The Definitive Hydraulic Pump Resistor Thread - Take 2
#1
10-01-2011, 10:49 PM
The Definitive Hydraulic Pump Resistor Thread - Take 2
There was experimental error in these first results due to low battery. Please jump to post 30 in this thread for the correct data.
What an amazing coincidence!! I also was taking my own ‘definitive’ measurements this weekend.
I took a different measurement approach. I used an electronic pressure sensor with a range of 0-3000 PSI feeding into a laptop via a little USB data acquisition device. Sample rate was 120 samples per second. The precise value of the resistor I used was .207 ohms.
I monitored pump voltage and pressure for the top closing for:
-Battery (ignition off) operation without resistor
-Ignition on operation without resistor
-Battery (ignition off) operation with 0.2 ohm resistor
-Ignition on operation with 0.2 ohm resistor
I calculated the absolute worst case error for my measurements as +/- 65 PSI and +/-.128 volts based on the test equipment published specifications.
Observations and Conclusion:
My results are quite close to Rev. Sam’s (thank goodness!!!), supporting the conclusion the resistor provides a modest pressure drop, but it is not nearly as effective as the hydraulic limiting valve.
Interestingly, pressures with the ignition on and off, with no resistor were surprisingly close, refuting the commonly held wisdom that operation with the ignition off offers a significant advantage. With the resistor, however, operating on battery does offer more of an advantage.
I maintain that Dennis, Gus and Walt all published their results in good faith.
In my opinion, Dennis’ paper overstates the efficacy of the resistor and this was due to the deficiencies of the method chosen to measure the results (unmodified manual gauge). I would hope that Dennis updates his paper with the latest results from Sam and from me.
What an amazing coincidence!! I also was taking my own ‘definitive’ measurements this weekend.
I took a different measurement approach. I used an electronic pressure sensor with a range of 0-3000 PSI feeding into a laptop via a little USB data acquisition device. Sample rate was 120 samples per second. The precise value of the resistor I used was .207 ohms.
I monitored pump voltage and pressure for the top closing for:
-Battery (ignition off) operation without resistor
-Ignition on operation without resistor
-Battery (ignition off) operation with 0.2 ohm resistor
-Ignition on operation with 0.2 ohm resistor
I calculated the absolute worst case error for my measurements as +/- 65 PSI and +/-.128 volts based on the test equipment published specifications.
Observations and Conclusion:
My results are quite close to Rev. Sam’s (thank goodness!!!), supporting the conclusion the resistor provides a modest pressure drop, but it is not nearly as effective as the hydraulic limiting valve.
Interestingly, pressures with the ignition on and off, with no resistor were surprisingly close, refuting the commonly held wisdom that operation with the ignition off offers a significant advantage. With the resistor, however, operating on battery does offer more of an advantage.
I maintain that Dennis, Gus and Walt all published their results in good faith.
In my opinion, Dennis’ paper overstates the efficacy of the resistor and this was due to the deficiencies of the method chosen to measure the results (unmodified manual gauge). I would hope that Dennis updates his paper with the latest results from Sam and from me.
Last edited by WhiteXKR; 10-05-2011 at 08:21 PM. Reason: Data retaken due to low battery...see post 30
#2
10-01-2011, 11:03 PM
Veteran Member
I agree with you that Dennis' paper overstates the efficacy of the resistor. Your results are remarkably similar to mine. I believe that Dennis thought the resistor was reducing the pressure down to the 1000 PSI range because some people experienced a failure to latch with the 0.2 ohm resistor. I experience that myself on occasion, and I don't know why it happens. When it does happen, I simply have to press the button one more time and the latch finishes closing. I'm at a loss to explain why that happens. Dennis was also trying to calculate pressure based on the voltage across the motor. He can explain his theory better than me, but I think he was thinking that if the pressure is 1600 PSI at X volts, then it must be 800 PSI at X/2 volts and so on.
#4
10-02-2011, 12:34 AM
Veteran Member
Just came across another post of someone that had the resistor and probably thought it would help prevent a green shower, but it didn't.
So what about the costs of repairing a green shower? Chances seem higher with the resistor of a failure, so just looking at $10 seems a bit false economy to me.
