I'm looking for a particular type of valve, and am having a lot of difficulty in doing so...hoping you folks can help.

The valve has to work off of line pressure, since instrument air and electrical power are not available at the valve chamber. Pressure in the main line should keep the valve closed, and the valve should open when the line pressure drops (it's a drain valve, on a T from the main pipeline).

The valve will be used to prevent pipeline freezing in an industrial temporary water pipeline (river to storage pond). It will be used to automatically drain the line in the event of a power loss to the pumps (or some other form of pump failure) without an operator having to go down to the valve chamber. Manual reset is fine. This is for a 6" line.

Everyone I've talked to has either said they don't exist, or has vaguely recalled something that "might work".

Worst-case pressure is just shy of 800 kPa, and temp will be somewhere between 4 and 15C, depending on the season.

The process fluid is river water, and the drain leads to a tributary leading back into the river, so loss of process fluid isn't a big deal.

The reason this drain is there is to serve as a low-point drain, necessitated by the geometry of the line. Ambient conditions in the winter up in northern Alberta mean that the quicker the line gets drained, the happier everyone is. This is a temporary water supply system for construction, and having it freeze would be rather disasterous.

The spring loaded "Fail Open" actuator on the valve will work. Just make sure that the actuator is compatible with the water and will not freeze before the line pressure drops low enough to allow the spring to actuate. You may have problems starting the line up again though. Once the valve is open, you may not get enough pressure to close it; all flow being dumped to drain. In this case you may need to blind it off until pressure builds and then remove the blind.

Another approach is to use an external pilot steam back pressure valve installed in reverse. This solves your material comptibility problems, but you will still have the same problems on start up.

To drop the line pressure rapidly, you will need to install a small manual drain somewhere that is close and easily accesible.

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