Engineering the Perfect Hydraulic Pressure Reduction System
#21
10-04-2011, 09:46 AM
Senior Member
Walt...I appreciate your comments. I believe your company's valve is an excellent product that works as intended, is not terribly difficult to install and is provides a fair value for the dollar. I also think your engineering decision to go in that direction was a prudent one.
I also think that the variablilty that you mentioned, if anything might be the reason my idea turns out not to be feasible...but I am not fully convinced of that yet. It is an interesting challenge, so I plan to explore it.
I would hope that neither one of us loses sleep over competition in this very small market.
And yes, I believe that you are correct that my battery is not in the best of condition and that could have skewed my results slightly, especially with the engine off. The only way to be sure,though, is for you and Gus to monitor voltage during your tests.
I also think that the variablilty that you mentioned, if anything might be the reason my idea turns out not to be feasible...but I am not fully convinced of that yet. It is an interesting challenge, so I plan to explore it.
I would hope that neither one of us loses sleep over competition in this very small market.
And yes, I believe that you are correct that my battery is not in the best of condition and that could have skewed my results slightly, especially with the engine off. The only way to be sure,though, is for you and Gus to monitor voltage during your tests.
I have lots of resources in the form of embedded processor controls that could do what you talk about if I can be of any assistance. Our stuff is all PIC based in case you have those development tools. I didn't note what the motor current is but that would obviously affect the PWM design. We have various PWM motor control products that could potentially do what you would like. We can do anything up to about 100A DC so probably have something that would fit once you sort out how this would get connected. You sound like you are in the business so probably have your own way of getting there.
I'm dubious regarding the economics and installation issues especially since certain parties seem to struggle with removing an NPT plug and someone has managed to damage a hose (not sure how you can do that?). Clearly some people need to understand their limitations. The original pump I dissected was available because the owner had ripped the solenoid connectors off while trying to remove it. I had to take the solenoids apart and repair them so I could trace out the galleries in the pump body. The DIY world requires a different thought process as normally we are supplying product to companies that are staffed with trained technicians. That said I'm completely in tune with your thought process.
I also noted that someone reports that an 11 year old hose broke after the relief valve was installed. As stated in the relief valve instructions, the valve has no remedial capability. The only amazing thing to me was that a stock hose lasted that long. Mine from a 2000 XKR only made it to 2003. There are some who are replacing them every year. 11 years is a miracle.
The following 2 users liked this post by walt_00XKRConv:
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#22
10-04-2011, 10:19 AM
Veteran Member
Well said Walt! By the way, it seems like measurements by ALL parties now have pretty much demonstrated that the using the "other" system still results in an appreciable spike in pressure at the dead-head condition. Yet the most recent posts on the "other" forum claim the measurements were somehow erroneous and that pressure is significantly reduced with both systems. It like "who are you going to believe, me or your lying eyes?"
Even though I am an engineer and can deal with theory, I am really an old-fashioned type who is much more satisfied with real-life empirical data. Show me some graphs and charts and I'm a happy guy!
Doug
Even though I am an engineer and can deal with theory, I am really an old-fashioned type who is much more satisfied with real-life empirical data. Show me some graphs and charts and I'm a happy guy!
Doug
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Gus (10-04-2011)
#23
10-04-2011, 06:25 PM
Veteran Member
it's no secret, but still grist for the mill I guess, that my measurements were deficient. But they were out there for more than a year; and they were all that I had.
But I really wanted to say two things about providing "reliable information":
- The motor: Not mentioned above are the recurring, unsupportable claims (still out there in web-land, last I looked) of damage to the motor. Electrical or mechanical damage we were not told, but it's untrue in either case. The motor draws less current, consumes less power, turns lower RPM, and sees lower mechanical forces with voltage reduction.
Recent measurements reported here by Rev. Sam and WhiteXKR show pressure reductions on the order of 300 PSI. Some as high as 350. The most important of these are those done "engine-off" (i.e. per user instructions, and please note that the resistor value was selected for engine-off operation).
The valve team reported a pressure reduction of ... ~ 75 PSI.
I've provided links to all known measurements of the voltage reduction system, including the valve team's, at
http://www.scorekeeper.com/jaguar/jaguar01.htm
But I really wanted to say two things about providing "reliable information":
- The motor: Not mentioned above are the recurring, unsupportable claims (still out there in web-land, last I looked) of damage to the motor. Electrical or mechanical damage we were not told, but it's untrue in either case. The motor draws less current, consumes less power, turns lower RPM, and sees lower mechanical forces with voltage reduction.
