Do I need an additional Relief Valve?

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Luthor

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The operating manual that came with my FFC Mini Back Hoe attachment states that you must remove a plug from the hydraulic control valve and replace it with Bobcat P/No 6599161 (for Bobcats without BICS, mine is a 743). This is said to protect the base end of the tilt cylinder.
These instructions have confussed me because the parts manual shows a valve with the above P/No already fitted to the Melroe hydraulic control valve although the location of it and the so called 'plug' and anti cavition valve may be a bit misleading ( pages 75 to 78 if anyone has the 743 parts manual.)
The service manual for the 743 has no information on the Melroe control valve but does mention that repair information can be found in the component repair manual. Does anyone have this information? The operating manual for the mini hoe can be found at www.ffcattachment.com/products if you are interested.
Basically I am asking do I need to fit this additional relief valve and if so why and where does it go?
Thanks guys.
 

Tazza

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Working link.
http://www.ffcattachments.com/
I think i understand them now.
If you look at your control block for the section that controls the lift arms, it has a relief valve installed, i think its around 5,000 PSI. I spoke to my local dealer about this and he said its to protect the lift rams and hoses from pressure spikes generated if a load was to be drooped on the bucket. Basically when the spool is in centre no oil can flow either way, so essentially if you got a ram and pit it in a press you could create so much pressure that the cylinder or hoses could rupture.
Now for the why its needed, with the hoe attached to the QA plate. You have more leverage with the extra boom length and powerful hydraulic cylinder for the bucket curl. You hook into a hard bit of rock that would pull at the tilt ram causing excessive pressure, essentially like i said earlier with putting the ram in a large press. I do believe the cylinders and hoses could take the extra load but it also puts more load on your pins and where the stick is welded at the bobtach.
As for where to install the relief, look at the back of the control block, there will be a round plug rite next to the alloy cup that holds the centering spring, thats the plug you want. The ones facing the LH wheel either side of the ports are your load checks.
If any of that doesn't make sense i'll try and explain it a bit better.
 
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Luthor

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I think i understand them now.
If you look at your control block for the section that controls the lift arms, it has a relief valve installed, i think its around 5,000 PSI. I spoke to my local dealer about this and he said its to protect the lift rams and hoses from pressure spikes generated if a load was to be drooped on the bucket. Basically when the spool is in centre no oil can flow either way, so essentially if you got a ram and pit it in a press you could create so much pressure that the cylinder or hoses could rupture.
Now for the why its needed, with the hoe attached to the QA plate. You have more leverage with the extra boom length and powerful hydraulic cylinder for the bucket curl. You hook into a hard bit of rock that would pull at the tilt ram causing excessive pressure, essentially like i said earlier with putting the ram in a large press. I do believe the cylinders and hoses could take the extra load but it also puts more load on your pins and where the stick is welded at the bobtach.
As for where to install the relief, look at the back of the control block, there will be a round plug rite next to the alloy cup that holds the centering spring, thats the plug you want. The ones facing the LH wheel either side of the ports are your load checks.
If any of that doesn't make sense i'll try and explain it a bit better.
Thanks Tazza for that explanation. Yes I thought it had something to do with the high pressures that could be generated while digging that could burst a hose or damage some other part of the system.
The only problem is that to fit the relief valve into the tilt circuit I would have to remove the anti cavitation valve. What is more important, the anti cav or the relief valve?
 

Tazza

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Thanks Tazza for that explanation. Yes I thought it had something to do with the high pressures that could be generated while digging that could burst a hose or damage some other part of the system.
The only problem is that to fit the relief valve into the tilt circuit I would have to remove the anti cavitation valve. What is more important, the anti cav or the relief valve?
I have never understood how the anti-cav valves actually work and more to the point how they prevent cavetation. In your case i'd rather have the slight chance of cavetation rather than blowing a cylinder or hose.
 
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Luthor

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I have never understood how the anti-cav valves actually work and more to the point how they prevent cavetation. In your case i'd rather have the slight chance of cavetation rather than blowing a cylinder or hose.
A combination anti cav/ relief valve would solve my problems.
 

