The Series 500 can be supplied with a field test connection consisting of a check valve, hand valve, and visual actuation indicator. Pressure from an external source can be applied to check the opening point of the valve while in service.

This will not affect normal operation. If a system overpressure occurs during testing, the valve will still open and relieve, maintaining system protection. In contrast, a direct spring operated valve must be removed from service to effectively test set pressure.

Because it is pilot operated, there is no simmer or leakage of the Series 500 main valve at process pressure - up to set pressure.

The modulating action operates similar to a back pressure regulator, opening only enough to relieve the upset. It has a variable relieving capacity with minimum blowdown. This type of action provides the least amount of wasted product per relieving cycle, yet protects against the maximum upset. If the upset is so severe-that full rated capacity is required, the main valve will achieve full lift.

Unlike direct spring valves, when the Series 500 is vented into closed headers or long tail pipes, superimposed or built-up back pressure will not affect the set pressure, blowdown, or lift. 

In the larger Series 500 valves, a patented, pressure-responsive piston drag system, with a wedge ring that creates a pressure-actuated sliding friction force between the piston and liner, prevents resonant chatter and the severe valve and/or piping damage it can cause.