Difference Between Self Actuated Pressure Control Valve And Pressure Reducing VA

Usually a self actuated pressure control valve is used to maintain a set downstream pressure. It does it by sensing the pressure and making adjustments, all within the unit, to maintain setpoint irrespective of changes in upstream pressure and flow through the valve (within design limits).

A pressure reducing valve might be doing the same, but it depends on the actual installation. If it's part of an automatic system it has a separate pressure element and controller, but it could be just a manual trim set-up, depends on the case.

See the response above for pressure control. Pressure reducing valve will not let the pressure rise above a preset value.

One of the biggest problems with this question is that the terms mean different things to different people in different industries in different countries.

So my 2KRW based on 20+ years in oil and gas contracting

In all control valves the pressure on the downstream side is lower than the upstream side so they could all be described as pressure reducing even if the controlled parameter is something else entirely.

I think though the question you are asking goes to the actuation method.

In a control valve there is a cylinder that drives the plug to effect the pressure control. In a self acting valve this uses the process fluid to drive the control mechanism. For a conventional control valve "instrument Air' is used. This air which has been dried (typically to a -40°C level) and is used at 5 - 7 barg.

In theory any fluid can be used for a self acting valve. In my experience they are being used less frequently and the most common usage is for blanketing gas on tanks - low pressure service, nitrogen gas used so a clean and safe fluid - although the outbreathing valve may see hydrocarbon vapours. These are often in remote locations and this is the reason for making them self acting.

A pressure reducing valve is just a control valve with an outlet target of a specific pressure. Upsets to the process (up and down stream) or the control algorithm or just the natural offset could result in other pressures being seen.

The self acting valves I have described on tanks could be described as pressure reducing valves, similarly some self acting valves may be self acting but may NOT be described as such. The description of a valve depends on what aspects are important to the person making the description.