| Author | Message | ||
     Chris Miller Prolific User Username: cjm51213 Post Number: 250 Registered: 5-2013 |
Hi Folks, I was lying under the '72 this weekend looking around and I noticed for the first time that my exhaust flows right under the accumulators. I've seen that many times, but this is the first time it hit home. Why do I care? Let's suppose I have an accumulator with 1,000 PSI of nitrogen and I charged it on a pleasant day of 80 degrees F. (300 degrees K) Let's assume I have calibrated my ACV to 2,500 PSI "Cut-Out". So far so good. Now let's take the corner case that I am driving on a hot day and there is a horrible traffic jam with zero movement and I get caught. With my final application of the brake, I hit "Cut-In" and the accumulator recharges to a full compliment of fluid at 2,500 PSI. But now I'm stuck with a fully charged accumulator. No fluid is going anywhere. My accumulators are directly over the exhaust pipe, which is the hottest part of the engine bay. Let's assume that on this particularly hot day, the temperature in that region of the engine bay rises to 500 degrees F (533 degrees K). (Is 500 degrees a reasonable value? Could it be higher? Could it never be this high, except on the sun? That's a question I can't answer, so corrections here would be helpful.) Here's the problem. Since fluid is not being consumed, the pressure of the nitrogen, which was 2,500 PSI will grow to (533/300) = 4,441 PSI! (... plus any additional reduction of nitrogen volume caused by brake fluid thermal expansion!) This raises all kinds of questions, not the least is, has my exhaust been re-routed by some previous maintainer? Seems like heating the accumulators is a design defect that should be avoided. There is no obvious "failsafe" on the ACV, although I suspect that the regulator valve piston sealing ring will probably leak long before 4,441 PSI, but I don't know, and I can't test it. Is the regulator valve piston sealing ring a "failsafe"? What would be the maximum pressure? Has Rolls Royce accounted for this corner case? Does Rolls Royce publish any of their engineering data where the design pressure rating of the regulator valve piston sealing ring is disclosed? Chris. | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 902 Registered: 9-2004 |
"Is 500 degrees a reasonable value? Could it be higher" A hot engine will always have air flow past the engine sides if the car is stationery or slow moving due to the viscous fan or electric fan as well if fitted to later cars and working correctly Change the dot 363 every two years and forget as recomended by RR Bentley. Are you having some sort of other problems to cause you think about this situation. | ||
| Chris Miller Prolific User Username: cjm51213 Post Number: 251 Registered: 5-2013 |
Hi Patrick, > A hot engine will always have air flow past the engine sides if the > car is stationery or slow moving due to the viscous fan or electric > fan as well if fitted to later cars and working correctly So, maybe 500 degrees F is not a reasonable estimate? What would be a better guess? > Are you having some sort of other problems to cause you think about this situation. Yes. Nitrogen loss. In spite of a good check valve, and good secondary and tertiary sealing, and a tight containment ring, I measured my forward sphere and found 600 PSI, instead of the 1,000 PSI I put there. When I rebuilt these guys, I filled them and left them on my bench with a pressure gauge for two days and I saw no degradation of pressure, so 2,500 PSI is not a problem, therefore the pressure must be rising above 2,500 PSI. So, why is nitrogen escaping? I have to conclude something like the scenario above -- excessive heat. So, do you think my exhaust has been rerouted and is causing excessive heat near the accumulators? On a more theoretical bent, do you think the regulator valve piston sealing ring acts like a failsafe, meaning it can hold 2,500 PSI conveniently, but, at say, 3,500 PSI is the maximum and at that point it will leak impounded fluid to the by-pass. Chris. | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1265 Registered: 6-2006 |
sounds like it's right, but post some photos so we can confirm. If it is correct, then don't worry about it. They work in the middle east etc, nice and warm there  | ||
| Bob uk Unregistered guest Posted From: 94.197.122.88 |
It does not get that hot. Else the screen wash bottle would boil. The spheres are there to soak up any pressure changes due to temperature expansion, as well as the spheres other duties. My exhaust is near the spheres. As Pat says there is a air passing over the spheres from the fan and the movement of the car. Note, do not drive in reverse for more than 100 miles and do not exceed 50 mph in reverse. Because you will get a neck ache. (Message approved by david_gore) | ||
| David Gore Moderator Username: david_gore Post Number: 1472 Registered: 4-2003 |
