Is it allowed to place a butterfly valve with post indicator to isolate some seccion of a underground fire water circuit, or it should be a gate valve.
Butterfly valves are used, with a burial extension. This is a torque-tube extension that bolts to the bonnet flange,and a (usually) tubular drive shaft which is concentric. The top of the extension is usually made to mimic the mounting flange on the valve, so actuators are simple bolt-in installation with the same hardware that would be used to mount them without the extension.
You might check the code (NFPA, local codes) to see if there are any special requirements.
219D,
Most jurisdictions will probably allow it, but why? A butterfly valve that is infrequently operated will generally accumulate solids on the seat and flapper, and will seldom give you very good shut off. If your fire circut is normaly quiescent, then solids will settle out. If it is normally flowing, then the bluff body in the flow puts interesting stress on stuff.
I really don't like butterfly valves in locations that are difficult to access.
Settled solids will accumulate in the bottom bearing and cause it to fail or jam. Butterfly valves are also not approved by everybody because they are quarter turn and can be closed very quickly. In a fire system this can cause high transient pressures.
Also butterfy valves have been known to jam open and then you cant get them out of the line easily.
Butterfly valves should be installed at 9 o'clock (stem horisontal) to distribute the stress on both the top & bottom bearing. This way you avoid the problem with accumulation of solids at the bearing. Also beeing that the valve is an isolation valve, it's most likely a manual valve (gear or level operated), so the quick closing will not be a major problem.
On the other hand, I work with low pressure / high flow applications and consequently just love 'em butterfly valves.
If a butterfly valve is used in a horizontal line the shaft should be horizontal as the other gentlemen said. Second a gear operator would be preferred over a torque tube extention because the travel stops will be on the valve. With the input shaft of the gear operator pointing up, this will allow the extention to be designed for a much lower torque requirement. This extention could be a piece of pipe. No mention was made as to where this valve would be buried. In Northern climates with road salts naval bronze and monel are best. Obviously a triple offset butterfly would be best.
