YS 170 DZ CDI
08-23-2010, 01:55 PM
#77
Senior Member
Join Date: Mar 2003
Location: Teesside, UNITED KINGDOM
Posts: 134
Likes: 0
Received 0 Likes
on
0 Posts
RE: YS 170 DZ CDI
Hello Dick,
I'm not quite sure.
I think I read a post somewhere (it may have been based on information that came from Richard V) that the YS175 was unlikely to be available outside Japan until the beginning of the 2011 season at the earliest.
If that is so, it would follow the pattern that YS have adopted for bringing out their previous new upgrades and designs.
I also supect that a 175 will be just about the limit for stretching the existing crankcase without a new casting.
Best wishes
Bob
PS:
I also hope that the YS175 will be available as a glow. I know I'm a bit of a dinosaur, but I like the low weight and simplicity that the glow has to offer. If the CDi version had been the one to be developed first, I sometimes wonder in my madder moments whether the glow would be the version that was now being hailed as the new breakthrough in design!
I'm not quite sure.
I think I read a post somewhere (it may have been based on information that came from Richard V) that the YS175 was unlikely to be available outside Japan until the beginning of the 2011 season at the earliest.
If that is so, it would follow the pattern that YS have adopted for bringing out their previous new upgrades and designs.
I also supect that a 175 will be just about the limit for stretching the existing crankcase without a new casting.
Best wishes
Bob
PS:
I also hope that the YS175 will be available as a glow. I know I'm a bit of a dinosaur, but I like the low weight and simplicity that the glow has to offer. If the CDi version had been the one to be developed first, I sometimes wonder in my madder moments whether the glow would be the version that was now being hailed as the new breakthrough in design!
08-23-2010, 02:14 PM
#78
RE: YS 170 DZ CDI
Bob
I agree.
There was no discernable power difference between my 170 CDI and Brett's 175 CDI on identical Valiants, same weight, with identical APC 19.5x11.5 props, both on 30% LS fuel and on a hot humid day. I too hope the 175 parts that are related to reducing heat are interchangeable with our 170 CDI's! That would be the best solution for consumers and YS.
Dick
I agree.
There was no discernable power difference between my 170 CDI and Brett's 175 CDI on identical Valiants, same weight, with identical APC 19.5x11.5 props, both on 30% LS fuel and on a hot humid day. I too hope the 175 parts that are related to reducing heat are interchangeable with our 170 CDI's! That would be the best solution for consumers and YS.
Dick
08-23-2010, 02:48 PM
#79
Join Date: Feb 2005
Location: oakland,
CA
Posts: 1,081
Likes: 0
Received 0 Likes
on
0 Posts
RE: YS 170 DZ CDI
I had a long discussion with Richard this morning, and he's glad that YS Japan is taking care of the problem.
As we are all aware, we all flies in different climate with different plane configuration. As stated before, I have not yet had the same pump issue, even flying in over 100 degrees weather. However, that does not mean it will not happen in different parts of the country/ world. As long as YS is aware of this issue, and is willing to take steps to improve the situation, is a good thing.
There are no set rules on props, fuel, ventilation on the cdi, only guidelines & suggestions. One person's set up may not be suitable for the next, as long as you find one combo that works for you, stick to it.
As we are all aware, we all flies in different climate with different plane configuration. As stated before, I have not yet had the same pump issue, even flying in over 100 degrees weather. However, that does not mean it will not happen in different parts of the country/ world. As long as YS is aware of this issue, and is willing to take steps to improve the situation, is a good thing.
There are no set rules on props, fuel, ventilation on the cdi, only guidelines & suggestions. One person's set up may not be suitable for the next, as long as you find one combo that works for you, stick to it.
08-23-2010, 07:52 PM
#82
Join Date: Sep 2006
Location: boca raton,
FL
Posts: 415
Likes: 0
Received 0 Likes
on
0 Posts
RE: YS 170 DZ CDI
This has been a well written thread and I certainly appreciate the approach folks have taken for displaying their findings. Because there seems to be different ways of setting up or breaking in the motors, I thought I would share my experience last week and this one. I had been running 30% heli fuel, and last weekend ran 30% Heli Low Smoke. Truth be told, my motors were more finiky on this super hot humid day and I wasn't happy with the performance. At that point I decided to back to the 30% heli for the remainder of the summer.
This Sunday morning I installed a new engine (thanks YS, 170, glow plug) and started it up in the driveway. All I did was install the 18.1x10 for break in, flip it by hand till I saw fuel coming, then put the glow ignitor on and hit it with the starter. The motor started right up without any problem. I ran it at 1/3 thottle for about 1 minute and shut it down for a 100% cool down. About 30 minutes later I did the same thing, but ran it for about 2 minutes. Shut it down for another 20 minutes. 3rd run I began throttleing it enough to see that it idles reliabily, transitioned well, and had a reasonably clean top end, mix of throttling for 3 minutes or so (no more). I shut it down and turned "in" the pump 0.5 turn. 15 minutes or so later started it one more time, checked the idle, transition, top end, no more than about 3 minutes, and shut it down.
