One of the simplest but most important instruments that I encounter, which is used not for displaying or monitoring the process, but for safety, is the pressure safety valve.
Pressure safety valves (PSVs) do not show readings, trends, or alarms—but they protect your system when everything else fails. If a vessel over-pressurizes, the PSV is the last line of defense. That is why you must verify it works exactly at its set pressure.
I learned this early in my career while testing a PSV installed on a nitrogen tank. There was no indication it was working—until it suddenly “popped” at pressure. That moment defines whether your system stays safe or fails.
This guide walks you through what a PSV is, why calibration matters, and how to test and adjust it correctly.
This article is part of our Pressure Calibration Hub
👉Pressure calibration
What is a pressure safety valve (PSV)?
A pressure safety valve is a mechanical device that protects a system from overpressure. It opens rapidly (“pop action”) once the pressure reaches its set value, then releases fluid to prevent damage or explosion.
You typically see PSVs installed on:
- Pressure vessels
- Boilers
- Gas storage tanks
Unlike control devices, a PSV does not regulate pressure. It acts only during abnormal conditions.
I usually encounter PSV in gas industries manufacturing cryogenics like liquid oxygen, argon, nitrogen, and carbon dioxide. Installed in permanent tanks or mobile tanks (in trucks).
PSV is used specifically for safety concerns. It is simple in use, but one of the very important parts of safety. Only powered by the fluid pressure to do its safety job, it does not use electrical power. This makes it the last line of protection when every other device fails.
The main purpose is to open and release pressure when it reaches a set pressure and then return to close position when the pressure level is normalized.
PSV is comparable to a pressure switch, which is also triggered when it reaches a set pressure. It is in the ON and OFF states.
Read more about safety valves in this link: more about safety valves
Safety Valve vs Relief Valve (Clear Difference)
Do not treat these as the same device—they behave differently.
Pressure Safety Valve (PSV):
- Used mainly for gas systems
- Opens instantly (pop action)
- Discharges to the atmosphere
Pressure Relief Valve (PRV):
- Used for liquid systems
- Opens gradually or in proportion with the increasing pressure
- Returns fluid back to the system
This difference matters during testing. A PSV gives you a clear “event” (pop), while a PRV requires proportional observation.
PSV vs PRV
This is where many technicians make mistakes during testing.
| Feature | PSV | PRV |
|---|---|---|
| Medium | Gas | Liquid |
| Operation | Instant pop | Gradual opening |
| Behavior | Full release | Controlled flow |
| Test observation | Audible/visible pop | Smooth pressure change |
👉 If you expect a gradual response from a PSV, you will misread the result.
I have read a good article about its differences. Read more here:
Difference between a relief valve and a safety valve
Why You Must Calibrate a PSV
Every PSV has a set pressure stamped on its body. You cannot assume it still opens at that value.
You calibrate a PSV to confirm:
- It opens at the correct set pressure
- It reseals properly after discharge
- Internal parts (spring, disc, seat) still perform correctly
Real example:
A PSV installed on a dusty compressed air line failed to reseat after testing. Debris on the seat caused a slow leak—something you would never catch without testing.
Common failure causes:
Real failure modes:
- Spring fatigue → opens too late
- Seat contamination → leaks after test
- Corrosion → sticking or delayed lift
- Long periods without activation (sticking)- valve “freezes” ,a good time to exercise the valve.
👉 I’ve seen a PSV pass visual inspection but fail to reseat because of dust on the seat. That creates a continuous leak after activation.
Different Classifications of Pressure Safety Valves
Safety relief valves are classified as:
- Conventional type safety relief valve
- Balanced bellows type
- Pilot operated
- Power actuated
- Temperature and pressure actuated
You can read more about the different types of safety valves. Visit the link below.
PSV Calibration Setup (What Actually Works in the Field)
The calibration setup is the same as the pressure gauge, the only difference is that PSV has no display to be seen.
You don’t need a complex lab setup. You need a controlled pressure source and a reliable reference.
