TheSamba.com :: View topic - High Pressure Power Steering hose 251422893C cut open

Sun Dec 03, 2017 7:43 pm

Aloha folks!

I had a leak on a PS hose , so I cut it open to hopefully re use the fittings.

One might find interesting about the flow restrictor, I saw it mentioned often but never seen one yet.

The actual sleeve crimp you see in the middle of the hose is actually not a restrictor but rather a component of the restrictor system. It restricts and holds the restrictor tube that is inside the power steering hose. That plastic tube has 3 holes going trough it perpendicularly and are located on the pump side of the restrictor sleeve.

The rubber hose is 21.25" long , the crimp sleeve is in the middle
The hose is not cut in the middle

Picture time :P

Sun Dec 03, 2017 10:03 pm

Thanks for the postmortem on the hose. I too had wondered what the internals of the hose looked like, now we all know! Barring any problems with the internal restriction hose itself do you think the external hose could be replaced instead of paying big $$$ for a new one?

Sun Dec 03, 2017 10:46 pm

Thanks for doing that but I miss understanding a few things.

The hard plastic inner pipe seems to be perforated along its length.

This means the high pressure oil runs both inside and along the outside of the inner hard plastic pipe?

Help me understand the relationship of the "restrictor" and the hard plastic pipe.

Does the "restrictor" sleeve simply slip over the hard plastic pipe?
It is then crimped in place as basically a weight?
Or....
Does the "restrictor" prevent oil flow along the exterior of the hard plastic pipe?

How does the hard plastic pipe attach to the end you removed? The banjo end seems to have a provision for attachment, the straight end does not have that stepped attachment provision. (Red circles I added)
Does the hard plastic just slip inside the fitting and the outside rubber hose clamped to the fitting holds it all together??

Thanks!

Dave

Mon Dec 04, 2017 2:09 am

Farf wrote: Thanks for the postmortem on the hose. I too had wondered what the internals of the hose looked like, now we all know! Barring any problems with the internal restriction hose itself do you think the external hose could be replaced instead of paying big $$$ for a new one?

I'm gonna try that for sure , I will report back. The hard part must be the crimp sleeve compatibility....

It is DN10 hose, meaning I think 10mm ID, 3/8" should do.

Mon Dec 04, 2017 2:23 am

djkeev wrote: Thanks for doing that but I miss understanding a few things.

The hard plastic inner pipe seems to be perforated along its length. Correct, 3 holes, BEFORE the restrictor

This means the high pressure oil runs both inside and along the outside of the inner hard plastic pipe? No, the pressure oil goes through the plastic tube, the plastic tube is attached to the end of the fitting on the pump side only of the restrictor, so you're correct but downstream of the restrictor :wink:

Help me understand the relationship of the "restrictor" and the hard plastic pipe.

Does the "restrictor" sleeve simply slip over the hard plastic pipe? The small metal sleeve does slip over the hard plastic tube and is held in place by the outer visible big sleeve pinched over the rubber hose. The plastic is slightly deformed where the sleeve was sitting.From inner to outer you have the plastic tube, then the small sleeve, then the rubber hose then the big sleeve to squeeze that whole assembly.
It is then crimped in place as basically a weight?
Or....
Does the "restrictor" prevent oil flow along the exterior of the hard plastic pipe?
The way I see it, the pressure oil goes through the plastic tube and reaches the opposite end of the rubber hose, unrestricted , the plastic tube just shoots out oil into the bigger ID rubber hose. Before the restrictor, there is static oil sitting between the plastic tube and the outer rubber hose. That oil got there only by the 3 holes into the plastic tube. I think that non running static oil must act as a damper somehow.

How does the hard plastic pipe attach to the end you removed? The banjo end seems to have a provision for attachment,yes a nipple kind of thing the straight end does not have that stepped attachment provision. (Red circles I added) no it does not have an attachment, it just ends about 2" or so before the male threaded fitting metal tip.
Does the hard plastic just slip inside the fitting and the outside rubber hose clamped to the fitting holds it all together?? Nein, I didn't take it apart, it is shorter than the rubber hose like I just described above :wink:

Thanks Dave! You're welcome, I hope my explanations are clear 8)

Dave

Mon Dec 04, 2017 4:23 am

Thanks for the clarifications!

I wish I was smarter and understood high pressure oil properties more.

We know from others that the replacement hoses made with just standard hydraulic hose make noises.

Some now put in an orifice to dampen the noise.

This seems like a complex system ((unlike VW) to solve a noise problem.

Piecing hoses,two piece hose, proprietary fittings, etc.

Dave

Mon Dec 04, 2017 4:33 am

I want the name of the guy in the VW Hydraulic Anti-Noise in Power Steering Hose Department!
Who in the hell thought of this? 😨

Thanks for the disection!

Mon Dec 04, 2017 5:48 am

Makes sense to me:noise, which is caused by waves traveling fast and reflecting, are dampened (slowed down) by expansion against the “sitting still” oil in the outer area. Pressure is maintained, but not the wave height. Works like an oil-filled shock absorber.

