the direction of the axis of said plunger members, said plunger members also possessing means permitting variation of the length of each plunger member between a maximum and a minimum length, and spring means urging said plunger members to occupy their maximum lengths, whereby the force with which said plunger members press against the membrane wall is limited to a value governed by said spring means, each plunger member comprising a sleeve open at one end and closed at another end, and a plunger head carried in the bore of said sleeve and slidably movable therein, a forward portion of said plunger head projecting outwardly from the bore of said sleeve, and spring means between said plunger head and the closed end of said sleeve for biasing said plunger head into an axially outward position with respect to said sleeve, said plunger head further defining a first flange positioned adjacent its rear end, said sleeve defining a second flange extending radially inwardly from its open mouth, whereby said second flange prevents removal of said plunger head from the sleeve by engagement with the first flange.