[curiouscat]

I was looking at a sketch for a lab scale flow reactor system (see below) and was nitpicking about some details.

What's a check valve? Same as a non-return valve?

What's a metering valve? Is that like a needle valve etc. that will let us control fine flows?

An actuator valve would be just a metering valve that has some sort of controller or pneumatics?

And those regulators are just keeping outlet pressure at a constant value?

[DrCMS]

Isn't a check valve a non return valve that only lets flow go in the one direction above a set (adjustable) pressure?

A metering valve is any valve that allows fine and reproducible control of the flow rate (does not have to be a low flow rate). 
In this case I'd guess they are needle valves but a slide valve that can open in say 10% increments from 0-100% could be called a metering valve.

No an actuator valve is typically a fully closed to fully open and back again valve,  remotely operated either manually or electronically and quite often pneumatically powered.

The regulators are just on the gas lines to reduce the cylinder pressure down to something workable.  Rather than have a regulator on each gas cylinder they have a manifold with two inlets with manual on/off valves set to a single regulator so they can change cylinders without stopping the process.

[Corribus]

Isn't a check valve a non return valve that only lets flow go in the one direction above a set (adjustable) pressure?

Yes. If you have a sump-pump system in your home's basement, you probably have at least one check valve that allows water to go out when the pump is on, but closes afterward so the water doesn't return.

[curiouscat]

Thanks both!

So, an actuator valve is bistable? Only fully open or fully closed? I didn't know that! Thanks!