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A stream selector for a process analyzer prevents contamination of one sample from previous samples without requiring a common outlet header. The stream selector includes a valve manifold having a base plate and a series of valve modules individually removeably attached to the base plate. The base p

A stream selector for a process analyzer prevents contamination of one sample from previous samples without requiring a common outlet header. The stream selector includes a valve manifold having a base plate and a series of valve modules individually removeably attached to the base plate. The base plate includes all the process connections for the fluid lines. Each valve module includes a module body with a pair of valve assemblies. The valve assemblies in each module are operated simultaneously through a common actuation passage. A poppet valve in each valve assembly has a valve head with a double-seated seal. The double seated seal controls the flow of fluid through a vent passage in the valve body; and between inlet and outlet passages in the valve body. The outlet passage from one valve assembly is fluidly-connected to the inlet passage of an adjacent valve assembly to create a double-block and bleed configuration. The downstream valve assembly is then connected to the process analyzer. If additional valve module(s) are used, the outlet of the downstream valve assembly in the first module can be routed through the vent passage of the downstream valve assembly of the second module, and so on. A cover encloses the valve assembly in each valve module. The cover is attached with a series of threaded bolts to the module body. At least some of the bolts fix the module body to the base plate. Removing the bolts allows individual modules to be removed from the base plate without removing adjacent modules.

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1. A valve module for a stream selector, the valve module including: a module body having a valve receiving cavity, the valve receiving cavity including a control chamber portion, a vent chamber portion, and an actuation chamber portion, with the vent chamber portion being located between the con

1. A valve module for a stream selector, the valve module including: a module body having a valve receiving cavity, the valve receiving cavity including a control chamber portion, a vent chamber portion, and an actuation chamber portion, with the vent chamber portion being located between the control chamber portion and the actuation chamber portion; the module body including a) inlet and outlet passages into the control chamber portion with one of said inlet and outlet passages aligned along a geometric axis of the module body and defining an annular front valve seat into the control chamber portion; b) a vent passage into the vent chamber portion; and c) an actuation passage into the actuation chamber portion; and a valve assembly received in the valve receiving cavity, the valve assembly including i) a valve body having a piston receiving cavity and an axially extending central through-bore into the piston receiving cavity, the valve body received in the actuation chamber portion of the valve receiving cavity, a piston moveably received in the piston receiving cavity of the valve body, the piston and valve body defining an actuation chamber therebetween, the actuation passage fluidly connected to the actuation chamber through a port in the valve body; ii) a bonnet received in the vent chamber portion of the valve receiving cavity, the bonnet having a vent cavity, the vent passage fluidly connected to the vent cavity, the vent passage including an annular rear valve seat and an axially-extending central through-bore fluidly connecting the outlet passage and the vent cavity and co-axially aligned with the central through-bore in the valve body; and iii) a poppet valve having a valve head disposed in the control chamber portion, the valve head having an annular rear seal holder facing toward the bonnet and an annular front seal holder facing away from the bonnet and toward the one of the inlet and outlet passages, the poppet valve further including a stem extending axially through the through-bore in the bonnet and the through-bore in the valve body to a fixed connection with the piston such that the valve head of the poppet valve moves axially in conjunction with the axial movement of the piston, the poppet valve including an annular rear seal plug received around the poppet stem and within the annular rear seal holder of the valve head, the rear seal plug adapted to seal against the rear valve seat surrounding the poppet stem during movement of the poppet valve in a rearward axial direction, and the poppet valve also including a cylindrical front seal plug received in the annular front seal holder, the front seal adapted to seal against the front valve seat during movement of the poppet valve in a forward axial direction. 2. The valve module as in claim 1, wherein said rear seal plug includes a tapered outer surface to facilitate sealing with the rear valve seat. 3. The valve module as in claim 2, wherein the rear seal plug includes a cylindrical outer surface closely received with a friction fit in the rear seal holder of the valve head. 4. The valve module as in claim 1, wherein the front seal plug has a solid disk-shaped configuration. 5. The valve module as in claim 4, wherein the front seal plug includes a tapered outer surface to facilitate sealing with the front valve seat. 6. The valve module as in claim 5, wherein the front seal plug includes a cylindrical outer surface closely received with a friction fit in the front seal holder of the valve head. 7. The valve module as in claim 1, wherein said front seal plug and said rear seal plug are both located in the control chamber portion of the valve receiving cavity.