Option 1 – Manual Pump Setup
- Pressure test pump
- Reference pressure module or test gauge
- PSV connected through fittings
Option 2 – Gas Supply Setup
- Nitrogen or compressed air
- Pressure regulator + manifold
- Reference standard
👉 Key rule: your reference standard must be traceable and more accurate than the PSV tolerance.
PSV calibration is done by comparing the set pressure, which is the rapid releasing action (popping) of the PSV, to the displayed value of the reference standard. The pressure relief valve testing procedure to verify the accuracy of the output pressure (set pressure) is the same.
If you want to know other types of valve testing to determine its full performance like leak testing and flow characteristics, you may need to refer to ISO 4126-1.
Pressure Safety Valve Calibration or Testing Reference Standards Needed:
- A pressure module or a test gauge
- Fluke 754 as a display for the pressure module
- A pressure source like a compressed gas, nitrogen gas or a pneumatic pump
- Set of Fittings
Step-by-Step PSV Calibration Procedure
1. Identify Set Pressure
Read the stamped value (e.g., 25 bar).
This defines your target. Be aware of this set point to anticipate the opening of the valve while controlling the pressure source.
2. Prepare the Setup
- Check all fittings
- Ensure no leaks
- Stabilize pressure source
3. Increase Pressure Slowly
Raise pressure gradually.
At a certain point, the valve will pop open suddenly.
👉 This is your actual set pressure.
4. Record the Set Pressure
Capture the exact reading at the moment of lift.
Use a proper data sheet, record it in your Measurement Data Sheet (MDS).
5. Record Reseating Pressure
Reduce pressure slowly.
Record when the valve fully closes.
6. Repeat the Test (Minimum 3 Times)
Consistency matters.
If results vary:
- Valve may be unstable
- Internal wear likely exists
7. Label and Seal
After calibration:
- Apply calibration label
- Seal adjustment screw
👉 This prevents unauthorized changes.
Calibration Frequency (Real Strategy)
Start with:
👉 12 months
Then adjust based on performance:
- Stable → extend interval
- Frequent drift → shorten interval
👉 This aligns with ISO thinking: evidence-based intervals, not fixed guesswork
How to implement this? Visit my other post in this link >> calibration frequency
The 3 Critical Parameters You Must Observe
1. Set Pressure
Pressure where the valve pops or opens rapidly.
Typical tolerance: ±3% of set pressure
2. Overpressure
Pressure above setpoint where the valve fully opens.
Typical allowance: up to +10%
3. Reseating Pressure (Blowdown)
Pressure where the valve closes again. also known as reseating pressure.
Blowdown = Set Pressure – Reseating Pressure
Because of the rapid popping action during the discharge, it is hard to notice the difference of set pressure and overpressure. Without the tolerance specified, set pressure and overpressure readings are the same, mostly for results higher than the set pressure.
We are using a 10% tolerance or the tolerance specified by the manufacturer or as per the requirement of the user as the basis for a pass or failed verification.
How to Verify Acceptance of PSV Reading (Simple Calculation)
As per international standards ISO 4126-1, the tolerance limit during safety valve testing or calibration is +/- 3% of set pressure.
Example: set pressure is 25 Bar
The tolerance limit of the PSV is 3% of the set value, simply multiply the set value by 0.03.
> 25 X 0.03 = 0.75
The reading should be within
> 25+/-0.75 or (24.25 to 25.75)
If the reading is not acceptable or out of specs, you need to perform an adjustment. Read further below.
How to Adjust a Pressure Safety Valve (Practical Method)
Since a PSV is purely mechanical. It can be repaired or adjusted. The adjustment is simple; you just need the right tool.
PSV has a set pressure that is determined by the strength of the spring inside it. The more the spring it is compressed, the stronger or higher the pressure it can withstand or create.
In order to adjust the set pressure, we need to change the compression and/or the elongation of the spring by rotating the adjusting screw located just above the spring.
Watch below the step-by-step assembly of a pressure safety valve and learn more about its parts and how it is positioned inside the PSV body.
