When draining a steam trap to a high level return line the trap should be sized by accounting for the back pressure created by the rise to avoid logging of condensate and chances of water hammer.
Often plants return condensate to a high level return line using the steam pressure within the steam trap. The discharge capacity of the steam trap depends not only on its orifice size but also on the differential pressure that is created during its operation. The traps essentially being orifice based devices, their performance depends on the differential pressure created and this lift to a high level return line increases the backpressure on the steam trap. For example, a lift of 5.3m translated to a backpressure of 0.5bar.
The reduction in differential pressure available to push condensate through the trap will be significantly lower in applications which have a low upstream steam pressure. Especially at start up, the steam pressure will be low for a significantly long period of time leading to backing up of condensate in the piping upstream of the steam trap.
This can lead to water hammer in the section of the piping where the condensate has been collected. Waterhammer is caused by slugs of condensate colliding at high velocity into pipe-work fittings, plant, and equipment. Indications of waterhammer include a banging noise, and perhaps movement of the pipe. In severe cases, waterhammer may fracture pipeline equipment with almost explosive effect, with consequent loss of live steam at the fracture, leading to an extremely hazardous situation. Thus when draining a steam trap to a high level return line the trap should be sized by accounting for the back pressure created by the rise. This will reduce the chance of water hammer thereby leading to lesser loss through leakages.