Email this pageSteam Locking and Air Binding
What is steam locking and air binding?
In the plant, have you ever experienced a loss in temperature for which you were unable to find an explanation? There is a phenomenon under which condensate doesn’t discharge from the trap as it should, even though the trap is in good operating condition. It is known as ‘steam locking’ when caused by steam, and ‘air binding’ when caused by air (or non-condensable gases such as carbon dioxide).
The mechanism is the same for both; steam or non-condensable gas such as air enters the trap before the condensate that is trying to flow into it has a chance to enter, causing the trap’s valve to shut.
A steam trap is a type of automatic valve designed to discharge condensate without allowing the leakage of steam, so the valve in the trap closes as soon as it senses the arrival of steam. This action in and of itself indicates a properly operating trap. However, as shown in the illustration below, condensate cannot flow into the trap due to the valve being closed, so the discharge of condensate is delayed. Thus, the system as a whole cannot be said to be operating properly. This phenomenon is known as ‘steam locking.’ When the same phenomenon is caused by air, it is known as ‘air binding.’ They are the same in that no condensate is being discharged even though the trap itself is operating properly.
Illustration of ‘steam locking’
The causes of this phenomenon can be roughly divided into the following 2 categories:
- A problem in the piping near the trap is causing the inflow of condensate into the trap not to be given the highest priority.
- A mixture of steam and condensate is being discharged from the equipment and flowing into the trap.
The remedies for the problem differ, depending on the cause. The next section will cover this in detail, but in principle there are 2 types:
- If the cause falls under category (1), the piping must be corrected to allow condensate to properly displace the steam or air in front of the trap.
- If the cause falls under 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 be resolved 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
There are several reasons steam locking occurs, and the countermeasures to remedy steam locking differ in each case depending on the cause. Air binding is remedied by the addition of a pressure-balancing line. Some typical causes of steam locking and their respective remedies are discussed in the examples below.