These two get confused constantly, and the confusion is expensive — because a safety valve used as a regulator fails early, and a system without a safety valve isn’t protected at all.
The question to start with is simple: what are you trying to achieve?
A safety relief valve is an emergency device
It sits closed. It does nothing at all until system pressure reaches its set point, and then it opens to relieve. That’s the whole job.
It is a last line of defence — the thing that stops a vessel or boiler from being damaged when something else has already gone wrong. It’s sized for a worst-case relieving event, it’s stamped and certified for that duty, and most of its life is spent doing nothing.
A regulator is a control device
A regulator works continuously. It modulates flow to hold downstream pressure at a target, and it brings pressure back down when the system spikes. It’s designed for steady-state control, not for emergency relief.
If your problem is “pressure in this line is higher than I want it to be, all the time”, you have a regulator problem.
Why using a relief valve to regulate destroys it
This is the failure we see most.
If a safety valve is opening regularly — because operating pressure keeps reaching set pressure — it is being used as a pressure control device. It isn’t built for that. Every lift cycles the disc against the seat, and a valve that cycles constantly will wear its seat, start leaking below set pressure, and stop sealing altogether. Safety relief valves aren’t designed for continuous duty.
Worse, once it’s leaking you’ve lost your overpressure protection at the moment you’re most likely to need it.
How to tell which you have
| Emergency overpressure protection | Continuous pressure control | |
| Normal state | Closed, doing nothing | Actively modulating |
| Opens | Only at set pressure | Constantly, by design |
| Duty | Infrequent | Continuous |
| Certified | ASME stamped, NB certified | Not a code safety device |
If your safety valve is opening as part of normal operation, you need a regulator upstream — and the safety valve is probably due for testing or replacement after the cycling it’s already done.
The two aren’t alternatives. Most systems need both: a regulator to control pressure, and a safety valve behind it for the day the regulator fails.
Not sure which you’re looking at?
Send us the part number off the nameplate and we’ll tell you what it is and what it’s rated for. Requests received before 3 PM ET are typically quoted the same business day.
For information only. This article is general technical guidance, not a specification or a recommendation for any particular installation. Valve selection, sizing, set pressure and inspection intervals depend on the equipment’s design data and the code it was built to. Always confirm with a qualified engineer and your jurisdiction’s boiler or pressure vessel inspector before specifying, changing or relying on a relief device.