A PSV is a mechanical device. You adjust it by changing spring compression.
Steps:
- Remove the bonnet
- Loosen the lock nut
- Turn the adjusting screw:
- Clockwise → increases set pressure
- Counterclockwise → decreases set pressure
Then repeat the calibration.
⚠️ Do not over-rotate. You can damage the spring or shift the calibration too far.
Common Mistakes (That Cause Failures)
- Increasing pressure too fast → wrong reading
- Not repeating tests → unreliable result
- Ignoring reseating pressure → hidden leak risk
- Using uncalibrated reference → invalid result
- Skipping sealing → unauthorized adjustments
Final Takeaway
A pressure safety valve does not give second chances.
It activates once—at the exact moment your system reaches its limit.
If it opens too late, you risk damage.
If it doesn’t reseat, you lose containment.
Calibration is not optional.
👉 It is a direct verification of system safety.
Frequnetly Asked Questions (FAQ)
What is the tolerance of a pressure safety valve?
Most PSVs use ±3% of set pressure, but always verify with manufacturer or code requirements.
How do you know if a PSV is faulty?
Inconsistent set pressure, delayed opening, or failure to reseat indicate internal issues.
Can you calibrate a PSV without removing it?
Possible in some systems, but bench calibration gives more reliable results.
Why is reseating pressure important?
It ensures the valve fully seals after activation and prevents leaks.
What happens if a PSV opens late?
System pressure can exceed design limits, leading to equipment damage or failure.
Conclusion
Pressure safety valve or PSV is the last line of protection for all pressured vessel or tanks from overpressure using only the system pressure as the source of power. In this post, I have presented what a safety valve is, its difference with a relief valve, why do we need to calibrate a Pressure Safety Valve, PSV Calibration Setup and procedure, the 3 stages to observe during calibration,how to verify a safety valve, and how to adjust a safety valve inlcuding the main parts of a PSV.
Thank you for visiting my site.
Please comment and subscribe.
You can also connect with me in my Facebook page.
Best Regards,
Edwin
62 Responses
Sudarshan Chandrasekhar
Thanks for a great valuable piece of advice.
edsponce
Hi Sudarshan,
You are welcome. Thank you for reading my post.
Best Regards,
Edwin
mshalaby
Excellent
But there is a question
What are the factors affecting the calibration PSV
I mean, is there a difference between PSV calibration in liquids and gases in terms of set point or no difference?
edsponce
Dear Sir,
You are very welcome. I tried calibrating a PSV that uses gas as a fluid with water but with a minimal difference or negligible effect in terms of set points. But when you do this, make sure to blow or dry the PSV before returning. Some valves like the one used in liquid nitrogen can freeze the water inside which can cause problems.
So, as a good rule to follow, calibrate a PSV with a fluid that is the same with its actual usage. If a PSV is used in a gas fluid, calibrate also using a gas pressure source. If PSV is used for water as the fluid, use also water as the medium for calibration.
Hope this helps,
Edwin
Owais
Great information in one place.
Thanks
Regards,
Owais
edsponce
Hi Owais,
You are welcome. Thank you for reading my post.
I appreciate your comment.
Regards,
Edwin
Adeoye Adewale
I am going to calibrate my first ever PSV thanks to this article. Previous works with PRV over the years but never encounter a PSV. Good job.
edsponce
Hi Adeoye,
I am glad this post has helped you in some way. Thank you for the comment.
Best regards,
Edwin
mohammed abdullah
could you please explain what is the acceptable difference between the set pressure and the reseat pressure? and what is the governing standard for this acceptance?
edsponce
Hi Mr. Mohammed,
Reseating pressure or the closing pressure can be best understood as the blowdown pressure, it is the difference of the set pressure and reseating pressure.
