pescador775
Contributor
- Messages
- 2,652
- Reaction score
- 11
Within the world of tribology there are a lot of opinions and a few generally accepted principles. One of these principles concerns viscosity. Comparing reciprocating machines of approximately the same output, the large, beefy slow turning machine requires a higher viscosity oil and the smaller, fast turning machine requires an oil of lower viscosity. This is refected in compressor practice insofar as the oil recommended for the beefy Bauer Mariner is SAE 40 and the oil recommended for the Noah Howden is SAE 10. Both compressors output about 6 cfm. The Bauer speed is about 1200 rpm and the Howden about 3600 rpm.
Generally, higher viscosity oils have a higher flash point but not always. Jet turbine oil, though only SAE 10, has a flash point equal to the thicker oils. Therefore, if there is a carbon monoxide problem with either compressor type it would be more closely tied to the compressor's head temp than to flash point of the respective oils which are the both about 500F.
How hot does the Mariner run? Bauer has published data for this three stage compressor which indicates gas outlet temps in the range of 230F-270F and head temps about 150F. These data are valid at ambient 65F. Given this, bear in mind that compressors have been operated in temps approaching 100F.
Unfortunately, equivalent data for the Noah Howden are not available to me so any comments would have to be on the basis of mechanical theory. The Howden is a four stage machine which means that the thermal stress on individual cylinders should be less than with a three stage. This is due to lower compression ratios at each stage. Also, the four stage design has three sets of interstage cooling coils instead of two. Moreover, the four stage Howden rotates at three times the speed of the Mariner which also means that the cooling fan turns three times as fast. Ah ha! you say, doesn't the faster turning compressor generate more heat? The answer is no, all compressors operate at about 90% efficiency. This can be verified by comparing engine size. It takes no more power to drive a high speed compressor than for a low speed machine.
The Bauer has a fairly large oil sump. Jim can tell us what size is the sump in the Howden. I don't recall. However this may be, the Howden uses a dry sump design which pumps recirculating oil into a separate tank which is exposed to air flow. Oil in the rather small tank on my 4 cfm Kidde doesn't get much hotter than warm. It certainly won't burn the finger.
All this says that the Howden should operate cooler than the Mariner if ambient temps and installation factors (space, air flow) are equal. Many NITROX pumpers use diester oils in Bauer and other compressors without reported problems. (There have been a few cases summarized at Decostop involving excess heat in the compressor room). Others have switched to PAO's which are without reported problems to my knowledge. We are constantly learning as new information comes in so this anything which I have said here could be modified later. Reality is we can't wait forever to learn new stuff before moving ahead and the state of knowledge at this point says to use ordinary care and diligence whatever oil is used.
Generally, higher viscosity oils have a higher flash point but not always. Jet turbine oil, though only SAE 10, has a flash point equal to the thicker oils. Therefore, if there is a carbon monoxide problem with either compressor type it would be more closely tied to the compressor's head temp than to flash point of the respective oils which are the both about 500F.
How hot does the Mariner run? Bauer has published data for this three stage compressor which indicates gas outlet temps in the range of 230F-270F and head temps about 150F. These data are valid at ambient 65F. Given this, bear in mind that compressors have been operated in temps approaching 100F.
Unfortunately, equivalent data for the Noah Howden are not available to me so any comments would have to be on the basis of mechanical theory. The Howden is a four stage machine which means that the thermal stress on individual cylinders should be less than with a three stage. This is due to lower compression ratios at each stage. Also, the four stage design has three sets of interstage cooling coils instead of two. Moreover, the four stage Howden rotates at three times the speed of the Mariner which also means that the cooling fan turns three times as fast. Ah ha! you say, doesn't the faster turning compressor generate more heat? The answer is no, all compressors operate at about 90% efficiency. This can be verified by comparing engine size. It takes no more power to drive a high speed compressor than for a low speed machine.
The Bauer has a fairly large oil sump. Jim can tell us what size is the sump in the Howden. I don't recall. However this may be, the Howden uses a dry sump design which pumps recirculating oil into a separate tank which is exposed to air flow. Oil in the rather small tank on my 4 cfm Kidde doesn't get much hotter than warm. It certainly won't burn the finger.
All this says that the Howden should operate cooler than the Mariner if ambient temps and installation factors (space, air flow) are equal. Many NITROX pumpers use diester oils in Bauer and other compressors without reported problems. (There have been a few cases summarized at Decostop involving excess heat in the compressor room). Others have switched to PAO's which are without reported problems to my knowledge. We are constantly learning as new information comes in so this anything which I have said here could be modified later. Reality is we can't wait forever to learn new stuff before moving ahead and the state of knowledge at this point says to use ordinary care and diligence whatever oil is used.
