How durable are the piston type of water hammer arrestors? If there wasn't obvious noise in the plumbing before an arrestor was installed, how can you determine if the arrestor is still working?
Articles on the web say that the type of arrestor that is simply a dead end section of pipe can get filled with water and stop working. To fix the problem ( according to the articles) requires draining the line to admit air. Is there a simpler way to keep air in the dead end?