Boom pressure

[IceHole]

Zx40U3 Hitachi.

Bought last fall, haven't used a ton but felt weak.

Was going up a bank and realized the boom is weak to the point it won't lift the machine without alot of fuss. Just hits pressure relief.

I turned the relief up about half a turn, seemed to be fine. Buttoned it up and still an issue.

BUT if I give it just a tad bit of dipper, not even enough to really move it, the boom lifts without trouble.

In the book it shows the main pressure relief is adjustable. But mine is different, has a small pilot line sized hydraulic going to it with a T. So something sends hydraulic pressure to the relief and adjusts it.

Wondering if that's causing it.


Also having related issues with the grapple. I thought it was weak bucket curl, but pretty sure it's the grapple not "backfeeding" when pushed by the bucket. It's a well installed kit that feeds off the boom swing circuit (uses electric diverter valve to switch between the 2).

They are using a DCRV110-12N valve on the boom, which I think is supposed to allow backfeed/crossfeed? I've adjusted all over and either it works as normal or makes it no longer function, or function Verrry slow.

Thought it was a speed control at first asit acts like that.

 

[KOBE STEEL]

Hi

You may have an issue in the control valve within the boom segment or possibly with the pilot signal from the joystick for the boom operation that may be causing the weak boom down issue.

I'm not sure what the pilot hoses would be on the end of your relief valve as it does not show this in the parts diagram I'm looking at for both the 40U-3 and the -2. The only time I've seen this on a main relief is when a remote solenoid operated low pressure signal can be activated and supplied to the end of the main relief to boost its pressure to a higher setting, otherwise the hoses could be an external drain for the relief valve.

The DCRV110-12N fitted to the grapple is a dual cross port relief which may need to be reviewed to ensure that when the grapple cylinder is being opened or closed by an external force, that there is enough displacement in the circuit on the low pressure side of the port relief to allow for oil to flow into. If this relief valve set up is being used on a single grapple cylinder with unequal areas then this type of valve should not be used. Instead, use a 5 port relief with ant cavitation that relieves back to tank instead of cross port. The DCRV110 factory setting is also too low (150 bar) and needs to be increased to at least 265 bar or higher.

 

[IceHole]

Tried to chase down the lines but they blend into bundles of a ton of lines.
None of the books I have show it either.
It has crane mode, so have to wonder. I tried that and still hits relief. Only thing crane mode does that I can tell is not allow bucket curl, kicks on a tonnage reading on the cluster, which doesn't read any weight,and a strobe light comes on.

It's definitely hitting a relief, can hear it. I guess next step is putting guages to see what's going on.

 

[IceHole]

Hi

You may have an issue in the control valve within the boom segment or possibly with the pilot signal from the joystick for the boom operation that may be causing the weak boom down issue.

I'm not sure what the pilot hoses would be on the end of your relief valve as it does not show this in the parts diagram I'm looking at for both the 40U-3 and the -2. The only time I've seen this on a main relief is when a remote solenoid operated low pressure signal can be activated and supplied to the end of the main relief to boost its pressure to a higher setting, otherwise the hoses could be an external drain for the relief valve.

The DCRV110-12N fitted to the grapple is a dual cross port relief which may need to be reviewed to ensure that when the grapple cylinder is being opened or closed by an external force, that there is enough displacement in the circuit on the low pressure side of the port relief to allow for oil to flow into. If this relief valve set up is being used on a single grapple cylinder with unequal areas then this type of valve should not be used. Instead, use a 5 port relief with ant cavitation that relieves back to tank instead of cross port. The DCRV110 factory setting is also too low (150 bar) and needs to be increased to at least 265 bar or higher.

Why would ~2200 psi be too low? It needs to be less than the bucket curl relief right? That's 3200 psi I believe.

 

[KOBE STEEL]

main relief is 3550 psi in the circuit diagram and the port reliefs are 3840 psi so you would normally want your grapple to match those port reliefs.

 

[IceHole]

I'm not understanding.

If the bucket relief is 3550 (left my.computer at the shop so can't check), the grapple relief has to be less right?

 

[KOBE STEEL]

Not necessarily. when using the grapple or any other function besides swing, that operation should relieve at the main relief of 3550 psi at end of stroke or when stalled, but if the grapple is not in use and it takes a shunt from the ground or another object, this will cause an internal hydraulic shock wave which needs to relieved back to tank. As the control valve is not in operation, the control valve is therefor a dead end and the shock wave must then pass through the overload relief / port relief if one has been fitted (such as the DCRV110-12V). If port relief is set too low the attachment can be slow to operate or weak to clamp and hold. If the main relief or port relief is set too high there is a risk of damage to the attachment during operation or under shock load conditions. Some attachments require lower operating pressures in which case the port relieves will usually be set to this requirement and can sometimes be provided with the attachment.

 

[IceHole]

Not necessarily. when using the grapple or any other function besides swing, that operation should relieve at the main relief of 3550 psi at end of stroke or when stalled, but if the grapple is not in use and it takes a shunt from the ground or another object, this will cause an internal hydraulic shock wave which needs to relieved back to tank. As the control valve is not in operation, the control valve is therefor a dead end and the shock wave must then pass through the overload relief / port relief if one has been fitted (such as the DCRV110-12V). If port relief is set too low the attachment can be slow to operate or weak to clamp and hold. If the main relief or port relief is set too high there is a risk of damage to the attachment during operation or under shock load conditions. Some attachments require lower operating pressures in which case the port relieves will usually be set to this requirement and can sometimes be provided with the attachment.

I looked it up.

Main relief is 3550
Bucket relief is 3840.

I assumed all functions went through main relief?

 

[KOBE STEEL]

may have to do some tests with some pressure gauges. Let us know what you find if you get the issue sorted and if you need any help just post back.

 

[IceHole]

may have to do some tests with some pressure gauges. Let us know what you find if you get the issue sorted and if you need any help just post back.

I have pressure and flow guages, just had to order hoses. Someone decided they wanted them more than me apparently.
Least my flow gauges didn't walk off, the bigger one was $6 or 700.