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  #1  
Old 10-01-2011, 06:40 PM
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Default The Definitive Hydraulic Pump Resistor Thread (with videos)

There has obviously been much discussion and debate over the efficacy of the convertible top resistor. I bought my Jaguar in the Spring of 2010, and then I joined this forum and Roadfly. That's when I learned of the problem with the exploding latch hoses. I have a background in electronics and a degree in electrical engineering. When I heard about the hose problem, my immediate thought was just to "turn down" the pressure by installing a resistor. Shortly thereafter, I started reading posts, primarily on the Roadfly forum, in which Dennis07 was discussing how it might be possible to install a resistor, just like I had been thinking.

Dennis actually took it a step further and started doing some experiments to determine how much resistance it would take to reduce the pressure in the hoses without reducing it so much that the top wouldn't latch. Dennis and I never spoke about this, I just knew it was a viable solution and I was interested in the outcome from Dennis' experiments. I followed along without commenting, but then another member of Roadfly started criticizing Dennis' idea.

Those criticisms were wide ranging. First came the claim that reducing the voltage would damage the motor because it would cause the motor to stall. That criticism was proven wrong because the motor never stalls with the resistor, it simply slows down a little. Then came the claim that the lower voltage through the motor would cause a higher current through the motor and the motor would burn up. That claim was obviously made by someone with zero knowledge of electronics. Dennis' resistor was ADDING resistance to the total circuit. By adding the resistor, the current through the motor was decreasing, meaning the motor would get less hot rather than more hot.

Then came the claim that running the pump on battery power would tax the battery, and users of the resistor would end up having to buy a new battery. Dennis quickly pointed out that the total amp-hours used was minuscule, and it would have no effect on the battery. The arguments against the resistor were getting weaker and weaker, yet they kept coming.

About that time, Gus claimed that he installed a resistor on his car, exactly the way Dennis had described, and it caused his top to stall. He wasn't claiming that the latch wouldn't close, he was claiming that the resistor reduced the pressure in the hydraulic lines so much that there was not enough pressure to get the top over the hump. It stalled in the middle of the cycle. Obviously, that's a bad thing. If I had been thinking about installing a resistor, I would have had second thoughts about it. In fact, I might have even decided to buy one of those $300 kits that him and Walt were selling.

A couple of weeks ago, Gus posted a graph that he claims shows the actual hydraulic pressure with the resistor installed. On this graph, the peak pressure during latch closure is nearly identical, regardless of whether or not there is a resistor installed. Also, that graph showed that the peak pressure "over the hump", was the same with or without the resistor. By "over the hump" I'm talking about the point in the cycle where the convertible top is putting the most pressure on the hydraulic cylinders. Gus' graph makes perfect sense at that point. As a member on roadfly explained, the pressure to lift a weight suspended in a well is the same, regardless of how fast the weight is moving. In other words, let's imagine that we're talking about a 10 pound weight hanging on a string. If you attach a motor to the string and wind up the weight, the string will remain under ten pounds of tension whether or not there is a resistor installed in series with the motor. With the resistor, the motor might turn more slowly, but it still has to generate ten pounds of force to lift the weight.

The pressure in the hydraulic lines for the top rams works the same way. If it takes 950 PSI of pressure to get over the top, it will take 950 PSI regardless of whether or not a resistor is installed. The resistor will slow down the motor making the top move more slowly, but no matter what, the hydraulic pump has to generate 950 PSI, otherwise the top will stall.

So now let's compare Gus' statement with his graph. Gus said the top stalled. The graph said the pump generated 1578 PSI. If the pump is generating 1578 PSI with the resistor installed, then it is generating more than enough pressure lift the top over the hump. So how can those two items be reconciled? One of them has to be false. In fact, I believe that both of them are false. The videos below will show definitive proof that the resistor reduces the hydraulic pressure at latch closure, but still allow the pump to generate enough pressure to lift the top over the hump.

The experiments:

First of all, the hydraulic gauge I used is normally filled with glycerin. Glycerin is a viscous liquid and it is used to stabilize the needle on the gauge. If the gauge was hooked to something with a lot of vibrations, or vibrations in the hydraulic line, the needle would vibrate. The glycerin prevents that. But it would also prevent the needle from showing the TRUE peak pressure during short spikes. So I drilled two holes in the plexiglass cover on the gauge and drained all of the glycerin.

As you'll see in the videos, the peak pressure on my gauge with no resistor installed is nearly identical to the peak pressure shown on Gus' graphs. That confirms that the gauge is showing the pressure accurately enough for this discussion.

