The future of Hydrolastic suspension

[rich@minispares.com]

I've not seen a displacer that is rusted thru the body. .

I will take a photo of one next week for you....

[Dr S]

I ran one for some years with a hammered metal shell and a pair of massive jubilees holding it all in...

[Peter Laidler]

I've never seen one completely rusted through but know they exist in our salt laden winter climate! But the denso tape stuff would certainly stop a wire brushed badly rusted one deteriorating further.

[geroch]

Unfortunately a 21a2014 unit is broken... it looked beautiful out, but the lower membrane is totally cracked, to filter water.

20170820_135506

To clean the inside I used a broken original fitting. And 2 old valves, drilled 3mm inside. An old shower tube.

20170820_134247

[nileseh]

geroch: I'm not sure I'd give up on the displacer with the cracked lower diaphragm. I don't think the rubberized fabric element is intended to seal the fluid. There is another separate rubber membrane inside that seals. I think the rubberized fabric is only intended to support the cone that attaches to the strut. Unless it was leaking, it's probably okay.

I tired to clean the interior thru the hose as well. Not much luck. I placed a smaller diameter nylon tube thru the hose all the way to the upper cavity and injected high pressure water to back-flush the interior, I built a fixture so I could cycle the diaphragm and pump fluid out. I was never able to get the rinse water even the least bit clear. That's why I cut them open and found that the lower diaphragm cavity is pretty hard to get to because of the valving. There are some crossections out there that show it.

[mab01uk]

geroch: I'm not sure I'd give up on the displacer with the cracked lower diaphragm. I don't think the rubberized fabric element is intended to seal the fluid. There is another separate rubber membrane inside that seals. I think the rubberized fabric is only intended to support the cone that attaches to the strut. Unless it was leaking, it's probably okay.

I tired to clean the interior thru the hose as well. Not much luck. I placed a smaller diameter nylon tube thru the hose all the way to the upper cavity and injected high pressure water to back-flush the interior, I built a fixture so I could cycle the diaphragm and pump fluid out. I was never able to get the rinse water even the least bit clear. That's why I cut them open and found that the lower diaphragm cavity is pretty hard to get to because of the valving. There are some crossections out there that show it.

Section through a Mini Hydrolatic Unit - (Sectioning & Photo: Tim of Minimail)

[Peter Laidler]

I soft soldered the brass core of a standard schrader valve into a standard BSP concave adaptor that screwed onto the open end of the hydro hose. You can use a foot pump to pump up the hydro unit to a reasonably high pressure (62psi?) while it's in a bucket of water to see whether the air is leaking. If it does leak air from anywhere, then the rubber diaphragm is shagged. Or if not the diaphragm, the hose! I built a frame from bolt-together dexion shelving to test one unit using the hydraulic pump in an on-site JCB hose repair van. The pressure just broke the frame eventually but it showed that it was OK!

I was an Army engineer and to be honest, we had 25 pounder and 105mm pack howitzers that had recoil, recuperation and runout systems less complicated than Dr Moultons hydro systems

[geroch]

https://youtu.be/Hf1_REZDVp0

It's normal?

[Peter Laidler]

I couldn't understand that u-tube video. Yes, the bellows looked a bit knackered and threadbare but was the unit HOLDING the pressure (good unit) or was he quickly releasing it (knackered unit)? Interesting.

[geroch]

I'm sorry I can not explain in English. Is it normal to go back so fast? The inner membrane does not resist?

[Spider]

I'm sorry I can not explain in English. Is it normal to go back so fast? The inner membrane does not resist?

I think you are referring to damping here? Like a shock absorber to 'slow' the movement.

Using Air, I would expect a similar result to your youtube clip, however, with Hydro Fluid, it has a higher viscosity than air, so it would have better damping, but as with most Hydro Units these days, the damping is likely quite worn.

[nileseh]

Just for fun.......



So does it seem like I have too much time on my hands?

The cracking on the diaphragm doesn't matter; there in an interior rubber seal. The diaphragm is only to support the cone that attaches to the suspension strut. If it doesn't leak it should be good to go.

I'm not sure how the dampening would wear. I've cleaned a lot of the rubber valve bits and have yet to find one deformed or eroded. I suppose if the interior was rusted to the point that the metal retainer that restricts valve opening is disintegrated, most dampening would be lost, but if it is that far gone, it's likely that the the entire interior is disintegrated as well rendering the unit unusable.

