Another player has joined the game. A person who says he knows what he’s talking about. Karen Mulholland’s Brother Ken. Thank you Karen for referring our question to him.
Apparently the standpipes are not so much for shock absorption from changes in flow rate as they are vents to let out trapped air. Ken says:
“They are called "standpipes" and are all over California also. They are used primarily as air vents. Concrete lines are very sensitive to being damaged from large air bubbles that get compressed ahead of a surge of water, even at low pressure (gravity fed). The pipeline can literally explode from the force. The shock force created by a moving mass of water compressing a large bubble (as in an empty pipeline that is not totally open on the end or maybe has a low spot somewhere that is filled with water and acts as a blockage) can be enormous. The vents have to be tall enough to accept the pressure needed to maintain the desired flow. For example, a desired line pressure of 10 psi would require a standpipe 28 feet high! Put 11 psi into a pipeline with a shorter standpipe, and it will run over, so they are not very efficient in that regard. They also may contain one or more valves. Sometimes there are multiple valves, and the standpipe is used as a distribution point for multiple independent pipelines.”
This explanation has an air of authority to it. It even sounds right. I’m buying it. That is now my story and I’m sticking to it.
Thank you Ken.
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