PAS Questions...

[Welly]

OK - Many of you know I've had some issues with my high pressure line on my PAS.

Does anyone have an in depth knowledge of how the pressure relief valve works on these pumps, or more to the point, if they have one.

Also - the is a pressure switch in the top of the high pressure line banjo. My understanding of this is that it signals thge ECU to bring idle speed up if the pressure exceeds X load at idle, to help prevent stalling.

Any info useful.

 

[Welly]

The only useful thing I found at all was this: VWVortex.com - How to increase steering effort: modify power steering pump relief valve spring?

And it's not even that useful

 

[aragorn]

The relief valve will act on the output of the pump, and dump fluid back to the inlet.

Its not used much, probably the only time it will really open is if you jam the steering against full lock.

 

[Biggied]

There is defo some form of pressure relief system within the pump as its belt driven & when @ its highest pressure (high rpm) there is usually very little steering input so the pressure has to be regulated somewhere, your also correct about the pressure switch & the banjo joint on the pump, this is simply to tell the engine ecu to bring the revs up when higher pressure is needed @ low revs (ie parking etc) & dosn't control actual pump pressure, this much I'm sure! I'm away to stare under the bonnet of my S3 for a while & see if I can come up with any possable reason to your problem, is the pipe cracking on the metal section right after the flexi part around the area of the gearbox mount?

Ewan.

 

[Welly]

OK, I shall try and describe....

Out of the pump banjo, runs down and in front of the pump. Then heads back towards the block, at this point there is approx 120 degree bend to the right, before the pipe runs along the front of the block.

It is cracking just before that 120 degree bend. Long before the first flexi, it's literally about a foot away in pipe length from the pump.

 

[aragorn]

Pressure is generated by a restriction, and when your not moving the wheel, the rack offers little restriction, the fluid flows streight thru the rack and out the other side and the system pressure is low. This is nothing to to with the relief valve. At high rpm, theres still no restriction, so you just get a larger volume of fluid passing streight thru the rack and back to the reservoir, still at a low pressure.

When you steer, the pressure in the system climbs, as its the pressure thats doing the work. The valves inside the rack create a restriction in a particular direction and the resulting pressure is what helps move the rack.

At full lock the pressure is at its highest, because the rack is trying to provide assistance against something that wont move, which is why you somtimes hear the belt slipping on cars at full lock, along with a straining noise from the pump. This is also the point at which the relief valve would open, if the pressure limit is exceeded.


Welly: is the metal pipe bolted to the pump so that its supported on either side of the bend? If so, is there anything that could cause a miss alignment between the two supports, and if its not supported at all, why not?

 

[Welly]

^^ I like this - good info and good points.

 

[Biggied]

Ok I've had a good old look over my car at where the PAS pipe runs & is mounted etc, IF your pipe has cracked/fractured right after the flexi part I can only asume this to be due to exessive movment of the engine/box or miss alignment of the pipe etc. While I can see from your previous threads that your not shy with the spanners & seem to get on quite fine with your automotive diy the engine & subframe have been off the car, mistakes can & will happen & things can & will get missed(no offence intended at all mate) you also apear to still have an unkown knocking noise.

I'd suggest you double check that the main mount on the end of the gearbox is tight & not moving around, also check where the mount is sitting as the holes are sloted & theres a fare bit of adjustment to be had, this is a long shot a best but if your subframe was refitted (also sloted mounts) as far back as it will go & the mount was refitted as far forward as it will go there may not be any flexi left in the pipe (it ain't got alot of give) putting all the load of the engine/box movment on to the metal part of the pipe causing the crack/fracture??
Even just try getting sombody else to rock the engine back n forth by lifting the clutch while you watch what the pipe/mounts are doing. This lot may prove pointless but if it helps locate your noise & solve the PAS pipe problems then its worth a look.

Ewan.

 

[Welly]

Ok I've had a good old look over my car at where the PAS pipe runs & is mounted etc, IF your pipe has cracked/fractured right after the flexi part I can only asume this to be due to exessive movment of the engine/box or miss alignment of the pipe etc. While I can see from your previous threads that your not shy with the spanners & seem to get on quite fine with your automotive diy the engine & subframe have been off the car, mistakes can & will happen & things can & will get missed(no offence intended at all mate) you also apear to still have an unkown knocking noise.

