The formation and solutions to steam lock
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This post was last edited by gengen1115 on 2017-12-26 at 15:42. (Repost) Thanks to the original poster for their hard work. The steam trap automatically removes the condensate water that is continuously generated in steam-using equipment, and prevents steam from being discharged along with the water; its functions are to prevent steam from escaping, allow water to pass through, and remove air. If condensate and non-condensable gases cannot be quickly removed from the steam-using equipment, it can lead to part of the space within that equipment being occupied by condensate. This reduces the amount of steam that can enter, resulting in the heat transfer surfaces of the equipment being covered by condensate. As a result, the new steam cannot come into contact with these heat transfer surfaces and is unable to exchange heat with the medium being heated. Although steam has begun to form condensate in the equipment that uses it, the trap will open again only when the steam inside the trap and the drain pipes leading to it has condensed. Compared to the steam inside the equipment that uses steam, the condensed rate of the steam trapped in the steam traps and steam pipes is much slower, which can lead to the equipment being filled with condensed water. This condensed water can only be removed after the trapped steam has condensed. When steam and non-condensable gases in the steam trap cannot be discharged in a timely manner, a vapor lock phenomenon occurs. Those caused by steam are called steam locks, while those caused by non-condensable gases such as air are called air locks. The mechanisms behind these two phenomena are similar: steam or non-condensable gases enter the steam trap before the condensate, causing the valve to close and preventing the equipment that relies on steam from functioning properly.
This post was last edited by gengen1115 on 2017-12-26 at 15:46. An air lock occurs when non-condensable gases in the drain valve cannot be discharged in time. In drainage systems equipped with disc or inverted bucket type steam traps that do not have sufficient exhaust capacity, a large amount of air gets trapped inside the traps along with the condensed water when steam-using equipment is started, resulting in an air lock. For air locks, this issue can be resolved by installing a pressure balance pipe between the drain valve body and the equipment that uses steam.
1) When steam-powered equipment starts up in a long, straight hydrophobic pipeline, steam first pushes air and condensate toward the drain valve. At this point, the drain valve opens to release condensate and air. Immediately thereafter, steam enters the steam trap, causing the valve to close. At this point, both the long, straight hydrophobic pipe and the steam trap are filled with steam, while the condensate generated by the steam-using equipment is trapped in the hydrophobic pipe by the steam, preventing it from being discharged through the steam trap. The steam lock phenomenon is relieved only when the steam in the steam trap and the steam ducts condenses, as shown in Figure 3. To address the steam lock phenomenon in long and straight hydrophobic pipes, it is advisable to use hydrophobic pipes with larger diameters and to shorten the length of the pipe ahead of the steam trap as much as possible, so that the condensate can flow naturally into the steam trap, as shown in Figure 4.
2) Incorrect inclination of the drain pipe: When steam-powered equipment generates condensate, if the inclination of the drain pipe is opposite to the natural flow direction of the condensate due to gravity, steam will enter the drain valve first, which can easily lead to a steam lock, as shown in Figure 5. The main way to resolve this steam lock issue is to change the inclination of the hydrophobic pipes, allowing the condensate to flow naturally due to gravity. From the steam-using equipment to the drain pipe of the steam trap, the pipeline should have a certain slope in the direction of the condensate flow, and bends should be used as little as possible, as shown in Figure 6.
3) Vertical lift pipe: If the drain pipe is lifted vertically, steam enters the drain valve first, resulting in a steam lock, as shown in Figure 7. The solution to this steam lock issue is to modify the structure of the hydrophobic pipeline, as shown in Figure 8. This allows the condensate to flow naturally due to gravity, reducing the likelihood of steam lock.
4) Steam-using equipment equipped with siphon traps: When siphon traps are used (see Figure 9), the condensate in the steam-using equipment is pushed by steam into the trap pipes; as a result, the condensate can easily enter the steam trap along with the steam, leading to steam lock. At this point, some of the steam can be released by using a steam lock release valve, ensuring that the condensate mixed with steam can flow continuously into the steam trap without any obstacles