The Classic Machinery Network

Jeremy Rowland wrote:Mike glad you got it sorted the pressure you quoted sounds to be in the right ball park to me although somebody may now the exact figure.

Jeremy

Hi Mike, I'm glad your sorted too
You don't have to worry about bits from the blown filter going through the system. The filter that blew is the return line filter and any debris from there could not enter the system as it would be held back by the suction filter which you washed. There's nothing wrong with washing that out either.
I have just checked the 3CX manual on here for the pressure readings and was surprised to find that the "main line relief valve" setting is 3,500 lbs.ft.
Where are you taking your reading from Some parts of the loader system are regulated to lower pressures, ( 2,500 lbs.).
Pressures should be taken at 1,500 rpm.

Fred

It managed to get to 2500psi when the ram maxes out.
Gave her a bit of hard work and all seems good.


If anyone could confirm the actual pressure readings I should be expecting, would be much appreciated.

Hi Mike.
These are the loader valve pressure settings.

Main relief valve. (MRV) 3,420 to 3,500
[Unloader 3,000 to 3,100]
Auxiliary relief valve (ARV)
Ram (head side) 2,500 to 2,600
Ram (rod side) 4,500 to 4,600

In my previous post I asked you where you connected your pressure gauge
I suspected that you may have teed into the loader ram connections and you will see from the above figures that the MRV will over ride the ARV and prevent the pressures rising above 3,500 lbs. at the rod end of the ram.
The ARV for the head end of the ram will, in turn, over ride the MRV setting and the pressure at this end will be further reduced by the ARV to 2,500 lbs.
This would be close enough to your reading
I hope you can follow this.

Fred

FOWLER MAN wrote:Hi Mike.
These are the loader valve pressure settings.

Main relief valve. (MRV) 3,420 to 3,500
[Unloader 3,000 to 3,100]
Auxiliary relief valve (ARV)
Ram (head side) 2,500 to 2,600
Ram (rod side) 4,500 to 4,600

In my previous post I asked you where you connected your pressure gauge
I suspected that you may have teed into the loader ram connections and you will see from the above figures that the MRV will over ride the ARV and prevent the pressures rising above 3,500 lbs. at the rod end of the ram.
The ARV for the head end of the ram will, in turn, over ride the MRV setting and the pressure at this end will be further reduced by the ARV to 2,500 lbs.
This would be close enough to your reading
I hope you can follow this.

Fred

Hi Fred,

Sorry I missed that post some how, I have connected the tee directly onto the flow line from the pump, just before it connects to the first spool block (bucket controls) , so it will be an un-restricted reading. The 2500psi reading was maxing out a ram on the back hoe.

Am I right in thinking that it's working as expected?

Hi Mick,
You should have 3,500 lbs. The MRV in the loader valve block regulates the pressure to 3,500 lbs. through the whole system.
There is no separate MRV for the digger and the ARVs will be set to a higher pressure.
Is the pressure reading the same whichever service you load up The MRV. may be at fault

Fred

Hi Fred

From what I understand, if the ARV stops at 2500 then the MRV won't have a chance to kick in, so the reading would only be 2500 on the head side? So there should only be 3500 on the rod side because the MRV will kick in before the ARV at 4500?

I have only taken readings on the backhoe, while pulling towards me, which is all on the head side of the ram, which makes sense.
I'll do some other movements on the rod side and also with the bucket, and see if I get 3,420 to 3,500 from the MRV.

So the rod side needs more pressure, because the rod in the cylinder is reducing the surface area that the pressure is acting upon?

Would attaching the pressure gauge at the end of the flow hose connected to the pump (technically capping the pipe off) do any damage to the pump? I'm thinking this is the only way to check that the pump is actually working to full pressure, without any relief valves letting off pressure. The only problem being, my pressure gauge only goes up to 3000psi.

the test point is on the front valve block, when testing use jack legs as there is no arv in circuit,pressure should be 3000psi black cab,3300 grey cab

tom262 wrote:the test point is on the front valve block, when testing use jack legs as there is no arv in circuit,pressure should be 3000psi black cab,3300 grey cab

Hi Tom,
You obviously know your way around the 3CX and that is excellent advice.
I am not too clued up on the 3CX but I got the pressure settings from the JCB manual download below.
The Main Relief Valve setting is shown the same for the servo control and variable displacement pumps too but the settings may well be different for different serial No. machines as you say.

hi fowler man,i've taken the pressure settings from the black cab and grey cab manuals,the above pressures may be off a newer machine,i am guessing the age off 3cx going by the photo of hydraulic filter , cheers