The acceptable reseating pressure (blowdown pressure) is below:
1. For gas (maximum), it is 15 % or 0.3 bar, whichever is greater;
2. For liquid (maximum), it is 20 % or 0,6 bar, whichever is greater;
Blowdown = set pressure – reseating pressure
For example:
set pressure = 20 bar
Reseating pressure = 19.8 bar
Therefore : blowdown pressure = 20 – 19.8 = 0.2 bar
The governing standard for this is ISO 4126-1:2013
I hope this helps.
Thank you for reading my post.
Edwin
Elsakka
thanks for the valuable post
could you give us a brief about PSV preservation? and does the preservation overcome the need for calibration?
edsponce
Hi Mr. Elsakka,
Thank you for visiting my site.
My basic understanding of PSV Preservation means to increase its life span where the PSV is working as intended for a longer period of time. In my opinion, performing calibration is one way to preserve or increase the life span of the PSV.
During calibration, we preserve the PSV because we perform:
1. Preventive maintenance by cleaning the PSV and performing a leak test.
2. a simple test on its functionality like opening and closing the valve
3. performing calibration to determine the accuracy of its output
4. verification if it meets established specifications
5. adjustment if needed
Other preservation method includes shielding or having a good installation design of the PSV during installation in order to avoid:
1. too much vibration
2. exposure to contaminants like dust
3. exposure to temperature (too high or low temperature) that exceeds its specifications
As per the above importance of PSV calibration, preservation cannot overcome the need for calibration. What I can suggest is that after implementing the preservations above which include calibration, perform an assessment.
How to assess you might ask? Gather all the calibration certificates of the PSV, and record the history of its calibration results. Based on the collected results, where you observed that the PSV are within tolerance or passing the specifications, for example within a 3 year period, then you can increase the calibration interval for every 3 years.
Save your data, this will be your evidence if ever an auditor will question it.
If you need to know how to understand a calibration certificate, visit my post in this LINK.
Hope this helps.
Edwin
Cletus Ferrao
Dear Edwin,
Can you get in touch with me on my email. thanks
edsponce
Dear Cletus,
This is my email address: edwin@calibrationawareness.com.
Thanks and regards,
Edwin
John
The factory will send the PSV calibrated. Which standard I can find that I must calibrate the PSV in site In?. From the factory to the plant there are more than 200 Km
Tony
Hi guys,
Very interesting procedure.
But obviously you need to unmount the PSV to test it.
If there is only one PSV on a gas tank, how would you test it without releasing all the gas to atmosphere
I would have said to add a 3-way valve between the tank and the PSV to switch on the pneumatic pump whenever you want but then it’s not safe anymore if you forgot to put the 3-way back in position
Thanks for your advices
edsponce
Hi Tony,
Thank you for reading my post.
Yes, this procedure is performed where the PSV is removed or unmounted from its installation.
As per my experience, the majority of the PSV that I calibrated have an isolation valve. You just need to close the isolation valve then safely remove the PSV. For PSV without an isolation valve, we will wait for the customer to empty the tank before we perform the calibration.
Appreciate your comment.
Thanks and regards,
Edwin
Alex
Tony,
if your vessel only has 1 PSV you need to take the vessel off-line before you can isolate the PSV, otherwise your vessel will be unprotected!
As the vessel is off-line anyway removing the PSV physically should become your first option as it will be far simpler/faster/easier.
Rafael Michael
Thank you Sir for your valuable Input.
I have a certain question regarding the calibration/testing of the pressure safety valve;
If someone wants to work within this field (calibration of the valves) and needs to be internally certified for that. What the authorization/destination he has to get the certificate from !?
Thank you for your reply in advance.
edsponce
Hi Rafael,
You are welcome.
I do not know if it is available in your location but you can look for training provider under the sponsor of a national lab in your area, or a government established training center which specialized in Instrumentation and Control where Calibration is one of its core subjects.
Some private laboratories are also offering this kind of training under the field pressure calibration.
You can also try to inquire to some suppliers or manufacturers of the valves.
Try to look in your location.
I hope this helps,
Edwin
sam seth
How to use equipment in psv calibration
edsponce
Hi Sam,
What equipment are you referring to?