I have the gauge hooked to the port on the pump which is slightly below and to the left of the T-handle on the pump. I don't know why, but during the "open" cycle the gauge only shows the hydraulic pressure on the latch, it doesn't show the pressure as the top is moving. I think I need to hook to another port to measure the movement of the top during the "open" cycle. However, the pressure during the "close" cycle is displayed on the gauge. So here's the first video. This shows the top opening with NO resistor:

Opening the Top, No Resistor - YouTube

On my computer I was able to scroll through one frame at a time to see exactly where the needle peaked. It peaked at 1640 PSI, which is almost identical to the 1635 PSI shown on Gus' graph. I would obviously expect to see some variation between vehicles, but I was surprised when the peak pressure was so close to what Gus showed it to be.

Next we'll look at the peak pressure during the "open" cycle with a 0.2 ohm resistor installed:

Opening the Top, 0.2 Ohm Resistor - YouTube

With the 0.2 ohm resistor installed, the gauge peaked at 1340 PSI, which is a 300 PSI reduction in the peak pressure. The resistor absolutely, unquestionably reduced the pressure, contrary to what Gus and Walt have been saying.

Now let's look at the "close" cycle. The port I'm hooked to shows the pressure throughout the "close" cycle, so we get to see the pressure "over the hump" as well as the pressure as the latch opens and closes. The following video shows the top "close" cycle with no resistor installed:

Closing the Top, No Resistor.mp4 - YouTube

It happens very quickly, but in stepping through the video one frame at a time I can see that during "latch open" the pressure peaks at 965 PSI. The pressure then drops down to about 380 PSI, and gradually rises to 1060 PSI as the top goes over the hump. Then the pressure decreases to 320 before rising again, peaking at 1650 PSI as the latch closes. That 1650 PSI was the peak pressure I saw in the system throughout my experiments this afternoon. And that was with the engine off. I hate to think what it would be with the engine running. Also, as you can see in the video, that last pressure spike is maintained long enough for the analog gauge to accurately show the pressure, and it closely matches what is shown in the graph that Gus provided.

This next video shows the pressure of the top closing with a 0.2 ohm resistor installed:

Closing the top, 0.2 ohm resistor - YouTube

In that video, the latch open event generates 660 PSI, which is a 305 PSI reduction from the peak pressure with no resistor. The pressure drops down to 260 PSI, and then climbs back to 945 PSI as the top goes over the hump. That's also nearly identical to what Gus shows on his graph, and it's a 115 PSI reduction in the pressure over the hump with no resistor in place. The pressure decreases to about 200 PSI, then climbs to 1430 PSI, which is 230 PSI less than the pressure with no resistor. This is the point that differs greatly from Gus' graph.
I took this a little farther. I decided to add another 1/10th of an ohm into the circuit to see if I could reduce the pressure even more. On my first attempt with 0.3 ohms installed I used the handy-dandy remote control that I got from WhiteXKR. I had been using it for all of the other experiments, and it was working fine. On my first attempt with 0.3 ohms installed, however, the top did not latch. I thought that maybe it was because the timer on WhiteXKR's circuit had timed out. The resistor causes it to take a wee bit longer for the top to close, so I thought the timer had turned off before the latch could close. So I got my wife to come sit in the car and push the button for me while I made the video. Here's the video:

Closing the top, 0.3 Ohm Resistor, attempt 2 - YouTube

Conclusion:

The resistor reduces the pressure. There is no question about that. It doesn't reduce the pressure down to the 950-1000 PSI that the relief valve does, but it does reduce the peak pressure by 305 PSI during the latch open event and 230 PSI during the latch close event. It can also be installed for less than $10, compared to nearly $300 for the hydraulic relief valve. There is no risk of damaging the pump or the hoses while installing the resistor, and the pump doesn't have to be removed from the car. So really, it's a matter of trade-offs. The relief valve is theoretically more effective since it reduces the pressure more than the resistor. It also costs $300 and is more difficult to install. The resistor is cheap, easy to install, and still provides more protection than running the top without any type of protection.
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Last edited by Reverend Sam; 10-01-2011 at 06:52 PM. Reason: Spelling
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Old 10-01-2011, 08:31 PM
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Great analyst Sam! Thanks for documenting all aspects of this problem.
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Old 10-01-2011, 09:13 PM
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So, you're point is? It's clear the resistor drops the pressure by X amount depending on the voltage applied (car running/not running). The question is how much pressure drop consistently from car to car day to day. If you want a set limit to pressure all the time, go relief valve. Settle for decreased pressure, go resistor and pocket the difference. There has been no reason to doubt anyone on their sincerety to help fellow forum members. Rev, all you've done on the forum has been greatly appreciated by me and alot of others; Gus, same goes for you. Without the two of you there would be a lot less info out there for the folks who like to work on our own cars. For you techno/engineers out there, I know where you're coming from, I went to engineeing school and undertand. Keep supplying data as you see fit and we'll see where this goes. In the meantime, chill.
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Old 10-01-2011, 09:28 PM
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I presented video evidence that the resistor does what Dennis claims it does. If he'll present a video showing his top stalling with a 0.2 ohm resistor while at the same time another camera is showing the pressure gauge peaking at 1578 PSI, I'll gladly apologize.
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Old 10-01-2011, 09:42 PM
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OK, you're not going to back down. It's a free country, guess I'll not care or get involved in this battle any more. Hope you both continue with your valueable contributions.
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Old 10-01-2011, 09:45 PM
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Attached is a link to my information if you haven’t seen it Jaguar Voltage Reduction system for XK8/R 1997 - 2006 Roof Operation On it you will see the equipment used to gather that information. I hope this helps.
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Old 10-01-2011, 09:58 PM
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Sorry, Gus, you know... this wouldn't be an issue if you didn't take every opportunity to criticize Dennis. He has never made a derogatory comment about the hydraulic relief valve. Yet you have taken every opportunity to be critical of the resistor. The resistor works. I've provided video that shows it does. Why don't you post a video of the resistor installed on a car while the data logger logs the pressure?

