Installation Guide

1. This Butterfly Valve is bi-directional and may be installed in either direction.
2. Install this valve between any ANSI Class 125 or 150 flange. Cast iron, bronze, plastic or steel flanges may be used. No flange gaskets are required.
3. The stem can be installed in any position, but if a choice of stem positions exists, good practice dictates that the valve be installed with the stem horizontal. This will minimize liner wear by distributing stem and disc weight evenly.
4. Valves should be installed with the disc in the closed or almost closed position. This will prevent damage to the disc sealing edge.
5. Before any flange bolts are tightened, valves should be centered within the flanges and then carefully opened to assure free, unobstructed disc movement. Disc interference may result when valves are installed in pipelines having smaller than normal inside diameters, such as heavy wall pipe, plastic lined pipe, or as cast flanges. Suitable corrective measures must be taken to remove these obstructions, such as taper boring the pipe or installing a spacer.
6. After proper operation has been verified, tighten all bolts using the crossover method. Recommended tightening torques pattern is listed below.

7. Interference may also occur when butterfly valves are bolted directly to the outlet flange of a swing check, silent check, or reducing flange. Check valve and butterfly valve combinations are very popular; normally a short spool piece is required between the valves.

From: NVF valve knowledge