# I want to understand this pneumatic circuit

I have trouble understanding the following pneumatic circuit diagram:

I am new to reading circuit diagrams and i am unfamiliar with some of the symbols. I would appreciate if somebody could explain them to me. In particular I have the following questions:

1. What does the dotted line in bottom left of the directional control valve mean?
2. Why is a control valve with 5 ports used? Isn't one of the port on the left of the valve redundant and a 4/2 valve could be used instead?
3. Why are there four ports on the actuator? I am only familiar with actuators with two ports (which would correspond to the top two ports). What are the bottom port and the right port used for?
4. What does the symbol in the top right mean?
5. What do the triangles on top of the lines mean? Why is one white and one black?

I realize that these are a lot of questions. But as I said, I am new to this. I would also appreciate if anybody could link a free source, there such diagrams are explained systematically. So far I used the Wikipedia page, but there are a lot of symbols/subtleties which are not covered there.

• You need to check the source of your diagram - they will have a legend explaining the symbols - there can be subtle and not so subtle differences... Dec 4, 2018 at 12:28
• Unfortunately, there is no such legend Dec 4, 2018 at 12:54
• The dashed lines means pilot controle, these days are usually electronic devies but pure mechanical lines are also common, solid triangles means hydraulic flow direction (exhaust) hollow or white means pneumatic flow direction (exhaust), regarding your forth question, i suspect that's an accumulator is or lubricator reservoir, the rest of the circuit is missing, i don't know what norming system you work in so that's all for now. Dec 4, 2018 at 15:15
• @SamFarjamirad I don't think it would be an accumulator, the check valve is pointed out of the tank and there doesn't seem to be any workaround for building pressure in the tank.
– JMac
Dec 11, 2018 at 16:19
• its a piston running into a spring return piston. So i would hazzard a guess: Its a adjustable spring damper. Dec 11, 2018 at 17:06