 OK, I had already composed this story before I read your last post, so after all that, I'm sending it anyway. See sketch of hydraulic circuit on test port question. Hope this helps. Stay in touch.
JMOR Hang with me here, but I believe part of our (meaning everyone, I guess?) communications problem is nomenclature. 1) The FO-4 I&T manual refers to CONTROL VALVE for the 9N. It refers to the two "control" valves for the 8N as INTAKE CONTROL valve & EXHAUST CONTROL valve.
2) Same manual (for both 9N & 8N) refer to the pump valves (like those that you and I commonly talk about in an engine as Intake & Exhaust) as INLET VALVES & OUTLET VALVES.
3) In discussing these hydraulics, I find it clarifying to talk in more detail than to refer only to the CONTROL VALVE. It is actually two valves in one and I talk about those two functions. This CONTROL VALVE is doing exactly the same thing as the two (INTAKE CONTROL valve & EXHAUST CONTROL valve) of the 8N do. That is an INTAKE Control function & an EXHAUST Control function. I can easily see the potential for a headache here! :) In all of my discussions in these postings, I don't recall ever intentionally referring to the "INLET VALVES/OUTLET VALVES" of item 2 above. When I have used the terms 'Intake valve' and 'Exhaust valve', I have been careless and should have said, "Intake Control & Exhaust Control" valves. Even if I have slipped up and used the terms Inlet/ Outlet valves, I likely still was NOT referring to those of item 2 above, but intending INTAKE CONTROL & EXHAUST CONTROL. Sorry. With all that in mind, on to the next part of your last post:
"The control valve mounted in the base of the pump on the other hand directs the constant output flow to the work circuit (lift cylinder) in the raise position. In the neutral position it vents the output flow back to the sump and also acts as a check valve on the work circuit to prevent reverse flow (maintain the lift position). In the down position the control valve opens further and allows the oil in the work circuit to return to the sump." Don't get offended now, as I am just stating the direct facts. No attack/flaming intended. 1) It is not a constant output flow pump. The pump ONLY produces output flow when it can suck something in & that can only happen when the INTAKE CONTROL valve is open. Other wise it is just sucking against a capped off pipe, so to speak. The INTAKE CONTROL valve opens the path from pump suction to the sump/reservoir when the CONTROL VALVE on 9N is pushed forward/into the pump housing. On the 8N this would be when the INTAKE CONTROL valve is pushed forward into the housing and the EXHAUST CONTROL valve, via pivoting rocker lever, is pulled out/toward rear.
At this time, 8N's Exhaust Control valve is closed, preventing the dumping or exhausting of oil from the ram cylinder.
The same is true of 9N except that the function is accomplished by the opposite end of the "combination/dual function" CONTROL VALVE.
2) Neutral: The inlet to pump is shut off by INTAKE CONTROL valve (outside end of CONTROL VALVE of 9N), so there is no additional output flow from the pump since there is nothing for it to suck. (Note that it is not venting output flow back to the sump, nor is it acting as a check valve.) There is a CHECK VALVE. It is part of the Relief/Safety/Overpressure valve ASSEMBLY. This is actually two valves in one assembly. The part extending furtherest into the pump is the CHECK valve and the outermost part is the overpressure valve.
(Some I&T manual drawings actually show this as separate items, some as a single item...maybe old style/new style?).
3) The pump outlet is ALWAYS connected to the ram cylinder via Check valve. The CONTROL VALVE (valveS in 8N), does NOT disconnect pump outlet to ram cylinder. Yes, I know that is probably an eyebrow raiser, but what can I say? Lift position is being maintained by a closed CHECK VALVE, closed Relief valve (overpressure if you like, or Safety..you name it), AND the closed Exhaust Valve.
4) Down: INTAKE CONTROL valve remains closed, and EXHAUST CONTROL valve opens, EXHAUSTING the ram cylinder's oil back to the sump.
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- Inlet/Intake, Outlet/Exhaust - arrgh! Ok I'm up to speed and I think we are speaking the same language now - thank you. I also went back and read some of the archived exchanges from Llamas, tOTG, and Zane about this. TOTG had a mod for isolating the lift circuit from the rest of that mechanism altogether and controlling it with an external valve - I had his writeup on it once but I''ve lost it and tOTG's web site is long gone. I've posted in the past asking for someone with a copy to make it available but no one has come forward. I pretty much remember what he said to do and can probably reconstruct it from memory. It's a modestly aggresive mod to the top cover - probably not for the faint of heart or poorly equipped.