RAVICHANDRAN M
IS IT REQUIRED RECALIBRATION , WHEN PRV WAS POPPED AND RESEATED AND FOUND NO LEAK ?.
edsponce
No it is not required. That is what a PSV does. The need to recalibrate arises when the PSV will popped at more or less than the set value and/or tolerance.
kheddaoui
Hi sir
what about for the tolerance of the PSV if set pressure less than 5 bar.
edsponce
Hi Kheddaoui,
There is tolerance engraved usually in the body of the PSV, most small range PSV that I encounter has a tolerance of 5% of the set pressure.
If you follow a tolerance of 5%, then: 5×0.05 = 0.25 bar, 5-0.25 = 4.75, therefore, your lowest acceptable reading should not drop below 4.75 Bar.
I hope this helps.
Thank you for visiting my site.
Edwin
David
Hello, my question is with the rate of the pressure being applied. It has been my experience that the rate at which I apply the inlet pressure affects the cracking pressure of the PSV being tested. The slower the inlet pressure is applied it seems to produce a lower cracking point. Have you experienced this and if so what what would you suggest.
Thanks
edsponce
Hi David,
Thanks for visiting my site.
Yes, I have experienced it but as per my observation, it has no significant effect during calibration. The only effect that I observed is that popping sound is stronger compare to lower pressure flow. But as per accuracy, I did not yet experience any significant effect.
We are using nitrogen gas in a tank with a regulator wherein you can constantly control the flow of the fluid until it reaches the PSV set pressure.
I hope this helps.,
Edwin
taufiq abd rashid
Hi sir..what is actually the min required size for the nitrogen tank for calibration of the PSV? Is the tank size also depending on the size of the PSV/ set pressure? Can u give simple calculation to calculate the tank size?
If we are using water or oil for calibration of the PSV, are we also require the tank during calibration?
edsponce
Hi Taufiq,
I am not an expert regarding the calculation of tank sizes, I am only focused on the calibration of PSV. But as per my observation, the type of PSV is based on the size of the tank, the output pressure, the type of fluid (gas or liquid) it contains, and other more factors.
During calibration of PSV, it needs to be isolated and removed from the tank. We only use air or nitrogen gas and water for calibration.
Best regards,
Edwin
Javed Gulzar
Any person can share a Risk assessment for calibration of PSV,s
Manikantan
Hi, Nice work…
If my PRV Pops during operation due to over pressure and re-seat properly, then there is a requirement to bring down the PRV down and re-Calibrate the same.
Which is the standard says about this??
Regards
Manikantan
edsponce
Hi Manikatan
I am not aware of a standard that requires recalibration after a successful opening and closing during overpressure as you have mentioned. This is the normal operation of a PRV as far as I know unless it has a different design of operation in which the manufacturer manual is the best reference.
The reasons why we need to calibrate the PRV (or any other instruments) are:
1. When it has reached its calibration due date
2. After adjustment
3. Required by authorities
4. Out of specifications after verification
5. Suspected deviations on its performance during operation
6. Scheduled preventive maintenance
If there are no other acceptable reasons, then I do not see why you need to recalibrate the PSV.
If ever you had seen a related standard (or a manual), I appreciate it if you can comment back.
Thank you for visiting my site.
Best regards,
Edwin
Bayu Kuntoro
Hii…. Thanks for nicekind article and information. Very helpful for all of us.
My question is , How long interval for inspection and testing performance for High pressure and Low Pressure PSV on Boiler Unit ??( consist of Steam drum, HP drum etc).
Thanks
edsponce
Hi Bayu,
You are welcome.
There are no set standards regarding the interval of inspection or testing. The interval depends on the following:
1. The procedure of the user as per experience or company policy
2. The recommendation of the manufacturer
3. The reliability of the PSV that depends on its performance based on the available data or history. If you encounter an out of tolerance within the calibration period, you can decrease the next testing interval, or you can increase if it is always within tolerance every time you perform testing.
I hope this helps. Thanks for reading my post.
