PC1800 Front Shovel (1/12)

[sparkycuda]

Been pondering this... I was looking at Test #4 and you said it was delivering 3000 cc/min at 220 PSI, in neutral. I don't understand that with the valve in neutral the system is loaded so much. I'd expect a much lower back pressure (maybe 10-30 PSI) - appears there is a restriction going back to tank that is too high. Do you have a filter in the return line? If so, have you tried removing it for testing? Vented tank? Could vent be restricted? Did you get a schematic of the valve? Might look at it to see if anything unusual or unexpected in the guts of it.

Ken

[DADSGARAGE]

Originally Posted by sparkycuda

Been pondering this... I was looking at Test #4 and you said it was delivering 3000 cc/min at 220 PSI, in neutral. I don't understand that with the valve in neutral the system is loaded so much. I'd expect a much lower back pressure (maybe 10-30 PSI) - appears there is a restriction going back to tank that is too high. Do you have a filter in the return line? If so, have you tried removing it for testing? Vented tank? Could vent be restricted? Did you get a schematic of the valve? Might look at it to see if anything unusual or unexpected in the guts of it.

Ken

Sorry for the confusion in test number 4 ......what I did was to remove the return hose from the valve body to tank and only use the small 5/32" OD tubing instead......this forced all the flow in the return to pass through the small tube, which did two things....first it told me the total output volume of the pump, because all the oil from the pump had to return to tank through this small line, and it also proved that the small line could handle the required flow volume needed for one cylinder. Hope that makes sense.....

[DADSGARAGE]

I'm sure many of you are getting tired of reading about the 1:1 hydraulics I'm trying to use in this build, but now that I started down this road it needs to continue until I can get it to work properly or this whole idea will be a complete waste of time and money. So if this ideas tanks, at least the rest of you will know to avoid making the same mistake and just go buy the proper system for this type of application. (That would just be to easy....lol)

Did one last test to see what might be happening to the "mysterious vanishing flow".....turns out Ken and Mario called it !!! (Ken mention this right from the start) The full scale PRV on this valve body does not like to work very well at low pressure, and I know why it appeared to be working at the beginning.....the original small return line was restricting the flow which created the illusion of proper function....lol....long story.

[IMG]

This time I blocked off one port on one spool valve, connected both feed lines from the other port to the ball valve and directed all the flow into the second clear container, ran the pump....and all the flow was going through the return line back to the main black container, which is normal. Next opened the control valve attached to the ball valve, when fully open all the flow was going to the second clear container and there was no flow in the return line going to the main tank (black container), which is good, no problem with the spools. While doing this I slowly closed the ball valve....and finally got the answer to the problem...there was flow in the main return line at about 200-220 psi, should not have seen any flow until the PRV setting of 275 psi was reached. In the tests before this one the only time I would see the pressure hit the 275 psi was when the cylinders would reach the end of their travel, only then would pressure spike to 275 and then drop to about 200-220...lol...the problem was right in front of me all the time, but dumb dumb just didn't catch on...yikes..

[Supermario]

Don't feel bad about not seeing the issue sooner KP. Feel happy your still making progress and can move forward with the system you've created.

It's all about accuracy within a range. looking at the valve your using I'm guessing it's rated at probably 3,500 - 4,000psi? Maybe 2,500?
When trying to maintain 275 what's not working properly is the cracking pressure of the relief. It's supposed to hold closed and stay closed and then snap open when opening pressure is reached. When it's turned way down out of that " proper cracking pressure" range it opens slightly and slowly and in essence becomes a flow control and not a pressure relief if you know what I mean.
Question is, how to remedy? I wonder if a lower rated relief valve is available?
I think best thing would be to make your own relief externally or purchase a RC hydraulics type relief? The 4200 relief comes to mind but I know there are much better versions out there that might work ?

[DADSGARAGE]

Originally Posted by Supermario

Don't feel bad about not seeing the issue sooner KP. Feel happy your still making progress and can move forward with the system you've created.

It's all about accuracy within a range. looking at the valve your using I'm guessing it's rated at probably 3,500 - 4,000psi? Maybe 2,500?
When trying to maintain 275 what's not working properly is the cracking pressure of the relief. It's supposed to hold closed and stay closed and then snap open when opening pressure is reached. When it's turned way down out of that " proper cracking pressure" range it opens slightly and slowly and in essence becomes a flow control and not a pressure relief if you know what I mean.
Question is, how to remedy? I wonder if a lower rated relief valve is available?
I think best thing would be to make your own relief externally or purchase a RC hydraulics type relief? The 4200 relief comes to mind but I know there are much better versions out there that might work ?

Can't help but feel a bit like a dumb dumb and really disappointed in myself for missing the obvious problem...... but sometimes when you are trying to trouble shoot a problem you take for granted that one component is working properly.....wrong....I was convinced that the PRV wasn't the issue....not...so off we go on a wild goose chase....lol...the school of hard knocks did however teach me a fair amount more on hydraulics than what I knew at the beginning, so it's all good!!(just wish I wasn't such a slow learner...lol)

The stock PRV setting on the valve body is from 1500-3750 psi. I simply installed a smaller spring, and it worked...or so I thought...lol....you are right about it always bypassing like a flow control never really totally closing or holding pressure!! I will most likely have to make a stand alone PRV before the valve body, would really like a piloted version but can't seem to figure out how to make one, a simple poppet style will have to do. Should I use a ball bearing and seat or a tappered pin and seat...???