Differences Between Direct and Indirect Actuation

Can you explain your question a little more?

Anders

i was in my interpersonal communication class and one of the questions that is going to be on the exam is what is the difference between direct and indirect modes of power?

Yes, you can know the differences.

Unfortunately, I can't tell what you're talking about! Actuation of what? What for? Please be more specific and give as much details as you can.

If you are referencing solenoid valves, or similar control devices, direct actuation means that the actuator controls the valve (and outlet flow and/or pressure) directly, and must be sized appropriately. Indirect actuation means the actuator controls a small "pilot" flow which is then used to control the valve (and outlet flow and/or pressure). In this case, the actuator is much smaller than it would be if it had to control the flow directly. Indirect actuators of these types are also referred to as piloted valves, or piloted regulators. A piloted device of that type requires a specified minimum pressure to operate the pilot.

The pilot or "booster" portion may also be entirely electrical/electronic, similar in function to an amplifier.

Greg

Good answer. I just might add that there is also direct and inverse acting, which is another way of expressing increase to increase or increase to decrease. Given the phrasing of the question, it is difficult to ascertain exactly what in meant.

HerbVic,

"Given the phrasing of the question, it is difficult to ascertain exactly what in meant."

The well known fact that "Defining the problem is the first step in its solution" seems to escape most of the posters here.

Greg

Differences could be as well the reaction of control valve in accordance to the signal from controller. Proportional signals from controllers are mainly voltage 0(2)-10V or current 0(4)-20mA.

Let me start first describing valves as they are two type of control valve on market; one they close flow by moving stem down and another they close flow true the valve by pulling stem up. Difference are done if producers use dedicated 2 port valve or 2 port valve made from 3 port valve.

Actuator that is in connection to controller can push down valve stem for example by 0V signal (dedicated 2 port valve will close) but you may need to pull valve stem up by 0V (2 port valve is made from 3 port valve).

Producer of motorised control valves therefore make set ups on actuator electronic PCB (direct/indirect actuation) that make closing valve by (for example) 0V.