Steam Locking and Air Binding

What is Steam Locking / Air Binding?

In the plant, have you ever experienced an unexplainable drop in process temperature even though your traps appear to be working properly? The reason could be a condition known as 'steam locking' (when caused by steam) or 'air binding' (when caused by air or a non-condensable gas such as carbon dioxide).

Whichever the case, the mechanism behind the condition is the same: steam or non-condensable gas such as air enters the trap before condensate has the chance to flow into it. The trap valve then shuts and impedes the flow of condensate. This can result in a back-up of condensate, which reduces heating-efficiency.

As the fundamental purpose of a steam trap is the automatic discharge of condensate while preventing steam from leaking out, the valve closing in and of itself indicates a properly operating trap. However, as shown in the illustration below, this impedes the flow of condensate and delays its discharge. Thus, the system as a whole cannot be said to be operating properly.

Illustration of 'steam locking'

Conditions that lead to this type of problem can be roughly divided into two categories:

1. Piping near the trap is causing the flow of condensate not to be prioritized over steam, air, etc.
2. A mixture of steam and condensate is being discharged from the equipment and flowing into the trap

Remedies for the problem differ depending on the cause. The next section will cover this in greater detail, but in principle there are two types of remedies:

1. If the cause falls under above-mentioned category (1), the piping must be corrected to allow condensate to naturally flow into the trap.
2. If the cause falls under above-mentioned category (2), a steam trap with an optional 'lock release' valve or a needle valve must be used to create a bypass route for a small amount of steam to flow downstream of the trap.

Steam locking will gradually get worse and is unlikely to resolve on its own. In addition, though the heating equipment’s performance decreases, it is very difficult to pinpoint the cause of the problem because the 'locked' steam prevents the trap itself from experiencing abnormal cooling.

Causes and Remedies

Air binding is usually remedied by the addition of a pressure-balancing line. Steam locking, on the other hand, occurs for several reasons, and countermeasures differ accordingly. Some of the typical causes and remedies for these are discussed in the examples below.

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