Best Regards,
Edwin
Juandre
HI
Do you receive any documentation after calibration?
edsponce
Hi Juandre,
What kind of documentation, can you clarify more your question?
Thanks and regards,
Edwin
Dime Marine
Thanks for sharing valuable information. Is the PSV test is carried out by connecting through XP2i interface ?
edsponce
Hi Dime,
You are welcome.
The PSV is calibrated using only a regular calibrator.
Thanks for reading my post.
Edwin
Khoi
How we identify the reseating pressure of PSV?Any criteria for this pressure??
edsponce
Hi Khoi,
Reseating pressure can be best identified by taking blowdown pressure, which is the difference between the set pressure and the reseating pressure.
As per ISO 4126-1, blowdown pressure should not exceed the manufacturer specifications and within the limits of 2% to 15% of set pressure for compressible fluids and 2.5% to 20% for incompressible fluids.
I hope this helps,
Edwin
Premkumar
Dear sir
Please guide me how much bubble accepted for gases , oil , water , steam of PSV & psv setting like PTFE or metal to metal setting .as per safety standards .
Thank you.
edsponce
Hi Premkumar,
Sorry to inform you but that is out of my knowledge. I hope you can find your answers.
Thanks for visiting my site.
Edwin
Alex
For PRVs refer to API 527, i don’t think they differentiate between PRV vs PSV.
Soft seats/PTFE are not permitted to leak when checked at 90% of set pressure.
Metal seat valves depend on several variables.
edsponce
Hi Alex, Thanks for providing the answer for Premkumar.
Have a safe day!
Edwin
Etim sunday
thanks sir im really bless by ur lessons God bless u sir pls I want to ask a question can we use prv in place of psv? or can we use psv in place of prv? thanks sir r
edsponce
Hi Etim,
You are welcome.
Their use depends on the fluid used and the requirements of the system. I did not try yet to use them in place of each other. But you should not interchange their usage, they are designed for each fluid used to maintain safety. Do not risk it.
Thanks for reading my posts.
Edwin
EDUARDO
hola tengo que realizar calibraciones internas de mis patrones de temperatura con otro patrón de referencia que tengo, pero tienen la misma resolución , entonces que criterio puedo utilizar para argumenta que mi patrón de referencia es valido para calibrar mis patrones de trabajo?
edsponce
Hi Eduardo,
The recommended accuracy ratio is 4:1, You can use the TEST UNCERTAINTY RATIO (TUR) formula.
TUR = tolerance limit of the UUT divided by expanded measurement uncertainty of the ref STD. If the answer is 4 and above then it is acceptable to use. This would be possible if you have a high tolerance limit.
I have example of TUR Calculation in this link >> https://calibrationawareness.com/differences-between-accuracy-error-tolerance-and-uncertainty-in-a-calibration-results.
I hope this helps,
Edwin
Moditha
Hi, I need to know the pressure regulator use in the range of 0-6000 psi, however the local calibration firm inform the maximum pneumatic pressure value is 1500 psi that they can calibrated. The usage the gas tanks are rated at 2000 psi which is higher that the maximum calibration value. There is no any alternate calibration firm to cover the 0-6000 psi. What can be done for such situation if the pressure gauge need to be calibrated for accuracy?
Yash Pal
Hi Edsponce,
First thanks for great post and it is very helpful and valuable.
Could you please, also tell the popping time if there is any specified.
edsponce
Hi Yash,
There is no time specified for a popping time that I am aware of, it is based on the pressure level on when the valve will pop or close.
Thanks for reading.
Edwin
Muhammad Waleed
Hi Edwin! Your website is of great use, well-done.
could you please tell why requirement of calibration arises on safety valves once it has been calibrated? or what are the factor that causes a calibrated safety valve to operate out of range after a certain time?
edsponce
Hi Muhammad,
Thank you.
Safety valves need to be recalibrated because of its design.
Safety valves during calibration are set to desired range. But the following are some factors that can affect its accuracy after a certain time:
1. Since a valve is purely mechanical, which opens and closes every time a pressure limit is reached, there is a wear and tear, especially the disc and spring.
