�ǳ�web Knowledgebase - cycle life

When It Really Matters, How Can You Trust That a Valve Is Reliable?

Rachel Desenberg — Thu, 28 Mar 2019 15:45:36 +0000

Category:

Every device is designed for a particular need; therefore, product life is relative to the application. It stands to reason then that if an application only requires million cycles, that application does not require a billion cycle valve. Or does it?

We have all been in situations where a product we depend on has failed. The car broke down, the HVAC system went out, the ice maker quit—hopefully not all on the same day. Why do design engineers specify components that do not meet customer expectations for their products? Too often, the primary driver is to simply hit a cost target that will last through the warranty period. Important decisions, sometimes guided by cost concessions, must be made for each and every component installed in any product or device. However, just as a chain is only as strong as its weakest link, many products can only be considered as reliable as their least reliable component.

Valve Reliability vs. Cycle Life

When it comes to the lifespan of a valve, few applications need a valve that will reach a billion cycles. Yet �ǳ�web proudly designs valves that far exceed this requirement. Why? It could seem that a valve with an exceptionally long life is "too good." However, even when an application does not require billions of cycles, it may demand high reliability. What better way to measure reliability than with lifespan? Consider—few people shopping for a new car need it to last a billion miles, but what if there was an affordable one that would? Products that are proven to have long life instill confidence, provide customers with peace of mind, and can be relied upon in situations where failure is more than just a mere inconvenience. In this case, a valve's life cycle is not a feature to be coveted as much as it is an indicator of the product's overall quality and reliability.

Aerospace and defense manufacturers have multiple applications that require a valve for a one time use application. In this most extreme example of specifying a high life valve in a low life application, it is apparent that a billion cycle lifespan is not necessary, nor the buying decision. However, high reliability is crucial. A proven design with consistent performance provides the peace of mind that a component will function every cycle, regardless of the number of cycles the particular application requires.

Medical device manufacturers take reliability to heart and understand that in designing mechanical devices, all failures cannot be eliminated. The goal of good design engineers is to identify the most likely failure and outline appropriate actions to mitigate the effects of said failures. When valves for a fluid or gas are imperative in the application, a billion cycle valve claim adds legitimacy to the quality of the valve. It is not uncommon to find a low cost component performing a vital function at the center of a medical device, provided that the component is of high reliability.

The industrial automation market demands cost effective reliability. Although more and more equipment manufacturers specify valves based on price to get machines to market at the bottom dollar, some machine builders do still see value in producing machines that last. Years ago, �ǳ�web received a failed valve from a bottling plant. The customer shared the failure's consequence and requested an evaluation on what happened. The application included a line speed of 26,000 bottles filled and printed per hour, with 95% uptime, on a line which ran 24/7. The returned valve was over 15 years old and when it finally failed, had reached 3.24 billion cycles.

The Importance of Manufacturability

Of course, cost is always a factor. If someone designed a car to last a billion miles, but it cost a billion dollars, not many people would buy it. Consequently, you'd be lucky to get even one mile out of a car built for less than one hundred dollars. Good design engineers must take into account the design specification requirements as well as the product's cost target. The costs are primarily materials and process. Can we manufacture the parts to print repeatedly in a reasonable amount of time out of the required material? Do we understand all the processes needed to assemble the product? Customers do not pay for testing, they pay for product. Testing to the product's designed specifications is only there to assure that the manufacturing and assembly processes do what they are designed to do and that issues don't occur. Product reliability begins with the design, but the manufacturability of that design is critically important to produce a quality product repeatedly at an affordable price.

Ultimately, the best indication of a quality design and manufacturing process is life. And testing proves it. �ǳ�web's spider valve cycle life was tested by running at 32 Hz 24 hours a day for over a year. The valves were tested every 50 million cycles to ensure that they maintained a bubble tight seal until they reached 1 billion cycles. Testing continued until the standard valves reached over 7 billion cycles.

With today's low cost, throw-away market mentality, we are thankful that �ǳ�web serves industries that value quality and reliability. Cost is always a factor, but less so for products that start with what matters—a solid and manufacturable design. When this is done well, a better balance is achieved that allows the production of a more affordable, higher quality product. In this way, the proven reliability of �ǳ�web's spider valve design, paired with the quality of our proprietary manufacturing processes, delivers unmatched performance and reliability.