[geroch]

Thanks for the answers, so with compressed air it's almost normal that it does so, the ideal solution is to try it with water. If it is not locked in mid-expansion, the valves are damaged.

[geroch]

Nileseh, did you find the unit you missed? I'm curious about how your solution works in the street.

[Peter Laidler]

I have pumped up the hydro units in a light steel frame, made from DEXION racking using a commercial hose repairer friends hydraulic compressor - and the hydro unit bent the racking! I've made a schrader adaptor for the hose end and got it to 62psi using an air line pump and got the hose end to swell up quite well. This method shows a leak if the hydro unit is put in a bucket of water. But when I let it down through the valve it went down a lot slower than the u-tube video. And I have also connected up a unit to UK mains water pressure of approx 14/15psi and left it under pressure for 24 hrs. No leak. Admittedly, these are no great shakes in pressure terms but mind you, neither is 300psi any great shakes in hydraulic pressure terms.

What would be REALLY interesting Nileseh is a continuation of that schematic CAD drawing showing the fluid flow INto the top chamber, through the valve then INto the lower EXPANSION chamber, pushing the strut outwards. One picture describes a thousand words and all that

[nileseh]

Well, I received the displacer that timell sent, but I have so far just used it to get the outside dimension so I could finish the CAD depiction above. I have already cut all the ones I have up to evaluate the interior condition. I'm traveling this week but should be able to get into this part next week to open it and to see if the dampening settings are different from what I have for the 21A2014 units. The shop is building the reassembly components so I should be able to reassemble the things in the next few weeks.

But trying it in the car is another matter completely. The body is okay, no rust, but in need of a bit of work. I'm going to minimize it to presentable rather than concours condition (I drive cars rather than show them). It does need a new wiring harness as well. The engine/transmission is prepared and the subframes are all ready for assembly. that said, it is a few months out before it can serve as a test bed for the rebuilt displacers.

But I'll update on the displacers here with pictures when I can. I appreciate all the interest.

Oh, an animation in SolidWorks is a bit beyond my skill set but I'll enquire within my engineering staff to see it it can be done on this platform.

[69k1100]

I though the Dampening was controlled by the diameter of the hole in the valve body? In such a case rust would almost certainly affect this, the holes are only a little more than a 1mm to begin with, so minor rust or erosion could dramatically affect the dampening of the unit. I recall that hydro units were extremely good when new but quickly lost performance due to the dampening.

[Spider]

I recall that hydro units were extremely good when new but quickly lost performance due to the dampening.

That's been my experience too, hence the comment I made in an earlier post.

I don't know what wears, but something does 'give' and then all the Hydro Units feel the same. Even John at Mini King commented on this. This was why a few years back, as an experiment, I fitted external valving, so I could not only get some damping back, but set it in both compression and rebound how I wanted it.

[geroch]

Oh, an animation in SolidWorks is a bit beyond my skill set but I'll enquire within my engineering staff to see it it can be done on this platform.

You definitely know the program:
http://help.solidworks.com/2016/english ... dvideo.htm

The .avi format can be uploaded to youtube.

[nileseh]

These are a couple images of the valve assembly. The depiction is of the original configuration, my rebuild will be a bit different because I have to cut the top off the stamping in order to clean and reset the inner (rebound) valve.



The black rubber is the active part of the one way valve. The one on the top (shown) is the bump valve. as fluid flows from the inward diaphragm deflection, the rubber bit is flexed upwards to allow flow. the rubber is also constrained by the wing on the steel retainer. I have found that there is a difference in the vertical position of the wing on displacers which I take to control the "stiffness" of dampening. The lower the wing is positioned, the more restriction and stiffer dampening. I think this is the only part number differentiation of the displacers. All the other components on the displacers appear to be identical. Even the retainer is the same, the wings are simply bent to a different position.



In this view you can see the oval opening that services the lower valve (rebound). The components are identical, rotated 90 degrees from the upper and the wings are at a different height resulting in a different restriction and dampening.

There is a bypass hole in the stamping, a small diameter (about .070") in the Cooper S displacers and a larger diameter (about .120") in the standard cars. I'm not sure of the reason for the bypass, perhaps simply to let the fluid move unimpeded for small motions.

I'm not sure I can reason how the displacers lose dampening. The active rubber bit is in good condition in all the displacers I have disassembled. I suppose if the retainers rusted away completely all dampening would be lost. In the only unit I disassembled that exhibited that degree of corrosion the valve stamping was also completely destroyed. It was of no consequence, but the rubber bits were in good condition on this unit.