Went to the field, saw Gary Courtney, started the plane, checked transition, and took off for flight #1. About 10 minutes of mild flying, no sequence work, and one or two full power hits on 45 lines. Landed and gave it 100% cool down. 2nd Flight, now with 18x11 WPN, went through P11 and landed. Motor was billowing AWESOME smoke!!!!!!!! was running cool, and made crazy power!!!!!!!!!!!!! 3rd flight prop came a little loose. I tightned it without incident for rest of the day.
Flew other plane back to 30% heli - Awesome power! This one uses the 19x11. For me, the engines like the regular 30% heli fuel in the summer (my choice). WHen it cools off I'll use my reserve of the LS fuel. I'm kind of writing this because Gary was out there and a witness to how hot the day was, and to the new motor running good. I was fearful about breaking in an engine on such a dasterdly day, but it really wasn't an issue at all. Gary's motor was also taking the heat in stride and making huge power too (his using CDI).
Thanks,
Jim
This Sunday morning I installed a new engine (thanks YS, 170, glow plug) and started it up in the driveway. All I did was install the 18.1x10 for break in, flip it by hand till I saw fuel coming, then put the glow ignitor on and hit it with the starter. The motor started right up without any problem. I ran it at 1/3 thottle for about 1 minute and shut it down for a 100% cool down. About 30 minutes later I did the same thing, but ran it for about 2 minutes. Shut it down for another 20 minutes. 3rd run I began throttleing it enough to see that it idles reliabily, transitioned well, and had a reasonably clean top end, mix of throttling for 3 minutes or so (no more). I shut it down and turned "in" the pump 0.5 turn. 15 minutes or so later started it one more time, checked the idle, transition, top end, no more than about 3 minutes, and shut it down.
Went to the field, saw Gary Courtney, started the plane, checked transition, and took off for flight #1. About 10 minutes of mild flying, no sequence work, and one or two full power hits on 45 lines. Landed and gave it 100% cool down. 2nd Flight, now with 18x11 WPN, went through P11 and landed. Motor was billowing AWESOME smoke!!!!!!!! was running cool, and made crazy power!!!!!!!!!!!!! 3rd flight prop came a little loose. I tightned it without incident for rest of the day.
Flew other plane back to 30% heli - Awesome power! This one uses the 19x11. For me, the engines like the regular 30% heli fuel in the summer (my choice). WHen it cools off I'll use my reserve of the LS fuel. I'm kind of writing this because Gary was out there and a witness to how hot the day was, and to the new motor running good. I was fearful about breaking in an engine on such a dasterdly day, but it really wasn't an issue at all. Gary's motor was also taking the heat in stride and making huge power too (his using CDI).
Thanks,
Jim
08-24-2010, 08:55 AM
#83
RE: YS 170 DZ CDI
Here's some good info on cavitation and supports the explanation given by Bob et al
http://www.sunhydraulics.com/cmsnet/...1&title_id=288
There's quite a lot of heavy weight academic info on cavitation effects and the damage they cause to valve components. The file attached details a report that specifically mentions poppet valves and valve seat damage
Its probably possible to measure the vibration as a function of temperature caused by cavitation on the YS puel pump, if it exists...
Keith
http://www.sunhydraulics.com/cmsnet/...1&title_id=288
There's quite a lot of heavy weight academic info on cavitation effects and the damage they cause to valve components. The file attached details a report that specifically mentions poppet valves and valve seat damage
Its probably possible to measure the vibration as a function of temperature caused by cavitation on the YS puel pump, if it exists...
Keith
08-24-2010, 09:37 AM
#84
Senior Member
Join Date: Mar 2003
Location: Teesside, UNITED KINGDOM
Posts: 134
Likes: 0
Received 0 Likes
on
0 Posts
RE: YS 170 DZ CDI
Keith,
Excellent references.
Particulary interesting to note the following comments in the Sun Hydraulics Paper:
# Switching a manifold from aluminum to ductile iron will reduce the rate of erosion by a factor of 10.
# High temperatures raise the vapor pressure and increase the likelihood of cavitation
Hence the need to do everything within reason to reduce the pump operating temperature and also to change the material of the existing pump seats from alloy to either brass or stainless steel.
Regards
Bob
Excellent references.
Particulary interesting to note the following comments in the Sun Hydraulics Paper:
# Switching a manifold from aluminum to ductile iron will reduce the rate of erosion by a factor of 10.
# High temperatures raise the vapor pressure and increase the likelihood of cavitation
Hence the need to do everything within reason to reduce the pump operating temperature and also to change the material of the existing pump seats from alloy to either brass or stainless steel.
