This ratio is the unsupported length of the extension stem, divided by the “radius of gyration” of the stem cross section. The unsupported length is the distance between the extension stem Operating Nut and the Bottom Coupling, or when stem guides are used, the longest distance between any two “supports”.
It is typically used to determine the susceptibility of a column to buckling, from the load it is required to support. Picture any column, from a porch, to a monument, and imagine its shape. The heavier the load, or the longer the column, the more massive it needs to be, to sustain the weight.
Is there an industry standard for Slenderness Ratios?
The larger the ratio, the more susceptible to bending or buckling. Lowering the ratio adds rigidity to operate the valve. In general, a maximum Slenderness Ratio of 200 is considered acceptable, for applications with no axial load.
Typically, engineers state the maximum allowable ratio in their valve specifi cations.
For extension stems, there is practically no “axial”, or compressive load; it is almost purely torsion. Torque is applied to one end, and the stem transmits this torque to the opposite end, to operate the valve. For almost all applications, the operating torque determines the size of the stem, not the L/R ratio.
Why does it matter?
Imagine a 30 foot extension stem made of 1” pipe with no stem guides; the slenderness ratio is 885. The stem may bend or buckle while operating the valve. Increase the stem diameter to 1-1/4” pipe and add 2 equally spaced stem
guides, and the ratio drops to 222. Add a 3rd stem guide and the ratio drops further to 167.
If the ratio is too high, the extension stem may bend or buckle and not have the rigidity to properly operate the valve.
Increasing the stem diameter and/or the number of stem guides will reduce the ratio. In some cases, the diameter of the extension stem and number of stem guides can be varied to achieve an adequately designed and cost effi cient extension stem and stem guide system. Trumbull can assist in calculating the optimum combination for your project.
Meaning of H-20
The American Association of State Highway and Transportation Officials developed a standard, M306 that calls for proof load testing for iron castings. For an H-20 proof load test, that standard requires a 40,000 lb. load be applied to a 9” x 9” square plate for one minute. Any cracks or permanent deformation greater than 1/8” are cause for rejection.
What is “Lead Free?”
As of January 4, 2014, the Reduction of Lead in Drinking Water Act (RLDWA) changed the allowable lead free content definition in Section 1417 of the Safe Drinking Water Act (SDWA) to a weighted average of not more than 0.25 percent lead, with respect to the wetted surfaces of pipes, fittings, valves and other fixtures. These are Federal regulations.
Zinc Anode Caps
Zinc Anode Caps are threaded end caps, shaped like hex nuts, which are fastened to the ends of bolts or studs on a buried pipeline or related pipeline component. The zinc in an Anode Cap sacrificially corrodes before the steel of the fasteners, fittings or related components, which helps protect these items, thus extending their life and preventing possible damage from failed fasteners.