Recent measurements reported here by Rev. Sam and WhiteXKR show pressure reductions on the order of 300 PSI. Some as high as 350. The most important of these are those done "engine-off" (i.e. per user instructions, and please note that the resistor value was selected for engine-off operation).
The valve team reported a pressure reduction of ... ~ 75 PSI.
I've provided links to all known measurements of the voltage reduction system, including the valve team's, at
http://www.scorekeeper.com/jaguar/jaguar01.htm
Last edited by Translator; 10-05-2011 at 11:49 AM. Reason: Potential inflamatory comment removed as discussed via prior PM
#24
10-04-2011, 08:17 PM
Senior Member
Every time I read one of these threads, I feel like the dog in the Far Side cartoons.
People talk, all I hear is "blah, blah, blah, Pressure, blah, blah, Green Showers, blah
blah. I pretend I understand what is being said, but, I'm only fooling myself. In the
meantime, I'll just stick to praying.
People talk, all I hear is "blah, blah, blah, Pressure, blah, blah, Green Showers, blah
blah. I pretend I understand what is being said, but, I'm only fooling myself. In the
meantime, I'll just stick to praying.
#25
10-05-2011, 05:28 AM
Veteran Member
#26
10-05-2011, 09:56 AM
I do note that your battery (under 12V) is not in very good shape. The battery voltage directly impacts the ramp rate of the pressure (versus the constant width of the pulse) and accounts for the different peak with resistor. I am quite sure that is your battery was something like 12.5V you would get results similar to what Gus and I measured as the ramp rate would be steeper.
Walt...you apparently called it right. My battery was low from other work I had been doing on the car and not driving it recently. There is still a drop from the relays, wiring, fuse to the motor, but it was definitely low. I charged it yesterday. Then I waited 3 hours and ran 4 top cycles with headlights on to burn off the surface charge.
I am now getting results comparable to yours. I will be posting it as soon as a get a chance to write it all up.
Last edited by WhiteXKR; 10-05-2011 at 10:16 AM.
#27
10-05-2011, 11:06 AM
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#28
10-05-2011, 01:03 PM
Veteran Member
I just did some tests engine on/engine off, with resistor/without resistor. Here are the peak pressures.
Engine on without resistor:
Lowering the top: 1650
Raising the top: 1660
Engine on WITH resistor:
Lowering the top: 1530
Raising the top: 1610
Engine off without resistor:
Lowering the top: 1625
Raising the top: 1640
Engine off WITH resistor:
Lowering the top: 1320
Raising the top: 1480
I could go do it three more times, but it's a pain in the ***, and based on the consistency in Steve's results (we've been emailing each other. I'm sure he'll post his shortly) I don't see the point. By the way, these tests were done after driving the car for about an hour with a couple of short stops along the way, so the battery was fully charged. Even though the difference is not as great as my first test I ran, it still shows a drop of 180 PSI in the key test of raising the top with the engine on and no resistor compared to raising the top with the engine off and with a resistor installed. I'm going to leave my resistor installed.
The main difference between this test and the one I ran the other day was that for this test I had just driven the car, so the battery was as charged as it could possibly be. That's really more of a real-world simulation, since you're most likely to put up the top right after a drive. You're not very likely to wait an hour or two before raising the top.
So, based on these results, and the results of Steve's (WhiteXKR) tests, I owe Gus an apology. It is plausible that the graph Gus posted was not doctored or modified in any way. I should have kept my mouth shut until I had more data. But, I was operating from a preconceived assumption, and when my initial results were so vastly different from his, I felt that my assumption was confirmed. I'm sorry for accusing you of doctoring the graph, Gus.
I'd still like to know how the top could stall with such high pressure, though.
Engine on without resistor:
Lowering the top: 1650
Raising the top: 1660
Engine on WITH resistor:
Lowering the top: 1530
Raising the top: 1610
Engine off without resistor:
Lowering the top: 1625
Raising the top: 1640
Engine off WITH resistor:
Lowering the top: 1320
Raising the top: 1480
I could go do it three more times, but it's a pain in the ***, and based on the consistency in Steve's results (we've been emailing each other. I'm sure he'll post his shortly) I don't see the point. By the way, these tests were done after driving the car for about an hour with a couple of short stops along the way, so the battery was fully charged. Even though the difference is not as great as my first test I ran, it still shows a drop of 180 PSI in the key test of raising the top with the engine on and no resistor compared to raising the top with the engine off and with a resistor installed. I'm going to leave my resistor installed.
