Directional control valve symbols

[Student BE]

Hi,

I never had hydraulics and pneumatics related subject at my university so I decided to learn a bit in this field on my own. I started from learning how to read schematics of fluid power systems. And there's one thing that bothers me now - the way that type of operation and centering should be marked on the sides of directional control valve symbol. Is there any consistency in drawing them on the top and on the bottom ? Theoretically, from what I read, upper symbols should represent the method of valve centering (usually by springs) and lower ones should represent the method of valve operation. However, in some cases it is the other way around and centering springs are placed on the bottom and operation type (for example with solenoids) is on the top.

Particularly, this one schematic bothers me the most (the first one on that linked page, I can't give direct link - sorry):

http://www.hafner.pl/podstawy-pneumatyki/zawory-rozdzielajace-dydaktyka

First two directional control valves on that schematic show what I'm talking about. How to interpret their symbols ? The first one is manually operated in both ways and also has 2-level controls (solenoid and pneumatic pressure control)in both ways. There's no center position for that valve (as there are only 2 positions) so why are there so many symbols ? The second one is similar but has spring for one way and pressure control without solenoid. Does it mean that the switch (manual operation symbol) and what's marked under it are in parallel realation (OR) ?
The third valve is not a problem because it has 3 positions - centering springs for the center position plus 2-level controls.

Thanks in advance for your help

P.S. I learn from Polish sources but symbols should be the same worldwide as Polish standards are translated versions of ISO standards.

 

[hydtools]

The two position valve with no springs means the valve remains in the position of the last operated actuator. The two position valve with the one spring means the valve returns to that position after the powered operator is de-energized or released. Springs represent the position of the valve when operators are released or de-energized. The three position valve with two springs means the valve is spring-centered when the operators are released or de-energized.

Ted

 

[Student BE]

Thanks for reply. Byt why are there so many symbols for that ? For example the first one has parallel control (button OR pressure AND solenoid) on both sides. So it just means that these controls work in both ways ?

I will tell you how I would describe the meaning of these symbols and I would be very grateful for telling me if it’s correct:

1) first valve from the left - position can be changed by using manual operation (button) OR by solenoid which activates pressure control. It works for both sides (when switching between these 2 positions)

2) second valve from the left - for one way there is the same situation as mentioned above (manual operation OR by solenoid which activates pressure control), for the other way there is spring-actuated return OR pressure-actuated return

3) third valve is spring-centered and has 2-level operation (solenoid which activates pressure control) in both ways

 

[HPost]

The ISO standard for these symbols is ISO1219/2016

They are pneumatic symbols and you descriptions are correct.

The first valve on the left is a 5 port, 2 position valve, solenoid operated, with manual override.

The middle valve is 3 port, 2 position valve, with spring return and manual override.

The valve on the right is 5 5 port, 3 position valve with spring return.

All three valves have internal pilot operation. That is what the triangles show. It means that the solenoid connects the incoming pressure on port 1 to the end of the spool to shift it.

The convention for port locations is different for pneumatic and hydraulic systems. Hydraulic valves are labelled P,T,A,B and X and Y.

P = Pressure
T = Tank
A and B are the service lines to the actuator
X is the external pilot supply
Y is the external pilot drain

Pneumatic systems are labelled as 1,2,3,4 and 5

1 = Pressure supply
2 and 4 = Service lines to the actuator
3 and 5 are the exhaust ports.

Web search ISO 1219 to find out more...