The ringed clamp would also shorten and break apart the waves, because of the ridges. Kind of like making you climb up/down hills versus racing along a flat plain.

Mon Dec 04, 2017 10:24 am

I'm no expert either but Jeff summarized pretty well what comes out from the dissection :P

Mon Dec 04, 2017 12:40 pm

Steve M. wrote: I want the name of the guy in the VW Hydraulic Anti-Noise in Power Steering Hose Department!
Who in the hell thought of this? 😨

Thanks for the disection!

Its actually a common approach to develop a 'tortuous' path for fluid flow to reduce noise.

Mon Dec 04, 2017 12:45 pm

A description of how this thing works from the guys at VW when they submitted patent information. Designers names included.

https://patents.google.com/patent/US4611633A/en?q=B62D5%2f062

Mon Dec 04, 2017 12:51 pm

I don think its about noise, but about absorbing the energy of the fluid when the rack no longer requires pressure after a hard turn.

Mon Dec 04, 2017 1:40 pm

Farf wrote: A description of how this thing works from the guys at VW when they submitted patent information. Designers names included.

https://patents.google.com/patent/US4611633A/en?q=B62D5%2f062

Whoa!!!

Facts!
Answers!
Explanations!

Thanks!!!!

Dave

Mon Dec 04, 2017 2:12 pm

"Considering the hose length, cross-section and expandability and the working pressure as being fixed for each particular application, the degree of pulsation reduction will depend upon the dimensions of the inner hose 2, i.e., the flow cross section and the length, and the throttle cross section of the radial throttle passages 3 as well as of the axial throttle passage 8. When these quantities are properly coordinated, it is possible to achieve a nearly pulsation-free hydraulic flow with the use of the expansion hose in accordance with the invention.

Claims (1)
We claim:
1. In a hydraulic circuit an expansion hose for reducing pressure pulsations, the expansion hose comprising: an outer hose having a first hose chamber on an inlet side with an inlet end adapted to receive the pressure pulsations from the hydraulic circuit and a second hose chamber on an outlet side with an outlet end; a throttle element containing an axial throttle passage connecting the first and second chambers; and an inner hose connected at one end with the outer hose inlet end and having a portion extending through the first hose chamber and the throttle element and a portion extending into the second chamber, the inner hose further having its other end open so as to discharge directly into the second hose chamber, the portion of the inner hose within the first hose chamber having at least one radial throttle passage, and the portion of the inner hose within the second hose chamber having an imperforate wall."

Yeah, what I said.....lol

Tue Dec 19, 2017 6:19 pm

I got the hose re-crimped. So far so good :)

Tue Dec 19, 2017 7:08 pm

Looking good! Thanks again for taking the time to document this. Out of curiosity, how much "slop" does inner hose #2 have when it passes through the throttle sleeve #4 to achieve the flow passage #8? And if I've read the link correctly, you just need enough pressure from the middle crimp #5 to hold the throttle sleeve in place, correct?

Wed Dec 20, 2017 11:32 am

Farf wrote: Looking good! Thanks again for taking the time to document this. Out of curiosity, how much "slop" does inner hose #2 have when it passes through the throttle sleeve #4 to achieve the flow passage #8? And if I've read the link correctly, you just need enough pressure from the middle crimp #5 to hold the throttle sleeve in place, correct?

No problemo :wink:

There is no play between the inner hose and the metal sleeve and the rubber hose is clamped down to sandwhich it all.The fluid ONLY goes through the inner plastic tubing.
I was going to put a hose clamp for that sleeve but even without asking they crimped it like the original was. The inner plastic hose when disassembled showed a little bit of collapsing from that crimp assembly. It's tight.

Mon Jun 18, 2018 6:53 am

A similar hose was installed on Audi-s some years before it made it's way to the Vanagon.
On some of the Audi's the system also operates the brake power assist.
I think they adopted this from GM. GM calls it HydroBoost. There is no vacuum booster, just a small piston unit between the brake pedal and the master cylinder.
The system gives good brake feel, no mushy pedals. As long as it works.
Audi decided to change the fluid from ATF to a special hydraulic fluid which is way more expensive and harder to find than ATF.
Whenever something failed that put contamination into the system, everything needed to be replaced. Lines, steering rack, pump, and power brake unit. The only thing that could be cleaned successfully is the reservoir. Usually something would go bad in the pump and metal shavings were everywhere.
Big $$$ repair.
If only the failed component was replaced other parts would fail in a short time.

Mon Sep 23, 2019 3:49 pm

ALIKA T3 wrote: I got the hose re-crimped. So far so good :)

Reviving and old but important thread here... That re-crimp looks good! How does it work/sound?

I was wondering if anyone who tried the GoWesty reproduction hose (251422893C) tried putting some extra insulation around the hose to reduce the noise? They claim its about twice as noisy as factory. I was thinking about some of that foam stuff that they use to insulate copper air conditioning lines. A little bulky but seems like that would quiet it down a bit, no?