compressor for sailing

[Genesis]

is that their "GC" series of small engines use force-fed fuel pumps that run on crankcase pressure.

This is just fine until you have a problem with the carb seat - at which point you discover that the engine is running like crud and pumping raw fuel all over the place! NOT good....

From experience......

 

[pescador775]

Genesis, thanks for the info. I've been looking at the GC series. I heard it is a nice engine but a 'throwaway' (don't attempt rebuild).

 

[Genesis]

And the carb design can be downright dangerous if there is anywhere spilled gas can potentially go.

This would, for me at least, rule it out on a sailboat. Its just too easy to get a nice "boom" out of that kind of situation.

(The one I own is on a pressure-washer, and I got lucky in that I caught it before ignition occurred and was able to shut it down. The pucker factor was, however, considerable.)

 

[pescador775]

The Entec is looking better and better--- thanks, Curley.

 

[pescador775]

I know that some out there have bought military surplus pumps and sometimes I wonder how they made out. Were they put in service or gathering dust?

Well, it looks like many are out there gathering dust. Still, I know of some intrepid souls, besides myself, who use these machines. The key to long term reliability is the correct oil. Lately, I've begun some introspection on this subject. The military uses 'aircraft instrument oil' in the Kidde and Stewart Warner pumps. This oil is applicable in mechanisms which have high rotational speeds such as gyro bearings and high speed compressors. However, the crucial characteristic of this oil which appeals to the Air Force is the low viscosity allowing startup of the pump in temps down to -40 deg, typical for aircraft at high altitude and in arctic conditions. It appears to me that this low viscosity (less than 5W) may not be as advantageous for SCUBA compressor use (except maybe in Canada or Sweden). Another item for consideration is the flash point of instrument oil which is 430 deg, fairly high but not as high as some commercial oils. After a literature search, I found that certain aircraft turbine oils might be suitable. Like instrument oil, these oils are synthetic and have higher flash point (475 deg), a 10W viscosity (ISO 32), but lack the corrosion inhibiters so necessary for compressor oils. I then discovered that the military had recently requested the manufacturers to produce an inhibited oil. I obtained a quantity of this oil for testing. The tests are going well and I will report later if there is any interest. A note about the chemistry of these oils. They are listed as 'toxic'. However, a review of toxicology test results indicates otherwise. It turns out that test animals, fed the equivalent of a water glass of oil 5 days/week for 10 weeks, developed paralysis. The chemical which causes this is dubbed tricresyl phosphate. Reading these reports carefully, it turns out that the oil is considered safe at Grade E levels (5 mg/M3). Thus, the air produced by a good filtration system should be safe to breath. Personally, I cannot detect any oil odor coming from the test compressor's outlet or from tanks filled by this compressor. Anyone should be able to detect 5mg/M3 of oil which has been hammered and heated by a compressor, that is if the oil vapor is actually present. I doubt that I will actually have the air tested because I already know the results for the system. I just wanted to know if any unusual odors would be getting through the filtrants. The turbine oil is sometimes available through E bay for much less than the price of instrument oil. The spec is MIL PRF 23699F, Type C/I (corrosion inhibited).

 

[Isaac-1]

I have been following this thread for the last few days as I was in a similar position as the originaly poster. I have a sailboat and was looking for a small compressor to use onboard. Earlier today I lucked into very good price on a 1978 Mako Purus, the only downside is I must drive 800 miles to pick it up, and it currently is equiped with a 220 volt 3 phase motor. Plan to convert it to gas powered, and would like everyones oppinion on the best way to do this.

Thanks Ike

p.s. the current owner has some concern about traces oil getting through the compressor and into scuba tanks that have been filled, I don't know if this is only a filtration problem, etc. Based on photos this unit appears to be in mint condition, and has been lightly used.

 

[oxyhacker]

It's almost certainly a filtration problem, or else imagination. People unfamiliar with compressors usually have the impression that some hidden internal fault in the compressor can cause it to output tainted air, but the fact is, oil sump compressors output air that is just about as filthy as it can get, and then remove the filth before it goes into the tank. That being the case, if you stay on top of things with the filtration (which means mainly draining the separators faithfully, and changing the filters) the air is going to be OK. Yes there are internal probs that can lead to worse air but they will be almost immediately evident when you drain the condensor and get almost straight oil or heavy black or brown crud instead of a milky condenseate. And defects in the filter can usually be spotted by monitoring the moisture level of the output, either with a eyeball monitor or a handkerchef.

The one exception in CO, which is invisible, but this is mostly dependant on the installation (and the prevailing wind!) and so once again, under your control.

