| Author | Message | ||
     Brian Vogel Grand Master Username: guyslp Post Number: 615 Registered: 6-2009 |
Hello All, Over the last several weeks I put together a hydraulic pressure gauge, among other things. Today I got to put it to the test. If the person who gave me the design that I created a variant on frees me to share it, I will do so. I will note that I have a 5000 PSI gauge, so the level of precision in my knowing whether something's 2350 versus 2500 PSI is limited since these two are fairly close together. The gauge is glycerin filled so that I don't have lots of needle shake. Today I got the chance to test the gauge out and while it appears to work perfectly, something's amiss with my system 2 accumulator and control valve. Here's what I found: When I start the car with a completely depressurized system (but after having bled the gauge so that I know I have fluid all the way up to the dial) I get nothing at all happening for about 5 seconds or so (no flick-up to 1000 PSI) and then the gauge rises very rapidly to somewhere between 2400 and 2500 PSI, the cut-out pressure. After that, with absolutely no application of the brakes, etc., I am getting rapid cycling between the fall-back pressure around 2350-2400 and the cut-in pressure around 1750 PSI. The pump is relatively loud (ticking/knocking) until a couple of cycles complete then it quiets down. You can hear a very slight ticking when the pump kicks in when the dial reaches cut-in and it goes quiet for a second or so when cut-out is reached until the pressure drops back to cut-in from fall-back. The needle just yo-yos up and down cut-in and cut-out. I interpret the complete lack of flick-up as indicating that my nitrogen charge has leaked out or gotten so low that it doesn't register with the gauge I have. However, I do not have a pressure light immediately upon shutting off the car, but must press the brake pedal once or twice before that kicks in (and, yes, I know that's not how things should be). I always get the system 2 pressure light coming on if the car sits for a short while. None of this happens with System 1, and I get many, many pumps before the pressure light illuminates. I don't quite know how to interpret the bouncing between cut-in and fall-back pressures. Guidance as to what I need to tear apart and rebuild would be appreciated. I plan to simply recharge the accumulator, as I think that leak is probably from a bad seal with the secondary "plastic ball" at the charge port. I'll do a "bubble test" under water (except for the input port itself) to check for leaks after recharging. Brian | ||
| Geoff Wootton Grand Master Username: dounraey Post Number: 306 Registered: 5-2012 |
Hi Brian I agree, looks like you have lost the nitrogen. I have read in the past that the difference between fall-back and cut out pressure should be no more than 200 psi, so I guess you need to check out the ACV also. 2400 psi is correct, so the pumps are ok and the ACV is opening at the correct pressure, however the ACV should then close when pressure drops to 2200ish. 1750 seems to be a bit low. As I recall there is a good write-up in the series II workshop manual, on this. Geoff. | ||
| Geoff Wootton Grand Master Username: dounraey Post Number: 307 Registered: 5-2012 |
Hi Brian Just checked the manual - the relevant information is in the flow chart in the fault finding section, G17. It says the pressure difference between build-up and cut-off should be 150 psi ( I wonder how many of our cars operate within this spec - lol). If you can get clearance to publish the details of the pressure gauge it would be really useful. Geoff | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 616 Registered: 6-2009 |
Geoff, Look again, as the information I have came directly from the Shadow Hydraulics Workshop offered by the RROC/RRF. Cut-out pressure is approximately 2500 PSI This settles down to fall-back pressure of about 2350 PSI very quickly. After that each application of the brakes, activation of height control, etc., reduces pressure by bit by bit until it drops to something between 1850 and 1750 PSI (there is a bit of "slop" in all these figures) at which point the pressure begins to accumulate back up to cut-off with very quick fall back to about 2350 afterward. There are several things that really confuse me. It's taking much longer than I would have thought to pressurize the accumulator in the absence of a nitrogen charge. The light takes about 25 seconds to go out. Then I've got that yo-yo-ing between cut-it and cut-out without any application of anything. What malfunction in the ACV would cause it to allow pressure to immediately be released on a cyclic basis? I think there's a problem there, but I have no idea what it might be (unless I had more than one rogue seal, which seems highly doubtful, but not impossible. - It would be even weirder if more than one cropped up in the same accumulator/ACV valve pair when I rebuilt three at the same time). Brian, who will publish, for sure, once I get the OK | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1108 Registered: 6-2006 |
Brian, where are you checking the pressure? If from the accumulator bleed nippLe port, try again from the flex hose port. If you turn off the engine when pressurised what happens? If you run it to 2000 psi and turn off the engine what happens? initially it sounds like you have some crap under the accumulator valve seat. would that surprise me that it's the same accumulator pair? No - because the chance that some of the crap from the wrong o`ring went into the system is pretty high. Plus sods law dictates the same. :-) :-( Get a longer piece of accumulator return hose and return it to a bottle. Observe when fluid is flowing out of it. If it still does not make sense , report back. | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 617 Registered: 6-2009 |
Paul, I'm checking the pressure from the bleed screw port on the system 2 pressure switch itself. I've found this a bit easier to access than the bleed port screw on the accumulator. What I've been trying to say is that I cannot (at least not when alone) get the system up to over 2000 PSI and then turn the car off. The cycling between cut-in up to cut-out takes a few seconds, at most, and the drop from fall-back to cut in is slightly faster. It really is a continuous up-down, up-down, up-down cycle with no intervention from me. I'll check again what happens if I turn the car off, because I paid little attention, but I think the pressure holds quite steady at cut-in, but not perfectly so. If I press the brake pedal even once the pressure warning light comes on. It should already be on if the pressure were dropping below cut-in. If the car sits for a few hours the system 2 pressure light does come on. Brian | ||
