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# How To Find Degree Of Superheat For Steam

steam superheat psv control valve failure case degree of superheat control valve

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### #1 Rahul Maurya

Rahul Maurya

Brand New Member

• Members
• 8 posts

Posted 29 November 2018 - 06:01 AM

Hello All,

I have one system which I need to understand regarding PSV calculation.

First I wanted to know that how we can find out degree of super-heat in difference of 2 temperatures.

For example: If I want to calculate the flow across the control valve for CV Failure case based on control valve Cv value, I need to give the input of degree of super-heat which is based on temperature/pressure value across the control valve.

So in that case, how can I enter the degree of super-heat value for the same.

Second:

In case of I am calculating CV failure case, which flow rate I have to take for the orifice size calculation?? Is it of max fluid flow rate value (i.e. steam or any liquid) or calculated Cv value it should be arrived??

Thanks & Regards

Rahulkumar Maurya

### #2 Ahsan67

Ahsan67

Veteran Member

• Members
• 37 posts

Posted 30 November 2018 - 06:47 AM

1- Degree of super-heat can be calculated by subtracting saturation temperature(at operation temperature of super-heated steam) from super-heated steam temperature. The saturation temperature can be obtained from steam table.

2- CV value should be used for Control Valve failure case as it would give more than the max flow for which the valve is sized. The reason behind is that the control valve is generally sized  to operate and give min and max flow between 20% - 80 % respectively of its travel, thus for control valve failure the valve will be considered to operate at 100%.