[orbit1957]

It’s been a few years since I marched down the gold hydraulic block path but I’ll try to recall what I know. I have a spare block… part of the di$covery phase of my journey… 

My coach is a little different with a Cat-13 engine and VICKERS 20 hydraulic pump but I’m betting the manifold is the same. I’ll speak to mine

You’ve been introduced to the spool valve and the orifice used to determine fan RPM in either low or high speed. It’s been a while since I tried to chase down manifold info. 

The manifold was designed by HydraQuip in Tulsa OK. The designer has moved on. 

In addition to the spool valve system there are two pressure relief valves, RV5 and RV6. The RV5 valve is the overall system pressure regulator while the RV6 valve protects the ZF Steering Gear box.
The ZF Gearbox also has its own internal pressure relief system, the RV6 is an extra measure of protection. 
On mine… if I recall, RV5 should be set somewhere around 2250 psi and the RV6 is set at a lower pressure, 1800 psi ish. On the forward side of the block you should find the values stamped in the block. Your pressures may be different, I’m assuming a DD60 and a different hydraulic pump.

On mine, LOW SPEED FAN is equivalent to 1/2 the engine RPM. If the Engine ECM calls for HIGH SPEED FAN the ratio is 1 to 1.

If I recall, my orifice disc was stainless steel. 

Eliminating the orifice disc could change behavior of the fan RPM system. 

I do know that the system was designed to share hydraulics and in LOW priority goes to the ZF Steering Gearbox. In HIGH…. The fan is the priority and the gearbox gets what is left over. 

BTW
The ZF RAS System hydraulics is a separate closed loop system that incorporates a hydraulic pressure accumulator to function properly. 

The forward “MASTER CYLINDER” utilizes gearbox hydraulic pressure for assistance moving the internal components of the cylinder but is not directly involved in moving the TAG tires. I’ve posted extensive information about the ZF RAS system. 

The ZF RAS Pressure Accumulator has a 10 year life span. If you have an original it should be replaced or the TAG steering system will not funny properly and can become inoperative to the point you will not be able to back up your coach in certain circumstances. The TAGS will caster forward but not backwards like the front wheels of a shopping cart. 

I’m here to help if you need anything. 
JK

Hi Jeff, Great info to help understand our hydraulics better.  I'm lacking any low speed fan operation.  I thought I read that at some point it was suppose to be that way. If you or anyone else have any information on the low/high speed configuration please pass it on. Thanks for sharing.  Kevin