What is the acceptable diff. press. that  can size  The oil specific gravity is 0.85.
the line size is 3/4". needle valve for?Ball Valves

Two things to watch out for:  one is that many types of flow transmitters don't like to be downstream of a needle valve or any other device which produces a very non-uniform velocity profileCheck Valves.  You may need a long length of tubing/pipe between your valve and your flow transmitter to settle the velocity profile back down again.  Check with the flowmeter mfg to make sure, before you decide where the needle valve must go.Gate Valves

The other is to watch out for laminar flow.Butterfly Valves  Your flowrate is large enough that this may not be a problem, but remember that the Cv of a valve only valid in fully developed turbulent flow.  If your lube oil is viscous enough, flow through the valve trim you need may be transitional or even laminar, in which case it becomes strongly viscosity dependent.Globe Valves  The viscosity correction factor methods for large control valves DO NOT work well for small ones.  In laminar flow, the actual flow the valve will be capable of passing at a given pressure drop will be a great deal SMALLER than you predict.

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