Earthwerks Unlimited

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Maybe Im missing something...but if a backhoe is used on SSL, doesn't it have a positive mounting going back to the loader chassis other than just using the mounting plate and the tilt cylinders to prevent it from moving? I'm a New Holland guy so forgive me :)
 

Tazza

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Maybe Im missing something...but if a backhoe is used on SSL, doesn't it have a positive mounting going back to the loader chassis other than just using the mounting plate and the tilt cylinders to prevent it from moving? I'm a New Holland guy so forgive me :)
You are rite, the proper hoe attachments do mount to the main chassis but this one mounts to the quick attach plate only. It does not swing from side to side, it only curls the bucket. So you use your arms, bobtach tilt and drive wheels to pull and lift. Does that make any sense?
 
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Luthor

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You are rite, the proper hoe attachments do mount to the main chassis but this one mounts to the quick attach plate only. It does not swing from side to side, it only curls the bucket. So you use your arms, bobtach tilt and drive wheels to pull and lift. Does that make any sense?
Yes sorry Earthwerks, this is not a conventional backhoe attachment, it is a mini hoe as Tazza described above. You can see it by going to the FFC website and clicking on Mini Hoe from the list of attachments.
A little update after a day of chasing a relief valve and some flat faced hydraulic couplers: there actually is a combination anti cav/ relief valve available for this aplication on the 743, it is even shown in the parts manual (I missed it when I first looked there). The price approximately $250 for Bobcat Australia.
This little hoe is really quite good for trenching etc. as I used it for the first time today doing about 40 meters by 700mm deep in a couple of hours which seems aceptable for this type of machine and a first time operator, not to mention quite a few rocks along the way of 400 to 500 mm diameter.
 

skidsteer.ca

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Yes sorry Earthwerks, this is not a conventional backhoe attachment, it is a mini hoe as Tazza described above. You can see it by going to the FFC website and clicking on Mini Hoe from the list of attachments.
A little update after a day of chasing a relief valve and some flat faced hydraulic couplers: there actually is a combination anti cav/ relief valve available for this aplication on the 743, it is even shown in the parts manual (I missed it when I first looked there). The price approximately $250 for Bobcat Australia.
This little hoe is really quite good for trenching etc. as I used it for the first time today doing about 40 meters by 700mm deep in a couple of hours which seems aceptable for this type of machine and a first time operator, not to mention quite a few rocks along the way of 400 to 500 mm diameter.
Just don't get to rough with it. These mini hoes put alot of pressure on the QA lock pins and some have ripped the lower holes right out on the qa plate welded to the hoe. The bobtach was never really designed to have a long boom lifting up on the front of the machine. it was designed to have the stress pushing down.
Ken
 

Earthwerks Unlimited

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Just don't get to rough with it. These mini hoes put alot of pressure on the QA lock pins and some have ripped the lower holes right out on the qa plate welded to the hoe. The bobtach was never really designed to have a long boom lifting up on the front of the machine. it was designed to have the stress pushing down.
Ken
Ken I have to differ with you on the QA design not withstanding upward pressure. I have a 20' boom attachment on my New Holland LS185.b that I can pick up (tilting back off the rear bumper) the entire machine off the ground with no problems. In fact the Owners Manual says do not bull doze forward with the bucket fully dumped but it's okay to backdrag, which puts a lot of pressure on it. I do agree that if the GA attachment's holes are substandardly out of shape, in the wrong position even slightly, or the steel used at that point is not up to par, then yes--you will lose it. Also, if the QA mounting plate's locking pins are not up to par and don't or can't keep the proper down pressure, then yes you'll lose it. But those issues don't fall abck to a faulty design IMO. With my background in product liablility (automotive), IMHO, not one skid steer would be in use if there were even a small chance that a customer could lose a bucket or attachment by applying downforce. Now, some quick attach excavator buckets are a different story---many workers (in trenches for example) have been killed by a QA bucket falling off as they were not properly installed. Subsequent systems have a backup lock of some sort
 

