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Post by ChrisJ on Dec 8, 2020 14:45:21 GMT
I wanted to continue this discussion in a separate thread as not to distract from the main point of the CK cap tube conversion thread. I've been looking at the service manuals etc and trying to understand what went on back in the 20s and 30s. What changes were made, and why. To me, when the DR was designed Steenstrup made the housing the high side as he wanted to keep the oil out of the rest of the machine and keep it in the sump where it belonged. As they found out later, that wasn't happening. I guess oil mist etc ends up traveling through the system no matter how long you make that tube stick into the housing. I believe he also felt the heat would keep the refrigerant out of the oil which turned out to be counter productive as the increased pressure encourages it to condense. The DR was the very first released hermetic system and if you look at it, I don't think it's that bad with absolutely nothing to go on before it. I'm curious how long they lasted on average before having a problem. I've had two mini fridges die within a year or two made in 2018-2019 and they had plenty to go by. In the CA, the amount of oil dumping out of the compressor just because of it's nature I believe made it necessary to still keep the housing the high side. Modern rotary compressors and I think scrolls still have the housing as the highside, no? The CA has a fan, which I don't know if it's for cooling, or trying to deflect oil away from the exit. The CK there's some interesting changes. The compressor housing is the low side and it's using a reciprocating compressor, so oil discharge should be minimal, the discharge line loops around down through the oil to heat the oil. They then spray the oil at the top of the housing and let it run down the sides to dissipate heat created while it's running. Perhaps this was done for both cooling of the oil and to prevent the top of the housing from sweating? I also find the evaporator changes interesting. They basically got rid of the upper right side from the CA and that becomes the shelf and they were also able to eliminate the second header by doing this. coldspacesturbokinetic |
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Post by turbokinetic on Dec 8, 2020 15:14:08 GMT
I wanted to continue this discussion in a separate thread as not to distract from the main point of the CK cap tube conversion thread. I've been looking at the service manuals etc and trying to understand what went on back in the 20s and 30s. What changes were made, and why. To me, when the DR was designed Steenstrup made the housing the high side as he wanted to keep the oil out of the rest of the machine and keep it in the sump where it belonged. As they found out later, that wasn't happening. I guess oil mist etc ends up traveling through the system no matter how long you make that tube stick into the housing. I believe he also felt the heat would keep the refrigerant out of the oil which turned out to be counter productive as the increased pressure encourages it to condense. The DR was the very first released hermetic system and if you look at it, I don't think it's that bad with absolutely nothing to go on before it. I'm curious how long they lasted on average before having a problem. I've had two m In the CA, the amount of oil dumping out of the compressor just because of it's nature I believe made it necessary to still keep the housing the high side. Modern rotary compressors and I think scrolls still have the housing as the highside, no? The CA has a fan, which I don't know if it's for cooling, or trying to deflect oil away from the exit. The CK there's some interesting changes. The compressor housing is the low side and it's using a reciprocating compressor, so oil discharge should be minimal, the discharge line loops around down through the oil to heat the oil. They then spray the oil at the top of the housing and let it run down the sides to dissipate heat created while it's running. Perhaps this was done for both cooling of the oil and to prevent the top of the housing from sweating? I also find the evaporator changes interesting. They basically got rid of the upper right side from the CA and that becomes the shelf and they were also able to eliminate the second header by doing this. coldspaces turbokinetic Very interesting! The DR's are fascinating for a lot of reasons, including their being such an early design! I don't think they were all that unreliable back in the day. After all, there are still enough of them around now, 90 years later, to draw a following. Looking at the amount of machining and materials in them, it is clear that they were more costly to produce than the CK machine. Again while I don't think the DR's were "all that unreliable" when new, they aren't as reliable as a CK. If I remember reading, one of the reasons they chose the high-side dome was to have enough gas density to cool the motor winding. In spite of the gas being hot, the added density would provide more thermal mass to carry heat from the motor winding to the shell. Remember that SO2 units low side operate at less than atmospheric pressure, so