If my memory is correct, a serious problem with the early Shadows were fires caused by hydraulic fluid leaking from the accumulator and the flexible hoses onto the hot exhaust pipe which ran directly under the accumulators. The relocation of the accumulators on the Shadow II was most likely the outcome of this problem. As far as the engine bay temperature goes, I doubt if it would go much higher than 200 deg Celsius in hot climates; the hottest air from the radiator would be around 120/130 deg Celsius this being the boiling point of water at a pressure of 15psig and the only other source of heat would be from the manifolds/exhaust pipe which are cooled by the air drawn through the engine bay by the fan[s] and the vehicle motion. The exhaust heat will fluctuate with engine speed and load being least when the engine is idling and greatest when the engine is running under load on wide open throttle. The actual operating temperature of the accumulators [remember they are attached to the aluminium engine block which is a very efficient heat sink and is unlikely to be hotter than 130 deg Celsius] when the car is being driven is easily measured by putting a thermocouple on the sphere and using a multimeter to measure the voltage which can then be converted to the corresponding temperature for the type of thermocouple used. If nitrogen loss from thermal expansion due to engine bay temperatures was a problem, I am certain the R-RMC engineers would have found this when testing prototypes, designed the spheres accordingly and thoroughly tested the system on the experimental cars before approving the system for production. If there was an inherent design problem; why hasn't this problem shown up much earlier given the number of years that have elapsed since the Shadow was released and the large number of cars in service around the world? I suspect there is a much simpler reason for the nitrogen loss being encountered by Chris Miller; possibly wear and/or distortion of the components as a consequence of repeat disassembly and reassembly of the accumulator/ACV unit or the workshop practices being used. The only source of Nitrogen loss should be the inevitable and unavoidable diffusion of Nitrogen across the diaphragm into the hydraulic fluid; this is a known event which is reflected in the tests specified in the vehicle service schedule. | ||
| gordon le feuvre Experienced User Username: triumph Post Number: 50 Registered: 7-2012 |
There were instances of engine fires. The original flex hoses from brake pump to accumulator valves and output from valve to frame used to suffer with pipe blowing off unions at ends. They were not the metal braided type Also,no matter how hard Crewe tried they could not stop the long flex hose from each brake pump to accum. valves "flexing" on each stroke of pump and wearing through. Hence the retro fit of the rigid pipe kit from brake pump to accum valves. This then introduced issues with brake pump knock on stroking that was not present on early cars, but that is another story! | ||
| Chris Browne Prolific User Username: chrisb Post Number: 153 Registered: 2-2010 |
Hello David, I had always thought that the reason one of the accumulators was relocated on the opposite side of the engine was to accommodate the steering rack when rack and pinion steering was introduced on the Shadow II. Does that seem likely? Kind regards, Chris | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1266 Registered: 6-2006 |
I had always thought that the reason one of the accumulators was relocated on the opposite side of the engine was to accommodate the 'centre of the manifold' downpipe | ||
| Bob uk Unregistered guest Posted From: 94.197.122.71 |
Scary stuff a dot flame thrower under the car. Running with no nitrogen will hammer the braided pipes and blow them out eventually. The hammer from plunger pumps is not to be under estimated. I suspect as well that the sphere halves maybe distorted at the diaphragm joint. If they are then I see no way of repair. To check place on surface plate. Could a diaphragm have a slow puncture? When I first got interested in the design and layout of the system I wondered why the spheres are where they are. I came to the conclusion that the pumps must have solid pipes and therefore the acvs must be either bolted to the engine or gearbox RR chose the engine and squeezed them in under a bank until the rack got in the way. Citroen is the same except they have a seven piston swash plate pump driven by a belt with a SZ style acv bolted next to it with a six inch long pipe connecting the acv to the pump. The acv has an internal bleed screw like an SZ. I was surprised that RR didn't use the Citroen pump on the lhm system. The pump has more than enough capacity yo run two acvs and if the one pump isn't. Considered safe two smaller ones. The cheaper versions of some Citroens ( no power steering or variable rate self centering) had a single plunger pump running off the cam shaft (Message approved by david_gore) | ||
| Chris Miller Prolific User Username: cjm51213 Post Number: 252 Registered: 5-2013 |
