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Terms in the software

Allgemeine Diskussion » Terms in the software Posted: 21. Dezember 2021 - 10:18

Hi there!

I am new to Conval. I want to design PSV/PRV with it. Could anyone help me understanding the below terms and what are the right ranges of values for them within Pressure Relief Valve design module.

1- What is flow reserve for and what should its value be?

2- In which range should be the maximum set pressure?

3- how could I choose the right valve from the "select valve" section when no match with my required DN?

 

I would be grateful if someone could help me understanding these contents.

Kommentare

Andreas Vogt

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Terms in the software: PSV/PRV sizing

Posted: 21.12.2021 - 15:42

Dear Mrs. Badri,

Thank you for your enquiry. The questions you are asking have less to do with CONVAL® itself than with the general procedure for designing PSV/PRV.

  1. What is flow reserve for and what should its value be?

    General information about the fields can always be found in the online help in CONVAL® itself.

    In other words, the "flow reserve" is the percentage by which the flow possible with the selected valve exceeds the required flow.

It should never be less than 0%, but how high it may be depends on its application, but usually not more than 50%.

If it is greater than 50%, CONVAL® will advise you to look for a smaller valve.

 

The "flow reserve" can possibly be limited with a "lift stopper".

 

  1. The set pressure depends only on your application. An adjustable overpressure is applied to it to define the relieving pressure, depending on the application and sizing standard used. (typically 10%, but e.g. 21% for a fire case scenario). Please refer to the sizing standard you are using (AD2000, ISO4126, API520…)

  2. The valve selection via the database is filtered by default showing you suitable valves.
    You can switch off the filter, allowing to see / select any valve in the database.

But when selecting a no suitable valve, CONVAL® indicates the not matching parameters resulting out of your selection, e.g.:

 

Basically, however, your process requirements define the parameters for the calculation. CONVAL® is the tool that determines solutions with the given condition according to the rules of the applied standard.

Kind regards

CONVAL® Support Team

 

Semiramis Badri

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Orifice

Posted: 31.12.2021 - 13:40

Thank you Mr Vogt.

There is another question for me for an orifice design section; when I receive the warning message "The theoretical mass flow is used for calculation , the calculated throttle for the orifice may not be sufficient" what shall I do in this case to tackle this problem and not increasing dramatically my orifice diameter?

Dirk Hackländer

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Orifice

Posted: 07.01.2022 - 16:56

Dear Mrs. Badri,

 

The information "The theoretical mass flow is used for calculation, the calculated throttle for the orifice may not be sufficient" is displayed if you use the option safety-related applications and calculate the throttle orifice d for a given flow rate.

As an alternative to the standard calculation method, two further options methods are available in CONVAL.

  • For safety related applications, e.g. orifice plates which are limiting the upstream mass flow of safety valves, the modifiers xT respectively FL2 are set to one, in order to calculate the theoretical maximum flow at critical conditions.

Use this option if you want to ensure that the calculated flow is never exceeded.

  • The conditions for the critical flow in compressible media through long orifices can be calculated according to Richard W. Miller "Flow Measurement Engineering Handbook", 3rd edition, 1996. For common isentropic exponents, the result is a critical pressure difference Δpc of approx. p1 / 2. This equation applies under the assumption of a constant isentropic flow in nozzles and refers to the differential pressure Δp directly at the flow element and not to the permanent pressure loss Δϖ. For long orifice plates, a flow coefficient C = 0.84 is used. The calculated flow rate is usually smaller than the value calculated according to IEC 60534-2-1.

Use this option if you want to ensure that the calculated throttle orifice always allows the required flow rate.

 

Kind regards

CONVAL® Support Team

 

 

Semiramis Badri

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Calculation of the superimposed back pressure

Posted: 21.01.2022 - 11:13

Dear Dirk,

Many thanks for your comprehensive explanation. Today I noticed my appreciation message was not sent to you! strange!

There is another question for me regarding designing the pressure relief valves. In the "Medium" section of the software, there is "Pressure" part and there are Pb and Pae, but how could one calculate the superimposed back pressure? Could you help me out please.

Thank you in advance!

Best regards,

Semiramis

Benedict Nowak

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Calculation of the superimposed back pressure

Posted: 21.01.2022 - 14:44

Hallo Semiramis,

 

We gladly accept your thanks.

 

The superimposed backpressure (pu) is defined by the API 520  as the static pressure that exists at the outlet of a pressure relief device at the time the device is required to operate. It is the result of pressure in the discharge system coming from other sources and may be constant or variable.

 

The superimposed back pressure is a value which must be entered manually by the user in CONVAL. (The default setting is 0 bar(g) / blow off into atmosphere). The "calculation" / determination of the superimposed backpressure must therefore be done by the user based on design / process data of the blow-off line. 

 

Kind regards,

Benedict Nowak

Semiramis Badri

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Thank you Benedict!

Posted: 31.01.2022 - 16:29