So I wouldn't let any doubts the previous owner has about the air scare me off, if I did a trial run - filled a tank or two and monitored what was coming out of the drains - and it appeared normal.

p.s. the current owner has some concern about traces oil getting through the compressor and into scuba tanks that have been filled, I don't know if this is only a filtration problem, etc. Based on photos this unit appears to be in mint condition, and has been lightly used.

 

[MikeFerrara]

Yes there are internal probs that can lead to worse air but they will be almost immediately evident when you drain the condensor and get almost straight oil or heavy black or brown crud instead of a milky condenseate. .

Which problems cause what change in appearance in the condensate?

 

[pescador775]

Isaac, I'm trying to recall the specs for the 78 model. By then, Bauer had taken care of some of the problems with the ancient Purus design. The early models ('60-'70) were all cast iron with a totally inadequate filtration. The condenser was a steel tube which had a small charcoal canister within. There was no back pressure valve. I think that Bauer started using these valves as standard equipment about year '75. By that time they had also increased the output from 1.5 cfm to about 2.5 cfm (advertised 3.0 cfm). The Purus had the reputation of contaminated oil. Water would enter the oil sump via blowby since this compressor had no interstage separator. The oil would quickly become milky. The entire unit, being iron, would be subject to exterior rust. About Y'75, commensurate with the increased output the gas engine was changed from the small 2 cycle Sachs to a 3.0 HP Briggs. This engine was no longer supported by a spring and pivot but was bolted to the frame in a somewhat different manner. You must check to see if the condenser filter uses multilayer filtration designed to remove water and oil. At some point they changed over to the PO triplex design filter. However, I know for a fact that as late as '76 they were still using the inadequate steel tube with internal baffle and charcoal cartridge. The triplex is what you need and it is expensive. The owner has probably noticed water or rust in his tanks and hence his stated concerns about air quality. When Bauer intially installed backpressure valves these were set to 500 psi which is inadequate. This valve must be set to 1800 psi or higher to restrain water/oil pumping into the tank.

Changing over to gas may require the assistance of a machine shop. The Purus mounting system is different from the current replacement, the Junior, in which engine and motor can be interchanged readily. Anyway, the Purus frame/motor mount should be checked for interchangability.

I have been following this thread for the last few days as I was in a similar position as the originaly poster. I have a sailboat and was looking for a small compressor to use onboard. Earlier today I lucked into very good price on a 1978 Mako Purus, the only downside is I must drive 800 miles to pick it up, and it currently is equiped with a 220 volt 3 phase motor. Plan to convert it to gas powered, and would like everyones oppinion on the best way to do this.

Thanks Ike

p.s. the current owner has some concern about traces oil getting through the compressor and into scuba tanks that have been filled, I don't know if this is only a filtration problem, etc. Based on photos this unit appears to be in mint condition, and has been lightly used.

 

[Isaac-1]

Thanks for the detailed response, I plan to go pick up the compressor this weekend (On an ironic note, I will prbably spend almost as much on gas to go get it as the unit is costing me), after I get it in hand I will be in a better position to ask detailed questions. If this unit is like the '76 model you refer to, what upgrades would you recomend before putting it in service?

Thanks Ike

p.s. I have copies of the photos from the orignal ad posted at www.beau.lib.la.us/~ikes/compressor perhaps you can tell something about the filters, etc. from this.

Isaac, I'm trying to recall the specs for the 78 model. By then, Bauer had taken care of some of the problems with the ancient Purus design. The early models ('60-'70) were all cast iron with a totally inadequate filtration. The condenser was a steel tube which had a small charcoal canister within. There was no back pressure valve. I think that Bauer started using these valves as standard equipment about year '76. By that time they had also increased the output from 1.5 cfm to about 2.5 cfm (advertised 3.0 cfm). The Purus had the reputation of contaminated oil. Water would enter the oil sump via blowby since this compressor had no interstage separator. The oil would quickly become milky. The entire unit, being iron, would be subject to exterior rust. About Y'75, commensurate with the increased output the gas engine was changed from the small 2 cycle Sachs to a 3.0 HP Briggs. This engine was no longer supported by a spring and pivot but was simply bolted to the frame. You must check to see if the condenser filter uses multilayer filtration designed to remove water and oil. At some point they changed over to the PO triplex design filter. However, I know for a fact that as late as '76 they were still using the inadequate steel tube with internal baffle and charcoal cartridge. The triplex is what you need and it is expensive. The owner has probably noticed water or rust in his tanks and hence his stated concerns about air quality. When Bauer intially installed backpressure valves in 76 these were set to 500 psi which is inadequate. This valve must be set to 1800 psi or higher to restrain water/oil pumping into the tank.