| Geoff Wootton Grand Master Username: dounraey Post Number: 308 Registered: 5-2012 |
Brian I stand corrected. I must remember to put my brain into gear before writing. Reading back through this thread it seems that the ACV is functioning correctly in an abnormal system. I know you will have checked for fluid dripping from the re-gassing port on the sphere, so the diaphragm seems to not be punctured. In a sense all this speculation is academic as the sphere has to be re-charged. So here is my question: have you access to equipment so that you can do the re-charge in situ. I recall that you have a paintball tank so you may only need to buy the adapter and high pressure line to do this. If you need to remove the accumulator again, then you may as well check the O-rings in the ACV as a matter of course, once the unit is off the car. Geoff. | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 620 Registered: 6-2009 |
Geoff, Although theoretically possible to charge the sphere in situ if you removed the bracket that the charge port cap goes through to stabilize the whole contraption, it's still a huge pain to do this. I also want to check out whether it's possible that I have a leak from somewhere other than the charge port. When these were originally charged up by a friend I asked him to place all but the input port at the top under water to check for leaks and knowing Steve (an aircraft mechanic and instructor at our local community college in their aircraft maintenance program) I'm sure he did. If (or I should say when) I take the ACV/A assembly off of the car I full well intend to take a look inside the ACV again. I won't dismantle it entirely as I did for the rebuild, but can easily check the O-rings on the bobbin and look for other signs of irregularities. I agree that the speculation is academic, but sometimes someone else has experienced precisely the same symptoms and can guide you pretty directly to the issue. Once I've got all this out then in again at least there will exist data points related to having seen this behavior and what might be the cause. Brian | ||
| Geoff Wootton Grand Master Username: dounraey Post Number: 310 Registered: 5-2012 |
Hi Brian "the speculation is academic" sounded much more pointed than I had intended; an example of the limitations of communicating through forums (but infinitely better than having no forums at all). Geoff | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1109 Registered: 6-2006 |
try again from the flex hose port. TO RULE OUT FAULTY DISTRIBUTION VALVES AND HCV SYSTEM If you turn off the engine when pressurised what happens? If you run it to 2000 psi and turn off the engine what happens? The accumulator pressure valve isn't just a bleed by type of valve which opens at it's close pressure , it opens at the higher pressure and closes lower giving the fluctuations between it's opening and closing points. It should hold at around it's closing point when running. If there is no accumulator pressure to damp that difference then it will happen quickly. Obviously it does this without intervention from you. (internally) There is a test flow chart in the manual to follow. But you need to know if A: the accumulator valve is leaking by at low pressures. B: the pressure is leaking back through the hydraulic circuits. Did you use anti-seize grease near the diaphragm? | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 621 Registered: 6-2009 |
More data points for everyone: 1. If the car is started and I get to the "yo-yo" stage, then the car is shut off, the gauge drops from the cut-in pressure to zero within 10 seconds, far faster than it takes the system to come up to initial cut-out pressure from zero. 2. I've posted a picture recently in another thread, but if the car is on jack stands at the front and is started the height control activates and the rear end shoots up very noticeably. Once it does that it stays that way until the car is lowered in front and started again in a normal stance. (To me this suggests that the height control system is working normally and not leaking. The car should slowly lower itself over the course of several days [and it's had that long and longer to do so] if the height control valve were allowing pressure to exit the rams.) Paul, I presume you mean the high pressure hose port on top of the ACV. If not, please correct me on this point. Also, if the issue is downstream from the ACV I am presuming a pressure check at the high pressure hose port should look normal, eliminating the yo-yo behavior. I agree that if something isn't cutting off flow in the system after the high pressure line flow reaches the rat trap or height control the system will zero out very quickly. The only place "near the diaphragm" that anti-seize was used is on the ring threads that hold the two halves together. This has not proven problematic other times and isn't in contact with the diaphragm itself. Brian | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 622 Registered: 6-2009 |
Just one more data point: The pressure readings yo-yo if taken directly at the high pressure hose port on the ACV as well. It also rapidly decreases to zero once the engine is turned off when measured there, too. Brian, who now has wireless at the garage | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1110 Registered: 6-2006 |
Looks like the accumulator valve isn't working I'm afraid. Even with no accumulator pressure it should keep the pressure in the gauge pipes etc for a while. | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 625 Registered: 6-2009 |
One of today's tasks was also dismantling the ACV to see if I could find anything obvious that would be making it malfunction. There was nothing that I could see. Here are photos in case someone sees something I didn't.        Of course, everything will be washed in denatured alcohol/methylated spirits and all O-rings will be replaced before being put back together. Brian, who suspects there is an interaction between an entirely exhausted accumulator and the actions expected in the accumulator control valve due to lack of any "push back" from the accumulator | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 627 Registered: 6-2009 |
Oops, forgot the close-up of the bobbin & O-rings, and you can't add a missing image via edit post.  |