Hi Bob, > Could a diaphragm have a slow puncture? Good thought, but unlikely in this case. These are new diaphragms. I didn't bleed the accumulators to relieve the pressure before removing the spheres, which would have bubbled the escaped nitrogen, but next time, if there is a next time, I will, because it is a very good idea. These accumulators have survived on my bench fully pressurized at 2,500 PSI with no measurable degradation in pressure for two days, so they are fine unless I encounter higher pressure. My original thoughts were that the temperature wouldn't matter because the ACV "Cut-Out" is at 2,500 PSI regardless of temperature, so I couldn't explain nitrogen loss. When I realized that the exhaust was so close, I also realized that I was subject to higher pressure above "Cut-Out", if the accumulator was fully charged and then heated -- no escape. There is a way to test my accumulator at higher pressure, but I'm reluctant to try it. I could charge it and boil it. That would raise the pressure to (373/300)*2,500 = 3100 PSI, but as I say, I'm reluctant to try this. And it's not worth having to hear David Gore warn everybody that it is risky ... Unless the regulator valve piston sealing ring will leak at higher pressure, putting an upper limit on internal pressure, Rolls Royce had to design for internal pressure in excess of 4,500 PSI. (NB David Gore: 200 C is 473 K. My number was 533 K. Close enough.) This is why publishing engineering data is important. Did Rolls Royce account for this case? Without engineering data, nobody knows. Recently I discovered an article describing how to correctly lap a check valve and it explained an important detail that I didn't know, so this is where I'll work next. The detail is that you don't use a 5/16" stylus for a 5/16" valve sphere! You use a 4/16" and a 6/16" and the intersection of these two spheres leaves a cusp called a "lan" which should be as thin as possible. This lan is minutely tuned with the 5/16" stylus. This is how you get an air-tight seal, and I am assured that an air-tight seal is possible. You can see progress by sooting the seat with a candle. The lapping activity will leave shiny traces in the soot. Chris. P.S. Bob contact me through the personal message facility. I can't contact you. You're not registered. | ||
| Bob uk Unregistered guest Posted From: 94.197.122.75 |
Chris you are over complicating things. RR and Citroen combined have made thousands and thousands of these systems starting in 1955. In 60 years and millions of miles no one has had a temperature problem. The spheres do not need to be pressure tested. RR and other makers will have tested the snot out the system and done the maths. The data is not pertinent to the repair or testing of the system. I would suggest that the sphere will hold pressures well above working pressure. Small sphere pressure vessels with thick walls will take an enormous amount of psi and 10000 psi wouldn't surprise me. A factor of 4. The weak spot is the braided hoses which I guess double guess 5000 psi. Don't look for problems that don't exist Instead of chasing shadows concentrate on getting reliable spheres. A mistake I often see in this type of valve made is that the ball is hammered on the seat by more than one hit and allowing the ball or the punch to bounce. The nitrogen pressure of 1000 to 2500 psi will hold the valve shut higher pressure will do the same. If the ball has a not perfect seat then nitrogen will leak extra pressure will not lift the ball and allow a bigger leak. If the seat is perfect then it will hold extra pressure. This sort of design if not perfect will leak even at low pressure and given time will empty to atmospheric pressure. This is because the seat and the ball have no give. If the ball was softer then the pressure will drive it into the seat. Workshop manual page G27. Sphere to assemble. End of paragraph 4 note New STEEL ball and seal for charging cap and sphere to charge paragraph 4 new STEEL ball and seal fit charging cap. Page G26 fig G14 part 11 nylon ball. Its very confusing and one of the reason I dislike the charging cap design. If it were me I would use locktite hydraulic thread sealer on the cap. (Message approved by david_gore) | ||
| Chris Miller Prolific User Username: cjm51213 Post Number: 254 Registered: 5-2013 |
Hi Bob, I have two accumulators on the '72. They have different designs for their check valve seal caps. One has a "floor" where you'd expect it to be so it can crush a plastic ball, and is on the aft unit, which did not lose any nitrogen. The other has a void which could be filled by a stack of 1/2" disks 1/4" thick, which stack would completely eliminate any differences, but I haven't got such a stack, so I have had to improvise. Both units preserved pressure at 2,500 PSI for two days on the bench, and I couldn't understand why I would have a sudden depressurization, until I hit on this notion that the ACV prevents the pumps from developing more than 2,500 PSI, but not heat from developing more than 2,500 PSI. So, my original question was if the exhaust has been re-routed. I think the answer is, "No.", because other comments indicate that the exhaust travels directly under the accumulators. My second question was if the regulator valve sealing ring was a