Dr. Omar M. Shams
Post Number: 23
|Posted on Tuesday, 02 June, 2009 - 04:15 am: |
Since I started owning Rolls-Royce Shadow deratives cars, I have been disappointed with the standard that Rolls-Royce have used to keep nitrogen in the accumulator spheres. For years I have thought that there must be a better way of holding 1100 psi than to depend on a platic ball and a miniature circlip. Finally I decided to do something about it. I threw the Rolls-Royce system in the bin and installed a stainless steel check-valve (one-way valve) that has a working pressure of 6000 psi and utilises a larger diameter stainless steel ball. 4 months later and both my accumulators are holding the full pressure admirably. i expect that I will not need to charge my accumulators for a while.
Post Number: 77
|Posted on Tuesday, 02 June, 2009 - 07:42 am: |
When I repressurised the accumulators on The Old Girl I found that the pressure caps were already machined to take rubber donut seals. Fortunately I had a supply of seals of an identical size so I just replaced them with the new ones. That was over a year ago and they don't seem to have lost any pressure since.
Failing such seals being available, simple rubber (neoprene?) 'washers' should afford the same quality of pressure retention.
Post Number: 1120
|Posted on Tuesday, 02 June, 2009 - 08:47 am: |
Actually Omar the usual loss of gas is not through the charging valve but through the interstices in the diaphragm, about which you can do little. It has happened that sufficient gas has escaped this way to actually affect the braking which actually need bleeding. The Factory had a lot of trouble in the early production days getting diaphragms that did not leak and all were tested after manufacture. The problem is that in mixing up the brew to mould the diaphragms which is much like chocolate mousse there is inevitable entrapment of air bubbles however small. The gas eventually finds one just beneath the surface and gets through then hunts around for another bubble. MUltiply this and you have your leak. Overall it is largely serendipity whether you get a good sealing diaphragm or not.
Post Number: 885
|Posted on Tuesday, 02 June, 2009 - 11:41 am: |
Bill is absolutely correct however even a perfectly moulded diaphragm will still allow gas to permeate across it through a scientific process called "diffusion" or for the pedants "effusion".
Think of a gas-filled kids balloon, it will eventually go flat as the pressurised gas inside escapes to the lower pressure atmosphere outside as the molecules find a passage acrooss the rubber. What is important is the relative size of the gas and rubber molecules - a balloon filled to the same pressure with hydrogen goes flat faster than one with the same pressure of air as the hydrogen molecules are smaller and find their way across the rubber quicker than the larger oxygen and nitrogen molecules.
Post Number: 11
|Posted on Wednesday, 03 June, 2009 - 11:58 am: |
I serviced my accumulators approx. 2 months ago and upgraded to the small valve supplied via a UK RR parts dealer. So far, it appears to be working quite well and offered no difficulty during installation. The small valve was seated via an O-ring along with the standard O-ring under the cover/cap. I'm pleased with the results, although I'm quite new to working on these vehicles.
I would like to locate a source for new pins for the accumulator tool as my accumulators had been torqued substantially and were extremely difficult to separate even with an 3/4 impact gun. The pins in my tool are showing some battle damage
Dr. Omar M. Shams
Post Number: 34
|Posted on Friday, 14 August, 2009 - 05:29 am: |
David and Bill make some very good observations. I had noticed that over time I would get more and more air in the hydraulic system and that required frequent bleeding until all the nitrogen had escaped from the accumulators. I then replaced the rubbers in the accumulators again, and the problem has hopefully gone away now.
Obviously there are good and rogue diaphragms. How can you tell which are which? This is a job I hate doing any more than is absolutey necessary.
Post Number: 2
|Posted on Wednesday, 19 August, 2009 - 03:50 pm: |
Hi.Iam advised that my accumulators need regassing on my Bentley T1 chassis number SBH 17291 how does one do this.
Post Number: 93
|Posted on Wednesday, 19 August, 2009 - 08:31 pm: |
That information can be found here in .pdf format. (page G23)
However unless you have access to - and experience in using - high pressure gasses and associated equipment at well over 1,000 psi you should leave the job to a qualified mechanic!
As has been previously pointed out: Just recharging the spheres may not be sufficient. It is likely that the spheres may need to be overhauled or even replaced before they will work properly again - especially after all these years!
Dr. Omar M. Shams
Post Number: 37
|Posted on Thursday, 20 August, 2009 - 04:04 am: |
Well put Jan. Anything above 28psi is potntially dangerous. This point cannot be stressed enough. To work with fluids or gases at 1000+ psi require adequate measures to be in place to ensure everyone's safety. This point needs to be thoroughly understood by us all.
Post Number: 13
|Posted on Thursday, 20 August, 2009 - 08:38 am: |
Assume your talking brake accumulators. These guys have them as service exchange. Not cheap though at 120 pounds. Did my car (89 Turbo R) and they only cost 35 odd pounds each, they are a throw away item unlike the earlier cars. The Gas springs where a bit more but still not bad value for the difference it brings.
