Problem understanding pilot system in hydraulic schematic 1

[Rob47]

Hi, i'm not yet a very good schematic reader but i'm trying hard and eventually hope to do better with schematics.
I have a problem understanding the pilot system in this schematic. The schematic is of a concrete factory.

1 See red cross: Why is the other pilot side of the valve connected to tank. Is there a specific reason for it, because it doesn't
help to push the valve spool? It doesn't make sense to me.
2 See red circle: Is that valve a throttle or a release valve. The manual speaks of throttle valve but in articles on the internet
they speak of a release valve.
3 See red triangle: Pilot pressure line: The LVDT DC valves are proportional valves. The pilot oil pressure continuously push against the valve spool. The
opposite force of the solenoid on the spool is adjustable, so that's how the valve can control a precise flow of oil to the cylinders. If the system is not
operating the springs of the valves return the spool in the middle position. Am i correct on this. If not I would appreciate a brief explanation of the
pilot system if possible.

Many thanks in advance.

 

[HPost]

Hey...

The drawing is not right. It makes it very hard to understand what is going on when people supply drawings that just confuse us.

The red cross

That is a pilot operated proportional control valve. It will have an X port and Y port. The X port is the supply pressure and the Y port is the pilot drain. That is the standard convention. The pilot pressure supply will be routed within the valve to each end of the spool and the pressure acting on the spool is controlled by the proportional solenoids on the valve. When the current is backed off, the spring with push the spool to the neutral position and in doing so, oil is pushed into the Y port gallery and that drains off to the tank.

They have this drawing showing that the Y ports on the valves connect to the main tank line. That is asking for trouble as high pressure in the tank line (5 BAR or more) can affect the spools.

The red circle

That is a pilot operated blocking valve. It controls the cylinder somehow, I have not bothered to look how or why.

The red triangle

The valves show springs on each end of the spool. This tells you that the spool is centered by the spring and the current fed too the coils causes the valves to open up, gradually increasing the pilot pressure acting on the spool. The drawing shows one coil and 2 pilot ends. This suggests that, depending on the amount of current supplied, the valve will shift one way or the other.

cheers

 

[Rob47]

Many thanks HPost. The drawing is from a german company named HESS. Never mind the blocking valve. I know how it works. I only wanted a name for it. I understand the pilot system now. Thanks again.