Spring-Operated Pressure Reilef Valves 4

[IdanPV]

Dear Experts,

I heard and read that for spring-operated pressure relief valves, small amount of leakage start to occur at 92-95% of the set pressure.
I have read about it, and found this statement in several articles but I would like to know if there is any formal reference (e.g. Code or Standard)

Thank you very much.

 

[The Obturator]

Please follow this link for a more comprehensive catalogue from Conbraco (before Apollo)

https://www.steamspecialty.com/cd/engineering_specs/engineering_specs/Conbraco/IOM/19-29 series.pdf

Model number all checks out except the earlier stated capacity of 397 Kg/hr is for a larger 'E' orifice (as per attached catalogued capacity tables)

Capacity for 19K-DC-A-72.5 should be 446 Kg/hr (ASME I) - this should be on nameplate (or 981 lbs/hr)

You stated earlier that operating pressure is 4.5 barg with set pressure 5 bar That provides an adequate operating gap.

You original problem is that the valve is simmering. Potential issues can be;-

(Suggest you first exercise the valve by manually opening it using the lever - this to blow the seats and to see that all moving parts actually move)

Operating pressure is higher than 4.5 barg
Set pressure has been lowered (potentially by mishandling the valve) below 5 narg
Teflon seat is damaged
Spindle is not straight due to lever being used without any inlet supporting pressure
Piping arrangement affecting valve
Ring settings wrong - these can be adjusted in situ

Apollo has next to non existent maintenance sheets none of which details ring setting. Typically ring settings follow this convention'-
Raising the upper ring will decrease blowdown
Raising the lower ring will decrease simmer
Lowering the upper ring will increase blowdown
Lowering the lower ring will increase simmer

Personally, I would be requesting Apollo to supply the procedure for ring settings, only if other observations have been considered.

Hope this all helps.



Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[LittleInch]

Well judging by the two most recent posts we should hear from Ivan in about the end of March....2021.

Is the PV still "simmering" 8 months after the OP? that's a lot of simmering....

But the obdurator - great post.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[goutam_freelance]

According to ASME-I, 'The Set pressure has to be at or below the max working pressure. If more than one safety valves are used, the max set pressure shall not exceed max working pressure by 3%.'. In addition, there usually is already a margin between normal working pressure and max working pressure.
But at low pressure boilers there is little cost difference if you keep max working pressure little above normal working pressure (say 5-7%). But you need to design the whole system for this. So you get 5-7% margin in pressure before simmering starts.

For smaller boilers it is very unusual to have ERVs(electromatic relief valves) and the simmering problem is usually taken care of by this way.

 

[The Obturator]

goutam freelance You're confusing this long winded issue even more.
3% is the OVERPRESSURE for ASME I above the SET PRESSURE.
Operating pressure in this post is already established and commented upon.
You can't just 'jack up' a set pressure of a safety valve without first consulting the suitability of the installed springs range of pressure. Increasing set pressure also changes sizing and capacity of the safety valve.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[LittleInch]

I agree. Goutam, I think that is really bad and incorrect advice.

You may want to edit your response.

Also "ASME I" ?? which section? If you're going to quote a code give it a number and a section reference. Otherwise it's meaningless.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[goutam_freelance]

@LittleInch,@Obturator,
There was an error in my reading of code and I have corrected the same. But my main point was to have set pressure and max working pressure above the normal working pressure which is normally done to avoid simmering.

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[The Obturator]

Goutam freelance Your corrected post is still incorrect. For multiple safety valve installation, the overpressure can be higher for the additional valves acc. to ASME I.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[goutam_freelance]

@Obturator, pl see the image.

First and second sentences are clear.
Regarding third sentence, suppose your boiler max working pressure is 5 bar and you set the lowest set pressure as 4.6 bar (it is permitted as first set pressure is at or below the max working pressure) then you can not set the max set pressure above 4.6+0.1x4.6=5.05 bar (you can not use 5.15 bar using second sentence). But here this may not be relevant as we have only 1 safety valve.
The fourth sentence is also not relevant as this is not a high temperature boiler.
Hope this clarifies the matter and mistake was only once.

 

[The Obturator]

That's better. My point was in case of more than one safety valve, the supplementary safety valves can have a set pressure of 3% higher, meaning
1st valve set at MAWP.
2nd (or last valve) set at MAWP x 1.03
This was not made clear for other readers from your pre edited post Although your extract is correct, it is from the an earlier edition of ASME I (Currently 2019). I'll leave the post now as comments are now diverging from the original question.


Per ISO-4126, only the term Safety Valve is used regardless of application or design.