/ / Frequently Asked Questions
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1. What is Valve Live Loading?
The term "live loading" means using a Belleville spring to maintain load on a seal. Many valves utilitze studs or bolts to exert load on to the gland follower, which applies stress to the packing. As the valve is operated, the seal material consolidates during each operation. High temperature and thermal cycling can accelerate this loss. As this occurs, preload is lost on the seal, and once the preload falls below a certain threshold, a leak will occur. Since the stretch in the stud is small, loss of preload and packing stress can occur quickly.
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2. What materials can be cryogenically deburred?
Flange live loading with Solon Flange Washers manufactured with precipitation-hardened stainless steel are ideal in cryogenic applications where cold temperature and corrosion are factors in process leaks and fugitive emissions.
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3. What is the torque calculation?
The widely accepted forumal for torque calculation is: T=K*F*D, where K = estimated nut factor, T = bolt torque, D = nominal bolt diameter
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4. How do I know what material or finish would be best for my product?
Things to consider when choosing material are bolt material, temperature, environment, application, cost, availability.
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5. Under what condition is the deflection maximum and why?
The maximum deflection should normally be calculated as follows: MAX Deflection = MAX Overall Heigh - MIN Thickness
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6. Why is loosening prevention important for a bolted connection?
Download our technical white paper, Why Bolts Work (and Why Some don't), which discusses the three main important points to remember when bolting and why it is important to understand why factors such as embedment relaxation, differential thermal expansion (DTE), elastic interactions, vibration loosening, bolt creep, and component yielding cause bolts to lose load and how to counteract these phenomena.
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7. How to prevent bolt fatigue failures?
Download our technical white paper, Using Belleville Springs to Prevent Bolt Fatigue Failures, to learn how changes to a bolt, such as stiffness, will influence the cyclical load on the fastener. This paper takes a closer look at the science behind the elements of preventing bolting malfunctions, and explains how using Solon Belleville Springs & Washers increases the elasticity of the bolting system and maintains bolt preload.
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8. Are Solon Flange Washers corrosion-resistant?
Solon Flange Washers are heat treated using a recipe that achieves RH1065 condition while imposing an additional layer of protection from the elements, and undergoes a cryogenic sub-zero transformation and aging treatment.
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9. Can you stack Solon Flange Washers on one side of the flange?
There are some cases where flange springs must be stacked on one side of the flange. This might be because a tensioner is being used to load the studs. It also may be difficult to access one side of the flange. In addition, there are some applications where the flange is not bolted through, such as a valve bonnet or if one of the flanges is tapped. In these cases, if the recommendation is to use two springs (or parallel spring sets) in series, we recommend that it is verified that the clearance hole in the flange is less than or equal to the clearance hole of the flange washer. If the clearance hole is larger, then the convex side of the washer nearest the flange could "extend" into the hold of the flange and alter the loading charactertistics. Since the clearance holes in standard flanges is almost always larger than the clearance ID of the Solon Flange Washers, we would minimally recommend that a flat washer with an ID equal to the ID of the Solon spring be used. The flat washer should be a hardened washer to prevent embedment. Another option would be to use a thrid flange washer (or parallel washer set) on this side of the flange. Using an odd number of springs in series will ensure that the convex side of the first spring can contact the flange. The added spring will always provide additional elasticity so joint performance will be improved over two springs.
10. When do I need to use a flat washer with a Belleville?
It is common to use flat washers under the springs. Some general recommendations regarding flat washers for flange live loading applications include: a. We recommend that the flat washer material be in the same "family" as the Belleville. In other words, if the Belleville is stainless steel, the flat washer should also be stainless steel. b. The OD of the flat washer should be larger than the OD of the Belleville. This will ensure that the OD of the spring contact point bears on the top surface of the flat washer. c. We recommend that the flat washer be a hardened material. This will reduce the likelihood that the Belleville would embed into the flat washer. d. We generally recommend that the flat washer be 1/3 the thickness of the Belleville (or greater) when the flat washer is fully supported by the joint.
11. Do I install my washers on the nut or bolt head side?
Installing Solon Belleville of Flange Washers on the nut or bolt head side does not make a difference from a performance standpoint. Solon recommends that the user install them on the side that is most convenient to access. If this is equal, then we would opt to install them on the opposite side from the element that will rotate during install to reduce rotational galling on the spring. In other words, if the user plans to turn the nut during install, we would install them on the bolt head side and vice-versa.
12. How many times can a Belleville spring be used?
A Belleville spring can be used indefinitely as long as it is not damaged. It is perfectly acceptable to reuse the springs many times in bolted applications. However, it is important to note that as highly stressed parts, Belleville springs can be prone to failures if they have been compromised in some way. Parts can be damaged by excessive cycling, corrosion, exposure to temperatures beyond the material ratings, and mechanical damage such as galling.
13. What do you consider a cyclical application?
Load on a Belleville spring changes (or cycles) to some extent in all applications. We consider an application to be cyclical when these changes in load will eventually result in the failure of the part. If this is the case, we must then determine if the number of calculated cycles provides adequate life of the product. Cycle life is calculated by considering the maximum load (and resultant stress) for each cycle and the change in load. Generally, the calculated cycle life in a bolting application will be nearly infinite.
14. Should one or two Solon Belleville Springs be used on a bolt?
In general, Solon Belleville Springs are designed to be loaded to flat without damaging them. However, this does not mean they should be bolted to flat in every case. There are some applications where a spring should be employed at a load considerably lower than the flat load. For instance, when elevated temperatures may damage the springs, it may be necessary to use a heavier spring in order to keep the stresses below a certain threshold. In addition, in some elevated temperature applications it may be desirable to allow the spring to partially “absorb” the differential expansion to prevent excessive loading.
15. How do I know when a Belleville spring is flat?
In general, Solon Manufacturing Co. suggests that the following torque calculation be used to determine the bolt load.
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Imperial: (ft. – lbs.) - .2 X Bolt Diameter (in.) X Load (lbs.) / 12
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Metric: (N-m) = .2 X Bolt Diameter (mm) X Load (N) / 1000
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If lubricant is used on the joint, then the torque should be reduced.
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If the nuts and bolts are stainless, then torque may need to be increased. Your Solon application engineer can help determine the appropriate torque value for your requirement.
16. What load should be used on a Belleville spring?
The application will determine proper load. The following factors are important for live loading a bolted joint:
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Decide what load or torque should be used for a sound joint design. If the joint is a flange, the gasket manufacturer should provide this value. If the joint is a bus (electrical) connection, the designer of the system should provide this value.
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Decide which material the Belleville spring should be. We generally suggest a material that is similar to the bolt material.
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If the Belleville spring may be used at its flat load, use a spring whose flat load is close to the design preload. It may be necessary to use multiple Belleville springs in parallel in order to achieve the requisite flat load. Ideally, the design preload will be 70%-100% of the flat load.
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Confirm the spring arrangement fits into the space constraints of the application.
17. Shouldn’t the deflection plus the thickness of a Belleville equal the overall height (H)?
Actually, thickness plus deflection is not equal to H. This is because thickness is measured on an angle with respect to the deflection. However, since this angle is typically very small, the thickness plus deflection is approximately equal to H. In addition, if a spring is not prestressed, the H will usually be greater than the thickness plus deflection.