Regards
Bob
08-24-2010, 10:25 AM
#85
RE: YS 170 DZ CDI
Very good information about cavitation, and in my favor and taken form the text,
Cavitation is the formation of small bubbles in a liquid due to low pressures. The bubbles are dissolved gasses and liquid vapor.
The cavitation that Sun Hydraulics has to deal with is caused by low pressures that result from high velocities when the fluid takes a pressure drop. For instance, when a fluid takes a pressure drop of 3000 psi (200 bar) across an orifice or a metering edge, the velocity reaches trans-sonic, if not supersonic, velocities.
As I mentioned before, the fluid speed is very low, and the pressure differential is around 6psi, there is not enough pressure drop or fluid speed for cavitation to occur, that is pretty much basic in fluid dynamics, when they mention low pressure, it's related to the pressure drop based on Bernoulli's not just an actual number, but I understand some of you are convinced that's what's happening and is not my intention to lecture anybody.
Knowing what we already know about the engine, I have some questions,
Isn't the pump isolated form the engine with the two O rings on the guide tube, and the plastic bottom part? then radiation heat is the only way to warm the pump up as the air hits the pump first then the engine, not the other way around.
If the pump temperature is creating the cavitation, shouldn't the fuel boil in the silicon hose from the pump to the carb which is actually touching the cylinder and hotter?
When cavitation occurs as per Bernoulli's the engine should quit, as the fuel in the engine being subsonic can not be compressed.
Again, in my first post, I noted the vapor formation happens after the engine stops operation, because as the engine runs, the fuel keeps the temp down on the pump, specially on high Nitro, high Nitro decreases engine running temp not increase, there's a lot of information about this subject around. This will happens unless the pump setting is too lean as it is noted in the engine manual.
Cavitation is the formation of small bubbles in a liquid due to low pressures. The bubbles are dissolved gasses and liquid vapor.
The cavitation that Sun Hydraulics has to deal with is caused by low pressures that result from high velocities when the fluid takes a pressure drop. For instance, when a fluid takes a pressure drop of 3000 psi (200 bar) across an orifice or a metering edge, the velocity reaches trans-sonic, if not supersonic, velocities.
As I mentioned before, the fluid speed is very low, and the pressure differential is around 6psi, there is not enough pressure drop or fluid speed for cavitation to occur, that is pretty much basic in fluid dynamics, when they mention low pressure, it's related to the pressure drop based on Bernoulli's not just an actual number, but I understand some of you are convinced that's what's happening and is not my intention to lecture anybody.
Knowing what we already know about the engine, I have some questions,
Isn't the pump isolated form the engine with the two O rings on the guide tube, and the plastic bottom part? then radiation heat is the only way to warm the pump up as the air hits the pump first then the engine, not the other way around.
If the pump temperature is creating the cavitation, shouldn't the fuel boil in the silicon hose from the pump to the carb which is actually touching the cylinder and hotter?
When cavitation occurs as per Bernoulli's the engine should quit, as the fuel in the engine being subsonic can not be compressed.
Again, in my first post, I noted the vapor formation happens after the engine stops operation, because as the engine runs, the fuel keeps the temp down on the pump, specially on high Nitro, high Nitro decreases engine running temp not increase, there's a lot of information about this subject around. This will happens unless the pump setting is too lean as it is noted in the engine manual.
08-24-2010, 02:28 PM
#86
RE: YS 170 DZ CDI
Adding to the heat is the lower pump pushrod in contact with the cam lobe and the bottom of the pump piston.
Also, the friction of the piston in the pump housing is causing more heat....and in my case, this piston must have 'cocked' slightly....digging into the housing wall and forming a huge ledge. Normally, this piston can be easily removed but in MY pump it could not be removed due to this ledge.
This problem showed up as a uncontrollable sudden huge lean condition at WOT causing the TT double jam nuts and prop to blow off the shaft.
The fuel was CP 30%, prop was APC 19x11. The engine had at least a season of perfect operation on glow. On inspection I didnt notice any undue erosion of the valve seats.
The engine is a conversion from glow to CDI and has the low oil crank and lifters as well....even though it dosent need them.
Attached is a picture of the prop nut and washer which went through the garage wall after hit by the prop....I havent found the jam nut....it's probably still sailing along somewhere. I aim the test stand somewhere else now!
All test runs were on the PSP test stand which withstood all sudden stops from 7300 rpm......unlike the nose of an airplane.
YS Parts and Service replaced the pump.....thanks a lot Richard.
Also, the friction of the piston in the pump housing is causing more heat....and in my case, this piston must have 'cocked' slightly....digging into the housing wall and forming a huge ledge. Normally, this piston can be easily removed but in MY pump it could not be removed due to this ledge.
This problem showed up as a uncontrollable sudden huge lean condition at WOT causing the TT double jam nuts and prop to blow off the shaft.
The fuel was CP 30%, prop was APC 19x11. The engine had at least a season of perfect operation on glow. On inspection I didnt notice any undue erosion of the valve seats.
