The Variable Support is a spring loaded device used for the support of piping and equipment where normal vertical movement is anticipated. Variable Supports are manufactured in five different Travel Series which allow up to ten inches of movement and twenty-five different sizes allowing up to 50,000 pounds of load. Seven different mounting Types allow the user the widest selection of configurations to accommodate practically every hanger design.
All spring units are designed to meet the requirements of:
- ASME Code for Pressure Piping, ASME B31.1, B31.3
- Manufacturers Standardization Society (MSS), SP-58,and SP-69
- Federal Specification A-A-1192-A and WW-H-171-E
standard design features
- Precompression – precompressing the spring coil into the hanger casing saves headroom by reducing the size of the casing, reduces the installed envelope size and also weight and erection time.
- Closed-coil spring casing design protects the coil from damage and weather.
- Steel Construction – spring, casing, and internal parts are fabricated of steel making them rugged and compact. All welding is done to the strict requirements of ASME Section IX.
- The Piston Plate serves as a centering device and guide maintaining coil concentricity under normal operating conditions.
- Load Indicators are visible in the slots and are clearly readable.
- Stainless steel nameplate and travel scale are corrosion resistant.
- All spring hangers are calibrated for accurate loading conditions.
- The unit is preset at the factory to the Cold Load upon request.
- For each series there is a reserve travel at the upper and lower limits of the working range of the spring.
- Allowable spring coil stresses conform to ANSI/MSS-SP-58.
- Standard finish is a quality rust resisting primer paint.
- A turnbuckle or other suitable coupling is utilized for adjustment of rod type spring units. F type springs utilize an adjustable load column.
- All F type units are supplied with a load flange.
OPTIONAL DESIGN FEATURES
- Travel Stop – set at the Cold load position changes the spring into a rigid support for hydrostatic testing or other purposes. The strength of the Travel Stop is designed so that it can withstand (up to) 2 times the normal load.
- Adjustable Travel Stop – allows the resetting of Preset/Travel Stop at any location within the normal operating range of the travel.
- Limit Stops – permanently installed to prevent the movement of the pipe beyond a predetermined distance or load within the travel range of the spring.
- Load Column Guide – for Type F units only, to prevent tipping of the Load Flange due to anticipated eccentric loading.
- Extended Load Column – for Type F units only, thelength of the load column is furnished longer than normalper customer request.
- Lifting Lugs – are available on larger sizes to facilitateerection and installation.
- Hot-dip Galvanized Finish – available for protection against weather and corrosive conditions. The unit is galvanized to ASTM A-153 except the spring coil which is epoxy powder coated to assure protection to the coil as it flexes. The load column of the F Type spring is electrogalvanized. Maximum ambient temperature for the epoxy powdered coating is 350° F (177° C).
- Epoxy Paint Finish – available for protection against weather and corrosive conditions. The unit is painted with a two-part zinc rich epoxy paint except the spring coil which is epoxy powder coated.
- Stainless Steel Construction – allows the greatest degree of corrosion protection. Constructed completely of stainless steel except the spring coil which can be epoxy powder coated for economy.
choosing your variable spring
In choosing the proper Variable Spring, Travel Series it must first be determined that the calculated movement will fall within the working range of the support and that the variability of the unit does not induce unacceptable loads on the other supports or connections. Five (5) standard Travel Series are available ranging from 11⁄4″ through 10″.
The size of the Variable Spring support selected depends upon the Hot Load (operating load) of the support, the Spring Rate of the selected variable support, the Movement, the Cold Load, and Variability.
Variability is a key criteria in selecting the size and series of a Variable Spring support. This is a calculation of the percentage change in the supporting force of a variable spring between the Hot (Operating Condition) and the Cold (Installed Condition). The formula is shown below:
The Hot Load is the actual Operating Load of the piping.
The Spring Rate is the amount of load required to deflect a spring coil over a given distance and is expressed in pounds per inch (Newtons per millimeter). Spring rates can be found in our selection table for a given travel range and size spring.
The Movement is the amount the piping system changes due to thermal growth when moving from the Cold to Hot position.
The Cold Load is calculated by adding (for UP movement) or subtracting (for DOWN movement) the product of Spring Rate times the Movement to or from the Hot Load.
If an allowable Variability is not specified, good practice would be to use 25% as specified by MSS-SP-58.
selecting size and series
- Find the Hot Load in one of Spring Size columns on the appropriate SIZE AND SERIES SELECTION CHART (click here to open the chart)
- Calculate the maximum allowable Spring Rate from the formula:
- Stay in the column and choose the Travel Series with a Spring Rate equal to or less than the value calculated.
- Calculate the Cold Load and check that both the Hot Load and Cold Load fall within the Working Range of the Travel Series selected.
- If your requirements are not met, move to an adjacent Spring Size column and recalculate again using the above procedure.
If the Movement or loading requirements cannot be satisfied, select a Travel Series with a greater Working Range and recalculate.
If any combination of Load, Movement and/or Variability cannot achieve the desired results the use of a Constant Support should be considered.
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