There have been various methods devised for the sizing of water hammer arresters, creating confusion regarding the proper method to use.
Issue: 5/05 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 hamme r arresters among engineers, contractors, and other persons engaged in the plumbing industry. To help clear up the confusion, the following article was ecerpted from the pertinent sections of the !lumbing " #rainage Institute$s %tandard !#I&'()0*, 'ater 'ater (ammer +rresters.
Table Table * %izing and !lacement #ata The members of !#I set out to establish establish a uniform method of sizing for water water hammer arresters. They sponsored a research and testing program with the intention of producing one standardized method of sizing and placement. %uch a method would benet the entire plumbing industry. industry.
Table Table ) !#I developed a protocol for identifying the various sizes of water hammer arresters. There were seven di-erent sizes of water hammer arresters developed. It was decided to identify the arrester size by a code or symbol. The size was wa s to be based on the capacity of the arrester to control the shoc wave in di-erent piping systems. The following symbols, ++, +, , , #, 1, and 2, have been devised to denote the range in sizes for water hammer arresters. 3++3
1ample * 'hen !#I certies and lists a water hammer arrester, each size is designated by one of the symbols to identify the appropriate size in accordance with %tandard !#I&'()0*.
1ample )
!lumbing engineers are most familiar with sizing a water distribution system by use of the ture unit method. ecause this is a familiar method of sizing, !#I used this method for sizing water hammer arresters. The sizing method is 4uic and easy using ture units. + water supply ture unit is dened as a non& dimensional unit of the probability of simultaneous use of water in a plumbing water distribution system.
2igure * Table * lists the ture unit values for various tures for both hot and cold water supply. This table is used in !#I&'()0* when sizing water hammer arresters.
2igure ) These ture unit values are the common values that most engineers utilize to size their water distribution systems. These values can be used in the sizing and placement of engineered water hammer arresters at the same time that the piping systems are sized.
Table In most installations where there are several tures, usually only one ture valve at a time will be closed. 6evertheless, occasionally two or more ture valves could be closed at the same instant. Table ) on sizing and selection taes into consideration all design factors, including simultaneous usage, pipe size, length, 7ow pressure and velocity. Table ), therefore, provides an easy, accurate method of determining the proper sized water hammer arrester for each multiple ture branch line, and automatically provides for all factors that must be considered or otherwise calculated.
Table 8 +fter calculating the ture unit load for a given branch, Table ) can be used for sizing the water hammer arrester. This table would apply to both hot and cold water. This table is based on a maimum water pressure in the branch of 55 psi. 'hen the pressure in the branch eceeds 55 psi, the water hammer arrester should be increased by one size. 2or eample, a 33
2igure
1amples Table ) will permit engineers and contractors to select the proper water hammer arrester for each application. 1amples * and ) show the relative ease with which sizing can be accomplished using Tables and 8.
It is relatively easy to select the proper sized water hammer arrester for a multiple ture branch. 2igure * represents a typical riser diagram of the type that an engineer may include with his set of drawings. 'hen sizing the cold and hot water branch lines, the total ture unit load is established for each branch line. This information is then applied to sizing charts to determine the re4uired size of the branch lines.
1amples of 9ule ) The proper sized water hammer arresters can be selected once the total of ture units for a cold or hot water branch line is nown. It is only necessary to apply the ture units to Table ) and select the appropriate water hammer arrester.
It is suggested that the engineers identify the water hammer arresters by the !#I 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 tures served. This location is shown in 2igure ).
2igure 5 The location of the water hammer arresters shown in 2igure ) applies to branch lines that do not eceed )0 feet in length, from the start of the horizontal branch line to the last ture supply on this branch line. 'hen the branch line eceeds the )0&foot length, an additional water hammer arrester must be installed. The location of the water hammer arresters is based on eperience in the industry as developed by !#I.
2igure ;ong 9uns of !iping to 14uipment The ma
2igure = 'hen long runs of piping are employed to serve a remote item of e4uipment, the water hammer arrester should be located as close as possible to the point of 4uic closure. +t this location, the water hammer arrester will control the developed energy and prevent the shoc wave from surging through the piping system. + typical eample of placement is given in 2igure .
2igure > 1amples dening the sizing and placement of water hammer arresters for single ture and e4uipment branch lines are illustrated in 2igures 5&>. 2or the sae of clarity, control valves, vacuum breaers and other necessary devices have been omitted in the illustrations.
