Double-block-and-bleed manifold
25 Sep 2002
Parker Instrumentation has released a new style of double-block-and-bleed manifold based on a one-piece construction that eliminates potential leak paths compared with traditional assemblies.
The manifold is suitable for implementing instrument take-offs on offshore oil and gas platforms as well as chemical/petrochemical plants.
Called Pro-Valve, the new manifold is fabricated from a one-piece valve body forged in the popular weldolet style, and requires just two joints: a welded joint at one end for connection to the process pipe, and a joint at the other end for connecting the instrument. The latter joint can be specified in the form of either standard thread, or an integrated compression tube fitting.
This arrangement reduces the number of potential leak paths in instrument take-offs by eliminating the need for flanged connectors to the pipeline, and with it, the use of problem-prone taper thread interfaces (which rely on the use of additives to ensure a seal-opening avenues for system contamination or mis-assembly). If integral tube fittings are specified for the instrument connection side of the manifold, this eliminates taper threads from the entire system - further boosting integrity.
Pro-Valve is rated for pressures to ANSI class 4500, and may be ordered with weld profiles to suit pipes from 3/4 to 36 inches in diameter. In addition to a choice of instrument interface (male or female threads in NPT, BSPT, BSPP or gauge sizes, or A-LOK or CPI twin- or single-ferrule tube fittings) users can specify Pro-Valve with either needle or OS&Y (outside screw and yoke) styles of isolation and vent valves, and in a range of materials to combat corrosion including 316L, monel, duplex, super duplex, hastelloy, incoloy and 6Mo.
The use of a one-piece forging substantially reduces the size of instrument take-offs. After welding to the pipe, the typical height to the top of the manifold is just 150 mm (6 inches). This is probably 25% of the height of an assembly using separate flanged connectors and manifold.
Weight is also reduced, with Pro-Valve weighing around 3.5 kg in its smallest variant.