The main difference between this test and the one I ran the other day was that for this test I had just driven the car, so the battery was as charged as it could possibly be. That's really more of a real-world simulation, since you're most likely to put up the top right after a drive. You're not very likely to wait an hour or two before raising the top.
So, based on these results, and the results of Steve's (WhiteXKR) tests, I owe Gus an apology. It is plausible that the graph Gus posted was not doctored or modified in any way. I should have kept my mouth shut until I had more data. But, I was operating from a preconceived assumption, and when my initial results were so vastly different from his, I felt that my assumption was confirmed. I'm sorry for accusing you of doctoring the graph, Gus.
I'd still like to know how the top could stall with such high pressure, though.
Last edited by Reverend Sam; 10-05-2011 at 01:08 PM. Reason: playing with colors, correcting mistake (meant to say pressures instead of voltages)
#30
10-05-2011, 01:37 PM
Veteran Member
I guess the obvious question is that if it was that (relatively) easy to make the measurements and get the answers, why all of the theoretical discussion?
As the Titanic disembarked on its maiden voyage from Southampton in 1912, I wonder if one would have heard Thomas Andrews say to J. Bruce Ismay ". . .you know, in theory the ship is unsinkable, but I wonder if we should have taken a few more measurements".
Probably not.
Doug
As the Titanic disembarked on its maiden voyage from Southampton in 1912, I wonder if one would have heard Thomas Andrews say to J. Bruce Ismay ". . .you know, in theory the ship is unsinkable, but I wonder if we should have taken a few more measurements".
Probably not.
Doug
#31
10-05-2011, 02:19 PM
Veteran Member
I guess the obvious question is that if it was that (relatively) easy to make the measurements and get the answers, why all of the theoretical discussion?
As the Titanic disembarked on its maiden voyage from Southampton in 1912, I wonder if one would have heard Thomas Andrews say to J. Bruce Ismay ". . .you know, in theory the ship is unsinkable, but I wonder if we should have taken a few more measurements".
Probably not.
Doug
As the Titanic disembarked on its maiden voyage from Southampton in 1912, I wonder if one would have heard Thomas Andrews say to J. Bruce Ismay ". . .you know, in theory the ship is unsinkable, but I wonder if we should have taken a few more measurements".
Probably not.
Doug
Anyway, the answer to your question is money. I wasn't going to spend a load of money to prove a point.
#32
10-05-2011, 02:32 PM
Veteran Member
But as I recall I thought the originator of the resistor system did take some measurements initially with a crude set-up and did not say that the pressure was only minimally reduced at the spikes. So how is that explained?
Again, not at all blaming you since why should you go through the time and effort to validate the idea. But the originator certainly should have, especially once the discussion got into advanced hydrodynamic theories and other controversy.
Doug
Again, not at all blaming you since why should you go through the time and effort to validate the idea. But the originator certainly should have, especially once the discussion got into advanced hydrodynamic theories and other controversy.
Doug
#33
10-05-2011, 02:40 PM
Veteran Member
You'll have to ask Dennis about that. He took measurements, and those measurements showed a pressure reduction. He posted them for others to see. Keep in mind that my tests earlier today show an 11-12% pressure reduction. The way I see it, that's better than no pressure reduction at all. The resistor has NOT been shown to be ineffective. It's reducing the pressure by nearly 200 PSI on my car. That's just not the reduction that we originally thought we were getting based upon the fact that on occasion there's not enough pressure to close the latch with the resistor installed. I'm still at a loss as to why that happens.
#34
10-05-2011, 06:17 PM
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[quote=Reverend Sam;413317]
I could go do it three more times, but it's a pain in the ***, and based on the consistency in Steve's results (we've been emailing each other. I'm sure he'll post his shortly) I don't see the point........
The main difference between this test and the one I ran the other day was that for this test I had just driven the car, so the battery was as charged as it could possibly be..........
So, based on these results, and the results of Steve's (WhiteXKR) tests, I owe Gus an apology. It is plausible that the graph Gus posted was not doctored or modified in any way. I should have kept my mouth shut until I had more data. But, I was operating from a preconceived assumption, and when my initial results were so vastly different from his, I felt that my assumption was confirmed. I'm sorry for accusing you of doctoring the graph, Gus.
quote]
Sounds very much like we're starting to see some light at the end of this particular tunnel, thank the lord.
I'd just like to say that as far as I'm concerned the only winners here, ultimately are Jag owners and members of this site and others like it where the info is shared around.