Tazza

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Just don't get to rough with it. These mini hoes put alot of pressure on the QA lock pins and some have ripped the lower holes right out on the qa plate welded to the hoe. The bobtach was never really designed to have a long boom lifting up on the front of the machine. it was designed to have the stress pushing down.
Ken
That price is insane! Its the sort of thing if you knew the sizes and thread you should be able to get it from a hydraulics store cheaper. I don't think i'd go out especially to buy flat face couplers, they are expensive and i hear changing the O rings really isn't easy if even possible for *normal* people. If you really feel you need the relief valve, i'd talk to bobcat parts manager first. His prices are better than anything i can get from my local dealer and it only takes a few days from Utah to Australia.
Glad your hoe works for you, i dug about 40-50m over the last few days, its 300 wide and up to 1m deep. That was through shale and clay. It was hard going, some sections even needed a jack hammer to cut through the rock, thankfully only a few spots.
 
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Luthor

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That price is insane! Its the sort of thing if you knew the sizes and thread you should be able to get it from a hydraulics store cheaper. I don't think i'd go out especially to buy flat face couplers, they are expensive and i hear changing the O rings really isn't easy if even possible for *normal* people. If you really feel you need the relief valve, i'd talk to bobcat parts manager first. His prices are better than anything i can get from my local dealer and it only takes a few days from Utah to Australia.
Glad your hoe works for you, i dug about 40-50m over the last few days, its 300 wide and up to 1m deep. That was through shale and clay. It was hard going, some sections even needed a jack hammer to cut through the rock, thankfully only a few spots.
Yes Ken I thought about that but this attatchment has some extra clamps that pull the Hoe up against the flat face of the Bobtach to relieve most if not all of the load on the QA pins. As long as these clamps are regularly checked for tightness I don't see a problem there.
Tazza I got 2 sets of flat faced coupler, one set for the Bobcat itself and the other for my 4 in 1 bucket so now I can easily swap attatchments and even fit hired ones as they all use the same coupling now. At $80 each piece ( $320 total) they are not cheap but certainly are superior to the old type.
 

Tazza

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Yes Ken I thought about that but this attatchment has some extra clamps that pull the Hoe up against the flat face of the Bobtach to relieve most if not all of the load on the QA pins. As long as these clamps are regularly checked for tightness I don't see a problem there.
Tazza I got 2 sets of flat faced coupler, one set for the Bobcat itself and the other for my 4 in 1 bucket so now I can easily swap attatchments and even fit hired ones as they all use the same coupling now. At $80 each piece ( $320 total) they are not cheap but certainly are superior to the old type.
You feel they are better? do they simply not leak or something?
I always figured they were essentially the same, just looked "prettier"
With that said, i like the fact they are easy to clean unlike the standard ones that you need to get into the female connector with a rag to remove and dirt that may have gotten in. My new 751 has the flat faced connectors, i guess i will find out in time the advantages of them.
 

skidsteer.ca

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You feel they are better? do they simply not leak or something?
I always figured they were essentially the same, just looked "prettier"
With that said, i like the fact they are easy to clean unlike the standard ones that you need to get into the female connector with a rag to remove and dirt that may have gotten in. My new 751 has the flat faced connectors, i guess i will find out in time the advantages of them.
Earthwerks
When you backdrag, the lever effect of the bucket is only 30" long, but with a mini hoe they are 2 times that, then the hoe bucket on the end has enough force (if its like my bobcat hoe) to drag the machine around. Mr Jimi (I believe it was) went to buy a used one and it had the lower holes ripped out. Glad to here this one has additional clamps. I'm sure it also depends alot on how its made/used.
As for the flat couplers, keeping them clean is the big advantage. The do wear out and I know of no way of fixing them. Some of the fellows on ebay will sell them for $45 a set if you buy 5 sets at a time. Ocasionally the bidding goes that low on one set. They can be vary hard to get together if they have hyd pressure behind them. The one on ebay have a 1/2" npt thread for the hose, the only place I know to get the #12 orb is from the dealer and they are 75 to |$80
Ken
 

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