failsafe, and I think the answer is, "Yes.", but that is still an open question, and interesting, but irrelevant to my depressurization. My current problem is to seal the check valve. I've used my pop-rivet design and it holds with zero leaks at 2,500 PSI, but at higher pressure, I clearly have a leak. I doubt that the sphere has deformed, so I doubt that the leak is at the equatorial diaphragm joint. That leaves my check valves, and they don't show any deformation, but that doesn't mean that they aren't leaking. They don't leak in any detectable amount at 2,500 PSI, but at 3,500 PSI? Who knows? My testing is not testing the "system"; my testing is testing my check valve. The design is a steel sphere, but without a lapping stylus, that was hopeless. My pop-rivet design was apparently perfect at 2,500 PSI, but has failed several times for reasons that, until recently, could not be explained. So, being the good citizen, I am sharing my experiences and my recent discovery of both the inexpensive tools and the correct technique to lap the seat of the check valve. I know I said I wasn't going to, but I've changed my mind; the experiment is intriguing. I'm going to boil some accumulators and measure both fluid and nitrogen losses for the three cases I have -- Fore unit with void in cap and pop-rivet check valve, aft unit with floor in cap and pop-rivet and spare from cadaver car with correctly lapped steel sphere valve and new cap. This will show if the regulator valve sealing ring is a failsafe and which, if any, of my check valves work. I have some really big, open fields, and I'm just going to have to endure David Gore's safety warnings... Chris. | ||
| Geoff Wootton Grand Master Username: dounraey Post Number: 474 Registered: 5-2012 |
Chris It comes as no surprise to me that your pop-rivet check valves have acquired slow leaks. Aluminum is a soft metal which is easily deformed. Also, since these pop-rivet valves are close to a hot exhaust pipe you are essentially heat treating them everytime you drive your car, with unpredictable consequences. I think you have proved that pop-rivets are not suitable to be used as valves in accumulators. No further testing is necessary. Geoff | ||
| David Gore Moderator Username: david_gore Post Number: 1474 Registered: 4-2003 |
I have been having problems with duplicate posts appearing in the threads form Bob UK when only one appeared in the approval queue. When I delete the duplicate post, both posts are deleted. Bob, I lost the post on inner tube rubber suitability but saved your post responding to Chris Miller as below; my apologies for losing the post but I do not know how this happened: Chris, You are not going to find anything thats not already known. Experiment away if you want to but what you discover will be of little value to the job in hand. Regardless of the charge cap design hydraulic sealer will seal the threads of the charge cap. If a perfect seal is obtained using thread sealer then the ball crush ball and other bits are there for the ride. 2 days isn't a long time because there are a few reported cases of 20 year old spheres that are still holding maybe not 1000 psi but 800 or so. Mine are 18 years old. Why not fix a pair of spheres then experiment on the left overs. You wouldn't want to damage a new diaphragm. Fluon seals are very strong and unlikely to pop. The max temperature of fluon before it degrades is less than 260c And over 200c. The pump push rod has a safety snap area to protect the system should the acv jam up. The pressure in the sphere is not protected by the push rod when the relief is open. The spheres gas protects that bit. Boiling the spheres will show at pressure increase which the gas will absorb. The nitrogen and dot will expand. Dot has low expansion not sure about nitrogen. I personally wouldn't heat up pressure vessels that are not vented. The volume of the nitrogen is known and the volume of the for in the sphere is known and the volume of the dot in the valve body is not known so once that has been measured with a petite the pressures can be calculated and plotted on a graph up to 300c. The danger is that while boiling a sudden loss of nitrogen and you are in trouble. It will blow boiling water ever where at the speed of sound which will vaporize the hot water to steam which expands to 600 fold. The pressure in the sphere will drop fast but if the heating continues the dot is now hydraulically locked and something will crack probably the valve body or a nipple will get pushed out. Hydraulic testing is usually done with water and solvable oil if corrosion is of concern. Because liquids are not compressible there is no stores energy. So if anything breaks then the pressure drops to zero and the water leaks out. To test boilers fill boiler with water and hand pump via the water injector mote water until water is coming out of the top, shut the top valve and pump until the gauge shows twice the relief pressure then visual revits etc inside the fire box. I did a steam boiler just before I retired and the top of the fire box split and water went everywhere no