FIG 98 AND C-98 TYPE G DOUBLE VARIABLE SPRING HANGERS
Figure 98 Type G Double Spring Can
The Type G Spring Can is a complete trapeze assembly. The hanger consists of two standard spring units plus a pair of back-to-back channels welded at each end to the hanger casing. The “P” dimension can be varied with the customer’s instructions. In sizing a Type G hanger, it must be remembered that each standard spring unit carries one-half of the total pipe load. Therefore, in using the hanger selection chart, use one-half of the total pipe load as the hot load. When the pipe line is designed so as not to be centered on the channel, one spring of the trapeze will carry a heavier load, the other a lighter load. Care should be taken in calculating the load of each hanger and in choosing the proper sized spring in such cases. The center-to-center rod dimension must be specified when ordering. Being a double spring can design, it is intended for applications where more vertical travel will occur than can be handled by the standard Figure 268.
How to use hanger selection table: In order to choose a proper size hanger, it is necessary to know the actual load which the spring is to support and the amount and direction of the pipe line movement from the cold to the hot position. Find the actual load of the pipe in the load table. As it is desirable to support the actual weight of the pipe when the line is hot, the actual load is the hot load. To determine the cold load, read the spring scale, up or down, for the amount of expected movement. The chart must be read opposite from the direction of the pipe’s movement. The load arrived at is the cold load. If the cold load falls outside of the working load range of the hanger selected, relocate the actual or hot load in the adjacent column and find the cold load. When the hot and cold loads are both within the working range of a hanger, the size number of that hanger will be found at the top of the column.
Should it be impossible to select a hanger in a particular series such that both loads occur within the working range, consideration should be given to a variable spring hanger with a wider working range or a constant support hanger. The cold load is calculated by adding (for up movement) or subtracting (for down movement) the product of spring rate times movement to or from the hot load.
Cold load = (hot load) ± (movement) x (spring rate) A key criteria in selecting the size and series of a variable spring is a factor known as variability. This is a measurement of the percentage change in supporting force between the hot and cold positions of a spring and is calculated from the formula:
Variability = (Movement) x (Spring Rate) / (Hot Load) If an allowable variability is not specified, good practice would be to use 25% as recommended by MSS-SP-58.
General rule for series selection use Fig. 82 for up to 1⁄2″ of movement, up to 1″ use Fig. B-268, up to 2″ use Fig. 98, up to 3″ use a Triple, up to 4″ use a Quadruple. Double check to assure desired variability is achieved.
The above drawings represent some common installations of the pipe support represented on this page. Installation types and configurations are not limited to the drawings above, but should always follow the manufacturers guidelines for application and installation.
The functional design of the pre-compressed variable spring hanger permits the incorporation of a two-piece travel stop that locks the hanger spring against upward or downward movement for temporary conditions of underload or overload. The complete travel stop, the up travel stop only for cold set purposes or the down travel stop only which may be employed during erection, hydrostatic test (Anvil permits a hydrostatic test load of 2 times the normal operating load for the spring hanger) or chemical cleanout will be furnished only when specified. The travel stop is painted red and is installed at the factory with a caution tag attached calling attention that the device must be removed before the pipe line is put in service. Permanently attached travel stops available upon request.
ADJUSTMENT OF HANGER:
Once installed in the line; the hanger should be adjusted until the load indicator moves to the white button marked “C” (cold position). On inspection of the system, after a reasonable period of operation, the load indicator should be at the red button marked “H” (hot position). If it is not, the hanger should be readjusted to the hot position. No other adjustment is necessary.
Note: All material included on this page is informational only, and should not be used as one’s sole source for design purposes. STS Industrial, Inc. and its affiliates do not guarantee the accuracy of the information on this site, and retain no liability for the use or misuse of the information contained on this site.
Sources: Anvil International Pipe Hangers and Supports, Carpenter and Paterson Pipe Support Hardware