67CFR Fisher Pressure Regulator

[gguliye]

Dear All,
i have the following question. i am completely new to regulators. so i am reading the datasheet for 67C regulator and found the following. it has the check valve assembly as being smart bleed option and is activated when the upstream pressure is lost and all air in the output enters to input through this check valve and regulator plug.
1) as far as i understood, this regulator is normally open when there is higher pressure (below the SP)in downstream. suppose the regulator is set to 3 barg. if the downstream pressure is 2 barg under the diagram the regulator will be open. am I right?
2) if the outler(pressure under diagram) reaches 3 barg, the regulator will be closed. am I right?
3) if the inlet pressure is lost, the plug will go down, and the regulator will open. why do i need smart bleed option? to have higher back flow Cv or?
regards

 

[LittleInch]

This is, as far as I can see, a air pressure regulator.

This implies that the upstream pressure is normally more than downstream and that there is flow through the valve.

ON no flow, the pressure downstream will reach 3 bar and close the regulator against the higher pressure upstream.

Your item 3 is incorrect. Position of the plug is dependant on the downstream pressure

The fisher bulletin says

"In some cases, it is desired to exhaust downstream pressure
if inlet pressure is lost or drops below the setpoint of the
regulator. For example, if the regulator is installed on
equipment that at times has no flow demand but is expected
to backflow on loss of inlet pressure. The Type 67CFR or
67CFSR can be ordered with the Smart Bleed option which
includes an internal check valve for this application. During
operation, if inlet pressure is lost or decreases below the
setpoint of the regulator, the downstream pressure will back
flow upstream through the regulator and check valve. This
option eliminates the need for a fixed bleed downstream of
the regulator, thereby conserving plant air


Hence the smart bleed option just slowly de pressurises the downstream section if you loose instrument air upstream of the regulator. .i.e if your loss of upstream pressure occurs when the downstream system has reached 3 bar but isn't flowing without the smart bleed device it could easily stay there at 3 bar causing potential issues of air at pressure when people weren't expecting it, i.e. the regualtor would be acting like a check valve and locking in air pressure downstream of the regulator.

This way ythat trapped air will slowly release into the upstream section until the pressure drops below 3 bar when the regulator will open and air would back flow through the regulator.

Does that make sense?


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