drama no bang just a click and lots of water. To test spheres they need to be assembled with a split diaphragm so that the halves seal or an o ring and pumped up with a liquid such as water with soluable oil. This well only test the robustness of the sphere. It won't test the sphere as a sphere ready to use. Because the robustness of the design has been tested and calculated already there is nothing to be gained unless the test is to burst pressure. The maths used to calculate hoop stress in pressure vessels is well developed and 150 years old and very accurate. Hydraulic designer use the formula and charts to calculate theoretical burst pressures and then work back with a safety factor to arrive at a maximum working pressure then factor in the actual working pressure. Meaning the spheres will most definitely not break using 10000 psi. This is because pressure pushes equally in all directions and spheres are equally stressed in all directions. The only way pressure can alter the sphere shape to make more volume is to make the sphere get bigger is by stretching the steel. To actually burst the sphere the steel would have to be stressed beyond it's critical point. The spheres are most likely made from EN40 steel which is excellent for this application and all round tough with a good youngs modulas. Us engineers favour these grades of steel for its toughness and easy machinablity and heat treatment to further enhance its toughness. Notice that there are not sharp corners any where. Sharp corners are stress raisers and will propagate cracks. Crankshafts are an obvious example. (Message approved by david_gore) | ||
| Chris Miller Prolific User Username: cjm51213 Post Number: 256 Registered: 5-2013 |
Hi Geoff, > It comes as no surprise to me that your pop-rivet check valves have acquired slow leaks. I don't think I would characterize this as "acquiring slow leaks". They work perfectly at 2,500 PSI. It is only when pressure exceeds that that I get leaks, and then only on the one unit. > Aluminum is a soft metal which is easily deformed. Yeah, you'd think, huh? But they aren't. I've inspected them and they show no deformation. In fact, they still work perfectly at 2,500 PSI. The force they experience as check valves is against the flange and in exactly the same place as the force they would experience in use as rivets. > No further testing is necessary. Well, I still need to get both spheres to hold nitrogen... I can put them on and wait and see, again, or I can test them with more severe testing than 2,500 PSI sitting on a bench, which I though was a boundary case and I was wrong. I have four ACVs and four spheres. And I think I have a pot big enough to boil all four at once. Since one '72 sphere holds pressure, and one does not, I need to examine the differences. They are in different positions, one fore and one aft; they are on different ACVs; their sealing caps are different. Both have the same pop-rivet check valve design. Don't get me wrong, it is possible that the check valve is the problem, but I think it is more likely that the secondary and tertiary seals are not sufficient. Unless a check valve has zero leakage, which is highly unlikely, eventually the pressure on both sides of the check valve will equilibrate, rendering it inconsequential. The entire seal becomes the secondary and tertiary seal. Since that is where the difference is, I suspect that is where the problem is, not the check valve proper. Chris. | ||
| Chris Miller Prolific User Username: cjm51213 Post Number: 257 Registered: 5-2013 |
Hi Bob, > Experiment away if you want to but what you discover > will be of little value to the job in hand. ... unless I discover why one unit depressurizes and how to prevent that... > Regardless of the charge cap design hydraulic sealer will > seal the threads of the charge cap. If a perfect seal is > obtained using thread sealer then the ball crush ball and > other bits are there for the ride. Where have you been all my life?!? I think that is a perfect solution! Tell me more about this hydraulic thread sealer. > Why not fix a pair of spheres then experiment on the left overs. > You wouldn't want to damage a new diaphragm. I have four ACVs and spheres. Two from the '72 and two from the '66 cadaver car, and five diaphragms. The design of the spheres is different enough that results from the '66 don't translate to the '72 and vice versa. I'm testing the two from the '72 so I can be sure that when I put them in this time, they will stay in. I'm really not all that interested in publishing an academic treatise of how to seal this guys. I think you've solved that operational detail with your hydraulic thread sealer suggestion. > Fluon seals are very strong and unlikely to pop. Right. Not “Pop”, simply exceed the hydraulic friction imposed. I think Rolls Royce planned for failsafe. I also think it is less obvious than a single component that fails; I think that are a bunch. If I measure the impounded fluid before and after and there is a difference, it had to go somewhere. I count five paths to escape – o-ring 2 to by-pass, check