#35
10-05-2011, 07:37 PM
I have had a few dealings with Gus, and I NEVER for a minute thought that he was doctoring his results.
My impression of him was and is that he is a man of impeccable integrity.
I wish that I could say the same for everyone that I deal with.
In fact, here is an exchange in PM between he and I back in 2009
Re: Convertible top fix Quote:
Originally Posted by Kevin D
Quote:
Originally Posted by Kevin D
Here is my question about this issue. Clearly, this is a significant problem with this vehicle. What is the nature of this failure? Does the hose rupture along its length, or at a fitting? Is there is more pressure in the line than it is capable of holding,or is it an eventual failure of the actual material the line is made of? Is it conceivable that if the pressure output by the pump were reduced somehow that the line might not fail? Is there anything that those of us who have yet to encounter this problem can do to try to avoid it? Thanks.
So, Gus, it looks like the reduction of the pressure in the hydraulic system turned out to be the solution after all.
You are correct! The hoses began to fail and then I began seeing the latch and lifts were leaking. By the time the replacement hose was developed I identified the latch seal leak and then the lifts. Well it is a good thing because I think the hoses from Jag are going to be hard to get.
__________________
Gus
XK8 1999 122,000mi K&N Filter
S-Type 2000 3.0 83,000mi K&N Filter
www.jagrepair.com
What it is what it ain’t and what it ought to be!
Don’t ask the question if you don’t want to hear the answer!
In theory, there is no difference between theory and practice. But in practice, there is.-Yogi Berra
Insanity: doing the same thing over and over again and expecting different results.-Albert Einstein
My impression of him was and is that he is a man of impeccable integrity.
I wish that I could say the same for everyone that I deal with.
In fact, here is an exchange in PM between he and I back in 2009
Re: Convertible top fix Quote:
Originally Posted by Kevin D
Quote:
Originally Posted by Kevin D
Here is my question about this issue. Clearly, this is a significant problem with this vehicle. What is the nature of this failure? Does the hose rupture along its length, or at a fitting? Is there is more pressure in the line than it is capable of holding,or is it an eventual failure of the actual material the line is made of? Is it conceivable that if the pressure output by the pump were reduced somehow that the line might not fail? Is there anything that those of us who have yet to encounter this problem can do to try to avoid it? Thanks.
So, Gus, it looks like the reduction of the pressure in the hydraulic system turned out to be the solution after all.
You are correct! The hoses began to fail and then I began seeing the latch and lifts were leaking. By the time the replacement hose was developed I identified the latch seal leak and then the lifts. Well it is a good thing because I think the hoses from Jag are going to be hard to get.
__________________
Gus
XK8 1999 122,000mi K&N Filter
S-Type 2000 3.0 83,000mi K&N Filter
www.jagrepair.com
What it is what it ain’t and what it ought to be!
Don’t ask the question if you don’t want to hear the answer!
In theory, there is no difference between theory and practice. But in practice, there is.-Yogi Berra
Insanity: doing the same thing over and over again and expecting different results.-Albert Einstein
#37
11-12-2011, 04:35 PM
Success, but I am gettng hammered!
Now that we have mostly settled just what the pressure reduction resistor does and does not do, the obvious question (which some are already asking) is what can we do to reach converitible top pump pressure reduction nirvana.
Let start out with a set of desired features:
-Sharply limits the presssure to 950 PSI like the relief valve, in other words a true regulator
-Does not require opening up the hydraulics to install like the relief valve
-Totally plug and play in 3 minutes like the resistor
-Inexpensive
-Does not slow down the top like the resistor or effect it in any other way
-Reliable
As others have noted, there are two commonly used approaches to do this in industry: one is a mechanical pressure relief valve and the other is electronic closed loop feedback PWM. In a nutshell, closed loop feedback PWM drives the pump motor with pulses whose width is set by measuring the actual pressure. This sets the speed of the motor, and thereby can control the pressure of the pump. Simple PWM circuitry itself can be fairly inexpensive, but it requires an electronic pressure sensor. That would bring it to at least a cost level in the same ballpark as the mechanical pressure relief valve and requires openning up the hydraulics to connect.
So if these two 'in the box' solutions are too expensive and difficult to install, we have to look a bit outside the box. If you look at the pressure and voltage plots I took with the .2 ohm resistor, you will notice that the voltage reduces across the motor somewhat in proportion to the pressure increasing. Since the voltage source is a close to a constant, this means the voltage across the resistor in increasing. By ohms law, when you have a constant resistance and an increasing voltage, the current is increasing. So the conclusion is that the current increases roughly in proportion to the pressure. This allows us to monitor the motor current (cheap and easy) and determine with a fair bit of accuracy what the pressure is. This means we should be able to build an accurate enough PWM controller and without an expensive pressure sensor!