Reaching billions of cycles with a �ǳ�web valve is an exceptional feature, but the value this delivers is not limited to the potential life of the product. Ultimately, the benefit is the peace of mind this provides at an affordable price. When it really matters, you can trust a valve's lifespan as a measure of its reliability.

By Rob �ǳ�web • Vice President of Sales & Marketing • �ǳ�web

How to Extend the Cycle Life of Your Valve

Rachel Desenberg — Thu, 17 Jan 2019 21:36:17 +0000

Category:

Troubleshooting

What can you do to maximize the life of your valves? Valve cycle life is the valve's expected life under ideal conditions, but few applications are ideal. An understanding of the factors that affect valve life is important for selecting the proper valve and materials.

A valve's cycle life is a reference point for how many cycles the valve could be expected to function in an ideal or standard application. This could also be referred to as the mean time to failure. One cycle for a valve is defined as the valve going from the unactuated state to the actuated state and returning to the unactuated state. In most applications, the cycle life of the valve is measured from when the valve was installed to the time that the valve—in some way, shape, or form—failed. The definition of failure can vary from application to application. Certain applications may see minor leakage and determine the valve has failed, while other applications may not consider a valve failed until the valve ceases to actuate. The cycle life of a valve is for reference only and is not a guarantee of the expected performance from a component.

Pressure

Temperature

Cleanliness

Cycle Rate

Lubrication

Materials

Construction

What Factors Affect the Cycle Life of a Valve?

There are many factors which influence the life of a valve, including: pressure, temperature, cleanliness of the media, cycle rate, lubrication, seal material, and valve construction. Depending on the application, there may also be other additional factors.

Pressure

Excessive system pressure or spikes in pressure can increase the wear on seals and may even damage them. In extreme cases, exceeding rated pressures on valves can lead to catastrophic failure such as cracking parts that compose the valve, or even breaking the valve and launching components, which can be dangerous.

Compared to spool valves, poppet valves generally have higher pressure ratings due to the fact that on a spool valve, high pressure can push harder on the seals and create extra wear on them. However, exceeding the rated inlet pressure on a poppet valve can damage the poppet seal or lift it off of the seat and create a leak.

Temperature

Temperature extremes can have a major impact on the life of a valve. Below 32°F, any moisture in the pneumatic systems can freeze into shards of ice. These ice shards can cut and damage seals in the valve. Moisture can also freeze on valve components, preventing valves from actuating. This is why some manufacturers will only rate valves down to 32°F. High temperatures can also break down seal material and cause failures. For example, a stainless steel valve with nitrile seals will see decreased cycle life if used outside the temperature specification for nitrile. For reference, this seal material property chart outlines temperature ratings for a variety of different seal materials. However, temperature extremes are not limited to only affecting the seals of a valve. For example, on many electronic valves, extreme heat can melt the coil encapsulation material and cause the coil to fail.

Compared to spool valves, poppet valves have relatively good resistance to extreme temperatures. With minimal friction, actuation of most poppet valves does not generate additional heat and is not dependent on lubrication. By contrast, spool valve life is not only dependent on the seal material in the valve, but also its lubrication. High temperature applications can turn lubrication into a liquid that is flushed right out of the valve, while low temperature applications can freeze lubrication, preventing the spool from shifting.

Cleanliness

Contaminated media can quickly destroy a valve. Contamination is anything in the media that is not intended to be there, which can include—but is not limited to—water, metal shavings, or dust. It only takes one tiny piece of debris to damage the seals in a valve. A metal shaving can cut and destroy seals, and dust can build up causing leaks and wear to seals. Manufacturers of valves publish a micron rating for filters that should be used with their valves. Using the appropriate filtration system can help to maintain clean media and extend the life of your valve.

Compared to spool valves, poppet valves have decent resistance to debris in the media. Debris in poppet valves can sometimes get stuck on the poppet seal and cause a leak, but it can also sometimes be flushed off the poppet. If the debris did not cut the poppet seal, there would be little to no noticeable damage done. Spool valves, however, can easily be damaged by debris in the media. One piece of debris on a seal that slides across the housing is all that it takes to destroy a seal in a spool valve.

Cycle Rate

The cycle rate of a valve is the frequency that it is actuated. Some applications cycle a valve once a day, while others cycle a valve tens of thousands of times a day. High cycle rates can generate heat from friction which can lead to premature failure.

