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Spring-Operated Pressure Reilef Valves
4

Spring-Operated Pressure Reilef Valves

Spring-Operated Pressure Reilef Valves

(OP)
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.

RE: Spring-Operated Pressure Reilef Valves

Depending on the manufacturer/design of PRV, spring operated pressure relief valves will have a small amount of leakage prior to set pressure. This is referred to a "simmer". A good reference to get you on board with such definitions etc is API-RP-520 Part I.

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

RE: Spring-Operated Pressure Reilef Valves

(OP)
Hi The Obturator,

Thank you very much for your answer.

RE: Spring-Operated Pressure Reilef Valves

Vendors will supply you with their set point accuracy.

If you need closer than 8 to 10% then you need to look into pilot operated relief valves which are good for 2-3% below set point.

But I don't think you'll find it written anywhere specifically because it depends on the vendor and type of relief valve.

Any pulsations in the fluid will also affect the simmering action.

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

RE: Spring-Operated Pressure Reilef Valves

(OP)
@ LittleInch,

Thank you for your comment.

RE: Spring-Operated Pressure Reilef Valves

Hello,
normally spring operated valves with metal seats are recommended till 90 % of the SP
regards,

RE: Spring-Operated Pressure Reilef Valves

(OP)
Does the seat material has any influence?
Does safety valve with PTFE seat might be better?

RE: Spring-Operated Pressure Reilef Valves

REVISED for correction and clarity

Your initial question was of spring operated PRVS just before opening. The phenomenon advised is simmer.

Seat tightness is normally the measure at typically a pressure of 90% of set pressure, simulating the normal operating condition. Ie., a 10 % operating gap.

The standard API-527 specifies seat tightness levels.

For all metal to metal seated PRV''s there is an allowable leakage rate at 90% variant by size, pressure..

For soft seats there is no leakage allowance at 90%.

Some companies offer enhanced/better than API-527.

You can expect leakage for spring operated PRV's at 95% metal and O ring seta, regardless what the claims are.

Using soft seats - O Rings, the leakage is minimised. It is more difficult with PTFE. PTFE Seats(which are not O Rings) require some degree of heat to plasticise the seat. Testing at room temperature requires the PRV to be warmed up.

If you are looking for zero leakage at a higher factor then a pilot operated PRV is recommended. The higher the operating pressure the tighter the seats until September point. Pilot PRV''s use O Rings.

What is your specific application and leakage criteria?

Another way is to install a bursting disc upstream of the PRV.

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

RE: Spring-Operated Pressure Reilef Valves

Hello IdanPV
so the normally CROSBY says that soft seated valves are tight till 95-98 percent of SP no matter material is. i havent seen the material problem.
HOWEVER,
if u are still in doubt, please proceed AG 81 83 series for gas and thermal relief applications and 81P for the liquid applications. 81P is hard to calibrate on the field though. they are super tight OR POPRV
regards,

RE: Spring-Operated Pressure Reilef Valves

(OP)
The Obturator,
Thank you for your detailed response.
The application is power boiler which is designed and constructed in accordance with ASME Section I.
MAWP=5BAR @ 160°C - Steam.

I don't have any leakage criteria, I just want to minimize it.

gguliue,
Thank you very much sir.

RE: Spring-Operated Pressure Reilef Valves

Then we need to talk about about a completely different thing...

More information required to make a better judgement/recommendation;-

1. What Safety Valve are you using (incl. size and type)?
2. What is your normal operating and set pressure?
3. How has existing valve been tested?
4. What is current SV experiencing (leakage, blowdown etc.)?
5. Installation of SV, if other than vertical on top of vessel with inlet pressure loss no more than 3%

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

RE: Spring-Operated Pressure Reilef Valves

Sir,
if u are talking about ASME Section i that's completely another story
AG 80 series is not used for this purpose. as Obturator said, we need to know the several details
regards,

RE: Spring-Operated Pressure Reilef Valves

(OP)
1. Ø3/4" , Spring Operated Safety Valve, metal seat.
2. Normal operating pressure=4.5bar, set pressure (of the safety valve)=5bar.
3. I don't know.
4. The current SV experiencing "simmering".
5. The SV is installed in acc. with the requirements of ASME I

RE: Spring-Operated Pressure Reilef Valves

It is simply simmering because it is most probably not a boiler designed safety valve to ASME I. You appear to have a close operating to set pressure differential for this size of valve.

What is the make and model number?

Better still, do you have a data sheet you can share of the valves application?

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

RE: Spring-Operated Pressure Reilef Valves

(OP)
The Safety Valve is approve for power boilers and it is marked with "V" designator.
The SV discharge (Kg./Hr @ 3% overpressure) is 397 Kg./Hr. (90% of actual) as per the SV data sheet.

RE: Spring-Operated Pressure Reilef Valves

It;s difficult to help you more if you can't provide the name/model and/or SV Data Sheet.

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

RE: Spring-Operated Pressure Reilef Valves

(OP)
Hello all.
The SV is Apollo 19 Model:
19K-DC-L(or A)-40
Model 19 - Brass Trim/Teflon Seat - 1/2M x 3/4F - For VIII-1 Steam or Sec. I - 40psi

RE: Spring-Operated Pressure Reilef Valves

Well according to the manuals etc, the -40 in your model is 40 psi ( 2.6 bar). Now sure you can reset the valve, but how accurately was this done?

did you actually buy a valve pre set to 5 bar?? or did someone "adjust " it?

But operating these simple valves at 90% of set pressure is going to risk simmering, especially when the margins are so tight.
How accurately is your operating pressure being measured? Is it really 4.6 or 4.7?

Was the valve bench tested to 5.01 bar?



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

RE: Spring-Operated Pressure Reilef Valves

Another thing. Acc to the valve style, the seats are Teflon. Testing at ambient conditions will result in leakage. The valve is designed to work on steam and ideally should be tested on steam. Really need to know your comments on Little Inch's pressure comments above and also whether it is ASME I or VIII.

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

RE: Spring-Operated Pressure Reilef Valves

(OP)
Correction:
I made a mistake.
the valve is
Apollo: 19K-DC-A-72.5
It's a brass trim/teflon seat, Section I Steam Service at 5BARG (72.5 psi)

Sorry for that.

RE: Spring-Operated Pressure Reilef Valves

2
Please follow this link for a more comprehensive catalogue from Conbraco (before Apollo) https://www.steamspecialty.com/cd/engineering_spec...

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.

RE: Spring-Operated Pressure Reilef Valves

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.

RE: Spring-Operated Pressure Reilef Valves

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.

RE: Spring-Operated Pressure Reilef Valves

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.

RE: Spring-Operated Pressure Reilef Valves

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.

RE: Spring-Operated Pressure Reilef Valves

@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/

RE: Spring-Operated Pressure Reilef Valves

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.

RE: Spring-Operated Pressure Reilef Valves

@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.

RE: Spring-Operated Pressure Reilef Valves

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.

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