PAS pressure line to rack - restrictor / valve?

[Error404]

I'm working on a custom adjustable bleed valve on the hydraulic line from the pump to the rack, bleeding off pressure back to the return line to the reservoir. this will reduce the assistance at the rack and add some much needed weight to the steering.

I know there is a restrictor valve or similar in the factory feed line to the rack, does anyone have any details on it? IIRC removing makes the rack noisier?

[mcandmar]

Clever idea, but dosent the servotronic rack do the same thing?

[Error404]

yeah thats the basis of what servotronic does, but at the rotary valve in the rack - not sure it could be easily modified. Even with it disconnected though its still way too light anyway.

The stock operating pressure is AFAIK 140 bar. Does anyone know the approximate flow rate of the vane pump?

[quattro]

brilliant i will be watching this very close.

[Pirvu Eugen]

I have read before something from ZF...about the steering systems...but i cant remember something about the flow rate...just pressure.
I will use the Merc A classe electric steering pump...and i will use an adjustable brake pressure regulator to adjust the steering feedback.
Dont know iff will be good or will force the pump too much
I will test.

[quattro]

Could look at something to re circulate the excess in to the header tank to stop the pump being over pressurized maybe, like a flow controlling 'T'.

[Pirvu Eugen]

This is what servotronic does....but how big the hole should be to keep the pressure in the system lower than the pump bypass valve.
At electric pumps..this is easy...but at engine driven pumps...not soo....at idle you have a flow...at 7440 rpm...totaly diferent..
Hmmm..good question Alex!

[Error404]

You need to bleed off excess pressure so you don't simply restric the pressure line and overload the pump. An adjustable pressure relief valve is required that returns excess pressure (fluid) to the reservoir. I am looking to adapt a stock pressure line by adding fittings to plumb in a relief valve, and a new return line to T into the return line back to the res before / after the bomb return.

I have been looking at 250bar valves with a 30L/min flow capacity which should be plenty enough, i can't see that the PAS system circulates its circa 2L capacity in 4 seconds!

[Pirvu Eugen]

250 bar is too much! The power steering side of the pump has the pressure relief valve built in adjusted at Aprox 75-90 bar. The brake side has no relief valve....and is pumping aprox 150 bar....the relief valve for that is in the bomb.

[Error404]

no, the max operating pressure of the valve is 250bar

You can adjust the relief setting down to approx 50 bar