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Construction Equipment If it digs, pushes, hauls dirt "off road" post it here. |
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#121
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Re: PC1800 Front Shovel (1/12)
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Here is what I understand....if a pump at a given RPM moves 2 gal/min is attached to a cylinder that has a total volume of 2 gallons it should take one minute to fill the cylinder....if you have two of these 2 gallons cylinders it will take longer to fill them both, in this case twice as long. The larger the total volume of the cylinders being used the longer it takes to fill them all and the cylinder movement speed will be reduced accordingly. What I don't understands is why this isn't happening like it should....this pump supplies much more volume than what is really needed....there should be a surplus of volume left over when using multiple cylinders....but where is this surplus going??? I think that in this valve body there is always some flow allowed to bypass the spools and flow to the return port even when the spools are totally open to the cylinders!!?? One would think that all the flow would be channeled through the spools that are being used and only allowed back to the return through the return hoses on the cylinders. Yes/No ??? |
#122
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Re: PC1800 Front Shovel (1/12)
Interesting?!?! Have you confirmed the volume of oil being supplied by the pump? Disconnect the return line at the tank and put a container that is calibrated or that you can measure the actual quantity easily. Depending on how large your reservoir is, run the pump without actuating any circuits and measure the amount returned. May have to run for only 15 or 30 seconds, but confirm pump delivery. What pressure is being displayed during this test? Confirm system maximum pressure will make 275 PSI. Bottom a cylinder (either direction) by fully stroking control valve and see if relief valve actually is 275 PSI. Also, at this condition, return oil volume should match max output of pump. (You may see a slight decrease if the motor reduces RPM while under relief pressure, plus no pump is 100% efficient. Most big gear pumps can be up to 98% efficient when new. I'm guessing yours should be near that.) When you saw the system operate at 210 PSI, was that while cylinders were actually moving? Should go to 275 PSI when cylinder hits end of stroke. If there is a question about individual circuit flow, disconnect a cylinder line and put it into a container for measuring. Stroke valve fully and measure volume delivered to circuit. At same time, see if any oil is being returned via the valve return to tank. Should be practically nothing. If is significant amount, the valve may have something going goofy. Also, observe system pressure at this condition.
Ken
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Big iron is awesome! |
#123
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Re: PC1800 Front Shovel (1/12)
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) |
#124
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Re: PC1800 Front Shovel (1/12)
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"
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#125
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Re: PC1800 Front Shovel (1/12)
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. |
#126
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Re: PC1800 Front Shovel (1/12)
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
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Big iron is awesome! |
#127
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Re: PC1800 Front Shovel (1/12)
Speed in hydraulic's can only be changed by two things, pump rpm and volume of oil. The pump is designed to give max cc at the max diameter hose that can be fitted to the pump output.
If you put on small hose it acts like a restriction in the circuit. Also to get max flow every hose from tank to pump to valve and back to tank has to be the same diameter or you'll have the same restriction in the circuit. If the pump is the same as what I think you have the inlet and outlet in 9/16" Dia. =1.767 sq. in. Sizing the hose down to 1/4" .785 brings you down to about 2.25 less volume than the pump can produce = slow cylinders. I think if you up size all the primary circuit hoses to the proper diameter then you'll able to control it from there with motor rpm. Hope this helps. Rob |
#128
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Re: PC1800 Front Shovel (1/12)
Pressure makes a dramatic difference in hyd speed too... looking back to pg1 I see the size cyl bores you're using are 25% bigger than my 850 hoe that has its working pressure at 475psi, but your front shovel is likely going to be 25% bigger too... try your cycle speed tests at 450psi.
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Sharing knowledge is one thing that defies basic arithmetic logic --- the more you share, the more you get! Joe |
#129
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Re: PC1800 Front Shovel (1/12)
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Hey Joe.....yes pressure does have its advantages....the only way to increase pressure with what I'm working with is to increase pump RPM, if the resistance or load isn't there the system will not make more pressure. The open center valve pressure with the controls in neutral is zero...I'll bet with your system the pressure is always at operating pressure. This build might be bigger than your 850 but I'm hoping to run it on half the pressure, so I have over sizes the cylinders to somewhat compensate for running a lower operating pressure...this may end up being a bad idea....lol |
#130
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Re: PC1800 Front Shovel (1/12)
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#131
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Re: PC1800 Front Shovel (1/12)
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#132
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Re: PC1800 Front Shovel (1/12)
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#133
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Re: PC1800 Front Shovel (1/12)
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.. |
#134
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Re: PC1800 Front Shovel (1/12)
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 ? |
#135
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Re: PC1800 Front Shovel (1/12)
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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...??? |
#136
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Re: PC1800 Front Shovel (1/12)
I may not be the best advise but I would think a tapered pin and seat would be better. Assuming you have the capabilities to hold tolerances. And I'm sure you do . I would think the hard part would be getting the right spring. I've been wanting to make one myself and have just assumed a taper would snap and flow better than a round bearing surface. ill be following how you make out so my learning curve might not end up with more parts for the recycling bin. . Appriciate you posting your progress good or bad.
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Always wasting money, as the wife says. To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. |
#137
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Re: PC1800 Front Shovel (1/12)
This goes beyond my knowledge and experience with hydraulics. I troubleshoot and fix existing systems made by people much smarter than me, never designed or thought about making a relief but based on hyd principals the ideal relief would be a needle type seat.
Just like cylinder diameter and surface area effects the amount of power generated , so does the smaller the surface area of a relief needle valve effects the strength and sensitivity of a relief and better for that cracking pressure type operation. Like I say.... Beyond my pay grade but that's how I see it. Nice thing is you already know flow rates and the amount your dealing with and I wonder if there's a formula out there that would tell you port size and needle dimensions to get what your looking for? Hmmmm, i might be able to get you a pilot relief valve that runs at about 350psi come to think of it! I'll let you know next week. |
#138
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Re: PC1800 Front Shovel (1/12)
Tapered pin and seat sound good but would not be my choice for a PRV. I deal with tapers every day at my real job. We make our tapers down to .000015" tolerance on diameter and .000015" tolerance on taper. These tight tolerances are used for a pressure fit of the male and female tapers. The parts are not held together by any bolt or screw just the mating of the 2 tapers under any type of pressure. A PRV using a tapered pin may lock up on you if the 2 surfaces were close to a perfect match on tapers. It takes a lot of force to get 2 matching tapers apart. Some times they don't have to be that actual close to make a very secure fit. This is in the medical field for replacement hips, shoulders, and knees.
I would use a ball bearing rather than make a tapered pin. Just my thoughts and opinion.
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LYNN |
#139
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Re: PC1800 Front Shovel (1/12)
Try a weaker spring first.
Cheers! |
#140
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Re: PC1800 Front Shovel (1/12)
I am real happy to see someone has beat me to development of this type. I love Princess Auto and am currently on a $100 budget from wife. I go over she will chaperone, I stay under and am free....lol. I think you are doing a great job of figuring this all out. Keep up the excellent work.
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