I'm confident enough in the data I found that I'll gladly hook the gauge up to anyone's car in the Raleigh area to test their setup. Why don't you ask for volunteers to come to the hydraulic shop where you tested the resistor? Check a few other cars. Let some neutral parties examine the data.
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Old 10-01-2011, 10:28 PM
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My comments towards the resister system were as a result of a question asked. “Don’t ask the question if you don’t want to hear the answer! “ As for taking a cheap shot that is not my nature but it seems to be for others. This stuff is a hobby and derive a great deal of pleasure helping others as strange as that might sound. And what is it about VIDEO? I need to do a VIDEO? Why? To satisfy you!?!?
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Old 10-01-2011, 10:29 PM
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I thought you guys were going to get together and do a combined test to try and put this to rest.

Is that not going to happen now?

I don't see any advantage in starting yet another thread to hash over this issue if there is nothing positive to add and the joint test is not going to happen we're just treading water.
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Old 10-02-2011, 02:05 AM
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Great job Rev. You have proved what was my personal gut feeling all along. I know nothing about electronics but I always felt the resistor would lower the hydraulic pressure. Well, it does.
My other feeling was that a pressure relief valve would limit the pressure to a specific psi. That also appears to be true.
Now the $64,000 question, which one to use. Here's my thoughts, and yes, I realize how little value my thoughts have. ha
The resistor is certainly better than doing nothing at all (which, at this point is exactly what I have done) It seems it would offer at least some protection from hose failure and it is inexpensive. Also easy to install.
The pressure relief valve seems to limit pressure even further and seems the best choice IF, big IF, you are mechanically inclined enough to install it, AND, big AND, are willing to part with the cash for it.
Now, you two quit squabling. You are both a valuable asset to this forum. Sam, I love your videos and have learned a great deal from them. I have not completed everthing I need to do to my xkr, but, I'll get there. Keep the videos coming, they are great.
Gus, you are probably the reason I joined this forum in the first place. Your how to's and pictures helped with several problems that I had early on with my xkr.
Neither of you have anything to be ashamed of, and your knowledge and advice has been valuable to many, many jag owners.
My advice..........just agree to disagree...............and move on.
If we all liked the same thing, we'd probably all be driving toyotas.....................now there's a dreadful thought. ha
Thanks Gus and Thanks Sam. You guys both rock..........maybe to a different drummer..........but, it's all good.
Thanks again, to both of you.
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Old 10-02-2011, 08:27 AM
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Quote:
Originally Posted by Friarshuck View Post
Great job Rev. You have proved what was my personal gut feeling all along. I know nothing about electronics but I always felt the resistor would lower the hydraulic pressure. Well, it does.
My other feeling was that a pressure relief valve would limit the pressure to a specific psi. That also appears to be true.
Now the $64,000 question, which one to use. Here's my thoughts, and yes, I realize how little value my thoughts have. ha
The resistor is certainly better than doing nothing at all (which, at this point is exactly what I have done) It seems it would offer at least some protection from hose failure and it is inexpensive. Also easy to install.
The pressure relief valve seems to limit pressure even further and seems the best choice IF, big IF, you are mechanically inclined enough to install it, AND, big AND, are willing to part with the cash for it.
Now, you two quit squabling. You are both a valuable asset to this forum. Sam, I love your videos and have learned a great deal from them. I have not completed everthing I need to do to my xkr, but, I'll get there. Keep the videos coming, they are great.
Gus, you are probably the reason I joined this forum in the first place. Your how to's and pictures helped with several problems that I had early on with my xkr.
Neither of you have anything to be ashamed of, and your knowledge and advice has been valuable to many, many jag owners.
My advice..........just agree to disagree...............and move on.
If we all liked the same thing, we'd probably all be driving toyotas.....................now there's a dreadful thought. ha
Thanks Gus and Thanks Sam. You guys both rock..........maybe to a different drummer..........but, it's all good.
Thanks again, to both of you.
Well said, sir!
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Old 10-02-2011, 09:59 AM
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I had some thoughts on the measurements, but decided to post over in the "Definitive ... Take 2" thread, as WhiteXKRs graphs there are ideal for referring to.