#5
10-02-2011, 01:05 AM
Veteran Member
1309PSI is still about 40% higher pressure then the pressure relief valve, so seems pretty significant to me. I never operate the top without the engine running, most of the time I already drive whilst operating it, so that would be 1435PSI, which is about 50% higher than the pressure relief valve.
Just came across another post of someone that had the resistor and probably thought it would help prevent a green shower, but it didn't.
So what about the costs of repairing a green shower? Chances seem higher with the resistor of a failure, so just looking at $10 seems a bit false economy to me.
Just came across another post of someone that had the resistor and probably thought it would help prevent a green shower, but it didn't.
So what about the costs of repairing a green shower? Chances seem higher with the resistor of a failure, so just looking at $10 seems a bit false economy to me.
#6
10-02-2011, 01:17 AM
Veteran Member
Agree with the pressure hose, although I have installed the pressure relief valve and hope it will extend the time so it never becomes an issue, I have also bought the one from colliflower to be prepared if it happens.
Maybe it should be noted for the pressure relief valve (but also with many things), if you are not sure what you are doing, leave it to someone who does.
Maybe it should be noted for the pressure relief valve (but also with many things), if you are not sure what you are doing, leave it to someone who does.
#7
10-02-2011, 09:45 AM
Veteran Member
Thanks to everyone for their efforts and noodling on this. Some initial conclusions, as I see things.
* I am convinced that I overestimated pressure reduction, both in my paper and in posts here. I apologize for that error, will be editing the paper, and will be glad to reimburse anyone who installed a resistor (or Rev. Sam's kit) and has second thoughts. PM or email please; no questions asked. (This is no excuse, but I think I got fooled by more gauge error than I figured on, and /or over-reliance on "failure to latch" as an indicator that pressure was below 1000 PSI.)
* [Edit: On the other hand, I believe the "voltage-controls-pressure" principle is now confirmed.] Based on Rev. Sam's and White XKRs data, it seems the best estimate we now have for peak pressure reduction at 0.2 ohms, engine-off (as recommended) vs. stock, engine-on (as recommended) is ~ 350 PSI ... on the "close latch" hose (see below).
* These results are for a specific amount of resistance, 0.21 ohms (rounded) as recommended. I believe more pressure reduction is possible with higher resistance, or a slightly more involved circuit (EEs: think zener diode). Will be looking into that. I hope Rev. Sam and WhiteXXR will be up for some further testing down the road.
* There may be more variability among cars, including effect of battery condition, than we thought. This would effect the engine-on/engine-off prressure difference.
* There may be some "area under the curve" advantage to the resistor, as it reduces not just the peak pressure but also the time during which the pressure is high (the pressure bumps are narrower as well as lower). Just speculation as of now ... no idea about how to quantify this.
* [Edit: looks like I misread something. This paragraph probably N/A]. Gus has posted a number of times that it is the hose that is pressurized to open the latch that fails. While our eyes normally go to the big pressure bumps on the right of the graphs, the smaller ones on the left measure pressure in the "open latch" hose (at least during the "raise top" operation). Just started chewing on that ...
* I disagree with Avos. Pointing to a case of a failure with a resistor in place does not tell us anything. Last I heard, we had two reported failures with a resistor, two with a valve, and the failure rates of both appeared to be lower than with a "stock" system. We do not know more than that.
That's how it looks from here ...
* I am convinced that I overestimated pressure reduction, both in my paper and in posts here. I apologize for that error, will be editing the paper, and will be glad to reimburse anyone who installed a resistor (or Rev. Sam's kit) and has second thoughts. PM or email please; no questions asked. (This is no excuse, but I think I got fooled by more gauge error than I figured on, and /or over-reliance on "failure to latch" as an indicator that pressure was below 1000 PSI.)
* [Edit: On the other hand, I believe the "voltage-controls-pressure" principle is now confirmed.] Based on Rev. Sam's and White XKRs data, it seems the best estimate we now have for peak pressure reduction at 0.2 ohms, engine-off (as recommended) vs. stock, engine-on (as recommended) is ~ 350 PSI ... on the "close latch" hose (see below).
