Valve system for a coulometric analyte sensing instrument

A bidirectional valve system, comprising:

• (a) first and second longitudinally facing members defining a gap therebetween in fluid communication with a first inlet and a first outlet orifice through one member and a second inlet and a second outlet orifice through the other member, wherein (i) the inlet orifices are transversely offset, (ii) the outlet orifices are transversely offset, and (iii) one of the members is longitudinally repositionable relative to the other member for adjusting the longitudinal height of the gap,
• (b) an inlet larger-diameter elastic O-ring positioned within the gap and encompassing both the first and second inlet orifices,
• (c) an inlet smaller-diameter elastic O-ring positioned within the gap and surrounding only one of the first or second inlet orifices,
• (d) an outlet larger-diameter elastic O-ring positioned within the gap and encompassing both the first and second outlet orifices,
• (e) an outlet smaller-diameter elastic O-ring positioned within the gap and surrounding only one of the first or second outlet orifices,
• (f) a repositioning means for longitudinally repositioning the repositionable member towards the other member against the bias of the larger-diameter elastic O-rings as between (i) a first position wherein the larger-diameter O-rings are compressed between the members and seal the gap so as to prevent fluid flow through the gap from the inlet orifices to the outlet orifices without compressing the smaller-diameter O-rings between the members so as to allow fluid flow from the first inlet orifice to the second inlet orifice through the gap and from the first outlet orifice to the second outlet orifice through the gap, and (ii) a second position wherein both larger-diameter O-rings are compressed between the members and seal the gap so as to prevent fluid flow through the gap from the inlet orifices to the outlet orifices, the inlet smaller-diameter O-ring is compressed between the members so as to prevent fluid flow from the first inlet orifice to the second inlet orifice through the gap, and the inlet smaller-diameter O-ring is compressed between the members so as to prevent fluid flow from the first outlet orifice to the second outlet orifice through the gap.