Function and Operation of Steam Traps
The Role of Steam Traps
A steam trap is an automatic valve which removes condensate and air out of the steam system. As described below, steam traps have several types, but all types of steam traps have the ability to remove condensate and air. The details of its functions are as follows.
① Discharge large quantities of condensate in initial operation (start of operation and start-up process)
At the beginning of venting to start steam supply to the steam system, a lot of cold condensate and air needs to be removed quickly under low pressure conditions. Under these circumstances, the steam trap will be fully open, so the valve should have as large a hole as possible.
② Condensate removal during normal operation
It is better to remove condensate promptly, and close the valve completely as soon as the discharge is completed to prevent steam leakage.
③ Early release of air locking
Air locking is the phenomenon in which air occupies a space near a valve hole of the steam strap, with the result that condensate cannot reach the valve hole and thus accumulates. It is necessary for air to be removed immediately when air locking occurs.
The valve hole size of steam traps (hole diameter of the condensate discharge valve) is designed based on its operating pressure and condensate discharge volume for normal operation Therefore, this is based on the operating pressure and condensate capacity for ② above. However, for ➀ or ③, in many situations, it is better for condensate to discharge immediately with a larger valve hole size. Thus, in general, bypass valves or air vent which remove low temperature condensate and air are automatically fitted with steam traps in parallel. Air vents consist of a thermosensitive element, such as a bimetallic disk or capsule element, which contains liquid and alcohol to allow them functionally to open at low temperatures and close at high temperatures.
In addition to these original functions of steam traps, some steam traps have a built-in strainer to capture dust and scale generated in the steam piping.