[AT] 8.9 liter Perkins

[Cecil Bearden]

On an open center system the pump flow is going through the valve and 
returning to tank at near zero pressure.  When the valve is actuated the 
relief valve comes into the circuit.

Cecil


On 2/23/2019 10:30 PM, Rena Glover Goss wrote:
> What do you think is happening when the engine on your log splitter is running but the control valve is not actuated and the cylinder is not moving?
>
>
> Larry
> ---- Dennis Johnson <moscowengnr at outlook.com> wrote:
>> James,
>>
>> I agree that using relief valves to regulate pressure or flow is not a good thing, especially with a fixed displacement pump. I have seen it done before, but agree that it generally just makes heat. It might work with open center valves where there is no pressure in the circuit until a valve is actuated. With closed center valves it is just a heat generator that wears out relief valves and hydraulic fluid.
>>
>> I have trouble believing a tractor manufacturer would design a system like this. I think a more probable design would be a 3 stage pump or multiple pumps. If they were pressure compensated pumps it would be a great circuit.
>>
>> Thanks
>> Dennis
>>
>>
>> Sent from my iPad
>>
>>> On Feb 23, 2019, at 3:52 PM, James Peck <jamesgpeck at hotmail.com> wrote:
>>>
>>> Pressure Relief Valves used to regulate pressure on fixed displacement pump systems waste energy by relieving pressurized fluid back to tank. In one mobile equipment project, we used flow over a pressure relief valve to heat hydraulic fluid to the minimum temperature needed to allow the main pumps to operate.
>>>
>>> Three pressure relief valves may generate the heat Cecil was mentioning.
>>>
>>> Maybe one of us can dig up a hydraulic schematic for an MF 1155.
>>>
>>> With pressure compensating pumps you only need to use a pressure relief valve to set the pilot pressure to the pump. This wastes much less energy as you only have pilot flow going back to tank.
>>>
>>> https://www.hydraulicspneumatics.com/other-technologies/book-2-chapter-18-pressure-relief-valves
>>>
>>> [Larry Goss] It's not uncommon to find multiple pressures on various portions of a hydraulic system.  The easy way to do it is just to "daisy chain"  the control valves with lower and lower operating pressures on the relief valves. The last system simply dumps back into the reservoir.
>>>
>>> [ James Peck]  3 pressure systems? Does that mean three hydraulic pumps? Where were they all located?
>>>
>>> [Cecil Bearden]The high pressure 3000+ psi for lift, the 1500+ for steering and then the  +/-500 psi for multi power clutches controls and PTO controls.   We had one for several years.  MF left out a snap ring in the PTO clutch and it did not work for the original owner.  It was 6 years old when we bought it.  We had to pull the cab and the top deck to find the problem.  A few years later my Dad put the wrong oil in the hydraulics and the multi power and PTO started to have problems.   Later found the O-rings were going bad and to repair meant nearly a complete disassembly of the tractor.   It went to Mexico.
>>>
>>> A few years later we bought a 7030 Allis Chalmers to replace that tractor.  The Allis has the same features and a few more, but only one pressure system.   After I sealed off the dash to get the Air conditioner working it was  very good tractor and very simple. The problem with it now is a large diameter O-ring in the main clutch is going bad.  It means a split of the tractor, but can be repaired for a 2 day job...
>>>
>>> I really liked that 1155 Massey, but it developed so many problems and used so much fuel it was a pain.  The V-8 has to be kept running above
>>> 1900 rpm or it gets hot...    Our 1155 was built while Massey was having a lot of problems.  I grew up in a MF dealership, and I bled red & grey, had red & grey underwear too.  But that 1155 we had just ruined Massey as far as I am concerned.   They got more complicated than necessary.
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