DP Flowmeter Works Unstable

>close high and low side then open equal key

The high side and low side valves are closed to isolate the transmitter from the process (steam) and the equalizing valve is opened to zero the transmitter.There should be no flow of steam under those conditions

>"came up too much water"

I'm not sure what that means. There should never be steam flow through the impulse lines. A steam service installtion has impulse lines filled with condensate to isolate the transmitter from the steam. Impulse lines are 'dead headed' and the liquid condensate in the impulse line conducts pressure, but greatly limits heat transfer. Steam can not be allowed to flow through the impulse lines because the presence of the steam's extreme heat will damage the transmitter.

>There is a key [valve] befor a dp trinsmitter for drain on the pipe but when I opened it only came up a super steam without water ???

Not only is that a safety issue, the steam heat probably ruined the transmitter. If the drain is opened, the root valve at the pipe needs to be closed first! If there is no water is the impulse lines then the impulse line condensate is flashing back to steam.

Here are a variety of steam service installation showing impulse tubing that needs to be filled with water before the steam line is charged. Note the slopes used to maintain drainage from the high point or condensate pot back into the steam line to maintain a constant head level in the impulse line.