So, if anyone's still interested ...
The Definitive Hydraulic Pump Resistor Thread - Take 2
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Old 10-02-2011, 12:33 PM
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I want to try and help in solving all of this. The first question that I have is whether the mechanical pump is a multi-stage centrifugal pump or if it is a positive displacement pump (either screw type or piston). This makes a big difference in the whole "loss of pressure" argument.

The second thing I need to know is where the pressures were being tapped off of (both Gus and Sam). The pressure at the outlet of the pump is going to be different than the pressure seen at the operating cylinder due to losses through the hosing, valves, etc.

Now, I don't have a degree in mechanical engineering, but I have been working around hydraulic systems for more years than I care to admit to and have had to learn their internal designs quite a bit. So, I have a pretty good understanding of what is going on here. But, without knowing a lot about the XK's and specifically how things are built inside of the cars, things can go either way at this point for me.

I also understand the electrical side of things (this is my specialty at work). So, I can hopefully help weave this all into a nice simple answer.

Just so I can get a better idea of what the system is like, what is the outer diameter of the hosing running between the pump and the operating cylinder? What is the diameter of the operating cylinder piston (if that is not known, what is the outside diameter of the operating piston)?

Hopefully I can atleast put a paper explanation of what is going on and see if there is not a logical answer to this.
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Old 10-02-2011, 12:59 PM
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I have a lot of this information on my page but will try to answer the best I can. The pump itself has been a mystery for sometime. The best way I can describe the pump is that it runs like a rotary engine. I can get additional information on the pump but it may take a day or two. The access for the pressure that I used is the plug below the petcock that is used for the pressure relief valve.
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Old 10-02-2011, 01:50 PM
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I used the same port as Gus. It's below and to the left of the petcock.
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Old 10-02-2011, 01:51 PM
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I have not tracked back through all of my early postings about the resistor solution when it was originally offered but I am pretty sure my initial concerns were more to do with the issue of screwing around with anything electrical on these already electrically buggy cars. I was pretty convinced that pressure would be lowered during the phases where there was significant movement of parts (i.e., top going up/down) since the motor driving the pump was now turning slower, but I had wondered whether pressure would still build up to high levels at the very end where not much was moving except for the latch (the condition that others have designated as dead-head or stall condition).

In retrospect it looks like my instinct was correct in that pressure would still build up considerably at that final latching stage. I still wonder about my original concern re: impacts on the electrical system.

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Old 10-03-2011, 12:48 PM
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This has been a long and hard road to this point. A lot of energy was exhausted in achieving the end results along with a few battle scars that I hope will go away. With the charts from Steve (WhiteXKR) to confirm my results and Sam who used a mechanical device that did the same thing only confirmed what Walt and I have been trying to say from the beginning. Yes you can see a few variations in the pressures taken between tests and that can be contributed to the MY car, the mechanical operation, Devices used and the battery voltages used of the vehicle taking the test. Each play a part in the end results. I will not squabble over 143psi difference, however, I may test it again.

I see that Steve has another option that may have value called PWM (Pressure Limiting Relay) and I wish him great success, because he will test it to confirm that it will work and it will bring another option to the table.
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Old 10-03-2011, 07:29 PM
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Click the image to open in full size.






It'd be nice if some really knowledgable people could work together on this issue for ALL OUR sakes, for Jag owners and forum members alike. It would be amazing if this could happen.



As it stands there are now several threads dedicated to this issue, and back n forth it goes. All mods will be made aware to check these threads constantly, any bickering, name calling of any kind etc to be removed, infractions given, threads will be closed and persistant offenders removed from the site.


From today, edits will be made, posts removed as deemed necessary, infractions given and more, with regard to these threads, without any further warnings, so please try to get along!



Personally, I'd much rather go with option 1 if humanly possible
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Old 10-04-2011, 04:13 AM
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No need to make things bigger than they actually are guys , you know opinions may vary but respect and friendship are what we like to have in these lovely forums
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Old 10-04-2011, 12:19 PM
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I'm glad I have a Coupe! One less thing to worry about.
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Old 10-04-2011, 12:19 PM
 
 
 
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