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PostPosted: Mon Sep 04, 2017 3:24 pm 
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Location: Eugene, Oregon USA
Hmm. Much to consider.

External valving occured to me as well. Theoretically removal of internal restrictions and the addition of external would deal with dampening. To match the factory performance, there would have to be two paths, inflow and outflow, because measurements suggest there is a difference between bounce and rebound dampening. I haven't quite reasoned out the impact of full fluid flow on the spring. I think we tend to discuss the "hydro" element of the system more that the "lastic" bit. The springing on the car is flexure of the rubber donut just as in the dry cars. The donut is deflected in response to suspension travel operating thru the in-compressible fluid. The valving is a restriction to flow that provides dampening (as in shock absorber). External valving should do the same, its just a matter of where the flow is restricted. It would require a fair amount of plumbing to get the same action as provided by the rather simple internal valves.

One could perhaps achieve the same end by removing the internal valving and adding telescoping shock absorbers as in the dry cars. Make them adjustable (are they available with bounce and rebound adjustments separate?). If the fluid flow is impeded by dampening the motion of the suspension, it seems that the same effect is achieved as impeding fluid flow thru an aperture. But, as I think I noted previously, what's the fun in that?

The test car is interesting. The controls appear to be push-pull cables attached to rotary valves in the line from the front displacers and presumably elsewhere. There are three rows of controls, 2 in each row with one cable at the bottom. I think the 1st and 3rd rows are ganged together to be operated simultaneously, and placarding as I make it out is "front springs" and "rear springs". The left control in the 2nd row is placarded "fore-aft OUT". Can't make out the other side. Can't make out the bottom control either. The yellow tape on the side marks the un-laden and laden "CofG" (center of gravity). Another thing I find of interest is what appears to be a yellow pressure vessel under the front right wing. Do you suppose it's possible that this is a test bed for the development of "hydrogas" suspension rather than "hydrolastic"? Recall that the methods are similar, with the rubber donut replaced by compressible nitrogen to support the car. Ganging the front and rear controls could have been to level the car fore-aft with adjustable ride height afforded by gas suspensions, and the front-rear fluid transfer is the same.

Anyone know where this car is now?


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PostPosted: Fri Oct 27, 2017 10:40 am 
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I have been through the whole thread, and was surspised to see that the role of internal valves is not really understood. Only nileseh in his last message seems to address the problem that an external in-line valve will only damp the front-rear interconnection, but not the direct bump-rebound action of each wheel.
The placement of the valves in the port plate before the rubber spring, manages to damp the action of the spring. An equivalent valve after the spring, will allow the spring to deflect without control, so would be unsuitable.

By the way, has anyone's car failed the MOT or any equivalent roadworthiness test due to deteriorated displacer damping valves?


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PostPosted: Fri Oct 27, 2017 12:16 pm 
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Joined: Sat Jul 15, 2017 5:35 pm
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Location: Abingdon Oxfordshire
Mmmmmmmmm...... Glacier, you haven't given me/us (Spider, Nilseh, Mab) enough to get to the point but it seems that you're thinking of the hydro system as being too complicated. I/we seem to think that it's made to be AND sound complicated when really, it's just fluid moving between two inflatable bags. And you DO want to control the front to rear connection - that's the whole idea! I'll come back after giving a bit of thought but like all things on the forum, it's all our own opinions of course. Some based on mechanical and hydraulic facts, others based on fuzzy logic. But of itself, the hydro/liquid system is simple. It's the internal mechanicals that complicate things and it's these internal mechanicals that cause the problems...... apart from leaky bags of course which are another matter entirely.

Need to sit down with a glass of Scotch after Sunday lunch. Join me for a tot Spider and Niles?


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PostPosted: Mon Nov 06, 2017 11:52 pm 
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Location: Eugene, Oregon USA
Hmmmmm indeed.

I think I agree with Glacier on the placement of the valve on the suspension side of the rubber spring. In this location the velocity of the fluid is mitigated before the spring, or parallel to the spring as is the case with a shock absorber and the total fluid flow to the opposite displacer is also regulated.. On the other hand, since the fluid is non-compressible, it theoretically makes no difference where the flow is impeded. I don't know, it makes my head hurt. I'll just stick with Mr. Moulton's configuration.

I am making headway. The aluminum bits for resealing via a circumferential clamp are fabricated and out for anodize. I designed a valve body of plastic, and printed (3D printer, FDM process from ABS) a trial. I think it will work fine. I'll reuse the rubber valve bits, as well as steel valve restricter bridge. Unfortunately I was unable to get any useful dimensions off the rusted out displacer I was sent so I'll have to extrapolate the valve dimensions from what I have. I have to seal the large diameter standard relief holes and drill the smaller diameter Cooper S holes then I'll have the displacer bodys cadmium plated for corrosion resistance. I (I tested it on an unrecoverable unit and the plating process does not affect the rubber). I have a new hose material and I can crimp the connection to the chassis tubing, but I'll have to use hose clamps on the displacer nipple because I cant get a crimp tool in the cavity. So in a few weeks I should be able to assemble 4 of these things and start pressure testing. When I tested the prototype I took it to 300 psi with the factory service unit and left it connected for 4-5 days without any loss in pressure. Seem to work fine.

