Looking for an explanation of a hydraulic drawing relating to example

[TheHobgoblin]

Hi, Whilst searching the web i came accross this example of a hydrualic system, complete with drawing.

Pages 35 - 37

http://pirate4x4.com/tech/billavist...ical troubleshooting in Hydraulic Systems.pdf

But i have many questions about it as its confusing the hell outa me. please can someone take a look and share your thoguhts and ideas on it with me?

Looking at the sequence of ops from the solenoid chart my understanding of this system is:
1 - the dump valve [17] opens
2 - the bar is clamped with acctuators [51] [52]
3 - the carrige drive does something? i dont understand what since the bar hits a stop before its clamped so why would the carrige need to move?
4 - the actuator [49] cuts the bar and comes back ready for the next cut
5 - the carrige drive does something again? i dont know what
6 - the bar is unclamped and the ejector ejects it.

The drawing is very confusing i think.

I can just about make out that [17] is a PRV but why the DCV? its complicated as hell!

and DCV [35] looks wrong, as the right hand position shows the return line oposing the pressure inlet?

please help me understand this mess.

thanks

 

[hydtools]

The directional control valve[35] is there to change direction of the carriage drive which carries the bar to be cut. When centered, the valve blocks all ports and holds the carriage in place. The clamps hold the bar to the carriage. The carriage traverse drives a torch to cut the bar. The ejector pushes the cut piece away.
[17] is a pilot operated relief valve set to 80bar. The solenoid operated portion blocks a drain when energized and connects the drain to tank when de-energized.

Ted

 

[hydromech]

Valve 17 is a vented relief valve. That means that the pilot stage is piped to a directional control valve. The pressure can then be turned off and on by operating the directional control valve.

Valve 35 works just as Ted says.

It is an example of a hydraulic system, but not a good one to start with if you don't know much a bout hydraulic systems.

Adrian

 

[TheHobgoblin]

Thank you both Ted and Adrian.

Im still struggling to say i can confidently say how the sequence of the solenoid chart relates to the operations of the machine though.

Adrian, are you saying that, the dump valve is switched on, the bar (that was fed in*) is clamped, the carrige traverses back to the datum cutting position, the cut extends, then retracts, the very quickly, the carrige starts to feed the next length of the bar*, as the clamps are removed and the off cut is ejected? because that makes sense if its done super fast right?

Ted, Adrian. I have a basic understanding of hydraulics and systems, but im still not getting the picture on setup [17].

Pressure is relieved at 80bar, and at 80bar the port on the right of the PRV on the diargram will open. i think. but i just dont understand whats happening with the pilot line going from the top of the PRV to the DCV. why its there or its purpose, and what the functions of thes of the valves are in this circumstance.

Please could you help open my eyes a little further,

Thanks for taking the time to help me,
TheHobgoblin

 

[TheHobgoblin]

would it be correct for me to say, when the solenoid is activated the PRV is allowed to reach 80bar of system pressure, otherwise the pressure from the DCV is retarding the valve preventing the system to get to 80bar of pressure?

 

[hydromech]

Think of the PRV valve as having oil above and below it.

The system pressure below the valve will try to lift the valve, but the oil trapped above the valve stops it and the pressure builds.

The pressure on both sides of the valve is equal.

If the pressure above the valve is allowed to escape, there is nothing to stop the valve from opening and no pressure can be generated. The DCV is normally open and so the oil above valve escapes. Energise the DCV and it will close and pressure will build.

Now, if there was a smaller relief that can regulate the pressure above the main relief that was set 80 bar, that smaller valve would open the and vent the gallery above the main relief valve.

So...that's the way it works.

Pretty much the way you say.

The pump pressure compensator is set to 70 BAR so that is the working pressure of the system.

Adrian

 

[TheHobgoblin]

thanks adrian youve been very helpful there, you must really know your stuff!

another theory on the carrige and the bar feed:

what if the bar was fed externally from the circuit.
Either bar gravity with the full set up at an angle say 5 degrees?
Or if there was just an external feed.

Reason i say this is if perhaps the carrige track was for tollerance on the length, or for different lengths.

Say the datum is 999mm, after the cut the carrige traveres to datum, then goes to 1000mm before the cut. or goes to 1500mm for a 1500m length bar?

seriously i wont bother you guys anymore after this its just bugging me thats all.

Thanks bro.

 

[hydromech]

I am not sure what you mean here.

The bar is fed into the system from whatever way or method. It looks like it is pushed up against the cylinder on the right of the image, just above the rotary actuator.

Assuming the presence of the bar will make some sort of switch, the hydraulic system is 'switched on' and the sequence is launched.

1) the clamps come on
2) the carriage moves to the required position +/- 10mm
3) The arm traverses and cuts the bar, then moves back again
4) The carriage moves back to its 'home position'
5) The clamps release
6) The ejectors move the cut bar out of the way, then move back again

Then the next bar is moved into position. It doesn't matter how the bar is fed, nothing will happen until the system detect that the bar is there and ready to be cut.

I cant see how the position of the carriage is controlled, but the carriage will definitely not move past the first clamp. So the minimum length is from the stop cylinder to the left hand clamp...plus a bit to make sure the cutter does not cut the clamp off. The maximum length is dictated by the length of the track...which cannot be seen on the diagram.

It's all straight forward and a bit slow, many of the sequences can be simultaneous rather than sequential.

Adrian

 

[TheHobgoblin]

got it now, thanks so much adrian, your a credit to this website