The engine is a conversion from glow to CDI and has the low oil crank and lifters as well....even though it dosent need them.
Attached is a picture of the prop nut and washer which went through the garage wall after hit by the prop....I havent found the jam nut....it's probably still sailing along somewhere. I aim the test stand somewhere else now!
All test runs were on the PSP test stand which withstood all sudden stops from 7300 rpm......unlike the nose of an airplane.
YS Parts and Service replaced the pump.....thanks a lot Richard.
08-24-2010, 04:53 PM
#87
Join Date: Dec 2006
Location: ToowoombaQLD, AUSTRALIA
Posts: 1,026
Likes: 0
Received 17 Likes
on
15 Posts
RE: YS 170 DZ CDI
I think it's quite plausable that cavitation could be induced in the very thin layer of fuel mix trapped between the teflon pump valve and aluminium seat at the instant the valve begins to open. It's only for a fraction of a second but there are many fractions of a second at work...
08-24-2010, 05:00 PM
#88
RE: YS 170 DZ CDI
According to the literature it should be possible to measure the cavitation noise & vibration if it exists, as a function of temperature and pressure differential. I'll let you know when I've tried.
Not sure how to go about looking for 6psi across the valve seat? Is this a quoted or calculated value?
Keith
Not sure how to go about looking for 6psi across the valve seat? Is this a quoted or calculated value?
Keith
08-24-2010, 05:44 PM
#89
Senior Member
My Feedback: (1)
Join Date: Apr 2005
Location: huntsville,
AL
Posts: 864
Likes: 0
Received 0 Likes
on
0 Posts
RE: YS 170 DZ CDI
I have seen this on several occasions with my own engine and just a couple of others.That I observed seemed like a unduly lean run on the motor . I checked and rechecked the fuel system flushed looked for pin holes the works couldn't find any thing wrong still the lean run persisted. I put a glow plug in the motor the problem went away!!!! I found two distinct problems the first was a spark plug gap issue, the gap had opened up. replaced the spark plug and all ran well. The second was a loose spark plug cap that had vibrated around and cracked the spark plug. I squeezed the cap so that it would have a tight hold on the plug needing a tap to seat it and zip tying the lead to the intake tube. Poor ignition will cause these motors to seem like they are having a lean run. I have seen this condition spit the prop and spinner completely off the plane.
This may not be your issue but this is what I have seen first hand.
gary
This may not be your issue but this is what I have seen first hand.
gary
08-24-2010, 07:07 PM
#90
Join Date: Jan 2009
Location: NEWCASTLE, AUSTRALIA
Posts: 342
Likes: 0
Received 0 Likes
on
0 Posts
RE: YS 170 DZ CDI
Gday Bob,
22% oil sounds pretty high considering that the idea of the CDI 170 was to run less oil ........ie less residue on airframe and less people inclined to change to electrics.
Excuse my ignorence but I was just trying to contribute to the discusion.
kind regards
MAVROS
AUSTRALIA
08-25-2010, 10:09 AM
#91
RE: YS 170 DZ CDI
Gary
I have experienced the same issue. The symptons are exactly the same as a slow moving pump failure! I am currently testing some US domestic spark plugs as I am tired of paying $24 plus shipping & handling for a $5.00 to $8.00 spark plug.! I will let everyone know the results after the test.
Dick
I have experienced the same issue. The symptons are exactly the same as a slow moving pump failure! I am currently testing some US domestic spark plugs as I am tired of paying $24 plus shipping & handling for a $5.00 to $8.00 spark plug.! I will let everyone know the results after the test.
Dick
08-25-2010, 12:02 PM
#92
RE: YS 170 DZ CDI
Hey Bob
If the ambient temperature is in the 70's to 80's and you run the engine lean with say CP30% LS[20% oil or fuel with less oil], there will be a minimal smoke trail. The problem is as ambient temperature goes up pump life goes down dramatically! In my opinion it is going to take a completely different pump design to allow the pump to "live" in all temperature ranges we fly in! I could be wrong, but the 'fixes" being discussed seem to be "band aids" but it may be all it takes! Time & testing will tell.
Dick
If the ambient temperature is in the 70's to 80's and you run the engine lean with say CP30% LS[20% oil or fuel with less oil], there will be a minimal smoke trail. The problem is as ambient temperature goes up pump life goes down dramatically! In my opinion it is going to take a completely different pump design to allow the pump to "live" in all temperature ranges we fly in! I could be wrong, but the 'fixes" being discussed seem to be "band aids" but it may be all it takes! Time & testing will tell.
