How to Select a High-Pressure Relief Valve (8 Factors to Consider)

11 Aug.,2025

 

How to Select a High-Pressure Relief Valve (8 Factors to Consider)

Top Considerations When Selecting a High-Pressure Relief Valve

High-pressure relief valves fulfill a critical safety function in multiple applications, ranging from petrochemical to power, marine and aerospace industries.  Regardless of the application, certain primary features can help guide engineers when selecting a durable high-pressure relief valve that will help avoid catastrophic failure to protect your workers’ health and safety while also preserving capital equipment.

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What’s the Primary Purpose of a Relief Valve?

A relief valve functions as an operational safety feature, to help control and regulate the flow of high-pressure fluids and gases. It is designed to vent off extra pressure, whether from gas or a liquid. The design triggers the valve to open once a system reaches a predetermined set pressure.

This protects systems from experiencing pressures that exceed their design limits. Once a system reaches that predetermined level or valve set pressure, the relief valve opens, and a portion of the liquid or gas is removed from the system by diverting it through an outlet in the valve.

The relief valve helps maintain safe pressure levels to prevent potential damage or catastrophic failure. Once system pressure drops to its predetermined normal level, the relief valve closes or “reseats” until it is needed again. While a relief valve functions as a safety feature, it differs from a safety valve which only triggers in an emergency.

A safety valve opens instantly to its full venting capacity while a high-pressure relief valve opens gradually when system pressure reaches the preset level.

A catastrophic failure could mean loss of capital equipment such as pipes if the pressure doesn’t diminish. Pressure build up, if unrelieved, can lead to more serious consequences such as an explosion, potentially harming personnel and causing more widespread damage to equipment and surroundings.

High-pressure relief valves are found in several different industries including marine applications on naval and commercial vessels, aerospace, industrial gas, the petrochemical industry, power plants and many industrial applications as well.

Factors for Specifying a Relief Valve

There are several factors to take into consideration when specifying a relief valve. These can include:

1. Set pressure limit

The set pressure limit is the threshold that triggers the high-pressure relief valve action. For example, if the normal system pressure is PSI the engineer might determine the set pressure limit is PSI. Once pressure reaches that threshold it triggers the relief valve which then vents the excess liquid or gas. Consistent triggering of the relief valve often indicates a problem with the system.

2. Valve capacity

This relates to the amount of flow the valve is able to relieve.

Connection size and type—The connection of the valve or valve size needs to correspond to the size of the discharge piping. Operators must also determine the connection type for the inlet and outlet ends, typically threaded or flanged.

3. Shock and vibration

Material selection, design and testing will reveal the ability of the valve to withstand shock and vibration without triggering its action. Naval vessels require parts such as relief valves pass specifications for shock and vibration.

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4. Environment

This particularly plays a role in material selection for the valve construction when it will come into contact with a corrosive or abrasive substance. An example of this would be a marine relief valve that can or will regularly encounter salt water. All CPV Mfg. high-pressure relief valve specified for marine purposes are manufactured of bronze.

5. Temperature

This factor impacts O-ring material selection. Depending on the temperature range, CPV can specify a specialty elastomer or material for the O-ring.

6. Orifice size

This relates to the relief capacity of the valve. When the orifice size is smaller, the relief valve can rate to a higher pressure but relieve less capacity. The larger the orifice, the lower the pressure but the higher the relief capacity of the valve.

7. Positive Reseating

All relief valves manufactured by CPV have a positive reseating, which means after it blows at pressure, it reseats itself or reseals once the pressure drops into the normal range. This reseating capability allows for continuous operations. Look for a soft seating design which acts as a bubble tight seal, versus a metal-to-metal interface, which can be prone to leaking.

8. Spring adjustment

A sensitive spring, such as those incorporated into a CPV high-pressure relief valve, allows the operator to adjust the release for a very narrow PSI range. For example, the spring itself might be rated for 1,000 to 2,000 PSI, but the sensitivity enables the operator to set it at a specific target, such as 1,015 PSI, for example.

Add to this testing capabilities, and the cooperative efforts of the engineering design team and the valve manufacturer can produce a valve with the most accurate control of the blowdown pressure setting.

Why Choose CPV Manufacturing? 

CPV manufactures relief valves in two different series: the 150 series and our flagship O-SEAL® line. The 150 series is a line of soft-seated female threaded relief valves with set pressures that range from the low end of 5 PSI up to 300 PSI.

The O-SEAL® line of soft-seated valves and separable fittings allow for positive control of high-pressure liquids and gases.  This line offers leak proof performance from vacuum up to PSI (414 bar).

CPV has been supplying high-pressure relief valves to the U.S. Navy for mission critical applications since the s. Each individual valve built by CPV Manufacturing undergoes testing, not random or batch testing, but each valve.

Valves must meet a safety factor for the pressure rating of four to one.  If a valve is rated for 6,000 PSI for example, the valve strength is up to or in excess of 24,000 PSI. In addition, all valves meet the ASME Boiler and Pressure Vessel Code. Our valves are over-engineered to exceed the pressure strength rating, for the utmost in reliability.

