8 replies to this topic

[Ali4269278331]

dear guys

we have a fire fighting system that PID attached. the designer use of PCV & PSV on outlet line. in practice each of them are relief valve. which is different between PRV, PSV and Relief? do you think we can use of them instead of together?

so, why use of two valve on outlet line? for operation or safety(based on HAZOP)

 

thanks

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[fallah]

 

we have a fire fighting system that PID attached. the designer use of PCV & PSV on outlet line. in practice each of them are relief valve. which is different between PRV, PSV and Relief? do you think we can use of them instead of together?

so, why use of two valve on outlet line? for operation or safety(based on HAZOP)

 

 

Hi,

 

Each valve plays its own different role!

 

The PCV play the role of minimum flow control valve but triggered by a set pressure. When the pressure at the pump's header is increased beyond a prespecified set point, the PCV will be opened to prevent extra pressure and release the flow toward the pumps suction header.

 

Putting the PSV there, is another story and its main role is relieving the excess pressure due to probable overspeed of the diesel driven pump.

[shvet1]

PCV is a control system

PSV is a safety system

 

If there will be not a safety devide (PSV) then what devise will protect pump discharge header from overpressure caused by a failure of control system (PCV)?

 

You suggest to delete the "final protection layer", correct? Are control system reliability and failure rate so high&low accordingly that HAZOP team can take responsibility the risk rate is negligible?

Edited by shvet1, 29 June 2024 - 01:52 AM.

[breizh]

Hi,

Like others said pay attention to the definition and acknowledge the role of each piece of equipment.

Safety valve is not a control valve likewise a control valve is not a safety valve.

Pressure Relief Valve (wermac.org)

 

Breizh

[Ali4269278331]

 

 

we have a fire fighting system that PID attached. the designer use of PCV & PSV on outlet line. in practice each of them are relief valve. which is different between PRV, PSV and Relief? do you think we can use of them instead of together?

so, why use of two valve on outlet line? for operation or safety(based on HAZOP)

 

 

Hi,

 

Each valve plays its own different role!

 

The PCV play the role of minimum flow control valve but triggered by a set pressure. When the pressure at the pump's header is increased beyond a prespecified set point, the PCV will be opened to prevent extra pressure and release the flow toward the pumps suction header.

 

Putting the PSV there, is another story and its main role is relieving the excess pressure due to probable overspeed of the diesel driven pump.

 

thanks dear Fallah, but my client going to change with New PSV(spring type). i donot why?

[Ali4269278331]

Hi,

Like others said pay attention to the definition and acknowledge the role of each piece of equipment.

Safety valve is not a control valve likewise a control valve is not a safety valve.

Pressure Relief Valve (wermac.org)

 

Breizh

perfect, dear Breizh

[fallah]

 

 

Hi,

 

Each valve plays its own different role!

 

The PCV play the role of minimum flow control valve but triggered by a set pressure. When the pressure at the pump's header is increased beyond a prespecified set point, the PCV will be opened to prevent extra pressure and release the flow toward the pumps suction header.

 

Putting the PSV there, is another story and its main role is relieving the excess pressure due to probable overspeed of the diesel driven pump.

 

thanks dear Fallah, but my client going to change with New PSV(spring type). i donot why?

 

 

Client is going to change which valve with new PSV?

[Ali4269278331]

 

 

 

Hi,

 

Each valve plays its own different role!

 

The PCV play the role of minimum flow control valve but triggered by a set pressure. When the pressure at the pump's header is increased beyond a prespecified set point, the PCV will be opened to prevent extra pressure and release the flow toward the pumps suction header.

 

Putting the PSV there, is another story and its main role is relieving the excess pressure due to probable overspeed of the diesel driven pump.

 

thanks dear Fallah, but my client going to change with New PSV(spring type). i donot why?

 

 

Client is going to change which valve with new PSV?

 

yes, but i donot agree.

[snickster]

The PCV is a backpressure regulator which functions to keep the entire system at a constant pressure (9 bar) regardless of flow.  When the pressure decreases in system to the PSL set point due to opening small drain valve or some leakage, the jockey pump starts to get the system back to 9 bar and then shuts down.  I am not sure why the back pressure regulator is required.  It may be that there is a demand case for firewater that will require all 3 firewater pumps operating but the overall flow may be such that the pressure would get above 9 bar or even 12 bar, but it may be necessary to run all three pumps at one time to get the flow required, or during testing, but header pressure would then be too high.  Thus the PCV was installed to limit the normal operating pressure well below the point where the relief valve relieves but allows the maximum required pressure need by the end users.  Sometimes too high a pressure at say a fire hose that someone has to manually hold would create too high flow/velocity an hence too high of a jet reaction force for anyone to be able to hold and control, or there may be other reasons where you don't want to have too high pressure at the end users.  In fact it looks like all of the end users are fire hydrant/fire hoses so I think the ability for someone to hold the hose with jet reaction force limits the 9 bar pressure.  I would not remove it until I find out what is its function/functions.  You may find a description of its function in the Process Design Basis or site Operating Procedure, or other project documentation.

 

The PSV is the safety relief valve that operates to limit pressure to maximum piping design pressure (12 bar). Typically this is sized for engine overspeed per the appicable NFPA Standard for firewater pumps/systems.  This valve must be installed for safety to limit maximum pressue to piping design maximum and cannot be removed.  Firewater valves and other inline components are typically designed for a maximum of 175 psig cold working pressure which limits the maximum allowable pressure in the piping, and this corresponds to approximately 12 bar.

Edited by snickster, 14 July 2024 - 10:37 PM.