opinions on Stewart Warner compressor

[DA Aquamaster]

It's perhaps a bit late to ask but due to some changes at the LDS I decided that owing my own compressor made sense from a convenience standpoint if not from an economic one.

I have purchased a surplus 3.5 CFM Stewart Warner compressor with a 5.0 hp Honda engine from Protecair.

It seems well suited for use on the boat and from what I have read and heard they are quite durable and reliable. All of my tanks primary tanks are 2250-2400 psi so the 3500 psi pressure limit is not a concern.

I am interested in opinions on both the engine and compressor as well as information related to fill times and experience with over all maintainence and operating costs.

 

[pescador775]

The engine is a "throw away" meaning that they are not normally rebuilt. However, they cost very little and will last quite a while. The three stage, 3.5 cfm pump is honestly rated having an output equal or greater than similar Alkin, Aerosub Coltri and Bauer Junior. RPM is high but this is inconsequential as the block will last 3,000 hours if the correct oil is used. (Years ago, I saw 4 cfm units at NASA with 10,000 hours).Trouble points on other compressors such as valves are a minor concern with the SW. The 2nd and 3rd stages of the SW have no intake valve springs and the exhaust valves springs are serviceable from the outside. Needle and ball bearings throughout. Second and third stages are protected with burst disks and one relief valve. The correct oil is Mobil Jet II, production stamp no more than two years old. Recent production lots pass all US govt test for toxicity. Exxon Mobil provides data on their website. The very thin, 5W, aircraft instrument oil, MIL PRF 6085 sold by Bargain Marge is really not suitable for these machines unless the compressor is to be used in arctic temperatures.

 

[DA Aquamaster]

Thanks for the information.

From what I read the Honda does a better job of running the compressor than the original Continetal (and marge was out of $35.00 replacement Continetal engines) and I figured the replacement cost of the Honda would be under $200 anyway.

I am happy to hear that the valves are not an issue on them and it sounds like they are generally reliable. I anticipate it will fill around 100 tanks per year so it sounds like it will probably last long enough to pay for itself.

 

[pescador775]

The Honda engine is essential. The Continental engine, as all the components, was designed as the lightest package for humping over terrain by a soldier. Given the technology of the day, the lightest engine consistent with 2000 psi service was employed. This meant low power, certainly not enough to drive a 3500 psi compressor at full speed.

A few years ago, I heard from a friend who was running an SW at 4500 psi when the third stage head blew off. The problem was related to corrosion leading to weakening of the aluminum head in the old compressor. This long term problem can be prevented by running the compressor for ten seconds under no load at the end of day. Residual moisture is blown out.

 

[Black Jack]

Quick question about the proper oil, do you have a recommended source for Mobil Jet II that does not require I buy a 24 quart case? I'd greatly appreciate it. Also are there differences between Mobil Jet II and Chemlube 201 other than viscosity that make it a better choice? I'd like to keep mine alive as long as possible.

TIA,

Ed

PS if you need web space to host a SW/WK site let me know and I will help. I don't have a lot of time at the moment but I do have some web options that I'd be happy to sponsor.

 

[pescador775]

Sacramento Air Ranch sells jet turbine oil in small lots. This oil is known to the military and NATO as MIL PRF 23699. The commercial market calls it "JET II" but only Exxon Mobil JET II oil should be used. Chemlube 201 is an obsolete version of MIL PRF 6085C. This type of oil was specified for certain compressors which were used in aircraft applications such as Walter Kidde and some Stewart Warner. It is a 3W (ISO 10) fluid designed to flow at temps as low as -40F. However, for normal temps down to 0 F these manufacturers used mineral oils(breathing) or JET II. Due to improvements in the toxicity profile of JET II it now appears practical to use this superior oil in breathing air applications-- especially in view of modern filtration systems used with breathing air compressors. Far and away, this oil is superior for its mechanical properties such as wear resistance. It is not as heavily loaded with corrosion inhibitors as aircraft instrument oil (MIL PRF 6085C) but that is of little concern with respect to the SW compressor which does not use inconel plungers and steel barrels like the Kidde. It is a slight concern in the Kidde but I have experienced no problems in that application. However, I always blow the compressor clear after use.

 

[Black Jack]

Wow thanks so much for the information!