Dick
08-25-2010, 04:40 PM
#93
Senior Member
Join Date: Mar 2003
Location: Teesside, UNITED KINGDOM
Posts: 134
Likes: 0
Received 0 Likes
on
0 Posts
RE: YS 170 DZ CDI
Dick,
There is no doubt that higher ambient temperatures will place much greater demands on pump design. However I would take heart from the fact that YS 140 Dingos (apart from the Mark 1) and YS 160 Dingos both had a good record in respect of pump reliability. As stated earlier in the thread, I think the YS 170 design, particularly the CDi, may just have tipped the pump operating temperature into the region where reliability has suffered due to small amounts of cavitation and possible problems with operating clearances. If this theory is correct, it may not take too radical a design change to tip the balance back to where it was. As you rightly say, time and testing will tell.
Bjr 93 tz
What you say makes sense, especially since there is some evidence to suggest that in high ambient temperature conditions, the fuel is very close to its boiling point on the upstream side of the poppet valves. That being so, even slight reductions in pressure could cause small vapour bubbles to start forming. Your point about frequency is also relevant i.e:
(Even small amount of cavitation) x (> 7,000 RPM) + (alloy valve seats) = (erosion damage)
Mavros
In post #57 you seemed to be suggesting that we should increase the oil content. Now in post # 90 you seem to be saying that we ought to be decreasing it! I acknowledge that CDi’s were designed to run on a lower oil content, however several UK CDi users have been taking the precaution of running their engines on 20% to 22% oil until a clearer picture started to emerge about the long term effects of low oil operation. Even at these higher oil levels, pump damage has been evident. This would suggest that excessive temperature is more likely to be the prime cause of pump failure, rather than the percentage of oil in the fuel – always assuming that the percentage of oil is kept within sensible levels.
aperiera
If enough other readers were interested, I would be willing to take the time to address the various questions that you raise in your post #85. However rather than delve deeper into theory, I suspect that by now, most readers will more interested in the practical steps that YS are likely to take in order to improve the pump design, and in the timescale for the improvements. Yamada san has already said enough to suggest that he is taking the problem seriously and I think that we should now give him the time and space that he needs to conduct more tests following his return from the European Championships.
Historically, YS have taken a meticulous and painstaking approach to product development. That is one on the many things that they are good at.
I for one am confident that they will come up with a solution.
Regards
Bob
There is no doubt that higher ambient temperatures will place much greater demands on pump design. However I would take heart from the fact that YS 140 Dingos (apart from the Mark 1) and YS 160 Dingos both had a good record in respect of pump reliability. As stated earlier in the thread, I think the YS 170 design, particularly the CDi, may just have tipped the pump operating temperature into the region where reliability has suffered due to small amounts of cavitation and possible problems with operating clearances. If this theory is correct, it may not take too radical a design change to tip the balance back to where it was. As you rightly say, time and testing will tell.
Bjr 93 tz
What you say makes sense, especially since there is some evidence to suggest that in high ambient temperature conditions, the fuel is very close to its boiling point on the upstream side of the poppet valves. That being so, even slight reductions in pressure could cause small vapour bubbles to start forming. Your point about frequency is also relevant i.e:
(Even small amount of cavitation) x (> 7,000 RPM) + (alloy valve seats) = (erosion damage)
Mavros
In post #57 you seemed to be suggesting that we should increase the oil content. Now in post # 90 you seem to be saying that we ought to be decreasing it! I acknowledge that CDi’s were designed to run on a lower oil content, however several UK CDi users have been taking the precaution of running their engines on 20% to 22% oil until a clearer picture started to emerge about the long term effects of low oil operation. Even at these higher oil levels, pump damage has been evident. This would suggest that excessive temperature is more likely to be the prime cause of pump failure, rather than the percentage of oil in the fuel – always assuming that the percentage of oil is kept within sensible levels.
aperiera
If enough other readers were interested, I would be willing to take the time to address the various questions that you raise in your post #85. However rather than delve deeper into theory, I suspect that by now, most readers will more interested in the practical steps that YS are likely to take in order to improve the pump design, and in the timescale for the improvements. Yamada san has already said enough to suggest that he is taking the problem seriously and I think that we should now give him the time and space that he needs to conduct more tests following his return from the European Championships.
Historically, YS have taken a meticulous and painstaking approach to product development. That is one on the many things that they are good at.
I for one am confident that they will come up with a solution.
Regards
Bob
08-26-2010, 02:51 AM
#94
Senior Member
Join Date: Sep 2003
Location: Holon, ISRAEL
Posts: 358
Likes: 0
Received 0 Likes
on
0 Posts
RE: YS 170 DZ CDI
Hi
I got the 175 modified pump. See the pictures.
As you can see it is the entire assembly including the push road housing which is part of the modifications. I cannot add a scholar explanations like others but just god-feeling I had from day one that the push road housing is part of the problem. Also interesting to see that the regulator diaphragm is made of different material and more important its limiter is now a separate part and its all made of hard plastic..
I will test it in next few days. Temperature here about 35C (95F) in the shade so we shell see!
Regards
Amram
THANK YOU YAMADA SAN FOR A GREAT SUPPORT!!!!!
