The Craftmans Shop > New from Old
JCB 803 Saga
awemawson:
Then cut the male and female ends to form the adapter.
I decided to use those 'bonded washers' to avoid threading too close to the shoulder
awemawson:
Then with loads of Loctite Hydraulic seal it all went back together.
I'll leave it overnight to set fully as I reckon it's only a 25% chance it'll work anyway and no point in putting 3000 psi on it unless the gunge is fully cured
mattinker:
With baited breath!
awemawson:
Yes - me too Matthew :med: it needs 18-28 hours for full strength (Loctite 542)
Mean while I've bee trying get to grips with exactly what is inside this ridiculously expensive block of aluminium. In the attached picture the area marked '1' inside a dotted line represents the block:
1F are dual non-return valves
1B is the Digging and Tracking Main Relief Valve
1D is the Pressure Reducing Valve
So presumably high pressure oil from Pump 3 and Pump 2 pass straight though the block onward to various spool valves, but they both can vent back to the tank via the '1F' non return valves, and the '1B' Digging and Tracking Main Relief Valve, onward through the oil cooler '24' and the Return Filer 17 (which has a bypass).
Now to the bit I don't understand: there is a dotted line implying a control dependency, between 1B and 1D, and the input to 1D comes from Pump 1 via '23A' which is a 'Pressure Maintenance Valve' and this is associated with a 'Solenoid Lock Valve 21' that I know is operated by a micro-switch in the left hand hand rest preventing the servo circuits working unless the arm is folded down.
So everything in the block '1' could be replicated with off the shelf bits if I understood the linkage between 1B and 1D. Unscrewing the 1B Digging and Tracking Main Relief Valve there is visible a peg protruding from the device on the other side of the block that I suspect bears on the plunger of 1B opening it up. So I think that that is the physical linkage - there is a bit of verbage in the manual thus:
"The main relief valve for P1 is located on the inlet side of the four section control valve block and is set to open at 172 bar (2500 psi). The main relief valve for P2 and P3 is located in the Main Relief Valve Block (my problem child!) and has dual setting of 207 bar (3000 psi) and 175 bar (2550 psi) depending on the hydraulic load on the engine. The valves are designed to protect the pumps against over pressurisation when a selected service is stalled or the ram reaches the end of it's travel"
mattinker:
I agree, in the "verbage" I read that these are mechanical interlocks to prevent loss of pressure or damage through back pressure when two valves dump at the same time. The three circuits are running at different pressures but they dump through a common filter circuit. I imagine that there is some other security device so that if one is dumping another can dump elsewhere. How many of these circuits can function at the same time? What about dumping through separate circuits or adding non return valves to avoid the need for an interlock?
Thoughts! Regards, Matthew
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