For many years, the gate valve has been the “go to” valve for isolation, simplicity and availability for process containment. If an application required a block valve, the gate valve was selected 90% of the time. For extreme applications, when the process conditions exceeded the gate valve’s parameters, a ball valve was used. However, we are now seeing that, in certain applications, a triple offset butterfly valve could be a better solution. The triple offset valve offers many advantages like ease of operation, commercial availability with larger sizes even in alloy materials, and a smaller envelope size and weight.
Ease of Operation
Health and safety is the primary focus at any facility. The triple offset valve is much easier to operate and open and close, which can help reduce the danger of lower back and shoulder injuries to those operating the valve. The mechanical advantage offered by the utilization of a worm gear means that a maximum 50 lb. rim pull on the hand wheel is sufficient to operate the valve through its complete cycle. When manual operation is required, a triple offset valve can be cycled with much less manpower than a conventional gate valve. And more importantly, the ever present “valve wrench” is not needed.
Space savings are also realized with a triple offset valve. The envelope dimensions of a conventional gate valve are much larger and weights are much higher than that an equal pipe size triple offset valve. For example, a fully-rated 150# class, flanged triple offset valve with gear weighs about 1,000 lbs. Compare this to approximately 3,000 lbs. for a gate valve, and 3,500 lbs. for a ball valve. This means less piping support and easier installation. The envelope dimensions are also greatly reduced from approximately 74” in height clearance required for a 24” 150# class gate valve to less than 50” for the triple offset valve. The space savings could be even greater when the valve is installed with the shaft in the horizontal position and is only 40” tall. A ball valve generally has a very similar envelope dimensional requirements as the triple offset valve. This becomes especially relevant in tight piping configurations and the required support systems.
The triple offset valve offers commercial advantages over the conventional gate valve and ball valve in larger sizes, higher pressure ratings, and in stainless steel and alloy materials. Due to the realized weight reduction of the triple offset valve design, while maintaining a full ASME rating per valve class, the costs are often reduced proportionally when stainless steel or any higher alloy material are required, resulting in a cost savings without sacrificing performance. Using the same example as earlier, a 2,000 lb. weight reduction for a 24” 150# class valve, in CF8M 316 SST cast, represents a substantial cost savings in raw material. This material cost savings is even larger in higher alloys, as the costs per pound for raw material are increased. This same trend is realized in Carbon Steel WCB valves, but only in larger sizes where material costs represent a larger portion of the total valve cost of manufacturing. The crossover point is usually around the 20” – 24” size, if pricing is your only consideration. However, if the valve is going to be automated, the smaller actuator requirements of the triple offset valve, due to lower torques and quarter-turn design, will help offset some of the valve costs differential and the crossover point may be around the 10” - 12’ size. Triple offset valves are now being manufactured up to the AMSE 2500# Class, fully rated. Using the same comparison of weight and size, the triple offset valve can be a better option, commercially, in these higher pressure applications.
Another feature of the triple offset valve is it’s adaptability to existing piping configurations. The triple offset valve is available in a standard wafer/lug design with the standard API 609 face-to-face length. It is also available in an ISO 5752 double flanged and ASME B16.1 face-to-face which is the conventional gate valve take-out. The normal size range of manufacturing for TOV’s is 3” – 120” in 150# Class, 3” – 60” in 300# Class, 3” – 60” in 600# Class, 6” – 36” in 900# Class and higher pressures are totally dependent on the manufacturer. Most standard sizes and pressure classes are stock items, available for quick delivery. Gate valves still remain the most commonly used type of valve for isolation within its parameters. It is also the most heavily inventoried valve in the world. This is not likely to change anytime soon, but the TOV can be a better solution for some situations if you know where to use them. If you need help determining if the triple offset butterfly valve or the more traditional gate valve are the best solution for your application, contact us. We would be happy to help you understand your options and identify the best fit for your individual need.
About the Author
Ralph Chaney has been with MRC Global since 2009. Prior to joining our company, he worked in both the control valve and isolation valve arenas on the manufacturer side of the business. In his current role as Executive Director – Downstream Valves, Ralph continues to do what he has spent his entire 40+ year career doing every day – solving problems for customers, one order at a time.