I'd suggest you double check that the main mount on the end of the gearbox is tight & not moving around, also check where the mount is sitting as the holes are sloted & theres a fare bit of adjustment to be had, this is a long shot a best but if your subframe was refitted (also sloted mounts) as far back as it will go & the mount was refitted as far forward as it will go there may not be any flexi left in the pipe (it ain't got alot of give) putting all the load of the engine/box movment on to the metal part of the pipe causing the crack/fracture??
Even just try getting sombody else to rock the engine back n forth by lifting the clutch while you watch what the pipe/mounts are doing. This lot may prove pointless but if it helps locate your noise & solve the PAS pipe problems then its worth a look.

Ewan.

Whilst I appreciate your comments, you have the wrong end of the pipe (dum dum tsssh)...

It's right next to the PAS pump it's going mate, engine side.

Also, the subframe hasn't been off, so where you got that from I don't know....

I can also guarantee that it's not engine movement related - as there isn't much.

Further to this, the unknown knocking noise, isn't a knock, it's a clunk, and is coming from the top mount area....

Go and have a look at where I said it's split, I think from my description you should know where I mean. :thumbsup:

 

[aragorn]

Welly: is the metal pipe bolted to the pump so that its supported on either side of the bend? If so, is there anything that could cause a miss alignment between the two supports, and if its not supported at all, why not?

.

 

[Welly]

Sorry dude, I missed that...

No, there is no support there at all. There are 3 mounting points on the line. One on the side of the gearbox, visible through the wheel well.

The other two are on the front face of the gear box and support the 'windy' section.

The brand new pipe had white marks on it where there were supposed to be clamps holding it on. The clamps were fitted as they are supposed to be, and there were only three sets of marks in the places already mentioned.

The left hand section bolts solely into the PAS pump's high pressure output. There is a location lug on the banjo so it can only be fitted correctly.

So, in answer to your question, No, it is not bolted to the pump. Why not? Because there is no means of doing it at all.

 

[Biggied]

Doooooh, yea I was typing that wild goose chase of a reply at the same time you posted the description, I had the wrong end of the stick (or pipe as it may be) there mate. I thought I read in one of your posts you'd had your subframe off, oh well. wasn't trying to insult your intelagence/skill in that last post mate (although it probably came across like that) was just trying to help kick some ideas around. lol

 

[Welly]

Doooooh, yea I was typing that wild goose chase of a reply at the same time you posted the description, I had the wrong end of the stick (or pipe as it may be) there mate. I thought I read in one of your posts you'd had your subframe off, oh well. wasn't trying to insult your intelagence/skill in that last post mate (although it probably came across like that) was just trying to help kick some ideas around. lol

Thats cool, and my response wasn't meant to be bitey at all dude. I just don't get this problem at all. It's an odd place for it to go, and I don't understand it. There is nil movement there at all to cause this issue.

I'm picking my revised PAS pipe up from this dude tomorrow and the pipe will be mainly flexi until the gearbox now. It will come off the pump and run higher up.

I just don't like the fact I've had 3 sequential unexplained failures.

If it was excess pressure, why would it crack a hard pipe? Why would it not blow one of the flexi joints/hoses. They are weaker than metal.

 

[tompearson]

You haven't got a fray in your aux belt that is slapping against it have you?

I did mine like this, although the belt was completely foobared and the pipe was 6 years old or so at the time.

 

[Welly]

You haven't got a fray in your aux belt that is slapping against it have you?

I did mine like this, although the belt was completely foobared and the pipe was 6 years old or so at the time.

No mate, it's not that. There is no impact marks on the pipe at all.

 

[Welly]

OK, so, problem is now resolved with regard to the pipe.

I fitted my new, Welly design pipe yesterday and so far so good, it's behaving....

Obviously it remains to be seen as to longevity, but hopefully it will simply avoid my issue from here on.

Total cost of change, £19 plus VAT.

This is the change in design: