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[redboat219]

I've read several post mentioning some modelers using converted glow engines as air pumps for their ballast system. Does anybody have photos of these and info how it's done?

[Subculture]

A few modellers did this back in the day when small air pumps were not available. Two stroke glow or diesel motors were often used, with the glowplug or compression screw replaced with a one way valve. That was the air outlet, the inlet was usually the port located at bottom of the cylinder. Sometimes, modellers would replace the cylinder liner, and place two valves at the top for both the inlet and outlet- this gives the best efficiency.

A more popular choice was converting tyre inflator compressors, however I've only really seen these used in fairly low pressure systems, like converted Darnell boats, and you could quite easily substitute them for a diaphragm compressor.

These days you can get really nice miniature diaphragm pumps for very little money, they're very efficient at moving air, quiet, pretty much maintenance free, and take up little space.

The only benefit of a piston based compressor is if you want to compress air at pressures above one atmosphere. Diaphragm compressors need to be connected in series to reach higher pressures, pistons do it with ease, however if you're going to run high pressures it's important that the rest of the boat is built to handle it.

A piston based compressor will be larger, thirstier and require routine maintenance (lubrication) in order to remain reliable.

[Martin (Admin)]

The Darnell system used little oscillation steam engines as a pumps with an aquarium type one-way air valve if memory serves.....

[Subculture]

They used USE steam engines, but a lot of modellers modified them to use the tyre inflator compressors. This improved dive times, and the pump only had to be operated once as opposed to bi-directionally.

[sub john]

HI ALL
       The best way i have found converting a model glow plug engine in to a compressor is, if you look at how a 2 stroke engine works it compresses on both sides of the piston. If you bloke off what would be the exhaust port with epoxy putty what you can do then is use the crank case compression to increase the head compression so what would be the scavenger ports on the side of the piston liner act as valves, plus you now have another valve as the crank shaft rotates this opens and closes the air in from the carburetter. But if you attach a pipe to where the carburetter in let is when the engine first runs up there is a two way valve on the in let and when it first starts it switches over to oil in let for about 1.5 seconds this is done by electronic timing circuit then it switches back over to air in let as the compressor continues to run. The engine will now suck up droplets of oil with the air and lubricate engine as it runs any oil that comes out of one way valve on top of cylinder head will be separated off and court in catching chamber to separate oil from air, compressed air can be then passed on to main air tanks i have had this system pump the main air tanks up to 350PSI with out no trouble at all. Just to check air tanks and so on for leaks the tanks normally sit at 140 PSI and it has worked for 20 years i think you can say that it works, have never had to strip engine down in all this time if i was ever going to rebuild it the only thing i would change is fit brushless motor to compressor which i think would make a better unit
                     John

[richald]

As a complete ignoramus when it comes to R/C
submarine dive systems - has anybody considered using
the innards of a home blood pressure monitor ?

These systems are cheap (£15 or so), run off AAA
batteries and seem to generate quite high pressures
(if the one I have is anything to go by!)

There must be an electrically controlled valve in the
unit to handle the inflation and deflation of  the cuff.

I would be interested to know if anybody has tried to
modify and use one of these units

Richard

[Subculture]

It's been done quite a bit. Inside those monitors you will find a very small diaphragm pump and a solenoid valve.

The pumps will only make a few psi at best. So they're only suitable for low pressure systems. You can purchase the pumps separately from China and America. Companies make them in lots of different sizes.