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Volvo ecr48 main boom down pressure only 500psi

WNCFarmer

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The machine has never been able to push/lift its self up off of the tracks for years. Today I had the time to check the pressure and test the cylinder. The cylinder tested with no issues at 3500 psi. I then checked to see if I needed to turn the pressure up. The pressure would not reach more than 500psi pushing down but booming up to the max went to 3500psi. For some reason the boom down pressure will not go above 500psi checking it at the valve.

Any thoughts? Could there be a pressure bypass opening not allowing it to have down pressure?
 

WNCFarmer

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Yes sir and no change, still 500psi down and 3500psi on the up boom. Is there a pressure relief somewhere else besides on the bottom and top valve, maybe somewhere under the floor above the turntable?

Any other thoughts?
 

Ben Witter

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Where are you measuring your pressure? The only thing in the circuit from the spool to the boom rod end port is the port relief. Does this happen with the pattern change valve switched? Is the pattern change valve all the way in one position or the other?
 

WNCFarmer

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Thanks Ben, yes, I checked the pressure at the top and bottom of the spool with in-line gauges. I have not tried switching the control but this has been going on for sometime and I have switched from one method to the other (backhoe / track hoe modes). Is there any reliefs others than the ones adjacent the main boom spools for the main boom?
 

Ben Witter

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Not that would affect only the boom down circuit. The only reliefs are the circuit reliefs and the LS limiting valve, which affect all functions.

When you say you "checked the pressure at the top and bottom of the spool with in-line gauges", do you mean at the hoses to the boom cylinder or the servo caps that actuate the spool. There is a pressure tap on the right side of the valve looking from the counterweight, pointing straight down. This should be your LS pressure which will tell you your working pressure.
 

WNCFarmer

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Thanks Ben, yes, I checked the pressure at the servo caps for the main boom section. Any other thoughts?
 

WNCFarmer

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yes sir, my plan is to switch the lines from another source, say run a lines up from the blade to the main boom and switch them to determine if that tells me anything.
 

TVA

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Is your stand by and/or LS margin is 500 psi? You might have LS shuttle problem inside the DCV.
 

TVA

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yes sir, my plan is to switch the lines from another source, say run a lines up from the blade to the main boom and switch them to determine if that tells me anything.
You don’t have to switch anything, just disconnect the line from boom down, plug the hose, install the tee for the gauge in to the work port for boom down, cap/plug the free end. Then activate the boom down function and watch the pressure. If the pressure will go to spec - then the problem is downstream from the DCV. If not - start checking LS pressure while activating the function, and/or port relieve.
 

TVA

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Another thing - dead head some other cylinder while you reading the boom down pressure, if the boom down pressure will go higher than it does when you use only boom down - the problem is LS.
 

TVA

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Not that would affect only the boom down circuit. The only reliefs are the circuit reliefs and the LS limiting valve, which affect all functions.

When you say you "checked the pressure at the top and bottom of the spool with in-line gauges", do you mean at the hoses to the boom cylinder or the servo caps that actuate the spool. There is a pressure tap on the right side of the valve looking from the counterweight, pointing straight down. This should be your LS pressure which will tell you your working pressure.
You are not exactly right - there’s a port relief on both work ports. That can be a culprit.
 

Ben Witter

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Is your stand by and/or LS margin is 500 psi? You might have LS shuttle problem inside the DCV.
Standby pressure should be appr 310-335psi and there are no LS shuttles or check valves. That function is accomplished by the compensators in each spool section.
You are not exactly right - there’s a port relief on both work ports. That can be a culprit.
I had already asked him if he had swapped the port reliefs. If you look at his question before that post he asked if there were any reliefs other than the port reliefs.
 

TVA

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Standby pressure should be appr 310-335psi and there are no LS shuttles or check valves. That function is accomplished by the compensators in each spool section.

I had already asked him if he had swapped the port reliefs. If you look at his question before that post he asked if there were any reliefs other than the port reliefs.
Is that post compensated DCV?

Sorry I’ve missed the swapping port relief part.
 

TVA

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Not 100% certain of your terminology.
The only LS DCV that doesn’t have the LS shuttle I know - is what they call “post compensated” DCV.
Like CAT 420 backhoe have.
Even Danfoss PVG100, which is Post Compensated DCV still has LS shuttle valves. Without the shuttle valves in pre compensated DCV you will not be getting the correct LS signal.
 
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