Stirlingengineforum.com

What was it on?

Shanex-2, maybe who! Ian S C

Shanex,
http://www.diacom.com/generalhardware.html

Bellofram also makes "rolling diaphragm" seals. http://www.bellofram.com/ They have a "Design Guide" to download.

As I understand, Bellofram invented these seal for regulators and control valves (to replace bellows seals?). I'm a chemical engineer and our control valves still have them. But here the pressure differential is only 3-15 psi or 30psi max.

Some of the automotive stirlings used rolling diaphragms at one time. The problem is that they can only withstand so much pressure differential on either side, (their basically rubber, after all). So the automotive folks used oil pressure on the back side to reduce the pressure differential. The oil was pressurized up to about the engine operating pressure, was contained in a small seal chamber, and had O-ring seals to maintain the oil in the seal chamber. What leaked out of the seal chamber went in to the crankcase, which was okay. Their whole principle was to seal the crankcase oil from getting in to the working space, and for this, rolling diaphragm seals work well and could be replaced when the engine was overhauled.

Like Ian says, this is a little above most of us "mortals". But if you were only going to pressurize say to 30-60 psig, I think they would work without any backing fluid.

Great reading thanks for the links . In theory at least it looks like you can get more power per cubic inch or liter than the internal cumbustion engine can produce for the same volume. If you could contain the pressure you could in theory get twice the power as I.C.E. . I am starting to see how complex of a problem that can be . but seeing how little research is being done on this engine for transpertation use now as compared to the 70s its no wonder not alot of people know about this engines potential. I have researched Popular Science's archives they have alot of good info.

Didn't Ian say those seals are made of polyurethane, not rubber.

If you increase the pressure in a motor, you need to increase the amount of heat by a similar amount. Increasing the amount of heat does not mean that the temperature increases, but a larger amount of heat at the same temperature hat you started with, just picture the burners for a gas torch, they all burn at the same temperature, but the amount of heat increases as the burner gets bigger. Ian S C
Aviator168, yes I think polyurethane was right, although I imagine other materials may be used.

I am thinking if a "seat" for the rolling diaphragm can be built so to eliminated for the oil seal. The butt of the rolling diaphragm travels up/down with the piston; except only half of the distance. So a sleeve for the piston can be employed synchronizing with the piston. Hence the butt of the rolling diaphragm is always seating on the top of the sleeve, eliminating the need for an oil seal to provide back pressure.

The only thing I can think of against that system is the seal rubbing on the seat and causing wear, I imagine its possible to lubricate the rubber. Ian S C

Damn it Ian. Knew you were going to bring that up. Don't know if rolling balls on top of the seat help.

Edit. Another thought. Lubricating is not difficult at all.