A Relief Valve for Every Purpose

How Spring-Loaded Pressure Relief Valves can Save the Day

Pressure relief valves have been around since almost three and a half centuries ago. The first one was designed and crafted by French inventor Denis Papin. His solution to over-pressure within a pressurized cooking pot was to use weights that would lift up when the pressure within the pot got too high, allowing the excess pressure to escape.

Today pressure relief valves go far beyond the kitchen. Anywhere you find a pressurized system or vessel, you will find a pressure relief valve – in chemical and petrochemical plants, petroleum refineries, on ships and in spacecraft. They play a vital role in preventing system failure, explosions, and catastrophic loss, and in protecting life, assets, and the environment.

Spring-Loaded Pressure Relief Valves

When an overpressure situation arises, there has to be a means in place to relieve the excess pressure. And it must be fail-proof. The pressure relief valve needs to work when other systems do not and when there is no external power source.

And if relief of pressure becomes necessary, it is needed right away. Relying on someone to manually release the pressure could waste valuable time. Not to mention, the valve could be located in a hazardous environment making it difficult or impossible to reach.

What’s the solution? A self-actuating spring-loaded pressure relief valve that opens at a set pressure and closes once the pressure returns to normal.

What Makes a Spring-Loaded Pressure Relief Valve so Special?

The Spring

In a spring-loaded pressure relief valve, the force of the spring is what holds the valve closed and also what allows it to open.

An adjustment screw is used to tune the spring so that its force equals a specific limit over the maximum allowable working pressure (MAWP). It will remain closed until the internal pressure exceeds the MAWP and reaches that preset limit.

Once the pressure returns to a normal level, the opposing pressure of the spring automatically closes the valve.

The pressure at which the valve resets is aptly called the closing pressure. Due to the valve’s design, the closing pressure is lower than the set pressure.

The blowdown pressure is the difference between the two expressed as a percentage of the set pressure. It’s a measure of how far the pressure needs to drop in order to reseat itself.

One of the advantages of using a spring-loaded valve is that in most cases the spring can be adjusted to accurately control the blowdown pressure setting.

The Seat

A leaking valve seat on a pressure relief valve can cause loss of fluid and can result in damage to the seating surfaces. If it gets bad enough, it can open the valve prematurely.

The right seal and a regular preventative maintenance program will go a long way to keep leaks at bay.

Depending on temperature, the media, and how tight of a shut-off is needed, spring-loaded pressure relief valves can be either metal-seated or soft-seated. Soft seats will provide the tightest closure but have lower temperature limits and less resistance to corrosion than metal seats.


Pressure relief valves can be a source of noise and vibration. The media flow rate, pipeline design, and the valve’s design and construction can all contribute to mechanical vibration.

A carefully designed and precision machined valve constructed of the appropriate materials will go a long way in reducing vibration. CPV Pressure Relief Valves are all vibration approved per MIL-STD-167.



Although we’ve just touched on one type of valve here, there’s a relief valve for every purpose. For more about the different types check out this article.

CPV’s relief valves can be found in multiple industries and in many types of pressurized systems including high-pressure hydraulics, high-pressure pumping and piping systems, and both high- and low-pressure tanks.

Contact us for more information about how we can help with your high- or low-pressure relief valve needs.