I got the 175 modified pump. See the pictures.
As you can see it is the entire assembly including the push road housing which is part of the modifications. I cannot add a scholar explanations like others but just god-feeling I had from day one that the push road housing is part of the problem. Also interesting to see that the regulator diaphragm is made of different material and more important its limiter is now a separate part and its all made of hard plastic..
I will test it in next few days. Temperature here about 35C (95F) in the shade so we shell see!
Regards
Amram
THANK YOU YAMADA SAN FOR A GREAT SUPPORT!!!!!
08-26-2010, 09:25 AM
#95
RE: YS 170 DZ CDI
That's great Amram, glad you got it!
If there is something for sure is nobody beats Yamada or Richard in customer support!!
Keith, the pump output pressure is 6psi normally but it can go up a little more depending on the application, but it's under 10 psi, that's why I say there's no way cavitation can occur, given the pressure/fluid speed.
Now that Amram has the 175 pump, and it's going to try it, and Dick has it's new pumps from Richard, it's time to wait for their reports, and hopefully they will be successful .
Good luck guys.
If there is something for sure is nobody beats Yamada or Richard in customer support!!
Keith, the pump output pressure is 6psi normally but it can go up a little more depending on the application, but it's under 10 psi, that's why I say there's no way cavitation can occur, given the pressure/fluid speed.
Now that Amram has the 175 pump, and it's going to try it, and Dick has it's new pumps from Richard, it's time to wait for their reports, and hopefully they will be successful .
Good luck guys.
08-26-2010, 09:43 AM
#96
RE: YS 170 DZ CDI
Hi Apereira,
No just wondered where you got the 6psi figure from as I wanted to come up with a way of testing the pump outlet and wondered how best to measure it? I've measured the Cam lift and pump diameter which are ~ 3mm and 6mm accordngly. This gives a maximum volume output of 84.8 mm^3 per cam lift. Certainly some of this is fed back to the suction side via the regulator. I'm having a brain fade at the moment and can't think how to convert that to pressure, given the diameters of the check valve passages?
Thanks
Keith
No just wondered where you got the 6psi figure from as I wanted to come up with a way of testing the pump outlet and wondered how best to measure it? I've measured the Cam lift and pump diameter which are ~ 3mm and 6mm accordngly. This gives a maximum volume output of 84.8 mm^3 per cam lift. Certainly some of this is fed back to the suction side via the regulator. I'm having a brain fade at the moment and can't think how to convert that to pressure, given the diameters of the check valve passages?
Thanks
Keith
08-26-2010, 10:16 AM
#97
RE: YS 170 DZ CDI
Hi Keith,
Easier method of checking pump pressure, as well as the actuating is to to use a T fitting with a gage. It's the practical way, theoretical values might be off as there is no constant temperature and I don't think the value will be linear, rather will be exponential as the pump works on a membrane , depending of the engine RPM and then letting the engine temp to stabilize before taking readings or doing calculations will be the way.
The gage is the best way for sure, probably is easier to get the gauge in inches of water and then do the conversion if you want to make a study.
Hope we are not boring anyone, sorry if we do.
Best regards
Easier method of checking pump pressure, as well as the actuating is to to use a T fitting with a gage. It's the practical way, theoretical values might be off as there is no constant temperature and I don't think the value will be linear, rather will be exponential as the pump works on a membrane , depending of the engine RPM and then letting the engine temp to stabilize before taking readings or doing calculations will be the way.
The gage is the best way for sure, probably is easier to get the gauge in inches of water and then do the conversion if you want to make a study.
Hope we are not boring anyone, sorry if we do.
Best regards
08-26-2010, 10:36 AM
#98
RE: YS 170 DZ CDI
Hi Amram
I like what I see on the new pump. it has isolated and reduced the heat transfer from the case to the pump housing. What is not apparent is what they have done to isolate the heat from the "plunger" via both push rods on the intake side. It is my understanding that the plunger seal material[not sure what that is as I have never seen it] has been changed. It is my hope that the plunger will become a user accesed part for future mtc. & inspection! Looks like the new diaphram is made of a high temperature material to reduce the effect of heat deformity which was very apparent in the old material. The sealing valve appears to be non metalic and a seperate piece
Dick
I like what I see on the new pump. it has isolated and reduced the heat transfer from the case to the pump housing. What is not apparent is what they have done to isolate the heat from the "plunger" via both push rods on the intake side. It is my understanding that the plunger seal material[not sure what that is as I have never seen it] has been changed. It is my hope that the plunger will become a user accesed part for future mtc. & inspection! Looks like the new diaphram is made of a high temperature material to reduce the effect of heat deformity which was very apparent in the old material. The sealing valve appears to be non metalic and a seperate piece
Dick
08-26-2010, 05:27 PM
#99
Join Date: Dec 2006
Location: ToowoombaQLD, AUSTRALIA
Posts: 1,026
Likes: 0
Received 17 Likes
on
15 Posts
RE: YS 170 DZ CDI
ORIGINAL: apereira
.... Keith, the pump output pressure is 6psi normally but it can go up a little more depending on the application, but it's under 10 psi, that's why I say there's no way cavitation can occur, given the pressure/fluid speed....
