I have a storm drainage system that has a flow splitter to some treatment devices.  Gate valves are shown on each side of the flow splitter for either spill control or maintenance purposes, i.e. flow to treatment devices can be shut off while performing maintenance.  I normally show gate valves for this purpose.  I had a peer tell me to use a plug valve instead, as it is better at creating a good seal when flow streams in drainage systems have some grit and such.  However, I am concerned about the reduced port area that would restrict gravity flow, and I have heard plug valves are very hard to operate and if they are not maintained can be impossible to budge later on.  Comments?

Probably best choice for storm or waste water, is "None".
Gate valves are NOT designed to be used as throttling or flow control vales . They are intended to be shutoff valves to remain fully open or fully closed.

Other types to consider are :

Plug Valve
Slide Gates
Swing Gates
"Duck bill: Tide or backwater valves
Tainter Gates

Several valve makers offer Free Advice including
Globe
Golden
Crane
Many, many others

Several standards and professional groups such as AWWA, WPCF,
ASCE
The Ten State Standards
and your local agencies having jurisdiction will also offer advice, even if not asked.

Apologies for the acronyms.

Here is some additional input you may investigate. Although not relating to the cylinder head, the 4 cylinder oval migit engines have found for some time now, that the single most rpm extending area of attention is, the increased taper in the injector manifold to the butterfly. The port stays the same in the head, albeit the size of the butterfly has become remarkably larger in relation to what one would concider adaquate. It has nothing to do with airflow in, but affect the pressure wave in reverse. This wave is succesfully dampened enough to allow the flow to reverse forward into the port with decreased pumping loss, allowing these engines to hang on conciderably longer than without this taper. Although the power band your looking for may not apply, there is certainly a finger pointing in the manifolding direction IMO.

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