Another observation I made (but did not post yet) was that the motor, although it is driven both forward and reverse, only generates the high pressure spikes when driven forward. This information lets us make another simplifying assumption: that the existing relay in the car can be used to drive the pump in reverse, and the PWM circuit need only drive the pump forward. This assumption significantly reduces the complexity and cost of the PWM drive circuit. It also means that all of the signals needed can be accessed by unplugging one relay in the trunk fusebox and replacing it with this new device which I will call the 'pressure limiting relay'.
Right now this is just in the concept phase, but I have decided to put together a proof of concept device. I'll keep the forum posted.
Let start out with a set of desired features:
-Sharply limits the presssure to 950 PSI like the relief valve, in other words a true regulator
-Does not require opening up the hydraulics to install like the relief valve
-Totally plug and play in 3 minutes like the resistor
-Inexpensive
-Does not slow down the top like the resistor or effect it in any other way
-Reliable
As others have noted, there are two commonly used approaches to do this in industry: one is a mechanical pressure relief valve and the other is electronic closed loop feedback PWM. In a nutshell, closed loop feedback PWM drives the pump motor with pulses whose width is set by measuring the actual pressure. This sets the speed of the motor, and thereby can control the pressure of the pump. Simple PWM circuitry itself can be fairly inexpensive, but it requires an electronic pressure sensor. That would bring it to at least a cost level in the same ballpark as the mechanical pressure relief valve and requires openning up the hydraulics to connect.
So if these two 'in the box' solutions are too expensive and difficult to install, we have to look a bit outside the box. If you look at the pressure and voltage plots I took with the .2 ohm resistor, you will notice that the voltage reduces across the motor somewhat in proportion to the pressure increasing. Since the voltage source is a close to a constant, this means the voltage across the resistor in increasing. By ohms law, when you have a constant resistance and an increasing voltage, the current is increasing. So the conclusion is that the current increases roughly in proportion to the pressure. This allows us to monitor the motor current (cheap and easy) and determine with a fair bit of accuracy what the pressure is. This means we should be able to build an accurate enough PWM controller and without an expensive pressure sensor!
Another observation I made (but did not post yet) was that the motor, although it is driven both forward and reverse, only generates the high pressure spikes when driven forward. This information lets us make another simplifying assumption: that the existing relay in the car can be used to drive the pump in reverse, and the PWM circuit need only drive the pump forward. This assumption significantly reduces the complexity and cost of the PWM drive circuit. It also means that all of the signals needed can be accessed by unplugging one relay in the trunk fusebox and replacing it with this new device which I will call the 'pressure limiting relay'.
Right now this is just in the concept phase, but I have decided to put together a proof of concept device. I'll keep the forum posted.
Well, I was finally able to get a rudimentary proof of concept together. I built a PWM driver to replace the relays which drive the pump motor. For now I am running the PWM control open loop, and just monitoring current for my own information. It works great and runs cool. I can smoothly control the max pressure by turning a variable resistor that controls the pulse width driving the motor. I can easily set it to 950 or 1000 PSI and the top operates propertly. I am using a 22kHz PWM carrier to avoid vibrations that might be audible. The current clearly reflects the the pressure and should work quite well with closed loop feedback, which would be the next step in refinement of the design...But...
There is one problem. When the pump deadheads against the top latch, and the pressure is regulated down electronically, there is some type of 'water hammer' action taking place does not not oocur at full power to the motor. It manifests as a sharp audible vibration at deadhead (the pump vibrates hard), maybe 5-10 times per second. It make me think that internally the motor has a relief valve of some sort set around 1650 PSI (which seems to be where it normally self regulates when deadheaded). As it stands, this is not acceptable, since the vibration may be damaging to the system over time.
Right now I am stumped as to how to alleviate this without using some type of hydraulic component...and the whole point of this exercise was to avoid that. If anyone has a hydraulic backround and some possible insight, please let me know!
Last edited by WhiteXKR; 11-12-2011 at 07:32 PM.
#39
11-12-2011, 07:19 PM
Maybe, but I do not know how to detect that it is deadheading. Cut the power to soon and the latch will not operate properly. The current seems to hold relatively steady during this. Maybe I can put an engine knock sensor on the pump, lol.
#40
11-12-2011, 08:16 PM
Veteran Member