Compared to spool valves, poppet valves perform very well in high cycle rate applications. Since the poppet seal simply lifts on and off of the seat, this results in little wear and heat generation. This allows poppet valves to achieve high cycle counts with minimal degradation to the valve's life. However, high cycle rates can adversely affect the life of spool valves as the reciprocal action of sliding seals can generate friction, heat, and premature failure.

Lubrication

Depending on the valve's construction, some valves will require lubrication for the maximum cycle life. Lubrication can reduce wear on seals and help to reduce heat generated from cycling. It is important that any lubrication used in a valve is compatible with the materials that compose the valve and the media that will go through the valve, and that it is appropriate for the application. For example, certain applications—such as food and beverage, or medical applications—may be limited on the lubricants that are allowed to be used. Other analytical applications may not be able to use any lubrication due to outgassing. Therefore, lubrication restrictions of the application may limit a valve's cycle life.

As mentioned earlier, due to their frictionless cycle, poppet valves are not dependent on lubrication. By contrast, for a spool valve to achieve maximum cycle life, proper lubrication is important for reducing friction and wear on seals.

Materials

Valve seals are crucial for the prevention of leaks—both internally and externally. To choose the most appropriate seal material, it is important to consider not only the media the valve will handle and the application for the valve, but also the shelf life of the seal material. For example, a valve that is controlling the flow of an aggressive media will require seals that are compatible with that media. When selecting seal material, references such as �ǳ�web's Material Properties Chart provide a useful comparison of temperature ratings, shelf life, and other factors.

Construction

Valve construction can include the valve style, the actuator type (e.g., electronic, manual, air pilot), and the materials that compose the valve. There are also other types of less common valve constructions which, in addition to being affected by all the aforementioned factors, may also have other life restrictors. For example, stepper actuated valves, pinch valves, and piezo actuated valves are less common and could have other factors that affect life and performance.

When Does Cycle Life Matter?

Valve manufacturers design and build valves to exceed the standard requirements that most customers require for most applications. Yet, some applications demand billion of cycles while other may only need a few cycles. For example, a valve that delivers oxygen with every breath would need to work every time and may cycle millions of times in a year; while a valve that supplies compressed air to an assembly area may only be actuated once or twice a day. For an industrial valve that is cycled once, twice, or even dozens of times a day, cycle life may matter very little. However, for a valve that is delivering oxygen to a patient and must function perfectly every time, cycle life becomes very important. In this case, there is a significant benefit to having a valve that is proven to last well beyond the required life as it is likely to provide higher reliability.

How Can Valves Be Modified to Improve Cycle Life?

There are many factors that contribute to the cycle life of a valve. Because of this, adjustments can often be made to standard valves to better adapt them to meet the needs of specific applications. In many cases, this is where working together with a knowledgeable manufacturer will deliver a superior performing product.

For example, in one particular application, handling blood samples in a blood analysis machine required a minimum of 4 million cycles. However, standard valves used in the application were only able achieve 1 million cycles. �ǳ�web's engineering team researched the issues that were limiting the cycle life of the valves and determined that it could be extended by changing certain materials within the valve. This change was easily implemented, prototyped, and tested, resulting in a new, custom valve that not only met but exceeded the 4 million cycle target.

In a different application, mobile equipment was failing prematurely due to usage in an extreme environment. Mobile applications can be highly demanding—certain types of equipment may be in the desert one month, and the arctic another month. These extreme temperature variations can be tough to conquer, and when the valve is controlling vital machine functions, it must work properly every time. In this case, �ǳ�web's engineers started with the 1 billion cycle DV series electronic valve. With modifications to the coil, seals, and poppet seat they had a valve that was soon proven to handle the wide range of temperature fluctuations this application required.

The cycle life of a valve is the valve's expected life under ideal conditions. Not all applications are ideal, so understanding the factors in the application that affect the life of the valve is important for selecting the proper valve and the proper materials. Standard valves often meet or exceed the requirements, but sometimes modifications are necessary to better valve adapt the valve for the application. In many cases, simple adjustments can be made resulting in a product that delivers superior performance. If you need help extending the cycle life of your valve, contact �ǳ�web or your nearest �ǳ�web distributor for assistance.

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By Mike Kettering • Technical Sales Specialist • �ǳ�web