Replace the globe came with one which has the same CV characteristics of the main control valve.

Why is the main control valve" not available"?

We like new people but do you not have anyone else to ask where you work?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Just to get the basics of out of the way, is your globe valve oriented correctly relative to flow?

1/ Comments above.
2/ Find and partially close any valve downstream of the bypass globe valve. This will increase bypass outlet pressure => reduce pressure drop => reduce flashing&cavitation => reduce noise&vibration.
3/ Insert a flow orifice downstream of globe valve. The same effect as above.
4/ Replace the manual globe valve with a manual CV the same design of wet part as that of FV.
5/ Find and employ a qualified process engineer. This will reduce uncertainty, risks and expenses in future.

Hello,

Seeing the snip of your P&ID, (engineered) control valve 8"-300# and (a normal globe) bypass valve 10"-300#.
Short term solutions is to open bypass valve directly to approx. 25% and tweak the position (smaller or bigger) that meet your flow requirement. However please note that the 'last' position should be at the position where fairly minimum to no vibration. This is a best practice that is loooong forgotten by most (new) operators. simply open it from fully close 0% > 1% >> 2% and so on to find the right flow spot is a recipe for disaster.

Not a control valve expert myself, but I think your bypass Cv is more than 1.5-2x Cv of control valve. meaning if operating position of control valve let say 25%, then in the absence of main control valve, in order to meet the same flow condition, then bypass valve will only requires less than 10% of its open position. The smaller the opening the bigger the velocity and kinetic energy.

Vibration is a combination of velocity and kinetic energy. From Energy Vibration Institute, the threshold is 460kPa.
Your control valve might be looking something like this e.g. MarkOne with integrated spindle/plug and streamline Plug profile.


and your manual bypass valve is something like this. Spindle and plug is not integrated, Plug has flatter surface shall compared to control valve. With the right kinetic energy and velocity, there will be vortex shading after the Plug which vibrates the Plug and essentially also vibrates the spindle. Risk of gland burst/leakage.


You can calculate this by simple excel. Data needed are flow, specific gravity of medium, upstream/downstream pressure, Cv of bypass valve, spindle travel (with relation to opening area between seat and Plug). Just iterate the value based and you will find the minimum opening position.

Good luck,
regards
D

Thank you Mr Danlap for this helpful explanation

You're welcome youssouf,

I feel the necessity to tell you that even without doing calculation, it seems like you have an oversize bypass line.
Long term and more fool proof solution is to engineer the bypass valve aka control valve with a handwheel.
If Cv of the main 8"-300# control valve is the reference, then there might be a limitation for 10"-300# bypass valve to be within the same range of that Cv. Expect a respond from valve supplier that you might need to use also an 8" bypass valve. Or maybe even 6"

Regards
D