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Max Differential Pressure Across An On/off Valve Prior To Open It


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#1 Roark

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Posted 14 August 2018 - 07:40 PM

Gents,

  

It seems to be common practice amongst my colleagues that a full bore, ball on/off valve shall not be open before ensuring that the differential pressure between the upstream and downstream side is lower than 15-30 psi.  Some colleagues argue that this holds for liquid, but some of them consider this should be followed even for gas at, say, 300 psig (i.e. valve cannot be open until the downstream side is pressurised to 270-285 psig).

  

What is the rationale behind this?  Is it only aimed to prevent oversizing the actuator?  Does opening the valve across a large differential pressure creates high vibration or any other operational upset?

  

Any feedback on this would be deeply appreciated.

  

Regards.



#2 Technical Bard

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Posted 14 August 2018 - 08:17 PM

If you can turn the valve, you can open it against any differential pressure.  Depending on the valve design (soft seats), there is some risk of damage.  The valve manufacturer data book will describe such limits.  Often however, attempts are made to avoid opening large valves of all types against high differential pressures to avoid oversizing actuators (especially motor type).



#3 Bodhisatya

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Posted 16 August 2018 - 12:17 AM

Hello

 

In Oxygen service line (be it Liquid or Gas), it is an accepted practise of not opening the valve if dP across the valve is more than 45 psi(g). The system is interlocked with this provision to override operator error.

 

As Oxygen rich environment is prone to Fire incidents, this practice ensures that the probability of Adiabatic compression is negated.

 

With On-Off valves mostly being Line size valves, Actuator oversizing factor do hold merit to open those valves at low dP.

 

Bodhisatya






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