2. Dust or other particles can build-up that can cause leakage.
3. The spring can be over-stressed once a strong pressure is encountered.
There are other reasons but these are what I usually observed.
4. A schedule re-calibration is also one way to perform preventive maintenance and avoid any stuck-up or leakage problems.
Best regards,
Edwin
Yash Shah
Hi sir,
I am Calibration Engineer.
Once a time , I took a Safety Valve for Calibration and Mount On Hydraulic Pressure Comparator.
when I Increase The Pressure , the safety Valve Pop up at set Pressure.
But, The Problem is , It was a Decrease the Pressure.
But Not stable Pressure After Seat Down(Pressure Slowly Decreasing).
So , What is the Problem In Safety Valve.
I Check at Least 15 Safety Valve but Same Issue repeated(My Master Instrument was Working Good).
So , Is This A same Issue To All?
I want To know.
edsponce
Hi Yash,
I am not sure if I understand your concern but a non-stable decreasing pressure happens if you use a non-continuous pressure source like a hand pump. It is not the issue for all as per my experience.
You may want to use a pneumatic pressure source like liquid nitrogen gas if the pressure range is ok.
But the important thing is you have a good performance for the pop-up pressure or set pressure and then it is closing at the expected closing or reseating pressure.
I hope this helps, thank you for visiting my site.
Edwin
Avdell
Thanks a lot for your enormous effort, it’s appreciated, I went and read all the comments and the replies, and checked all the links in the article and I can assure you you made learning much more straightforward,
I have one question tho, about reseating pressure, if the pressure keeps decreasing you said this could be due to the use of a manual pump of a non-continuous pressure source,
what’s a continuous and non-continuous pressure source?
edsponce
Hi Avdell,
Pressure in an open valve keeps on releasing until it decreases and reached the reseating pressure to finally close, therefore, using a non-continuous pressure source is difficult to detect reseating pressure.
I refer to the hand pumps as the non-continuous pressure source because you need to manually pump the pressure depending on the speed of the hand, while the continuous source is the gas, specifically the nitrogen gas in a tank that supplies a continuous pressure once its valve is open.
I hope this helps.
I appreciate your comments and thank you as well for visiting my site.
Edwin
Daniyal Ahmed
Can we calibrate a safety valve of PN40 pressure rating that originally comes with an 11 barg set pressure to a higher 28 barg set pressure?
edsponce
Yes, I believe so since the maximum pressure it can handle is 40 bar. But to be sure, check the manufacturer’s specifications.
Thanks for visiting my site,
Edwin
Leo
Hi,
This is very well explained, but I think there is one detail that needs to be analysed a little bit more in depth:
leakage.
You procedure simply states to check that there is no leakage, but whoever works evert day with pressure (or vacuum) knows that “no leakage” can is a very optimistic statement.
Depending on what the PRV is used for, the chances that the seal gets contaminated and starts leaking over one year are very high… but if the volume/pressure of the system that uses the PRV valve is big enough and the flow rate from the pump allows it to be maintained, the leakage from the PRV may be negligible.
The problem is then to decide what is an acceptable leakage and what is not. I’ve read somewhere (unfortunately I’ve lost the source) that part of the calibration is performed by connecting the outlet of the PRV to a tank filled with water and then count the number of bubbles per minute (there was also a tolerance for this number). In my opinion this can be also achieved with a simple flowmeter but, again, it is yet to be decided what is acceptable and what is not…
Any thought on this? Is there any official (ISO/UKAS/whatever) document on this subject?
Regards
edsponce
Hi Leo,
You are correct, with the proper connector and fittings, most leaks are negligible during calibration. But in cases where the value of leak is needed,it should be included and documented.
Luckily, I have read a document stating the requirement for a leak test. It uses air to determine the number of bubbles or water flow after stabilization for 1 min.
You may check out this document >> API STANDARD 527,Seat Tightness of Pressure Relief
Valves.
Thanks for time reading my post.
Edwin