* These results are for a specific amount of resistance, 0.21 ohms (rounded) as recommended. I believe more pressure reduction is possible with higher resistance, or a slightly more involved circuit (EEs: think zener diode). Will be looking into that. I hope Rev. Sam and WhiteXXR will be up for some further testing down the road.
* There may be more variability among cars, including effect of battery condition, than we thought. This would effect the engine-on/engine-off prressure difference.
* There may be some "area under the curve" advantage to the resistor, as it reduces not just the peak pressure but also the time during which the pressure is high (the pressure bumps are narrower as well as lower). Just speculation as of now ... no idea about how to quantify this.
* [Edit: looks like I misread something. This paragraph probably N/A]. Gus has posted a number of times that it is the hose that is pressurized to open the latch that fails. While our eyes normally go to the big pressure bumps on the right of the graphs, the smaller ones on the left measure pressure in the "open latch" hose (at least during the "raise top" operation). Just started chewing on that ...
* I disagree with Avos. Pointing to a case of a failure with a resistor in place does not tell us anything. Last I heard, we had two reported failures with a resistor, two with a valve, and the failure rates of both appeared to be lower than with a "stock" system. We do not know more than that.
That's how it looks from here ...
Last edited by Dennis07; 10-02-2011 at 12:37 PM. Reason: clarity, a correction
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#8
10-02-2011, 10:31 AM
Veteran Member
The hose failure is on the close hose.
Thanks to everyone for their efforts and noodling on this. Some initial conclusions, as I see things.
* I am convinced that I overestimated pressure reduction, both in my paper and in posts here. I apologize for that error, will be editing the paper, and will be glad to reimburse anyone who installed a resistor (or Rev. Sam's kit) and has second thoughts. PM or email please; no questions asked. (This is no excuse, but I think I got fooled by more gauge error than I figured on, and /or over-reliance on "failure to latch" as an indicator that pressure was below 1000 PSI.)
* Based on Rev. Sam's and White XKRs data, it seems the best estimate we now have for peak pressure reduction at 0.2 ohms, engine-off (as recommended) vs. stock, engine-on (as recommended) is ~ 350 PSI ... on the "close latch" hose (see below).
* These results are for a specific amount of resistance, 0.21 ohms (rounded) as recommended. I believe more pressure reduction is possible with higher resistance, or a slightly more involved circuit (EEs: think zener diode). Will be looking into that. I hope Rev. Sam and WhiteXXR will be up for some further testing down the road.
* There may be more variability among cars, including effect of battery condition, than we thought. This would effect the engine-on/engine-off prressure difference.
* There may be some "area under the curve" advantage to the resistor, as it reduces not just the peak pressure but also the time during which the pressure is high (the pressure bumps are narrower as well as lower). Just speculation as of now ... no idea about how to quantify this.
* Gus has posted a number of times that it is the hose that is pressurized to open the latch that fails. While our eyes normally go to the big pressure bumps on the right of the graphs, the smaller ones on the left measure pressure in the "open latch" hose (at least during the "raise top" operation). Just started chewing on that ...
* I disagree with Avos. Pointing to a case of a failure with a resistor in place does not tell us anything. Last I heard, we had two reported failures with a resistor, two with a valve, and the failure rates of both appeared to be lower than with a "stock" system. We do not know more than that.
That's how it looks from here ...
* I am convinced that I overestimated pressure reduction, both in my paper and in posts here. I apologize for that error, will be editing the paper, and will be glad to reimburse anyone who installed a resistor (or Rev. Sam's kit) and has second thoughts. PM or email please; no questions asked. (This is no excuse, but I think I got fooled by more gauge error than I figured on, and /or over-reliance on "failure to latch" as an indicator that pressure was below 1000 PSI.)
* Based on Rev. Sam's and White XKRs data, it seems the best estimate we now have for peak pressure reduction at 0.2 ohms, engine-off (as recommended) vs. stock, engine-on (as recommended) is ~ 350 PSI ... on the "close latch" hose (see below).