Once they are assembled I'll try to post a picture.

Then move on the the Scotch.........


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PostPosted: Tue Nov 07, 2017 3:00 am 
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Location: Big Red, Australia
Wonderful work once again there Niles. Let's see how it all goes.

Peter Laidler wrote:
Need to sit down with a glass of Scotch after Sunday lunch. Join me for a tot Spider and Niles?


Yr on buddy :)


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PostPosted: Tue Nov 07, 2017 7:44 pm 
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Location: Abingdon Oxfordshire
Welcome to the discussion Glacier and thanks for your thought provoking input. Join Me, Spider and Niles with a large glass of scotch while I try to take the matter on a bit further along the simplicity route. I'm not a familiar with fluid transfer situations beyond large field gun recoil and recuperation systems which, believe it or not, are quite similar to Mr Moultons practice. What is different is that in field guns, we want the recoil to he short and well buffered but the recuperation (or run-out) has got to be a lot more gentle. Look at it in slow time next time you see an anti-tank gun or 25 pounder in action. That's the only system I can think of where it's necessary to have UNequal flow/transfer of fluid (there'll be others but I can't think of any because....., anyway). That's all I'm going to say.

In the mini system, has to be the same BOTH ways...... the transfer of fluid front to rear and rear to front MUST be the same. Here's an example why. Take the EMER or workshop manual, Chapter H, page 9, illustrative figures 10 and 11. When the front wheels ascent the hump in the road, the fluid transfers from the front and lifts the rear of the car via the hydro unit bags, struts and radius arms, keeping it level. To achieve all this and at the same time, the rear radius or swinging arm rotates downwards, stretching the helper spring. We've already got TWO facts of physics that we can't defeat.
a) you can't compress a liquid - it's moved from front bag to back bag (and yes, it's stretched the bags a bit too......)
b) a spring is simply a means of storing energy - and in this case, it's a strong spring storing a lot of energy.

Car moves along a bit, so what do you think is going to happen? Yes, the helpers immediately reassert themselves and pull the radius arms upwards. Yep....., immediately transferring the fluid forwards. Once again leveling the car out. Ready for the REAR wheels to repeat the same process, but in reverse........ The REAR wheels are going to lift and transfer the fluid FORWARDS to repeat the process

Just think of the mayhem if the IN-flow and OUT-flow of the valves were different. In this simple Fig H10 situation the front wheels would descent the bump and instead of the immediate transfer of fluid back to the front, it'd transfer slower. To achieve what?
Or think about it in the opposite direction, where it transferred SLOWLY to the rear and FASTER to the front. Nope, wouldn't work that way either.

The fact that both front and rear hydro units are identical just emphasises this point. I believe that the transfer of fluid to achieve the same effect can be achieved by in-line restrictors. The car is held level by the strength of the helper springs and the shock absorbing is the restricted flow of the fluid through the valves or restrictors (which in fluid applications are just valves).

Now where did I put that almost empty glass of Scotch. Want a top-up Spider? What about you Niles? Top-up Glacier.....? Cheers


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PostPosted: Tue Nov 07, 2017 8:46 pm 
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Do the helper springs not also act to counter the difference in leverage ration from the front to the rear of the car? If not then a bump on the front would have an excessive reaction at the rear?


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PostPosted: Tue Nov 07, 2017 10:33 pm 
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I thought on a hydro car the lever ratios front to rear were the same at 5:1.

As far as I can see all the helper springs do is prevent the front pulling down because most of the cars unladen weight is on the front units.

I don't see why the valving cannot be different front to rear, there is a big rubber 'spring' in there and while fluid is incompressible, the rubber is not. So and equalising of the bounce and jounce would be done in the rubber, with the fluid catching up a little later.


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PostPosted: Tue Nov 07, 2017 10:45 pm 
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Location: Abingdon Oxfordshire
Well, in my opinion until I think about it a bit and try to make my wooden classroom model a tad more realistic, I'd say no, they don't because all things being equal, such as rear weight = front weight, i'd say you could do without the helpers as the car would naturally sit level. But that's just speaking/thinking on my feet. The helpers pull the rear DOWN to help balance the car or equate the weight artificially - if that's the right word. I had both my helpers unhooked a few weeks ago and it just wallowed front down like a stuck pig of course. It's thought provoking Doc........ Come back with your thoughts because between us I think that we've got this pretty well cracked. Another Scotch on the verandah Niles, Spider?

You're right Smithy, but don't forget that once again, the rubber diaphragm is just another 'spring' in another form that will reassert itself PDQ


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PostPosted: Wed Nov 08, 2017 8:30 am 
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Peter Laidler wrote:
Another Scotch on the verandah Niles, Spider?


Respectfully, can we end this thread?

It's turning me in to an alcoholic :lol:


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