Pilot Operated vs Spring Operated Safety Relief Valves
On a boiler, tank, or another pressure-containing vessel, safety relief valves respond in an emergency event to prevent unsafe conditions. The consequences of overpressure can be dire and damaging, putting your people and equipment in harm’s way. As the last lines of defense for these vessels, finding a safety relief valve that works best for your equipment and company is key.
Here, we take a closer look at the differences and inherent design and operation benefits that come from these two types of pressure relief valves.
Pilot Operated Safety Relief Valves
Pilot operated safety relief valves use an auxiliary pressure pilot to sense the system’s pressure and either pressurize or vent the dome chamber to open or close the valve.
In normal operating conditions, at below set point, pressure is equal on both sides of the piston and holds the valve closed. If the set pressure is reached, the pilot opens to release pressure from the chamber, move the piston upward, and relieve the protected equipment of excess gas, steam, or fluid.
If the process pressure reduces to below a predetermined level, the pilot will close, the cavity above the piston will pressurize, and the valve will shut.
Benefits of Pilot Operated Pressure Relief Valves
Pilot operated safety relief valves work best for applications with a high amount of backpressure or fluctuating backpressure.
- Opting for modulating pilots allows the piston to lift only as high as is needed, venting off just enough pressure to prevent cycling (a common side effect of backpressure that can cause undue wear to valve parts).
Pilot operation is also recommended for equipment where low accumulation rates are required or when the set pressure level needs to be close to the operating pressure level.
- As pressure increases, the pilot maintains its seal tightly, allowing reliable operation closer to the set point for pack line, without product leakage.
- Pilot operated valves can work at an operating pressure of up to 98% of set pressure.
Although their initial investment price tends to be higher, pilot operated pressure relief valves are much smaller than their spring-loaded counterparts, making them easier to install, maintain, and repair.
Spring Operated Safety Relief Valves
Spring driven pressure relief systems use the force of a physical spring to control the valve’s action. The spring load is set to equal the force of the inlet fluid when the system is at set pressure. So, at below-set pressure, the disc and spring stay in position, and the valve is shut.
When pressure rises above the set limit, the spring force is overcome, causing the disc to be pushed upward to open the valve and excess pressure to be released. Once pressure returns back below the set level, the valve returns to its closed position.
Benefits of Spring Operated Pressure Relief Valves
Spring operated safety valves are very sensitive to backpressure in a system, so this variant of release valve is best suited to applications that have little to no backpressure present. Section I steam valves aren’t certified to use pilot operation, so these valves must be spring operated.
- Higher set pressures can be reached with spring operated relief valves vs. pilot operated valves. These valves feature larger passageways and can function better in applications that process chemicals or corrosive materials.
- Adding a bellows to this type of valve can further compensate for variable or built up backpressure to create an optimally balanced operation.
Spring operated relief valves tend to have a lower initial investment cost than pilot operated relief valves, but can be more expensive to maintain and repair.
Choosing the Right Valve for Your Application
Proconex application experts can help you find the right pressure relief valve to meet your application. A leader in process control and industrial automation, Proconex provides an Overpressure Protection and Process Safety offering, complete with pressure relief valves, Pressure Relief Device Services, rupture discs, explosion venting, and tank protection equipment.