Water Hammer Arrester - Must be Vertical?

I'm guessing this is a silly question, but..... Does the tube of a water arrester have to be vertical?

Since the arrester tube has a piston that separates the water from the contained gas, I thought there could be a chance that the tube could be horizontal.

I want to put arresters on the hot and cold lines to the clothes washer but the current flexible lines connect to shut-off valves with outlets that go straight down. So connecting something like the Sioux Chief Min-Restor at the shut-off valves would have the tube in the horizontal direction.

--Larry

They can be horizontal.
However, you can also mount them on the washer and keep them vertical is you want.

I wonder why I didn't think of mounting them on the washer? The connections on the washer are above each other so I could mount the top arrester vertically and the bottom one at a slight angle to miss the top one!

Thanks,
Larry

Ideally, the arrester is installed as close to the quick-acting valve as possible...and, with an engineered on, orientation is irrelelvant.

Point the top one up and the lower one down. They will work effectively in either direction.