carbs
 

does anyone know the advantages or disadvantages of either rotary valve or reed valve intakes on carbs?

thanks,

Greg

carbs
 

Heres my .02. I have owened both types. I still have all the reed valve engines. The rotor valves engines were nothing but trouble for me. Now this does not make a lot of sense but thats the way it was.

Kent

carbs
 

The devil is in the details. The rest of the engine design matters a lot more than if it has a rotary or reed intake. Gas flow in these engines starts with the intake (reed or rotary), but then has to go from the crankcase up the transfer ports. Port size, shape and timing of the transfers and exhaust have a huge influence on the power of an engine and the way it runs. I've got reed, rotary and piston port gas motors. If you count all the glow engines, rotary valves dominate.

carbs
 

Technically, what is the difference?

carbs
 

Rotary valves have timing that can be adjusted for total duration, opening timing and closing timing. When the valve is open, the port is unobstructed. It's a mechanical system driven by the crankshaft, very reliable and unlikely to break or wear out.

Reed valves are a demand system. They open and close by differential pressure. When the pressure in the crankcase is lower than the carb side of the valve, they start to open. Reed valves can flutter at high rpm (not typically a problem with out low rpm plane motors), and reeds can fatigue and crack over time from all the bending and flexing. If metal reeds break they can eat the motor. Most reeds are now made of fiberglass or carbon fiber composites, which don't damage the motor like a metal reed. Reeds obstruct the intake port, so for ultra high horsepower high rpm motors (like racing karts and glow motors - not gas plane motors), they are not often chosen.

Piston port is the least expensive system. Timing is a compromise. Same opening and closing timing. If the duration is long for good power, then there will be some fuel spitting out the carb. If the duration is short for no spitting, then there is low power. Nothing to wear out or replace in the piston port. No moving parts other than the piston. Piston porting doesn't cause the piston to wear out any sooner than it normally would.

All DA and 3W motors are reed valve.
Most ZDZ motors are rotary valve, although they make a budget version of the 40 single with a reed valve.
Brison singles are piston port, their twins are reed valve.
BME twins are all reed valve.
Zenoahs are all piston port.