.... Keith, the pump output pressure is 6psi normally but it can go up a little more depending on the application, but it's under 10 psi, that's why I say there's no way cavitation can occur, given the pressure/fluid speed....
As the valve closes the pressure will rise as the fluid is "squeazed" out from under the seat, at the instant the valve begins to open the pressure will drop as fuel is "sucked" into the rapidly opening space between the valve and seat. After the instant the "seal" is broken everything returns close to normal as the valve moves further away from the seat.
It's a very small thing and may have nothing to do with the problem of seat wear/errosion but I will be interested to inspect my pump in our materials lab if/when I have these problems. You can tell very quickly under a microscope if the seat damage is related to impact, cavitation, corrosion etc. and I'm sure that YS would know exactly which one it is....
Cheers
Brett
08-26-2010, 06:12 PM
#100
Senior Member
Join Date: Mar 2003
Location: Teesside, UNITED KINGDOM
Posts: 134
Likes: 0
Received 0 Likes
on
0 Posts
RE: YS 170 DZ CDI
Hello Aperiera,
The vexed question of cavitation!
I share your concerns about the possibility of boring other readers. However if I might add to Brett's valuable insight on the matter.
You keep repeating it as a fact that cavitation cannot take place at low pressure. I don’t believe this to be so. If a fluid is close to its boiling point, (as is likely to be the case in the suction line to a YS Pump on a hot day), then even small reductions in pressure (e.g via the inlet poppet valve) can cause vapour bubbles to form. It is this reduction in the pressure, rather than the absolute operating pressure that is key. When the pressure subsequently rises, due either to Bernoulli effect, or to the pressure raising effect of the pump itself, then the vapour bubbles will implode. When this implosion occurs, the gas dissipates into the surrounding liquid and releases considerable energy in the form of an acoustic shockwave. The energy dissipated is such, that even very small amounts of cavitation can cause very considerable damage.
Cavitation can take several forms and high operating pressures and/or high fluid velocities are not essential for cavitation to take place.
The following are not my words. They are quotes from reputable scientific sources:
# “Cavitation may occur when the local static pressure in a fluid reaches a level below the vapour pressure of the liquid at the actual temperature.â€
# “Many areas in hydraulic systems are prone to cavitation wear, such as in devices where fluid flow is subjected to sharp turns, reductions in cross section with subsequent expansion (in cocks, valves, diaphragms) and other deformations.â€
# “Pumps put liquid under pressure, but if the pressure drops or its temperature increases it begins to vaporise just like boiling water. Yet in such a small sensitive system the bubbles can’t escape, so they implode causing physical damage to parts of the pump.â€
# “A fast flowing river can cause cavitation on rock surfaces, particularly where there is a drop-off such as a waterfall.â€
# “In the last half decade, coastal erosion, in the form of inertial cavitation has been generally accepted. [16]. Air pockets in an incoming wave are forced into cracks in the cliff being eroded, then the force of the wave compresses the air pockets until the bubble implodes, becoming liquid, giving off various forms of energy that blast apart the rock.â€
Your post #85
“Isn't the pump isolated from the engine with the two O rings on the guide tube, and the plastic bottom part? then radiation heat is the only way to warm the pump up as the air hits the pump first then the engine, not the other way around.â€
The O rings associated with the pump assembly do offer some degree of insulation. However radiation is not the only way to warm the pump. The energy that the pump is expending through raising the pressure of the fluid, coupled with friction losses, will in itself cause the pump temperature to rise. (Ever put your hand on a cycle pump after blowing up a tyre?) I believe that is the main reason why YS fitted cooling fins to the main pump cylinder. A considerable amount of heat will also be transferred via conduction from the alloy cylinder at the top of the pump that slots into the cylinder head. In the new pump that Amram has posted pictures of, it is interesting to note that this alloy part has been replaced by some form of plastic. I believe YS have done this specifically to reduce conducted heat.
“If the pump temperature is creating the cavitation, shouldn't the fuel boil in the silicon hose from the pump to the carb which is actually touching the cylinder and hotter?â€
Not necessarily. For a start, the action of the pump itself, coupled with pressure recovery through the poppet valves (Bernoulli effect) will have elevated the pressure to a level at which boiling and vaporisation is less likely to occur. It is however good practice to ensure that the line between the pump and the carburettor is spaced apart from the cylinder head, or fitted with some form of insulation (see photograph in Post #61) in order to minimise radiated heat transfer. You might find this June 2006 post including a comment from Dave Shadel of interest - http://www.rcuniverse.com/forum/m_4449588/tm.htm. (RCU, YS Forum Page 52 - "YS160 DZ shuts down in verticals at WOT - Solution")
It is also worth noting the comment from Yamada san about the possible need for some additional cooling of the carburettor. I believe this comment is also made in the belief that it may be necessary to adopt additional measures to keep the fluid from flashing off on the delivery side of the pump, especially since the pressure of the fluid will reduce considerably after it passes through the tapered metering slot in the carburettor barrel.