Dr. Omar M. Shams
Post Number: 38
|Posted on Friday, 21 August, 2009 - 05:07 am: |
Yes Stefan - Accumulators. On the later cars (like yours) these were replaced with throw-away Citroen style spheres that you cannot dismantle or overhaul. For now, the newer style spheres are easy to buy and indeed cheap, but who knows what the market will be like in 15 yeras time. Perhaps then, the recharbale spheres like the ones on the Shadows will be easier to own and maintain.
Post Number: 96
|Posted on Thursday, 12 September, 2013 - 09:03 am: |
Gentlemen, sorry for jumping on to a fairly old posting but it is relevant to my needs.
I have been quoted $350.00 each for change-over spheres in Australia (a total of about $950.00 if fitted). Flying Spares offer them, apparently not change-over but reconditioned for about $205.00 each. They also have "throw away" aftermarket type spheres for $330.00 each. As I have neither the desire or equipment to recondition the ones I have I need to buy reconditioned pre-gassed ones. My questions are: (a) is there a logical reason why reconditioned change overs are so much more expensive in Australia. (b)why would anyone buy the aftermarket spheres rather than originals, especially in view of the extra cost.
As always the benefit to me of your combined wisdom will be greatly appreciated.
Post Number: 1124
|Posted on Thursday, 12 September, 2013 - 09:13 am: |
I think reconditioned ones will be exchange.
about 200 pounds. Each.
The non exchange are good if you do not have good ones to exchange because they are damaged or lost.
Post Number: 635
|Posted on Thursday, 12 September, 2013 - 09:47 am: |
I believe the aftermarket spheres you refer to are the RH2390P spheres.
The best reason I can come up with for buying the RH2390P spheres is this, which I originally offered in this thread on rollsroyceforums.com: CitroŽn, however, is the company that started all this technology and over the years they've gone from LHS (DOT3) to LHM (mineral oil) and back again. It became very tedious to keep producing spheres with the same pressure specs in two separate versions when these were used on both LHS and LHM based cars. Take a look at this thread on an XM forum, do a web search on "multicouche" along with CitroŽn, and take a look at one of the newest offerings in accumulators from Flying Spares, the RH2390P Sphere. That sphere is a CitroŽn multilayer diaphragm sphere that has been customized with the necessary threading to screw in to the accumulator control valves on RR363 cars.
My gut tells me (and it's only my gut, those who are using these spheres, whether on CitroŽn or RR/Bentley can confirm or refute) that this type of diaphragm will hold the nitrogen charge for far longer than the originals do.
Post Number: 2906
|Posted on Saturday, 14 September, 2013 - 11:47 pm: |
I must remark that genuine SY spheres should stay fully-charged for at least 6 years, and generally 20 years could be expected, which are likelihoods far longer than the scheduled overhaul period.
SZ spheres do not last as long, nor would the throwaway SY replacements. However, throwaways may be the best option before long. As a guide, SZ spheres are quite inexpensive, retailing for not much more than $200+GST in Australia now.
$330+GST is a pretty low price retail for a reconditioned SY sphere, so go for it, although SpurParts in Sydney has been a fair bit below than that recently. Trade prices are of course lower again. Those have a two-year warranty, Bear in mind that the diaphragm alone retails for over $130+GST, and that the sphere needs dismantling and regassing. Unfortunately, SY spheres are so old now that the failure rate of returned spheres for overhaul is high and the costs are not really stable.
As Paul comments, GBP200+GST/VAT is the UK price level, and that is over $400 before you even ship the thing.
Unless SY sphere overhaul costs can be contained, new disposable spheres will soon be the norm. Work is underway to find new replacements spheres for outright sale at a reasonable price. Introcar and Flying Spares have made a start but the prices are still rather high for their throwaway spheres.
Simply comparing UK prices at a GBP/A$ mid-rate of 1.7 as shown in the newspaper is misleading as you must look at the GBP buy-rate then add bank fees and shipping of pressurised units. The retail GBP bank rate is more like 1.9 plus fees, and to ship a sphere from the UK will cost you at least $100 as it is classed as a dangerous item. Also, a UK warranty is not much good in Australia once you ship the things back and forth, and especially as the GST and duty assessment thresholds are dropping to $200 soon.
Post Number: 97
|Posted on Sunday, 15 September, 2013 - 07:19 am: |
Thanks to you all. I have received a quote from Flying Spares (attached) and will be taking up a local original sphere exchange option.
Post Number: 80
|Posted on Thursday, 01 December, 2016 - 02:14 am: |
Resurrecting a truly old thread, ca 2009!
Omar, what you write implies to me that you recharge in situ. How about a part number, a description, or a photo of the parts you purchased? The paucity of photos on a site where the English language works at cross purposes sometimes (boot = trunk) is astonishing. Especially for Yanks like me! However, for a technical explanation, the lack of a photo or part number leads to further questions, like mine now. Please Omar, tell me more about the stainless steel check-valve (one-way valve), which you installed. A photo AND part number would be ideal.