Trust CPV Manufacturing for durable, reliable, high-pressure valves that meet the stringent requirements of the U.S. Navy, found in service in submarines, aircraft carries and other vessels throughout the fleet.  We can work within your specifications or consult for customized projects and applications.

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Pressure safety valve best practise - Eng-Tips

Hello!
I have a question about calculating safety valve and inlet/oulet pipe.
I know there are a lot of informmation in this forum about it but not exactly what I need. The thing is I'm working in russia with russian standart (GOST). In present time i'm worjing in unusual project and have some difficulties with using GOST in this case. So I'm going to describe shortly problem:

Project - natural gas preparation station.
Preparation - drying, reduction seprartion by consumer.
To reduce pressure I'm designed simple scheme: valve-reduction valve-valve-safety valve.
Trouble is that diameter of run pipe DN200 and using our "safety valve standart" I need design inlet-outlet pipe and safety equivalent by run pipe.

Now I have oulet pipe DN300 (which our opinion is too big) because standart safety valve already have manufacturer standart Inlet/oulet connection (in my case DN150/DN300).
So wee see that it's excessive demands (for equivalent) and want to find a way to reduce size of it. Why we think like that? Because all station have alert and special safety systam with manual and automatic valve which turn off/on if something goes wrong and we don't need a safety with run pipe equivalent flow rate.

Question is: how it designed, I'm about safety valve and pipe calculating, in USA or Europe natural gas preapration station?

Here P&ID.
I am not sure what you are asking.

Your PID shows 2 control valves RV1 & RV2 for downstream pressure reduction .
There are 2 automatic block valves upstream BV1 & 2, and manual block valves BV12 BV13 downstream.
It looks like there is a normally closed bypass , probably for maintenance purposes.
The downstream piping is protected from accidental overpressure by safety relief valves PSV1 & PSV2.
It looks like BV14 is a selection valve allowing use of PSV1 OR PSV2. So that is 100% redundancy.
Lines 7C1 & 7C3 are vent pipes to a safe location.
I do not know if both control valves RV1 and RV2 operate at the same time, or if only one operates alone, while the other is redundant spare.

Please correct my description, if I have something wrong.

The arrangement shown in the PID appears to be very typical of what is done in the west.
Having two relief valves, but using only one at any time is a little unusual. We would often have only one, but the number you install is a question of maintenance and repair convenience. It looks like you can repair one while continuing operation of the station. Very good.
Otherwise the arrangement is very typical. It is the recommended best practice in the west and safe to operate, because downstream piping is always fully protected from accidental overpressure. There are many different regulations in the west, so I am not sure, but I believe that the arrangement shown on your PID is required by local regulations in Germany and maybe other states as well.

I THINK you are asking about how to determine the size of the relief valves.
If only one relief valve operates at any given time, each valve must be designed for the greatest flow and highest pressure possible in pipe C6.7.
Due to the low pressure of the gas at the PSV outlet and usually a long distance to discharge at a flare, and the need to have low pressure loss, a large discharge pipe is usually required.

A typical calculation method for PSV sizing can be found here,

Please let me know if I have answered your questions.
-44 said: Your PID shows 2 control valves RV1 & RV2 for downstream pressure reduction .
There are 2 automatic block valves upstream BV1 & 2, and manual block valves BV12 BV13 downstream.
It looks like there is a normally closed bypass , probably for maintenance purposes.
The downstream piping is protected from accidental overpressure by safety relief valves PSV1 & PSV2.
It looks like BV14 is a selection valve allowing use of PSV1 OR PSV2. So that is 100% redundancy.
Lines 7C1 & 7C3 are vent pipes to a safe location.
I do not know if both control valves RV1 and RV2 operate at the same time, or if only one operates alone, while the other is redundant spare.
Right, sir. RV1 and RV2 operates in different time (redundant spare).

-44 said: I THINK you are asking about how to determine the size of the relief valves.
Right. Yeah, historically, in my department parametrs of safety valve and inlet outlet pipe choosing by manufacturer standart and run pipe diametr and always everything was allright, but now we have a problem with big safety valve and big outlet pipe. Most important that we haven't enough space because we made modular station, like 20ft container (Intermodal container) and two pipe DN300 above head when full celling high is 2.4 metr is awful.

Thank you for link, sir. I will look here. I have already found programm like that by Leser (valvestar).

I add station view with flare (non-fire) for better understanding. Red circles are flare.

[ OK. You have short stack vents, no flare.

Actually DN 300 is relatively small diameter for many of these kinds of gas PSV station outlets. It would be nice to eliminate PSVs, but then the downstream piping would not be positively protected from overpressure. I am not a big fan of "HIPSS", high integrity protection safety systems that sometimes are used to eliminate PSV and vents, because it increases the maintenance and testing work while safety and reliability is decreased. HIPSS are not prohibited by ASME B31.8 or EU gas codes, but they may be prohibited by the various national regulations, or company specifications. You must know the state and local regulations and also be sure that they are allowed under company policy. PSVs are much safer. A large explosion and many building fires were started near BostonMA, USA a few years ago, with over $1E9 in damages, because PSVs were not installed at a pressure regulation station.