Pressure limiter and pressure relief valve

There is a difference. A pressure limiter, or regulator, can be either on the input or the output side of the pressure controlled area. On the input side it will take a high pressure, high flow, input and allow passage of the gas or fluid only to the set pressure point and will only allow more passage if the pressure drops. On the output side you generally have to limit inflow volume and the limiter, properly called a back pressure valve, will relieve pressure to atmosphere or some type of recovery system in proportion to how fast the inflow is and you will also have good pressure control in a narrow band with either type if properly applied. A pressure relief valve is generally considered to be a safety valve and is also called a "popoff" valve. You can have a system with the pressure controlled by a limiting valve at say 100 psi. But the vessel can be safe to 150 psi. A relief valve is designed to "blow" open when the 150 psi level is reached and will only close again at a much lower pressure. This provides a safety function but does not provide any degree of regulation worth talking about. I hope this helps you.

Keep in mind that if the maximum design working pressure is 150 psi, the relief valve should theoretically be set below that pressure (i.e. 145 psi).