In summary, I still believe that the key to improving the reliability of the YS pump lies in introducing measures that a) reduce its operating temperature and b) increase the speed at which the pump cools between flights. If you know of other better solutions, please feel free to share them with us.
Regards
Bob
The vexed question of cavitation!
I share your concerns about the possibility of boring other readers. However if I might add to Brett's valuable insight on the matter.
You keep repeating it as a fact that cavitation cannot take place at low pressure. I don’t believe this to be so. If a fluid is close to its boiling point, (as is likely to be the case in the suction line to a YS Pump on a hot day), then even small reductions in pressure (e.g via the inlet poppet valve) can cause vapour bubbles to form. It is this reduction in the pressure, rather than the absolute operating pressure that is key. When the pressure subsequently rises, due either to Bernoulli effect, or to the pressure raising effect of the pump itself, then the vapour bubbles will implode. When this implosion occurs, the gas dissipates into the surrounding liquid and releases considerable energy in the form of an acoustic shockwave. The energy dissipated is such, that even very small amounts of cavitation can cause very considerable damage.
Cavitation can take several forms and high operating pressures and/or high fluid velocities are not essential for cavitation to take place.
The following are not my words. They are quotes from reputable scientific sources:
# “Cavitation may occur when the local static pressure in a fluid reaches a level below the vapour pressure of the liquid at the actual temperature.â€
# “Many areas in hydraulic systems are prone to cavitation wear, such as in devices where fluid flow is subjected to sharp turns, reductions in cross section with subsequent expansion (in cocks, valves, diaphragms) and other deformations.â€
# “Pumps put liquid under pressure, but if the pressure drops or its temperature increases it begins to vaporise just like boiling water. Yet in such a small sensitive system the bubbles can’t escape, so they implode causing physical damage to parts of the pump.â€
# “A fast flowing river can cause cavitation on rock surfaces, particularly where there is a drop-off such as a waterfall.â€
# “In the last half decade, coastal erosion, in the form of inertial cavitation has been generally accepted. [16]. Air pockets in an incoming wave are forced into cracks in the cliff being eroded, then the force of the wave compresses the air pockets until the bubble implodes, becoming liquid, giving off various forms of energy that blast apart the rock.â€
Your post #85
“Isn't the pump isolated from the engine with the two O rings on the guide tube, and the plastic bottom part? then radiation heat is the only way to warm the pump up as the air hits the pump first then the engine, not the other way around.â€
The O rings associated with the pump assembly do offer some degree of insulation. However radiation is not the only way to warm the pump. The energy that the pump is expending through raising the pressure of the fluid, coupled with friction losses, will in itself cause the pump temperature to rise. (Ever put your hand on a cycle pump after blowing up a tyre?) I believe that is the main reason why YS fitted cooling fins to the main pump cylinder. A considerable amount of heat will also be transferred via conduction from the alloy cylinder at the top of the pump that slots into the cylinder head. In the new pump that Amram has posted pictures of, it is interesting to note that this alloy part has been replaced by some form of plastic. I believe YS have done this specifically to reduce conducted heat.
“If the pump temperature is creating the cavitation, shouldn't the fuel boil in the silicon hose from the pump to the carb which is actually touching the cylinder and hotter?â€
Not necessarily. For a start, the action of the pump itself, coupled with pressure recovery through the poppet valves (Bernoulli effect) will have elevated the pressure to a level at which boiling and vaporisation is less likely to occur. It is however good practice to ensure that the line between the pump and the carburettor is spaced apart from the cylinder head, or fitted with some form of insulation (see photograph in Post #61) in order to minimise radiated heat transfer. You might find this June 2006 post including a comment from Dave Shadel of interest - http://www.rcuniverse.com/forum/m_4449588/tm.htm. (RCU, YS Forum Page 52 - "YS160 DZ shuts down in verticals at WOT - Solution")
It is also worth noting the comment from Yamada san about the possible need for some additional cooling of the carburettor. I believe this comment is also made in the belief that it may be necessary to adopt additional measures to keep the fluid from flashing off on the delivery side of the pump, especially since the pressure of the fluid will reduce considerably after it passes through the tapered metering slot in the carburettor barrel.
In summary, I still believe that the key to improving the reliability of the YS pump lies in introducing measures that a) reduce its operating temperature and b) increase the speed at which the pump cools between flights. If you know of other better solutions, please feel free to share them with us.
Regards
Bob