valve to by-pass, regulator valve piston sealing ring to by-pass, and o-ring 3 and 4 to external. I wouldn't be able to distinguish among these and I don't think it really matters where the pressure release is, but it will be interesting to see if it appears at 3,100 PSI. (2,500 PSI * (373/300) = 3,100) It probably shouldn't, but I don't plan to go any farther ... > I personally wouldn't heat up pressure vessels that are not vented. I'm going to be several hundred yards away looking at the stars. And "boiling" is not a temperature that is even out of operating range, so I'm nowhere near any critical thresholds. I'll attach a chain to the handle and put the pot on a Coleman stove and let it boil for half an hour. Then I'll pull it off the stove and let it sit long enough to cool. Then I'll collect my bits and pieces and go measure to determine what happened. > Hydraulic testing is usually done with water and solvable > oil if corrosion is of concern. I don't have a hydraulic problem; I have a gas leak, so I have to include the gas in the experiment. I could subject the check valve to hydraulic pressure by removing the diaphragm, but the ACV limits my pressure to the sphere and even absent that restriction, the friction of hydraulic fluid and nitrogen are so different that I think the results would be invalid. A check valve that holds hydraulic fluid may not necessarily hold nitrogen. N'est-ce Pas? Bob, I'd like to thank you for a considered discussion of the topic I raised. I don't always see your level of consideration and discourse – even from you and your laughing dog, but I want you to know that I appreciate it, when I do see it. For example, this discussion revealed the hydraulic thread sealer, which is now obvious but I would never have arrived at that solution. Thanks. Now, please, tell me more about the hydraulic thread sealer, and I can get on to my next project. Thanks for the help, Chris. | ||
| Geoff Wootton Grand Master Username: dounraey Post Number: 476 Registered: 5-2012 |
Hi Chris On a personal note, don't these things frighten you at all. They scare the life out of me. This is why when I reconditioned my accumulators I stuck rigidly to the tested procedures and used a reconditioning kit from a bona fide supplier. I also got comfort from the fact they had been pressure tested to 2500 psi (normal running pressure) when they were on the car and I was only going to put 1000 psi in them. I also carried out a careful visual check for any cracking once I'd cleaned up the hemispheres. This is all standard practice. Even so, on refitting them to my car I was very aware of the potential bombs I was holding just 12 inches away from my face. I doubt the safety glasses I was wearing would have offered any protection at all had there been a weak spot in the 40 year old spheres. I realize the chances of an explosion are extremely remote, but hey, there's a lot at stake here (most notably, the arrangement of my face). So, my question is, will you carry out safety precautions when you boil your accumulators or will you be standing over them in the kitchen, apron on, giving them the occasional stir. If I were to be doing this I would vacate the kitchen and then, after a period of boiling time, turn the cooker off by pulling a fuse in the garage. After an hour or so I would then cautiously venture back into the kitchen with my crash hat on. What are your thoughts on this. Geoff | ||
| Chris Miller Prolific User Username: cjm51213 Post Number: 258 Registered: 5-2013 |
Hi Geoff, > don't these things frighten you at all Well, frankly, yes, a little bit. And I think that is important. But it is not an ignorance based "Throw virgins into the volcano to appease the gods!" kind of fear that I think of whenever I see one of David Gore's safety warnings. Fearlessness leads to recklessness, and I am not reckless. This is a huge reason why I discuss this stuff. By the time I have had several thorough discussions and done the math, I have worked out all the kinks. I understand the problems I'm trying to solve well enough to contain collateral damage, and I do experiments to prove to myself that I do, in fact, understand. For example, when I boil the accumulators, they will be below grade in the middle of a field several hundred yards away. To get that number, I looked up "Pipe Bomb" to determine the internal pressure and blast radius. I learned that pipe bombs have internal pressure in the 10,000 PSI range and have a blast radius of several hundred yards. I won't be developing anywhere near 10,000 PSI and I will be several hundred yards away, so worst case, I lose some car parts, and maybe a Coleman stove and a soup pot, but I doubt that I will lose anything, because I will be in the 3,100 PSI range which is well within the safety limits. > or will you be standing over them in the kitchen, apron on, giving them the occasional stir Ha! (JTBC, humor, not derision.) "Accumulator Soup"! I can say, "I just souped up my Rolls Royce."? Ha! See above for more detailed description of the experiment, including locating the "lab" below grade and far away. the plan is: Dig hole. Embed electronic kitchen thermometer temperature probe with five foot sensor line. Place on pedestal to be visible from several hundred yards. Attach chain to pot handle, attach long rope to chain, and put pot on Coleman stove. Retreat to some safe distance. Watch thermometer with binoculars to verify boiling water. Boil for some time. Pull the pot off the stove with the chain and let cool. Collect residue and measure both remaining fluid and nitrogen in accumulators. Sound sound to you? Thanks for the help, Chris. | ||