that there would be very little gas to cool the motor, if the housing were under vacuum. Remember that the CK has an oil-cooled stator and doesn't depend on gas cooling. Therefore GE was able to capitalize on all the benefits of a low-side housing without motor temperature problems. Some of the benefits of higher pressure refrigerants is that there is enough gas density on the low side to cool the compressor. Back in this era, it was basically SO2 or bust so that choice wasn't an option for GE. Gill can probably answer more, since he's been in the industry longer. But for modern compressors, I think all recips are low-side dome. The Matsushita rotary (the one which is a copy of the Frigidaire Meter-Miser) is a high-side housing design. Scroll compressors are a low-side housing design because the scroll pumps from the periphery to the center of the mechanism. The belt-drive Frigidaire compressors are low-side housing, oil-sealed designs. They intentionally pump a lot of oil which circulates with the refrigerant. Not sure if this was to help lubricate the float mechanism, keep the valves clean in the head, or for what purpose. In looking at the CK compressor, it has a force-fed oil sealing groove around the piston. These discharge a lot of oil because of this design. It seems that most modern recip compressors are also oil sealed, with the crankshaft and conn rod bearings throwing oil up into the underside of the piston for sealing and lubrication. One interesting test would be to do a timed test to see how much oil per minute a given compressor pumps. Maybe next experiment?  The CA evaporator is very complex, with the feed tube going to the bottom, with manifold. I gave one of them to another enthusiast, who has installed it in a Westinghouse with an Embraco R134A compressor. He was told to expect it to trap a lot of oil so to be sure to compensate for that when charging the system! So far it is working for him. |
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Post by ChrisJ on Dec 8, 2020 16:01:55 GMT
turbokinetic I don't know if you saw, but last night I was talking to Travis and it was bothering me how huge the monitor top compressors are compared to new ones and I was trying to understand why. I then realized they're all four pole motors. This in theory means the motor and compressor need to be twice the size as one running at twice the speed. I'm sure there are other reasons, but it seems that's likely the main one? I'd love to know if modern 1/8HP etc refrigeration compressors have oil pumps and such. I found this but I suspect someone copied and pasted this from a much older Scotch yoke manual because there's way too much in common like the self aligning upper bearing, cast iron bearings etc. Of course, I guess they could be literally using a modern version of the same design? products.geappliances.com/appliance/gea-support-search-content?contentId=18739
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Post by turbokinetic on Dec 8, 2020 16:07:57 GMT
turbokinetic I don't know if you saw, but last night I was talking to Travis and it was bothering me how huge the monitor top compressors are compared to new ones and I was trying to understand why. I then realized they're all four pole motors. This in theory means the motor and compressor need to be twice the size as one running at twice the speed. I'm sure there are other reasons, but it seems that's likely the main one? I'd love to know if modern 1/8HP etc refrigeration compressors have oil pumps and such. I found this but I suspect someone copied and pasted this from a much older Scotch yoke manual because there's way too much in common like the self aligning upper bearing, cast iron bearings etc. Of course, I guess they could be literally using a modern version of the same design? products.geappliances.com/appliance/gea-support-search-content?contentId=18739 That does seem copy-paste from the old manuals! I have a new Embraco compressor with a large window in the side. Plan to tinker with it some time. You can see the oil and the motor inside, with the oil pickup tube. These don't have a mechanical oil pump in the traditional sense. They have a centrifugal pump, which is comprised of a specially shaped cavity in the shaft. The inlet is at the center of the shaft, at the very bottom, under the level of the oil. The opening is smaller than the bore of the shaft hole. There are side-holes drilled to the main and rod bearing journals. Because the exit point is off-center, but the inlet port is at the center of the shaft axis, centrifugal force will cause oil to flow up the shaft and reach the bearings. |
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Post by coldspaces on Dec 8, 2020 18:01:20 GMT
Yes one of the main reasons the new compressors are so small is that they doubled the RPM. In most cases they do a good job but the old slow ones did seem to run forever some times. I agree that the DRs when new must have been pretty reliable, like David said look haw many have survived. I still find it hard to believe all they had was cotton on the windings back then, no doubt the high side domes heat was much harder on the cotton than a nice cool low side dome.
