Does anyone have typical steam loss rates, which would give me the approximate consumption of steam through a passing steam trap.

Ideally, I need this information for standard trap sizes (1/2", 3/4" & 1"), and for different types of traps (inverted bucket, TD, float etc).

I've contacted a couple of trap manufacturers in the UK, but they seem very reluctant to supply this sort of information.

It may help if you think of a steam trap for what it essentially is - an automatic valve. It opens when it senses air or water, and closes when it senses steam. The amount of any fluid it will pass will depend on the orifice size, and the differential pressure across it. The upstream pressure can vary if there's a temperature control valve on the steam supply. Also, the downstream pressure can vary, depending upon what is happening with the condensate system. This means that the pressure drop across this orifice can swing by quite a large margin. The trick, as in most calculations, is getting accurate data from the field.

There are three things that will effect the loss of steam through a failed trap:
The differential pressure
The size and shape of the orifice
The presence of condensate

Much theoretical work has been done on this, it is the last item that effects (reduces) the steam loss, for example, in a large process trap that is flooded with condensate there will be no staam loss even if the trap is failed.  Also, if the orifice is long there will be choking effect when live steam passes through.

All this said, I have used (conservatively) 10% of the published condensate flow rate for each trap at each differential pressure in programs I have written to estimate steam loss for steam trap surveys.  It was a very large data base, but it was the best approximation that we could think of without getting into theoretical thermodynamics.

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