| Geoff Wootton Grand Master Username: dounraey Post Number: 477 Registered: 5-2012 |
Chris It was meant as humor, not derision. As far as safety goes, sounds great. I look forward to you publishing the results. Geoff | ||
| Chris Miller Prolific User Username: cjm51213 Post Number: 259 Registered: 5-2013 |
Hi Geoff, > It was meant as humor, not derision. Of course, it was, and it was quite funny! Chris. | ||
| Bob uk Unregistered guest Posted From: 94.197.122.92 |
Chris, Go to loctite web site. This company is the go to guys for high pressure sealing problems. Others are Dow 3M and of course DuPont. Loctite stuff is approximately £5 a 50ml bottle that will do many charge caps. I have one type which locks loose bearing races which is very effective and some manufacturers of mechanisms containing races use loctite for assembly as a matter of course. As far as I am aware nobody has used a chemical sealer on RR charge caps, so you could be the first. The position of the spheres is irrelevant to the loss of nitrogen gas. The nitrogen loss is caused by a defective sphere. Increasing pressure will prove nothing. If it leaks at 2500 it will leak at 500, just slower. The piston and bobbin are matched pairs and the clearance between the two is very small. The fluon seal wouldn't get through the gap and would probably jam the piston. All this is academic because the braided hoses would have burst long before the pressure got that high. Hydraulic testing with liquids in place of a gas is standard engineering practice because it is much much safer. Recently some Chinese engineers tested some pipework with nitrogen instead of a liquid and a mistake was made and the pipes exploded. Causing millions of dollars worth of damage. Pressurised gas contains stored energy. Pressurised liquids do not contain stored energy. Except when the volume huge like a 100 mile pipe line. The posting that got lost ( the CIA intercepted it.) was about the use of the correct material for the environment the material has to work in and how often the correct stuff is about the same price.  (Message approved by david_gore) | ||
| Bob uk Unregistered guest Posted From: 94.197.122.88 |
Loctite is a UK company that makes a huge range of industrial adhesives. Loctite 542 is a general purpose hydraulic and pneumatic fine thread sealant that dries to a solid with the exclusion of air. The sealant blocks the microscopic imperfections that exist between mated threads. The joint can be undone once cured by normal hand tools the breakaway strength is 11Nm. Curing takes 30 mins to allow for adjustments. My advice is to contact loctite and ask them for the best glue for the job which is nitrogen gas at say 4000 psi and a 5/8 UNF thread with a -50 to 150c range fitted to a hydraulic accumulator. I have thought about the sphere to diaphragm joint and decided due to no signs of dot oil leaking the joint must be good so therefore the cap is leaking. If no gas is obviously leaking from the sprung loaded valve in the sphere then there will be no need to separate the sphere. Continually taking the same bit apart leads to damage. Note RR suggest that a sphere is charged stored and then tested before fitting to the car. How to test it doesn't say. Connecting the sphere to a nitrogen bottle would mean removing the charge cap which invites a leak defeats the test. Invasive testing. So to test it's pressure gauge in an acv method and flick up pressure. RR say any loss of more than 25psi is cause for rejection. However the nitrogen is checked using a nitrogen gauge then checked using a dot gauge, this assumes that both gauges are accurate to less than 1% which is a tall order plus temperature changes from day to day. IMO There is a natural assumption that liquids are thicker than gas. Meaning that gases find leaks that liquids don't, this holds water at low pressures of say 5 psi but as the pressure rises the difference goes. By the time we get to 2500 psi the difference is gone. (Message approved by david_gore) | ||
| Bob uk Unregistered guest Posted From: 94.197.122.88 |
Forgot to write. The general hydraulic thinking is that 2500 psi is medium range and high pressure starts at 10000psi it's very flexible definition wise. Hydraulic and gas sealers are normally for medium pressures and loctite don't publish max working pressure. However sellers of their products do and I have seen 10000psi quoted by many others. Anaerobic is I believe the word for hydraulic glue. NASA and RR jet engines use hydraulic sealants. (Message approved by david_gore) |
