Series design of flow control valve and orifice plate
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In this renovation project, the foreign party’s technical requirements specify that a orifice plate should be installed downstream of the control valve. The maximum flow rate of this orifice plate is set to match that of the control valve, and the pressure drop is only around 1 KPa (with a system pressure of 5 KPa). It’s not clear what the purpose of such a setup is; I would appreciate everyone’s insights and discussions on this matter...
It is presumed that in the event the valve fails, a certain flow rate will still be ensured.
Does the downstream process have strict requirements regarding the maximum flow rate?
The orifice plate serves two functions: throttling and pressure reduction. It also ensures that the flow rate does not exceed the maximum design value. Additionally, it takes some of the pressure drop off, thereby reducing the pressure load on the control valve and making it easier to select the appropriate control valve.
One more thing: using a control valve along with an orifice plate is almost a standard practice. I’ve worked on few projects, but as far as I remember, this combination is always used in those projects
I’ve seen a similar setup: pressure control comes first, followed by a flow-limiting orifice plate; beyond that it’s essentially atmospheric pressure. By controlling the pressure before the flow-limiting orifice plate, the flow rate through that orifice plate can be kept consistently at the designed level.
Well, the system I recently designed for the Germans is similar; it’s a requirement imposed during PHA meetings – dual protection is needed. In case the instruments fail, we still have the orifice plates as a backup. This is basically standard practice
A more common setup is a device interlock system: a orifice plate is installed after the shut-off valve to limit the pressure release rate… An orifice plate installed after the control valve is less common! But the principle should be similar, right! In my humble opinion…
Yes, what I understand now is that the orifice plate can only be considered an effective mechanical protection measure
Such a design is sometimes used to control high pressure drops; when there is only a single control valve, high pressure drops can easily cause cavitation in that control valve. At this point, if a orifice plate is installed downstream, it can help to share some of the pressure drop. The pressure loss of the control valve can be kept relatively low.