The valves are staggered on either side of the catwalk, and handwheel extension stems are furnished when necessary to facilitate operation.
Process lines crossing units (within units or from unit to main pipeway) are normally provided with a block valve, spectacle blind and drain valve.
Block valves are to be grouped and locations of block valves in vertical run of pipe are preferred.
If the block valves have to be located in an overhead pipe-way, staircase access to a platform above the lines shall be provided.
Here, however, an elevation change is required between the process unit and the off-site pipe rack.
This design has the block valves installed in the vertical portion of the line, which allows for relative ease of operation.
Following drawing shows a two-level process unit pipe rack; the elevation change to the off-site area is either above or below the process unit pipe rack.