willie59
Administrator
Which is exactly the way you do it roddy, kudos for your curiosity. :drinkup
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Priority flow control valve
- Thread starter roddy
- Start date
Which is exactly the way you do it roddy, kudos for your curiosity. :drinkup
John C.
Senior Member
Probably one of the worst schematics I've seen in a long time. The direction of the arrows and the extra arrows provide no facts as to the logic of each component. Who is the manufacturer of this machine?
When I glanced at the drawing my first thought was inlet oil is hitting an orifice and there is a straight T going to the fan motor. That would mean the fan motor has priority over the brakes. Not supposed to happen! Second item you guys discussed was somehow controlling the fan motor on the return side of the motor which again is a huge no no. Restricting down stream flow will blow the seals in the motor.
Many engineers seem to treat schematics as some kind of art project and forget that it is supposed to be the interpretation of a function. I'm wondering if someone can design a software program to animate how one of these work? Even better would be to be able to set up a mapping program where you click on a line and it colors it all through the schematic.
When I glanced at the drawing my first thought was inlet oil is hitting an orifice and there is a straight T going to the fan motor. That would mean the fan motor has priority over the brakes. Not supposed to happen! Second item you guys discussed was somehow controlling the fan motor on the return side of the motor which again is a huge no no. Restricting down stream flow will blow the seals in the motor.
Many engineers seem to treat schematics as some kind of art project and forget that it is supposed to be the interpretation of a function. I'm wondering if someone can design a software program to animate how one of these work? Even better would be to be able to set up a mapping program where you click on a line and it colors it all through the schematic.
maytag
Well-Known Member
- Joined
- Mar 18, 2010
- Messages
- 124
- Location
- saraland al
- Occupation
- Hydraulic technician in a steel mill
pilot lines
I tried to add a schematic showing the difference of a pilot pressure line and a pilot drain line BUT got the run-around with the computer, SO basically a pilot pressure circuit will drawn/should be drawn with a longer dashed line. Pilot drains will be a shorter dashed line, In heavy industry they will also be noted a X/pilot pressure and Y/pilot drain. Have to say i'm glad I don't have priority valves to deal with in my world. Looks like the engineer here used pilot pressure symbol/lines in places where its definitely a pilot drain circuit.
good luck
Maytag
I tried to add a schematic showing the difference of a pilot pressure line and a pilot drain line BUT got the run-around with the computer, SO basically a pilot pressure circuit will drawn/should be drawn with a longer dashed line. Pilot drains will be a shorter dashed line, In heavy industry they will also be noted a X/pilot pressure and Y/pilot drain. Have to say i'm glad I don't have priority valves to deal with in my world. Looks like the engineer here used pilot pressure symbol/lines in places where its definitely a pilot drain circuit.
good luck
Maytag
willie59
Administrator
OMG, how I would love to have something like that, especially on large diagrams, including electrical! :notworthy
willie59
Administrator
Put the photobucket hyperlink here roddy.
willie59
Administrator
That worked roddy, I was able to download the original diagram to my computer. 
maytag
Well-Known Member
- Joined
- Mar 18, 2010
- Messages
- 124
- Location
- saraland al
- Occupation
- Hydraulic technician in a steel mill
willie59
Administrator
Schematics are to help people troubleshoot and should be accurate. It wouldn't be the first time I've come across errors (even in Cat drawings
Someone tell me if my eyeglasses are just dirty, or am I really seeing what I'm seeing. Check out this brake control valve on that full drawing. It has not only foot pedal manual control, but hydraulic pilot control as well. That in itself (having two forms of control) isn't the weird part, although not common, but look at the check valve in the pilot control line. Someone explain to me like I'm a 6 year old just how that would work?
Additionally, the way it's drawn, the valve is already in the shifted position, the lines should have been drawn connected to the spring end of the valve. :crazy
This is a SAHR braking system. It uses a reverse modulation brake valve. Please keep in mind I am learning to read prints (and not the best ones at that. To me it looks like the check valve would help keep the brakes in released position until the brake pedal is pressed releasing oil back to tank?
willie59
Administrator
No worries roddy, we commend you in "teaching yourself" in reading schematics, that's the way it's done and we've all been there. And I think I can speak for others that we'll do all we can to assist you. But at the same time...you picked (through no fault of your own) a helluva diagram to learn from.
willie59
Administrator
And I know what your saying about the "reverse modulation". It's sort of like a P&H T-300 crane I worked on once. Throttle from upper cab to lower engine was controlled by air. But it took air "pressure" from the upper control valve to make engine idle. Mash the foot valve or hand valve in the upper to "throttle engine up" meant it actually took air away from the engine actuator. Talk about a brain twister to diagnose problem with upper control valve and foot pedal. :dizzy
willie59
Administrator
Guys, I found another oddity. This is the redundant parking brake solenoid valve on the full drawing. At first glance it looks like a closed center 4 way valve, but it's shown shifted to the end section, and it shows a spring on one end and a solenoid coil on the other end. In all my years of looking at diagrams I have never seen something drawn like this. >
maytag
Well-Known Member
- Joined
- Mar 18, 2010
- Messages
- 124
- Location
- saraland al
- Occupation
- Hydraulic technician in a steel mill
symbol
That is a two position valve with an "all ports blocked condition" as the spool transitions from one position to another. On some applications it won't matter, on others it will. Been on the receiving end of some bad engineering with an 'all ports blocked" condition where the rod gland would be blown. fortunately Rexroth offers the same two position valve with an "all ports open" condition.
Have a good day,
Maytag
That is a two position valve with an "all ports blocked condition" as the spool transitions from one position to another. On some applications it won't matter, on others it will. Been on the receiving end of some bad engineering with an 'all ports blocked" condition where the rod gland would be blown. fortunately Rexroth offers the same two position valve with an "all ports open" condition.
Have a good day,
Maytag
willie59
Administrator
You may be right Maytag as I've never ran across an "all ports blocked" situation, but I have never seen a valve like that on mobile applications and I've looked at a bunch of drawings over the years. :crazy
maytag
Well-Known Member
- Joined
- Mar 18, 2010
- Messages
- 124
- Location
- saraland al
- Occupation
- Hydraulic technician in a steel mill
Willie,
Here is a sheet from rexroth from their catalog for DCVs. Pay particular attention to any envelope(square) that has the broken lines. Any time a broken line is used it denotes a "condition" rather than a "position", a condition the the valve and all downstream components see momentarily as the spool transitions from one position to another.
Hope this helps explain,
Maytag
Here is a sheet from rexroth from their catalog for DCVs. Pay particular attention to any envelope(square) that has the broken lines. Any time a broken line is used it denotes a "condition" rather than a "position", a condition the the valve and all downstream components see momentarily as the spool transitions from one position to another.
Hope this helps explain,
Maytag
