PC1800 Front Shovel (1/12)

[DADSGARAGE]

The best thing for me to do is share the results of all the different tests so you all know what is happening.....

The pump "should" be moving 3000cc/min or 50cc/sec. The total combined volume of the two boom cylinders is 241cc, so at 50cc/ sec it should take 4.82 seconds to fully extend both cylinders. Keep in mind this does not account for any slip in the pump and would be with no load or restrictions.

20lbs was used for the load in all the tests

First test

1/4" ID suction line tank to pump, the blue1/4" OD tubing from pump to valve body, the ID of the tubing is .180", the same 1/4" OD tubing was used on the return from pump to tank. PRV set at about 275 psi on a 0-600 psi gauge. System pressure with no load and the controls in neutral was about 60 psi. It took 7.5 seconds to fully extend both cylinders and pressure was about 220 psi.....funny not what I was hoping for...lol

Second test

Changed the suction from the tank to pump up to 3/8" ID and changed the return line from valve to tank up to 3/8" ID as well. Pressure in the neutral position was now zero, and operating pressure dropped to about 200 psi. The time to extend the cylinders increased to just over 9 seconds. So I was getting some restriction in the return using the smaller tubing...interesting.

Third test

Increased the feed line from the pump to valve body to 3/8" ID tubing....no changes

Forth test

Check the flow rate of the 5/32" OD tubing (.106" ID)....removed the 3/8" return line and installed one 5/32" OD tubing. With the controls in neutral I turned the pump on for 30 seconds (220psi) and got almost 1500cc which is 3000cc/min, again not what I was hoping for...lol....really thought the small tubing was restricting the flow to the cylinders but that is not what is happening.

Test 5

Increased pump speed 600 rpm to 2000....again very little change....scratching a hole in my head with this one...lol

Last test

Dropped the pump RPM back down to 1400, increased suction to 1/2" ID used the same 3/8" line pump to valve but reinstalled the blue 1/4" OD tubing on the return....the result where nearly the same as the first test. Which makes me think that some of the flow in this open center valve is still bypassing the spools even with them fully open to the cylinders. The pump is supplying the proper amount of flow but if all of that flow isn't getting to the cylinders where is it going?? (and no there isn't a leak some where...lol)

[DADSGARAGE]

Oops....need to correct something in my last post.....in the first test....it should read return from valve to tank, not "return from pump to tank"

[Supermario]

I noticed in a couple pictures the suction from tank to pump you had to use a reducer. The larger the suction line the better otherwise the pump is trying to suck through a straw and will drastically effect output.
One other thing that quickly comes to mind is the prv you are using. It is the original valve relief? What is the maximum working pressure of the valve?
The reason I ask is, if you have a circuit that uses a 5,000. Psi relief but you install an attachment like a clam or grapple which only needs let's say 2,200 psi, you can't just turn the 5,000 psi relief way down to the lower pressure. It must be replaced with a lower value relief.
Long story short, maybe the relief is rated too high and working at 275 psi is causing it to not work properly.

[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

I noticed in a couple pictures the suction from tank to pump you had to use a reducer. The larger the suction line the better otherwise the pump is trying to suck through a straw and will drastically effect output.
One other thing that quickly comes to mind is the prv you are using. It is the original valve relief? What is the maximum working pressure of the valve?
The reason I ask is, if you have a circuit that uses a 5,000. Psi relief but you install an attachment like a clam or grapple which only needs let's say 2,200 psi, you can't just turn the 5,000 psi relief way down to the lower pressure. It must be replaced with a lower value relief.
Long story short, maybe the relief is rated too high and working at 275 psi is causing it to not work properly.

Haha...you have a good eye for details....yup it did have a reducer, at the time I only had some 1/4" ID tubing and didn't have a 1/4" barbed fitting...but I did have a 5/16" barbed fitting and short section on 5/16" fuel line so I had to improvise....lol....used the 5/16 barb fitting and hose and pushed the 1/4" ID clear hose into it, knowing it was just a suction line the fit between the two hoses was tight enough to do the tests...got to do what you got to do with what you have at the time...lol...in any case using a 1/4" ID suction line was a bad idea, it was much to small. 1/2" ID hose is a much better match for the oil flow velocity. The PRV might still be the problem....I have it set much much below what it was set at and designed for. I have two more things to test which will tell me if the valve body is bypassing or if the PRV is acting flakey at the low setting.