* These results are for a specific amount of resistance, 0.21 ohms (rounded) as recommended. I believe more pressure reduction is possible with higher resistance, or a slightly more involved circuit (EEs: think zener diode). Will be looking into that. I hope Rev. Sam and WhiteXXR will be up for some further testing down the road.
* There may be more variability among cars, including effect of battery condition, than we thought. This would effect the engine-on/engine-off prressure difference.
* There may be some "area under the curve" advantage to the resistor, as it reduces not just the peak pressure but also the time during which the pressure is high (the pressure bumps are narrower as well as lower). Just speculation as of now ... no idea about how to quantify this.
* Gus has posted a number of times that it is the hose that is pressurized to open the latch that fails. While our eyes normally go to the big pressure bumps on the right of the graphs, the smaller ones on the left measure pressure in the "open latch" hose (at least during the "raise top" operation). Just started chewing on that ...
* I disagree with Avos. Pointing to a case of a failure with a resistor in place does not tell us anything. Last I heard, we had two reported failures with a resistor, two with a valve, and the failure rates of both appeared to be lower than with a "stock" system. We do not know more than that.
That's how it looks from here ...
#9
10-02-2011, 10:49 AM
Veteran Member
As I stated, my test was with the engine running and resister installed and came up with 1576psi and yours is showing 1435psi a difference of 141psi. I am unable to explain that other than maybe the MY. I was planning to retest anyway as you know to verify my findings so when I do I will post it on my page. Thank you Steve for posting your results this has confirmed what we thought to be correct and what we have been saying for a long time.
PS I will not insult you by asking if you had a witness when you took your test. I will take your word!!
PS I will not insult you by asking if you had a witness when you took your test. I will take your word!!
#10
10-02-2011, 11:31 AM
#11
10-02-2011, 12:02 PM
Veteran Member
[Edit: I should have added that the resistor, plus using engine-off operation as recommended, increased the pressure reduction further, to ~ 350 PSI in Sam's and Steve's measurements.]
As an objective reporter of fact, you'll be linking to their data from your site so people will have all the information, right?
Last edited by Dennis07; 10-02-2011 at 12:40 PM. Reason: added engine-off paragraph
#12
10-02-2011, 12:16 PM
Veteran Member
Walt & I
Well, that's an interesting interpretation. I don't think I heard Steve say any such thing. You claimed the resistor created ~ 50 PSI reduction; Steve's and Sam's measurements show ~ 300 PSI. But if it works for you.
As an objective reporter of fact, you'll be linking to their data from your site so people will have all the information, right?
As an objective reporter of fact, you'll be linking to their data from your site so people will have all the information, right?
#13
10-02-2011, 12:39 PM
Veteran Member
Good, now we have some more data.
White measured electronically, The Rev Sam with a pressure gauge, Gus electronically, Dennis with a pressure gauge.
All results, show a pressure reduction compared with the stock system.
Dennis apologizes for making an error in over estimation/interpretation and offers a reimbursement to anyone dissatisfied with their resistor kit, and he will amend his paper. (can't say fairer than that).
Gus is going to retest and post further findings.
Everyone agrees that the valve solution is the more efficient, albeit more expensive route for setting max pressure.
Sam now needs to go and buy another pressure gauge because he buggered his up by drilling it to remove the damping glycerine.
Not a bad day all in all.
Thanks guys for posting all of your results and interpretations, they are surely of benefit to owners of these affected XK8 models.
I have a question for the group.
Would I be wrong in thinking that the condition of the latch mechanism would have some bearing on the pressure required to get it to operate and hence possible fail to complete the cycle through one rotation.
Or is this deemed to be negligible?
White measured electronically, The Rev Sam with a pressure gauge, Gus electronically, Dennis with a pressure gauge.
All results, show a pressure reduction compared with the stock system.
Dennis apologizes for making an error in over estimation/interpretation and offers a reimbursement to anyone dissatisfied with their resistor kit, and he will amend his paper. (can't say fairer than that).
Gus is going to retest and post further findings.
Everyone agrees that the valve solution is the more efficient, albeit more expensive route for setting max pressure.
Sam now needs to go and buy another pressure gauge because he buggered his up by drilling it to remove the damping glycerine.
