Diaphragm or Piston Actuator Flow Control Valve

None. If you're talking about an electric actuator, it will be essentially an electric motor driven actuator through a reduction gearbox and auto brakes. But, if you're talking about an electrically controled hydraulic actuator, since you're dealing with kerosene and per your post that's the working fluid you have, you are closer to a piston actuated unit. If you have a reliable air line available, than, an electrically controlled diaphragm actuated pneumatic valve would be more feasible. Take it in account and give us details about how your setup would be, what will control your valve and if you're thinking about using the kerosene as the "muscle" power for your valve. Please inform also what would be your flowmeter to be read and what would be the signal to control the valve. If it needs to be precise, a controller would be required. If not, than, maybe a simpler valve with a depressive element for flow detection would be capable of, mechanically, control the flow (in this case, through a piston actuated unit).

The valve is electrically controlled hydraulic actuator and shall receive a signal from flow meter to maintain the flow rate to 1700 LPM. what are advantages of using piston type rather than diaphragm.

Well guest (whoever you are - register, dammit, it's not that hard),

My experience has been that piston pumps are more expensive than diaphragm pumps for matching flowrates.

I would go with a diaphragm pump.

Mike

PUMP?

Ok, so...

Hydraulic stuff is more for piston actuator than diaphragm. Piston actuators have leakage containment features that diaphragm units usually do not have.

Diaphragm is more often used for compressive fluids, usually air, where you need a greater area to obtain the required force to move the valve.

In high pressure, use piston type. Its smaller, ruggedized, will last longer. Diaphragms do fail more often. Much more area in flexible elements to give problems.

And the hazardous area implications are what, please? What is the preferred method of achieving explosion protection?