Water Hammer Arresters: Sizing and Placement
There have been various methods devised for the sizing of water hammer arresters. These methods have created confusion regarding the proper sizing and location of water hammer arresters among engineers, contractors, and other persons engaged in the plumbing industry. To help clear up the confusion, the following article was excerpted from the pertinent sections of the Plumbing & Drainage Institute's Standard PDI-WH201, Water Hammer Arresters.
Sizing and Placement DataThe members of PDI set out to establish a uniform method of sizing for water hammer arresters. They sponsored a research and testing program with the intention of producing one standardized method of sizing and placement. Such a method would benefit the entire plumbing industry.
ExamplesTable 2 will permit engineers and contractors to select the proper water hammer arrester for each application. Examples 1 and 2 show the relative ease with which sizing can be accomplished using Tables 3 and 4.
It is relatively easy to select the proper sized water hammer arrester for a multiple fixture branch. Figure 1 represents a typical riser diagram of the type that an engineer may include with his set of drawings.
When sizing the cold and hot water branch lines, the total fixture unit load is established for each branch line. This information is then applied to sizing charts to determine the required size of the branch lines.
It is suggested that the engineers identify the water hammer arresters by the PDI symbols on the riser diagrams, as shown in the illustration. This will assure that the contractor will provide the correct size when installing the water distribution system.
The recommended location for the water hammer arrester is at the end of the branch line between the last two fixtures served. This location is shown in Figure 2.