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Post by ChrisJ on Dec 8, 2020 18:10:49 GMT
Yes one of the main reasons the new compressors are so small is that they doubled the RPM. In most cases they do a good job but the old slow ones did seem to run forever some times. I agree that the DRs when new must have been pretty reliable, like David said look haw many have survived. I still find it hard to believe all they had was cotton on the windings back then, no doubt the high side domes heat was much harder on the cotton than a nice cool low side dome. It's been 90 years and we still don't seem to have anything other than cotton insulation for methyl formate and SO2. |
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Post by Travis on Dec 8, 2020 20:15:57 GMT
Material compatibility is a real concern when working on these units. The only reason I never have considered rewinding a CA or CK motor is that they seem plentiful and fail rarely.
The opposite is true with DR’s. They frequently are running very well until they fail.
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Post by ChrisJ on Dec 8, 2020 20:29:39 GMT
Material compatibility is a real concern when working on these units. The only reason I never have considered rewinding a CA or CK motor is that they seem plentiful and fail rarely. The opposite is true with DR’s. They frequently are running very well until they fail. Is it the way the stator is wound? The quality of the cotton? The type of control? Do the start relays tend to fail more often in a DR? |
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Post by Travis on Dec 8, 2020 22:17:17 GMT
Chris,
Heat of high side dome, age and no the control rarely fails.
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Post by ChrisJ on Dec 12, 2020 2:14:55 GMT
David,
I was just watching a video about a Copeland scroll and I saw the "oil pump" setup you talked about.
I'm actually surprised.
So even those do not have "force fed" bearings like the monitor top.
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Post by ckfan on Dec 12, 2020 14:06:58 GMT
Even most other compressors back then didn’t have force fed lubrication. They are pretty special.
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Post by turbokinetic on Dec 12, 2020 15:00:43 GMT
Even most other compressors back then didn’t have force fed lubrication. They are pretty special. Most definitely the Monitor Top compressors are on a level of their own. In today's world, you can get a compressor built along the same lines, as with forced lube and massive over-engineering. Some of the better built industrial semi-hermetics are built that way... but at a very high price! |
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Post by Travis on Dec 12, 2020 17:43:34 GMT
Am I wrong, but is this thread simply coming to terms that we don’t build much of high quality anymore at an affordable price? I also want to ask if we would consider a monitor top affordable if adjusted for inflation. The DR1 introduced in 1929 for $215 adjusted for inflation would be $3231 now. I suspect many would be outraged at that cost.
We, the American public, seem to be caught in a loop where we continue to reminisce about quality of yesterday while we fixate on low prices. My mother ordered me some pants the other day. $10.73 a pair. That’s cheap and no one made what we would consider a “living wage” making them.
My point is that quality was and is never affordable or cheap. Another factor of the cheapening of goods is that we want to be environmentally responsible here and doing so means many processes like porcelain and chrome are expensive or actual manufacturing is difficult. All of this has gone offshore and it’s imperative that the goods weigh less to ship them. I’d love to see a comparison of a cargo ship of DR’s vs one of modern refrigerators.
I apologize for going somewhat off topic, but this ties into why things are made differently.
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Post by ChrisJ on Dec 12, 2020 19:02:27 GMT
Travis,
No, I don't believe the thread was going political.
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Post by Travis on Dec 12, 2020 20:44:35 GMT
It’s not political. It’s the reality that you’re commenting on design changes which are most often made because of manufacturing costs. Then we question these changes and attempt to rationalize some other reason for them other than cost.
The answers are always cost or overly complicated which results in cost or simply a bad design.
Well, I can tell you that the CK wasn’t a bad design based upon decades of testing. Cost has to be the issue that we don’t have large CK units under our stainless steel monstrosities with water and ice in the door.
I whole heartily reject the thought that because it’s modern it’s better. We’ve been sold bs for years since the last real improvement has been made.
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