Not a bad day all in all.
Thanks guys for posting all of your results and interpretations, they are surely of benefit to owners of these affected XK8 models.
I have a question for the group.
Would I be wrong in thinking that the condition of the latch mechanism would have some bearing on the pressure required to get it to operate and hence possible fail to complete the cycle through one rotation.
Or is this deemed to be negligible?
#14
10-02-2011, 12:54 PM
Veteran Member
As you know this system is a series of switches, control units, pump and the overall mechanical devices that latch and lower and raise the roof with canvas on it and all work together. Yes the mechanics and proper maintenance are factors to it operating properly. What is also a factor is the MY. 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.
#15
10-02-2011, 12:57 PM
Veteran Member
Translator,
Just one quibble: The data shows that a particular value, 0.2 ohms of resistance does not give as much pressure reduction as I thought. It also establishes the (until now disputed) principle that voltage can be used to control pressure. (Maybe someone will still dispute this; we'll see.)
I think I fooled myself into picking too small a resistor value. Stay tuned.
Just one quibble: The data shows that a particular value, 0.2 ohms of resistance does not give as much pressure reduction as I thought. It also establishes the (until now disputed) principle that voltage can be used to control pressure. (Maybe someone will still dispute this; we'll see.)
I think I fooled myself into picking too small a resistor value. Stay tuned.
Last edited by Dennis07; 10-02-2011 at 01:04 PM.
#16
10-02-2011, 01:02 PM
Veteran Member
#17
10-02-2011, 01:05 PM
I would tend to agree. I changed the fluid on mine several years ago. The latch was jammed (in this case) by the gel substance that had evolved from the original fluid. I could hear the motor strain. Eventually the top would not close or open at all. The pressure on the hoses must have been very high.
#18
10-02-2011, 02:09 PM
Veteran Member
I have been looking at all the information related to the operation of the roof and the pressure. When I tested my roof it was with the engine running. Now I pulled all 3 charts WITH THE ENGINE Running and identified the peak pressure, after all this is what we are talking about and they all look near the same. I would like for someone to look at the figures and see what you come up with. Please!
#19
10-02-2011, 05:23 PM
As I stated, my test was with the engine running and resister installed and came up with 1576psi and yours is showing 1435psi a difference of 141psi. I am unable to explain that other than maybe the MY. I was planning to retest anyway as you know to verify my findings so when I do I will post it on my page. Thank you Steve for posting your results this has confirmed what we thought to be correct and what we have been saying for a long time.
PS I will not insult you by asking if you had a witness when you took your test. I will take your word!!
PS I will not insult you by asking if you had a witness when you took your test. I will take your word!!
Well, that's an interesting interpretation. I don't think I heard Steve say any such thing. You claimed the resistor created ~ 50 PSI reduction; Steve's and Sam's measurements show ~ 300 PSI. But if it works for you.
[Edit: I should have added that the resistor, plus using engine-off operation as recommended, increased the pressure reduction further, to ~ 350 PSI in Sam's and Steve's measurements.]
As an objective reporter of fact, you'll be linking to their data from your site so people will have all the information, right?
[Edit: I should have added that the resistor, plus using engine-off operation as recommended, increased the pressure reduction further, to ~ 350 PSI in Sam's and Steve's measurements.]
As an objective reporter of fact, you'll be linking to their data from your site so people will have all the information, right?
Please be careful to do apples to apples comparisons and you will have less to disagree on
Gus, your comment of 141 (actually 143) PSI difference refers to engine on with the resistor in both cases, your measurement vs. mine. (1578-1435)
Dennis, your comment of ~300 PSI difference refers my measured pressure reduction with the engine on, no resistor vs. resistor, and the number is actually 244 PSI. (1679-1435)
#20
10-02-2011, 07:25 PM
Senior Member
So Dennis, is there a variable low resistance component that can be added to the circuit that can be adjusted to produce just enough pressure to make the top work? Maybe just 0-5 ohms or so. I'm sure this may raise the cost, but might provide the optimal reduction in pressure w/o the valve. (Disclaimer, I have the valve installed in my car).